Interactions between Etonogestrel-releasing contraceptive im
Long-acting reversible contraceptives are effective contraceptives for women with HIV, but there are limited data on etonogestrel implant and antiretroviral therapy pharmacokinetic drug-drug interactions.

Researchers evaluated etonogestrel/antiretroviral therapy drug-drug interactions, and the effects of etonogestrel on ritonavir-boosted-atazanavir, ritonavir-boosted-lopinavir, and efavirenz pharmacokinetics.

They enrolled postpartum women using etonogestrel implants and receiving ritonavir-boosted-atazanavir, ritonavir-boosted-lopinavir, or efavirenz-based regimen. Etonogestrel implants were inserted 2 to 12 weeks postpartum. They performed pharmacokinetic sampling pre-etonogestrel insertion and 6 to 7 weeks post-insertion. They measured antiretroviral concentrations pre and post-etonogestrel insertion and compared etonogestrel concentrations between antiretroviral regimens. And considered a minimum serum etonogestrel concentration of 90 pg/ml adequate for ovulation suppression.

Investigators collected pharmacokinetic data for 74 postpartum women, 22 on ritonavir-boosted-atazanavir, 26 on ritonavir-boosted-lopinavir, and 26 on efavirenz.

- The median serum concentrations of etonogestrel when co-administered were highest with etonogestrel/ritonavir-boosted-atazanavir and etonogestrel/ritonavir-boosted-lopinavir, and lowest with etonogestrel/efavirenz.

- Minimum concentration (Cmin) of ritonavir-boosted-atazanavir and ritonavir-boosted-lopinavir were lower after etonogestrel implant insertion, but overall exposure, pre-dose concentrations, clearance, and half-lives were unchanged.

- They found no significant change in efavirenz exposure after etonogestrel insertion.

Conclusively, unlike efavirenz, ritonavir-boosted-atazanavir and ritonavir-boosted-lopinavir were not associated with significant decreases in etonogestrel concentrations. Efavirenz was associated with a significant decrease in etonogestrel concentrations.