Pharmacokinetics of betamethasone in healthy adults after intravenous administration

M. C. Petersen, R. L. Nation, W. G. McBride, J. J. Ashley, R. G. Moore

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Abstract

The pharmacokinetics of betamethasone and its phosphate ester are described in 8 healthy adults after i. v. bolus injection of 10.6 mg betamethasone phosphate. Both compounds were measured by high-performance liquid chromatography with ultraviolet detection using sample handling methods which prevented hydrolysis of the ester in vitro. Betamethasone phosphate disappeared rapidly from plasma (mean half-life=4.7 min) as betamethasone levels rose. Betamethasone plasma levels reached a peak 10-36 min after administration of the phosphate before declining in a biexponential manner. The terminal slow disposition phase had a mean half-life of 6.5 h. Only about 5% of the dose was recovered from urine as betamethasone, indicating extensive extrarenal clearance of betamethasone. Protein binding and blood/plasma concentration ratio were also determined. In comparison with its stereoisomer, dexamethasone, betamethasone is also cleared mainly by metabolism but has a lower plasma clearance, is less plasma bound, has a higher blood/plasma concentration ratio, and a higher volume of distribution. Endogenous cortisol levels were measured in the subjects who received betamethasone phosphate and in a matched control group of 4 subjects who did not. Betamethasone abolished the normal episodic secretion of cortisol and rapidly reduced its plasma concentration to a basal level. Cortisol plasma levels were not restored at 24 h but had returned to normal by 48 h after dosing.

Original languageEnglish
Pages (from-to)643-650
Number of pages8
JournalEuropean Journal of Clinical Pharmacology
Volume25
Issue number5
DOIs
Publication statusPublished - 1 Sep 1983

Keywords

  • betamethasone
  • cortisol
  • high-performance liquid chromatography
  • pharmacokinetics

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