Ouellet D, Hsu A, Qian J, Locke CS, Eason CJ, Cavanaugh JH, Leonard JM, Granneman GR. Effect of ritonavir on the pharmacokinetics of ethinyl oestradiol in healthy female volunteers.
Br J Clin Pharmacol 1998;
46:111-6. [PMID:
9723818 PMCID:
PMC1873670 DOI:
10.1046/j.1365-2125.1998.00749.x]
[Citation(s) in RCA: 124] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/1997] [Accepted: 03/03/1998] [Indexed: 11/20/2022] Open
Abstract
AIMS
To assess the effects of the protease inhibitor ritonavir on the pharmacokinetics of ethinyl oestradiol in healthy female volunteers.
METHODS
This was an open-label, single centre study in 23 subjects who received two single doses of oral contraceptive containing 50 microg ethinyl oestradiol on Day 1 (alone) and on Day 29 during concomitant ritonavir. Each subject received 16 days of every 12 h doses of ritonavir from Day 15 through Day 30. Blood samples were collected for serum ethinyl oestradiol concentrations for 48 h after each dose and for plasma ritonavir on Day 29 at 0 and 4 h postdose.
RESULTS
Statistically significant decreases in ethinyl oestradiol mean Cmax (-32%) and mean AUC (-41%), and a statistically significant increase in the mean terminal elimination rate constant (+31%) were observed during concomitant ritonavir. The harmonic mean terminal half-life decreased from 17 h to 13 h during concomitant ritonavir. No statistically significant change was noted in tmax. The ratios of means (95% confidence intervals) for Cmax and AUC were 0.682 (0.612-0.758) and 0.595 (0.506-0.694), respectively. The changes in ethinyl oestradiol pharmacokinetics were consistent with an increase in clearance from enzymatic induction of glucuronidation and/or cytochrome P450 hydroxylation. Mean steady-state ritonavir concentrations of 6.5 and 13.4 microg ml(-1) were observed at 0 and 4 h postdose, respectively.
CONCLUSIONS
Considering the extent of the decrease in ethinyl oestradiol concentrations, the use of alternate contraceptive measures should be considered when ritonavir is being administered.
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