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Prazosin kinetics in hypertension

Clin Pharmacol Ther. 1981 Oct;30(4):439-46. doi: 10.1038/clpt.1981.186.

Abstract

Prazosin kinetics were studied after single doses (intravenous and oral, 0.5 mg) and after increasing multiple doses (0.5 to 5 mg three times daily) in eight patients with hypertension. After intravenous administration the kinetics could be described by a linear two-compartment open model. Terminal half-life (t1/2 beta) was about 3 hr and apparent volume of distribution (Vd beta) about 0.6 l/kg. After oral doses bioavailability ranged between 55% and 82%. Since total plasma clearance was low (0.14 l/kg x hr) incomplete bioavailability was the result of incomplete absorption rather than of first-pass liver metabolism. The estimated extraction ratio was about 14%. Renal clearance was negligible; only 1% to 2% of the dose was recovered unchanged in urine. Binding to plasma proteins to both albumin and alpha 1-acid glycoprotein was substantial (97%), with albumin being most important. Increasing multiple doses showed that prazosin followed first-order kinetics with a linear correlation between dose and steady-state plasma concentration (P less than 0.001). There were substantial variations in plasma concentrations between patients and there were also day-to-day variations in concentration within the same patient.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biological Availability
  • Blood Proteins / metabolism
  • Female
  • Humans
  • Hypertension / drug therapy
  • Hypertension / metabolism*
  • Kidney / metabolism
  • Kinetics
  • Male
  • Middle Aged
  • Prazosin / administration & dosage
  • Prazosin / metabolism*
  • Protein Binding
  • Quinazolines / metabolism*

Substances

  • Blood Proteins
  • Quinazolines
  • Prazosin