Chart review exploring drug drug interactions among women using implants and antiretroviral therapy

What is it about?

Implants are one of the most effective contraceptives available. However, the mechanism of action relies on the hormones in the devices. There are drug-drug interactions for certain medications and hormonal contraceptives (for example medications for tuberculosis er epilepsy treatment). Certain types of antiretroviral therapy (ART) regimens, in the non-nucleoside reverse transcriptase inhibitor (NNRTI) family of drugs, have been known to have drug-drug interactions because they use the same metabolic pathways. And because implants release a lower dose of hormones than other contraceptives, the risk of contraceptive failure is higher. Studies nested in other trials or of the pharmacokinetics of these interactions, had identified an NNRTI called efavirenz as a cause of contraceptive failures. We sought out to ascertain how common these were in a review of medical records in clinics caring for people living with HIV in Western Kenya and whether the timing of the failure suggested that an earlier removal could compensate for it. We were surprised to find not only high rates of pregnancies among women using efavirenz, but that they also occurred among women using a different NNRTI, nevirapine. Other studies had not found this and even suggested that nevirapine boosts the level of hormone in the bloodstream. We sought explanations for this unexpected finding, for example to see if a triple drug interaction could be at play, with tuberculosis treatment, since this disease is common among people living with HIV, but we could not. It could be that there were errors in medical record abstractions that resulted in these findings, as medical chart reviews have many limitations. Because this is an emerging area of inquiry, we publish these anomalous findings and see whether further studies dispute or confirm the findings. Regardless of whether the nevirapine findings are true, we also discuss practice implications for women contemplating using implants and the ART regimen with efavirenz. We suggest that for women who are satisfied with their implants, perhaps they could opt for a different ART regimen, such one with dolutegravir (DTG), since the implant would protect them from the possible risk of birth defects associated with DTG.

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Why is it important?

Women who are using implants clearly want to avoid pregnancy, so when the device fails, it put the women at risk of medical complications of pregnancy and the disruptions that a pregnancy implies in their and their families' lives. Women living with HIV already have additional medical needs and a pregnancy puts them at even higher risk. Health care providers need clear and accurate information and guidance on how to advice women about their medical care and contraceptive needs. The issue of drug-drug interactions has not yet been well studied.

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