The effect of atazanavir/ritonavir on the pharmacokinetics of an oral contraceptive containing ethinyl estradiol and norgestimate in healthy women.

BACKGROUND

Coadministration of oral contraceptives with protease inhibitors is complicated by drug interactions. An open-label three-period single-sequence study assessed the effect of coadministration of atazanavir (ATV)/ritonavir (RTV) with Ortho Tri-Cyclen(®) and with Ortho Tri-Cyclen(®) LO (Ortho-McNeil-Janssen Pharmaceuticals, Inc., Raritan, NJ, USA) on the pharmacokinetics (PK) of ethinyl estradiol (EE), norgestimate (NGM), ATV and RTV.

METHODS

A total of 20 healthy women aged 18-45 years received study treatments. In the lead-in period and in period 1, participants received a full cycle of Ortho Tri-Cyclen (EE 35 μg with NGM 0.18/0.215/0.25 mg) from days 1-28. In period 2, participants received a full cycle of Ortho Tri-Cyclen LO (EE 25 μg with NGM 0.18/0.215/0.25 mg) plus ATV/RTV (300/100 mg once daily) on days 29-42. PK assessments were performed on days 14 and 42 in periods 1 and 2, respectively.

RESULTS

ATV/RTV with dose-normalized EE/NGM resulted in geometric mean reductions of 16% in EE peak plasma concentration (C(max)), 19% in EE area under the concentration-time curve for a dosing interval (AUC([τ])) and 37% in EE lowest plasma concentration (C(min)), compared with EE 35 μg with NGM in the absence of ATV/RTV. NGM with EE and ATV/RTV 300/100 mg once daily resulted in increases of approximately 68%, 85% and 102% in 17-deacetyl NGM C(max), AUC((τ)) and C(min), respectively. Two participants discontinued the study because of adverse events.

CONCLUSIONS

ATV/RTV with Ortho Tri-Cyclen was well-tolerated and reductions in EE were not predicted to decrease contraceptive efficacy if the formulation contained ≥30 μg of EE.