HK1191242B - Method of preparing a hyaluronic acid-based gel including lidocaine hcl. - Google Patents

Description

FIELD OF THE INVENTION

The present invention generally relates to a method of preparing injectable soft tissue fillers and more specifically hyaluronic acid-based dermal and subdermal fillers including an anesthetic agent.

BACKGROUND

It is generally accepted that as a person ages, the face begins to show effects of gravity, sun-exposure, and years of facial muscle movement, such as smiling, frowning, chewing and squinting. The underlying tissues that keep the skin appearing youthful begin to break down, often resulting in laugh lines, smile lines, "crow's feet" and facial creases often referred to as the "effects of aging."

In an effort to treat or correct the effects of aging, soft tissue fillers have been developed to help fill in facial lines and depressions and for restoring fat loss-related tissue volume loss. The soft tissue fillers thereby temporarily restore a smoother, more youthful appearance.

Ideally, soft tissue fillers are long-lasting, soft, smooth and natural appearing when implanted in the skin or beneath the skin. Further, soft tissue fillers are easy to implant into a patient using a fine gauge needle and require low extrusion force for injection. Ideal fillers would also cause no adverse side effects, and would be injectable with minimal or no discomfort to the patient.

Collagen based soft tissue fillers were developed over 20 years ago, and for some time, bovine collagen-based fillers were the only U.S. Food and Drug Administration (FDA)-approved dermal fillers. Because these dermal fillers are bovine based, one of the main disadvantages has been the potential for allergic reaction in patients. It is believed that approximately 3-5% of human subjects show serious allergic reactions to bovine collagen, thus requiring careful testing before using these fillers in any particular person. In addition to allergic reactions, collagen based fillers degrade rapidly upon injection and require frequent treatments to sustain a smoother, more youthful appearance.

In February 2003, human-derived collagen filler compositions received FDA approval. These collagens provide the advantage of a significantly reduced risk of allergic reactions. However, despite the reduced incidence of allergic reactions, the human derived collagen fillers still suffered from the rapid degradation of the injected product.

The search for fillers that do not provoke allergic reactions and sustain a smoother, more youthful appearance has brought about the development of hyaluronic acid (HA)-based products. In December 2003, the first HA-based filler was approved by the FDA. This was rapidly followed by the development of other HA-based fillers.

HA, also known as hyaluronan, is a naturally occurring, water soluble polysaccharide, specifically a glycosaminoglycan, which is a major component of the extra-cellular matrix and is widely distributed in animal tissues. HA has excellent biocompatibility and does not cause allergic reactions when implanted into a patient. In addition, HA has the ability to bind to large amounts of water, making it an excellent volumizer of soft tissues.

The development of HA-based fillers which exhibit ideal in vivo properties as well as ideal surgical usability has proven difficult. For example, HA-based fillers that exhibit desirable stability properties in vivo, can be so highly viscous that injection through fine gauge needles is difficult. Conversely, HA-based fillers that are relatively easily injected through fine gauge needles often have relatively inferior stability properties in vivo.

One method to overcome this problem is to use crosslinked HA-based fillers. Crosslinked HA is formed by reacting free HA with a crosslinking agent under suitable reaction conditions. Methods of preparing HA based soft tissue fillers including both crosslinked and free HA are well known.

It has been proposed to incorporate certain therapeutic agents, for example, anesthetic agents such as lidocaine, into injectable HA-based compositions. US2005/0136122 describes methods of preparing soft tissue filler compositions comprising a hyaluronic acid gel crosslinked with a biscarbodiimide and lidocaine HCl. Unfortunately, HA-based injectable compositions which incorporate lidocaine during the manufacturing process are prone to partial or almost complete degradation prior to injection, particularly during high temperature sterilization steps and/or when placed in storage for any significant length of time.

It is an objective of the HA-based soft filler compositions and methods of making and using them as described herein to provide soft tissue fillers that do not cause allergic reactions in patients, are biocompatible and are stable and usable in vivo and include one or more local anesthetic agents.

SUMMARY

The present description relates to a method of preparing soft tissue fillers. The method of the invention is as defined in the appended claim 1. The soft tissue filler composition is based on hyaluronic acid (HA) and pharmaceutically acceptable salts of HA, for example, sodium hyaluronate (NaHA). HA-based compositions described herein include a therapeutically effective amount of at least one anesthetic agent which is lidocaine HCI. The present method results in an enhanced stability, relative to conventional methods for making HA-based compositions including, for example, lidocaine, when subjected to sterilization techniques such as autoclaving, and/or when stored for long periods at ambient temperature.

The at least one anesthetic agent is lidocaine HCI. In a further embodiment, the amount of the anesthetic agent is present at a concentration between about 0.1% and about 5.0% by weight of the composition. In still another embodiment, the anesthetic agent is present at a concentration between about 0.2% and about 1.0% by weight of the composition. In one embodiment, the anesthetic agent is present at a concentration of about 0.3% by weight of the composition.

In still another embodiment, the soft tissue filler composition made by the claimed method has an extrusion force of between about 10 N and about 13 N, for example, at a rate of about 12.5 mm/minute. In yet another embodiment, the composition has a viscosity of between about 5 Pa*s and about 450 Pa*s, for example, when measured at about 5 Hz.

In one embodiment, the HA component is a gel, for example, a cohesive, hydrated gel.

In yet another embodiment, the HA component is a gel comprising particles of crosslinked HA in a relatively fluidic medium of free HA. In some embodiments, the HA component has an average particle size of greater than about 200 µm, for example, greater than about 250 µm.

Further described herein is a soft tissue filler composition comprising: a HA component crosslinked with 1,4-butanediol diglycidyl ether (BDDE), said HA component having a degree of crosslinking of less than about 5%, for example, about 2%, and an anesthetic component having a concentration between about 0.1% and about 5.0% by weight of the soft tissue filler composition, wherein the anesthetic is lidocaine HCI.

In another embodiment, the composition is sterilized, for example, by autoclaving, to form a sterilized composition and wherein the sterilized composition is stable at ambient temperature for at least about 6 months, for example, at least 9 months, at least about 12 months or more.

The adjusted pH is above 7.5. In another embodiment, the method further comprises the step of homogenizing the HA component during or after the step of adding the solution containing the at least one anesthetic agent. In a further embodiment, the step of homogenizing comprises subjecting the composition to mixing with a controlled shear.

In another embodiment, the step of providing a HA component comprises providing dry free NaHA material and hydrating the dry free NaHA material in an alkaline solution to obtain an alkaline, free NaHA gel. In yet another embodiment, the alkaline, free NaHA gel has a pH greater than about 8.0. In still another embodiment the pH is greater than about 10.

In a further embodiment, the HA component comprises greater than about 20% free HA and the crosslinked portion of the HA component has a degree of crosslinking of less than about 6% or less than about 5%.

In still a further embodiment, the soft tissue filler composition has a particulate nature in that it comprises particles of crosslinked HA dispersed in a fluid soluble HA medium. In some embodiments, the average size of such particles is at least about 200 µm, and in other embodiments the average size of such particles is at least about 250 µm.

Further described herein is a soft tissue filler composition comprising: a hyaluronic acid (HA) component crosslinked with 1,4-butanediol diglycidyl ether (BDDE), said HA component having a degree of crosslinking of less than about 5%, and an anesthetic component having a concentration between about 0.1% and about 5.0% by weight of the soft tissue filler composition, wherein the anesthetic is lidocaine HCl.

In a specific embodiment of the invention, a method of preparing a soft tissue filler composition is further described, the method comprising the steps of: providing dry free NaHA material and hydrating the dry free NaHA material in an alkaline solution to obtain an alkaline, free NaHA gel; crosslinking the free NaHA gel with BDDE to form a crosslinked alkaline HA composition with a degree of crosslinking less than about 5% and a pH above 7.5; adding a solution containing 0.3% lidocaine HCl to the HA component having the adjusted pH to obtain said HA-based filler composition; homogenizing the HA-based filler composition thereby forming a homogenized HA-based filler composition; and sterilizing the homogenized HA-based filler composition thereby forming a sterilized HA-based filler composition, wherein the soft tissue filler composition has a particle size of greater than about 200 µm, for example, a particle size of greater than about 250 µm.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 graphically illustrates the lidocaine concentration in the gel from Sample 5 in Example 4 made by the procedure of Test 2 versus time.

DEFINITIONS

Certain terms as used in the specification are intended to refer to the following definitions, as detailed below. Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions provided below, unless specifically indicated.

Autoclave stable or stable to autoclaving as used herein describes a product or composition that is resistant to degradation such that the product or composition maintains at least one, and preferably all, of the following aspects after effective autoclave sterilization: transparent appearance, pH, extrusion force and/or rheological characteristics, hyaluronic acid (HA) concentration, sterility, osmolarity, and lidocaine concentration.

High molecular weight HA as used herein describes a HA material having a molecular weight of at least about 1.0 million Daltons (mw ≥ 10⁶ Da or 1 MDa) to about 4.0 MDa. For example, the high molecular weight HA in the present compositions may have a molecular weight of about 2.0 MDa. In another example, the high molecular weight HA may have a molecular weight of about 2.8 MDa.

Low molecular weight HA as used herein describes a HA material having a molecular weight of less than about 1.0 MDa. Low molecular weight HA can have a molecular weight of between about 200,000 Da (0.2 MDa) to less than about 1.0 MDa, for example, between about 300,000 Da (0.3 M Da) to about 750,000 Da. (0.75 MDa).

Degree of Crosslinking as used herein refers to the intermolecular junctions joining the individual HA polymer molecules, or monomer chains, into a permanent structure, or as disclosed herein the soft tissue filler composition. Moreover, degree of crosslinking for purposes of the present disclosure is further defined as the percent weight ratio of the crosslinking agent to HA-monomeric units within the crosslinked portion of the HA based composition. It is measured by the weight ratio of HA monomers to crosslinker (HA monomers:crosslinker).

Free HA as used herein refers to individual HA polymer molecules that are not crosslinked to, or very lightly crosslinked to (very low degree of crosslinking) the highly crosslinked (higher degree of crosslinking) macromolecular structure making up the soft tissue filler composition. Free HA generally remains water soluble. Free HA can alternatively be defined as the "uncrosslinked," or lightly crosslinked component of the macromolecular structure making up the soft tissue filler composition disclosed herein.

Cohesive as used herein is the ability of a HA-based composition to retain its shape and resist deformation. Cohesiveness is affected by, among other factors, the molecular weight ratio of the initial free HA, the degree of crosslinking, the amount of residual free HA following crosslinking, and HA-based composition pH. A cohesive HA-based composition resists phase separation when tested according to the method disclosed in Example 1 herein.

DETAILED DESCRIPTION

The present disclosure generally relates to a method of preparing soft tissue fillers, for example, dermal and subdermal fillers, based on hyaluronic acids (HA) and pharmaceutically acceptable salts of HA, for example, sodium hyaluronate (NaHA). The invention is limited to the subject-matter defined in the appended claims. The HA-based compositions described herein include a therapeutically effective amount of at least one anesthetic agent, which is lidocaine HCl. The present HA-based compositions including at least one anesthetic agent have an enhanced stability, relative to conventional HA-based compositions including, for example, lidocaine, when subjected to high temperatures and pressures, for example, those experienced during heat and/or pressure sterilization techniques, for example, autoclaving, and/or for example, when stored at ambient temperature for an extended period of time.

The stable compositions maintain at least one of, or all of, the following aspects after effective autoclave sterilization and/or prolonged storage: transparent appearance, pH for use in a patient, extrusion force and/or rheological characteristics, HA concentration, sterility, osmolarity, and lidocaine concentration. Methods or processes of preparing such HA-based compositions are also provided as well as products made by such methods or processes.

As used herein, hyaluronic acid (HA) can refer to any of its hyaluronate salts, and includes, but is not limited to, sodium hyaluronate (NaHA), potassium hyaluronate, magnesium hyaluronate, calcium hyaluronate, and combinations thereof.

Generally, the concentration of HA in the compositions described herein is preferably at least 10 mg/mL and up to about 40 mg/mL. For example, the concentration of HA in some of the compositions is in a range between about 20 mg/mL and about 30 mg/mL. Further, for example, in some embodiments, the compositions have a HA concentration of about 22 mg/mL, about 24 mg/mL, about 26 mg/mL, or about 28 mg/mL.

In addition, the concentration of one or more anesthetics is in an amount effective to mitigate pain experienced upon injection of the composition. The at least one local anesthetic lidocainein the form of lidocaine HCl. The compositions described herein may have a lidocaine concentration of between about 0.1% and about 5% by weight of the composition, for example, about 0.2% to about 1.0% by weight of the composition. In one embodiment, the composition has a lidocaine concentration of about 0.3% by weight (w/w %) of the composition. The concentration of lidocaine in the compositions described herein can be therapeutically effective meaning the concentration is adequate to provide a therapeutic benefit without inflicting harm to the patient.

In one aspect of the invention, a method is provided for preparing a HA-based composition including an effective amount of lidocaine HCl wherein the method comprises providing a precursor composition further comprising a cohesive crosslinked HA-based gel, adding a solution containing lidocaine, in the form of lidocaine HCl, thereto and homogenizing the mixture to obtain a cohesive, at least partially crosslinked, HA-based composition including lidocaine that is stable to autoclaving. Without wishing to be bound by any particular theory of operability, it is believed that the high cohesivity of the precursor composition in some embodiments of the invention acts to substantially or entirely prevent or impede any breakdown or degradation of the crosslinked HA in the composition with the addition of lidocaine HCl.

It is believed that such degradation may primarily occur because many, perhaps most crosslinked HA based gels are conventionally manufactured in a manner that produces gels which are not sufficiently cohesive to prevent such degradation when lidocaine is added. It has now been discovered that the addition of lidocaine HCl to sufficiently cohesive crosslinked HA-based compositions does not cause substantial or significant degradation of the compositions, and the compositions maintain their integrity in terms of rheology, viscosity, appearance and other characteristics even when stored for a lengthy period of time, for example, for a period of time of at least 6 months to a year or more, and even after being subjected to sterilization procedures, for example, autoclaving.

It is a surprising discovery that formulations of crosslinked HA-based compositions including lidocaine can be manufactured in a manner in accordance with the invention to produce sterilization-stable, injectable HA/lidocaine compositions.

Further described herein is a method for preparing stable HA-based compositions containing an effective amount of lidocaine by preparing a cohesive, crosslinked HA-based precursor composition, adding lidocaine chlorhydrate to the precursor composition to form a HA/lidocaine gel mixture, and homogenizing the mixture, to obtain a crosslinked HA-based composition that is stable to autoclaving.

The precursor composition may comprise a first component including relatively highly crosslinked HA particles in a substantially solid phase, and a second component comprising free or relatively less crosslinked HA in a substantially fluidic phase in which the relatively highly crosslinked particles are dispersed. The composition includes 10% to 20% of free HA by volume.

For example, the precursor composition may comprise a cohesive, HA-based gel.

In some embodiments, the present compositions have a particulate nature and comprise particles of relatively highly crosslinked HA dispersed in a medium of relatively less crosslinked HA. In some embodiments, the average size of such particles of crosslinked HA is at least about 200 µm or at least about 250 µm. Such particulate compositions are generally less cohesive than otherwise similar compositions which have no discernable particles, or have particles having an average size of less than 200 µm.

For example, in some embodiments, the precursor composition may be manufactured by pressing a mass of relatively highly crosslinked HA-based gel through a sieve or a mesh to create relatively highly crosslinked HA particles of generally uniform size and shape. These particles are then mixed with a carrier material, for example, an amount of free HA to produce a gel.

Further, a method of preparing a HA-based composition including an effective amount of lidocaine is provided wherein the method comprises providing a precursor composition including a substantially pH neutral, at least partially crosslinked HA-based gel and adjusting the pH of the gel to a pH of greater than 7.5 to 8.0. The method further comprises the step of combining a solution containing lidocaine, in the form of lidocaine HCl, with the slightly alkaline gel after the pH has been so adjusted and obtaining a HA-based composition including lidocaine that is stable to autoclaving.

Another method of preparing a stable HA-based composition containing an effective amount of lidocaine, as described elsewhere herein, generally comprises the steps of: providing purified NaHA material, for example, in the form of fibers; hydrating the material; and crosslinking the hydrated material with a suitable crosslinking agent to form a crosslinked HA-based gel. The method further comprises the steps of neutralizing and swelling the gel, and adding to the gel a solution containing lidocaine, preferably an acidic salt of lidocaine chlorhydrate, to form a HA/lidocaine gel. Further still, the method further comprises homogenizing the HA/lidocaine gel and packaging the homogenized HA/lidocaine gel, for example, in syringes for dispensing. The syringes are then sterilized by autoclaving at an effective temperature and pressure. In accordance with the present description, the packaged and sterilized cohesive NaHA/lidocaine gels exhibit enhanced stability relative to HA-based compositions including lidocaine which are made using conventional methods.

The present products and compositions are considered to be sterile when exposed to temperatures of at least about 120°C to about 130°C and/or pressures of at least about 12 pounds per square inch (PSI) to about 20 PSI during autoclaving for a period of at least about 1 minute to about 15 minutes.

The present products and compositions also remain stable when stored for long periods of time at room temperature. Preferably, the present compositions remain stable for a period of at least about two months, or at least about six months, or at least about 9 months, or at least about 12 months, or at least about 36 months, at temperatures of at least about 25°C. In a specific embodiment, the compositions are stable at a temperature up to about 45°C for a period of at least two months.

The manufacturing process includes, in one embodiment, the initial step of providing raw HA material in the form of dry HA fibers or powder. The raw HA material may be HA, its salts and/or mixtures thereof. In a preferred embodiment, the HA material comprises fibers or powder of NaHA, and even more preferably, bacterial-sourced NaHA. In some aspects of the present description, the HA material may be animal derived. The HA material may be a combination of raw materials including HA and at least one other polysaccharide, for example, glycosaminoglycan (GAG).

In some embodiments, the HA material in the compositions nearly entirely comprises or consists of high molecular weight HA. That is, nearly 100% of the HA material in the present compositions may be high molecular weight HA as defined above. In other embodiments, the HA material in the compositions comprises a combination of relatively high molecular weight HA and relatively low molecular weight HA, as defined above.

The HA material of the compositions may comprise between about 5% to about 95% high molecular weight HA with the balance of the HA material including low molecular weight HA. In a typical embodiment of the invention, the ratio of high molecular weight to low molecular weight HA is at least about, and preferably greater than 2 (w/w ≥ 2) with the high molecular weight HA having a molecular weight of above 1.0 MDa.

It will be appreciated by those of ordinary skill in the art that the selection of high and low molecular weight HA material and their relative percentages or ratios is dependent upon the desired characteristics, for example, extrusion force, elastic modulus, viscous modulus and phase angle expressed as the ratio of viscous modulus to elastic modulus, cohesivity, etc. of the final HA-based product. For additional information that may be helpful in understanding this and other aspects of the present disclosure, see Lebreton, U.S. Patent Application Publication No. 2006/0194758 .

The HA-based gels can be prepared according to the present description by first cleaning and purifying dry or raw HA material having a desired high/low molecular weight ratio. These steps generally involve hydrating the dry HA fibers or powder in the desired high/low molecular weight ratio, for example, using pure water, and filtering the material to remove large foreign matters and/or other impurities. The filtered, hydrated material is then dried and purified. The high and low molecular weight HA may be cleaned and purified separately, or may be mixed together, for example, in the desired ratio, just prior to crosslinking.

In one aspect of the present disclosure, pure, dry NaHA fibers are hydrated in an alkaline solution to produce an free NaHA alkaline gel. Any suitable alkaline solution may be used to hydrate the NaHA in this step, for example, but not limited to aqueous solutions containing sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium bicarbonate (NaHCO₃), lithium hydroxide (LiOH), and the like. In another embodiment, the suitable alkaline solution is aqueous solutions containing NaOH. The resulting alkaline gel will have a pH above 7.5. The pH of the resulting alkaline gel can have a pH greater than 9, or a pH greater than 10, or a pH greater than 12, or a pH greater than 13.

The next step in the manufacturing process involves the step of crosslinking the hydrated, alkaline NaHA gel with a suitable crosslinking agent. The crosslinking agent may be any agent known to be suitable for crosslinking polysaccharides and their derivatives via their hydroxyl groups. Suitable crosslinking agents include but are not limited to, 1,4-butanediol diglycidyl ether (or 1,4-bis(2,3-epoxypropoxy)butane or 1,4-bisglycidyloxybutane, all of which are commonly known as BDDE), 1,2-bis(2,3-epoxypropoxy)ethylene and 1-(2,3-epoxypropyl)-2,3-epoxycyclohexane. The use of more than one crosslinking agent or a different crosslinking agent is not excluded from the scope of the present disclosure. In one aspect of the present disclosure, the HA gels described herein are crosslinked using BDDE.

The step of crosslinking may be carried out using any means known to those of ordinary skill in the art. Those skilled in the art appreciate how to optimize conditions of crosslinking according to the nature of the HA, and how to carry out crosslinking to an optimized degree.

Degree of crosslinking for purposes of the present disclosure is defined as the percent weight ratio of the crosslinking agent to HA-monomeric units within the crosslinked portion of the HA based composition. It is measured by the weight ratio of HA monomers to crosslinker (HA monomers:crosslinker).

The degree of crosslinking in the HA component of the present compositions is at least about 2% and is up to about 20%.

In some embodiments, the degree of crosslinking is between about 4% to about 12%. In some embodiments, the degree of crosslinking is less than about 6%, for example, is less than about 5%.

In other embodiments, the degree of crosslinking is greater than 5%, for example, is about 6% to about 8%.

In some embodiments, the HA component is capable of absorbing at least about one time its weight in water. When neutralized and swollen, the crosslinked HA component and water absorbed by the crosslinked HA component is in a weight ratio of about 1:1. The resulting hydrated HA-based gels have a characteristic of being highly cohesive.

The HA-based gels in accordance with some embodiments of the invention may have sufficient cohesivity such that the gels will not undergo substantial phase separation after centrifugation of the gel at 2000 rd/min for 5 minutes. In another embodiment, the gels have the characteristic of being capable of absorbing at least one time their weight of water and have sufficient cohesivity such that when swollen with water at a gel/water weight ratio of about 1:1, the gels maintain their integrity, for example, when subjected to centrifugation.

The hydrated crosslinked, HA gels may be swollen to obtain the desired cohesivity. This step can be accomplished by neutralizing the crosslinked, hydrated HA gel, for example by adding an aqueous solution containing of an acid, such as HCl. The gels are then swelled in a phosphate buffered saline (PBS) solution for a sufficient time and at a low temperature.

In one embodiment, the resulting swollen gels are highly cohesive with no visible distinct particles, for example, no visibly distinct particles when viewed with the naked eye. In a preferred embodiment, the gels have no visibly distinct particles under a magnification of less than 35X.

The gels are now purified by conventional means such as, dialysis or alcohol precipitation, to recover the crosslinked material, to stabilize the pH of the material and to remove any un-reacted crosslinking agent. Additional water or a slightly alkaline aqueous solution can be added to bring the concentration of the NaHA in the composition to a desired concentration.

The pH of the purified, substantially pH neutral, crosslinked HA gels are preferably adjusted to cause the gel to become slightly alkaline such that the gels have a pH of greater than 7.5 to 8.0. This step may be accomplished by any suitable means, for example, by adding a suitable amount of dilute NaOH, KOH, NaHCO₃ or LiOH, to the gels or any other alkaline molecule, solution and/or buffering composition know by one skilled in the art.

An effective amount of lidocaine, as lidocaine HCl, is then added to the purified cohesive NaHA gels. For example, in some embodiments, the lidocaine HCl is provided in a powder form which is solubilized using water for injection (WFI). The gels are kept neutral with a buffer or by adjustment with diluted NaOH in order that the final HA/lidocaine composition will have a desired, substantially neutral pH. Preferably, the final HA-based filler compositions including lidocaine will have a lidocaine concentration of between at least about 0.1% and about 5%, for example, about 2% by weight of the composition, or in another example about 0.3%.

After the addition of the lidocaine HCl, or alternatively, during the addition of the lidocaine HCl, the HA/lidocaine gels, or compositions, are homogenized to create highly homogenous cohesive HA/lidocaine gels having a desired consistency and stability. Preferably, the homogenization step comprises mixing, stirring, or beating the gels with a controlled shearing force obtaining substantially homogenous mixtures.

The HA/lidocaine compositions described herein display a viscosity which is dependent on the composition's properties and the presence of at least one anesthetic agent. The viscosity of the HA/lidocaine composition can be from about 50 Pa*s to about 450 Pa*s. In other embodiments, the viscosity can be from about 50 Pa*s to about 300 Pa*s, from about 100 Pa*s to about 400 Pa*s, or about 250 Pa*s to about 400 Pa*s, or about 50 Pa*s to about 250 Pa*s.

After homogenization, the HA/lidocaine compositions are introduced into syringes and sterilized. Syringes useful according to the present description include any syringe known in the art capable of delivering viscous dermafiller compositions. The syringes generally have an internal volume of about 0.4 mL to about 3 mL, more preferably between about 0.5 mL and about 1.5 mL or between about 0.8 mL and about 2.5 mL. This internal volume is associated with an internal diameter of the syringe which plays a key role in the extrusion force needed to inject high viscosity dermafiller compositions. The internal diameters are generally about 4 mm to about 9 mm, more preferably from about 4.5 mm to about 6.5 mm or from about 4.5 mm to about 8.8 mm. Further, the extrusion force needed to deliver the HA/lidocaine compositions from the syringe is dependent on the needle gauge. The gauges of needles used generally include gauges between about 18G and about 40G, more preferably about 25G to about 33G or from about 16G to about 25G. A person of ordinary skill in the art can determine the correct syringe dimensions and needle gauge required to arrive at a particular extrusion force requirement.

The extrusion forces displayed by the HA/lidocaine compositions described herein using the needle dimensions described above are at an injection speeds that are comfortable to a patient. Comfortable to a patient is used to define a rate of injection that does not injure or cause excess pain to a patient upon injection to the soft tissue. One skilled in the art will appreciate that comfortable as used herein includes not only patient comfort, but also comfort and ability of the physician or medical technician injecting the HA/lidocaine compositions. Although certain extrusion forces may be achievable with the HA/lidocaine compositions of the present description, one skilled in the art understands that high extrusion forces can lead to lack of control during injection and that such lack of control may result in additional pain to the patient. Extrusion forces of the present HA/lidocaine compositions can be from about 8 N to about 15 N, or more preferably from about 10 N to about 13 N, or about 11 N to about 12 N.

Sterilization, as used herein comprises any method known in the art to effectively kill or eliminate transmissible agents, preferably without substantially altering of degrading the HA/lidocaine compositions.

One preferable method of sterilization of the filled syringes is by autoclave. Autoclaving can be accomplished by applying a mixture of heat, pressure and moisture to a sample in need of sterilization. Many different sterilization temperatures, pressures and cycle times can be used for this step. For example, the filled syringes may be sterilized at a temperature of at least about 120°C to about 130°C or greater. Moisture may or may not be utilized. The pressure applied is in some embodiments depending on the temperature used in the sterilization process. The sterilization cycle may be at least about 1 minute to about 20 minutes or more.

Another method of sterilization incorporates the use of a gaseous species which is known to kill or eliminate transmissible agents. Preferably, ethylene oxide is used as the sterilization gas and is known in the art to be useful in sterilizing medical devices and products.

A further method of sterilization incorporates the use of an irradiation source which is known in the art to kill or eliminate transmissible agents. A beam of irradiation is targeted at the syringe containing the HA/lidocaine solution, and the wavelength of energy kills or eliminates the unwanted transmissible agents. Preferable energy useful include, but is not limited to ultraviolet (UV) light, gamma irradiation, visible light, microwaves, or any other wavelength or band of wavelengths which kills or eliminates the unwanted transmissible agents, preferably without substantially altering of degrading the HA/lidocaine composition.

Further described are methods of manufacturing HA-based compositions generally comprising the steps of providing a crosslinked HA-based gel without an anesthetic, (hereinafter, sometimes, a precursor gel) adjusting the pH of the precursor gel to obtain a gel having a pH of between 7.5 and 8.0, and adding a suitable amount of lidocaine HCl, to the pH-adjusted gel to obtain a HA-based composition that includes an anesthetic agent. The precursor gel is a relatively less cohesive gel comprising at least 10% to about 20% free HA by volume.

Example 1 Method for testing for cohesivitv of gel

The following tests may be performed in order to evidence cohesivity of a HA-based gel composition for purposes of the present disclosure.

First, 0.2 g or 0.4 g of a gel composition to be tested is placed in a glass syringe. Next, 0.2 g or more of phosphate buffer is added to the syringe and the mixture is thoroughly mixed for about 1 hour to obtain a homogenous mixture. Then, the homogenized mixture is centrifuged for 5 min at 2000 tr/min to remove the air bubbles and to allow the decantation of any particles. The syringe is then held in a vertical position and one drop of eosin colorant is deposited at the surface of the gel by means of a syringe and an 18G needle. After 10 min, the dye has slowly diffused through the gel.

After dilution of the gel, homogenization and decantation, a relatively low cohesivity gel shows a phase separation (an upper diluted less viscous phase without particles and a lower one composed of decanted particles that are visible with the naked eye or under microscope). Under the same conditions, a highly cohesive gel shows substantially no phase separation, and the dye is prevented from diffusing into the cohesive formulation. A relatively less cohesive gel, on the other hand, shows a clear phase separation.

Example 2 Synthesis of a Soft Tissue Filler with Lidocaine

NaHA fibers or powder are hydrated in an alkaline solution, for example, an aqueous solution containing NaOH. The mixture is mixed at ambient temperature, about 23°C, to form a substantially homogenous, alkaline HA gel.

A crosslinking agent, BDDE, is diluted in an aqueous solution and added to the alkaline HA gel. The mixture is homogenized for several minutes.

Alternatively, BDDE can be added directly to the HA fibers (dry state) at the beginning of the process, prior to the hydration. The crosslinking reaction will then start relatively slowly at ambient temperature, ensuring even better homogeneity and efficacy of the crosslinking. See, for example, Piron et al., U.S. Patent No. 6,921,819 which is incorporated herein by reference in its entirety as if it were part of the present specification.

The resulting crosslinked HA gel mixture is then heated at about 50°C for about 2.5 hours. The material is now a highly crosslinked HA/BDDE gel (aspect = solid gel). This crosslinked gel is then neutralized with a suitable acidic solution. The neutralized HA gel is then swollen in a phosphate buffer at a cold temperature, for example a temperature of about 5°C, to obtain a highly cohesive HA gel. In this specific example, the phosphate buffered saline solution contains water-for-injection (WFI), disodium hydrogen phosphate, and sodium dihydrogen phosphate. When neutralized and swollen, the crosslinked HA component and water absorbed by the crosslinked HA component is in a weight ratio of about 1:1.

The cohesive swollen HA gel is then mechanical stirred and filled into dialysis membranes and dialyzed against a phosphate buffer. The HA gel is filled into dialysis membranes and dialyzed against a phosphate buffer for up to several days with regular changes of the bath, in order to remove the un-reacted crosslinker, to stabilize the pH close to neutrality (pH=7.2) and to ensure proper osmolarity of the HA gel. The osmolarity of the resulting cohesive HA gel is between about 200 mOsmol and about 400 mOsmol, most preferably about 300 mOsmol.

After dialysis, the resulting cohesive HA gel has a substantially neutral pH, preferably about 7.2, and no visibly distinct particles in a fluidic media when viewed at a magnification of less than about 35X.

Lidocaine chlorhydrate (lidocaine HCl) in powder form is first solubilized in WFI and filtered through a 0.2 µm filter. Dilute NaOH solution is added to the cohesive HA gel in order to reach a slightly basic pH (for example, a pH of between about 7.5 and about 8). The lidocaine HCl solution is then added to the slightly basic gel to reach a final desired concentration, for example, a concentration of about 0.3% (w/w). The resulting pH of the HA/lidocaine mixture is then about 7 and the HA concentration is about 24 mg/mL. Mechanical mixing is performed in order to obtain a proper homogeneity in a standard reactor equipped with an appropriate blender mechanism.

If desired, a suitable amount of free HA gel may be added to the HA/lidocaine gel mixture with the advantage of increasing the kinetics of lidocaine delivery. For example, free HA fibers are swollen in a phosphate buffer solution, in order to obtain a homogeneous viscoelastic gel. This free HA gel is then added to the crosslinked HA/lidocaine gel (for example, at about 5%, w/w). The resulting gel is then filled into Ready-to-Fill sterile syringes and autoclaved at sufficient temperatures and pressures for sterilization for at least about 1 minutes.

After autoclaving, the final HA/lidocaine product is packaged and distributed to physicians. The product manufactured in accordance with this method exhibits one or more characteristics of stability as defined elsewhere herein. For example, the autoclaved HA/lidocaine product has a viscosity, cohesivity, and extrusion force that are acceptable. No degradation of the HA/lidocaine gel product is found during testing of the product after the product has spent several months in storage.

Example 3 Properties of Soft Tissue Fillers

Properties of HA/lidocaine compositions manufactured in accordance with methods described herein are shown in the Table 1 below. Extrusion force for example was measured using an INSTRON® Advanced Materials Testing System Model 5564 (Instron, Norwood, MA) running BLUEHILL® software version 2.11 (Instron, Norwood, MA). Table 1

Homogeneous transparent gel
7.2
10.8N
23.7 mg/g
321 mOsml/kg
0.29%
Conforms

In order to ensure that product specifications were maintained throughout the shelf life of the composition, multiple studies were performed. In addition, 2,6 dimethylaniline content was measured in order to confirm the absence of lidocaine degradation.

Table 2 provides a summary of stability testing results on the composition manufactured as described herein. Table 2

Aspect Transparent and homogeneous	Conforms	Conforms	Conforms
pH	7.2	7.2	7.2
Extrusion Force (N)	11.9	11.1	11.9
NaHA Concentration (mg/g)	23.8	23.1	24.2
Sterility	Conforms	Conforms	Conforms
Osmolarity (mOsm/kg)	349	329	342
Lidocaine Content (%)	0.29	0.29	0.29
2,6-dimethylaniline content	Conforms	Conforms	Conforms

It was discovered that at 9 months time (from manufacture date), the composition continues to meet the product specifications.

Example 4 Kinetic Release

The following example illustrates the kinetic of release of lidocaine from cohesive HA gels according to the present description. The aim of the Example is to show that the lidocaine contained in HA gels according to the present description is freely released from the gels when placed in the skin.

Dialysis was performed for different periods of time (about 10g of gel were placed in a small dialysis bag and then put in 30g of water). After each dialysis was stopped at a given time, the gel was homogenized with a spatula and the amount of lidocaine was determined by UV method. The final concentration of the dialysis bath met the theoretical concentration of lidocaine which indicates the free release of lidocaine from the gel.

Table 3 illustrates lidocaine concentration in % (w/w), correction of the value and determination of the % of released lidocaine. Additionally, Figure 9 graphically illustrates the results tabulated in Table 3 below. Within Figure 9 is indicated the theoretical equilibrium concentration of lidocaine that would exist if the lidocaine were retained in the gel or if it were to be freely released. As is graphically illustrated therein, the data suggest that the lidocaine is freely released from the gel. Table 3

	0 hr	1 hr 30 min	5 hr	7 hr	23 hr	48 hr	72 hr
	0.29	0.20	0.16	0.15	0.08	0.07	0.07

Figure 1 shows the concentration profile of lidocaine over time reaches an equilibrium that corresponds to free release of lidocaine. The formulation of the composition in Figure 1 is a cohesive crosslinked HA gel. The composition has a HA concentration of about 24 mg/mL, about 6% crosslinking, a G' of about 170 and a high molecular weight to low molecular weight HA ratio from about 95% to 5% to about 100% high molecular weight HA. This in vitro study shows that lidocaine is freely released from the gel and not retained in the gel once implanted.

Claims (1)

1. A method of preparing a soft tissue filler composition, the method comprising the steps of:

   providing a hyaluronic acid component crosslinked with at least one crosslinking agent selected from the group consisting of 1,4-butanediol diglycidyl ether (BDDE), 1,2-bis(2,3-epoxypropoxy)ethylene and 1-(2,3-epoxypropyl)-2,3- epoxycyclohexane, or combinations thereof;

   wherein the hyaluronic acid component comprises 10% to 20% free hyaluronic acid by volume;

   adjusting the pH of said hyaluronic acid component to an adjusted pH above 7.5; and

   adding a solution containing at least one anesthetic agent to said hyaluronic acid component having said adjusted pH to obtain a hyaluronic acid-based soft tissue filler composition,

   wherein the at least one anesthetic agent is lidocaine HCl.