The Effect of Protease Inhibitors on the Pharmacokinetics of Oral Norethindrone Contraception

BACKGROUND/RATIONALE : It is recognized that there is a dearth of clinically applied, population based, empiric data to guide contraceptive recommendations in HIV + women on ARVs.(1) Protease inhibitors (PI) and non nucleoside reverse transcriptase inhibitors (NNRTI ) induce micro enzyme systems such as CYP 3a4, which in turn alters the bio-availability and pharmacokinetics of other concurrently administered medications.(2) Empiric trials from small samples, often of 10-20 HIV negative subjects, have demonstrated that concurrent administration of combined oral contraceptives (COC) and a PI or a NNRTI have been associated with decreased plasma ethinyl estradiol (EE) levels. These pharmacokinetic findings have raised concern that decreased bio-availability of EE may result in decreased contraceptive efficacy, with possible increased unintended pregnancy. Some of these COC studies have demonstrated that there is no change in the serum levels of norethindrone (NET) on ARVs.(3-16) However, there are no published trials focused on oral NET or oral progestin-only pills (POP) to guide management in HIV+ women.(17)

OBJECTIVES:

Primary objective of this study is:

To detect a ±40% difference in AUC of serum NET in HIV+ women taking ATV/RTV as compared to AUC of NET in HIV+ women taking an ARV regimen that has demonstrated no interaction with NET in the past.

Primary endpoint: Natural log-transformed NET PK parameter AUC from 0 to 72 hours following oral administration, with multiple discrete serum data points for each subject on ATV/RTV. This will be compared to natural log-transformed NET PK AUC from 0 to 72 hours following oral administration, with multiple discrete serum data points for controls HIV+ women taking an ARV regimen that has demonstrated no interaction with NET in the past.