Health professionals have raised concerns over a potential drug interaction between Lenacapavir, a long-acting HIV prevention injection, and Viagra (Sildenafil), a common medication for erectile dysfunction. Experts say combining the two drugs may increase the risk of serious side effects, prompting calls for careful dose adjustments.
Lenacapavir is a biannual injection administered to HIV-negative individuals as part of pre-exposure prophylaxis (PrEP) and is intended to prevent HIV infection. However, medical experts have highlighted that Lenacapavir can slow the activity of the liver enzyme CYP3A4, which is responsible for metabolizing Viagra in the body.
“Lenacapavir increases the concentration of Viagra, hence it becomes toxic. Patients must start with a lower dose of Viagra,” said Dr. Elizabeth Irungu, Regional Technical Advisor for PrEP at Jhpiego.
As a result, taking Lenacapavir alongside Viagra may cause the latter to remain in the body longer and at higher concentrations than intended. Elevated Viagra levels can increase the risk of severe side effects, including low blood pressure, dizziness, headaches, vision changes, and priapism—a prolonged and painful erection.
Dr. Irungu emphasized that healthcare providers in Kenya now recommend starting patients on a lower dose of Viagra when used concurrently with Lenacapavir. She also urged patients to provide complete medical histories, including any medications for erectile dysfunction, high cholesterol, or tuberculosis, to allow clinicians to determine appropriate dose adjustments.
Lenacapavir is administered via injection in areas with higher fatty tissue, such as the abdomen or thighs. The standard initiation process involves two injections combined with two oral tablets on the first day, followed by two more oral tablets the following day. Subsequent injections are given every six months.
“If a client misses their six-month follow-up by more than two weeks, they must restart the dosing process,” Dr. Irungu explained.
Although the injection is given twice a year, its inhibitory effect on CYP3A4 can persist for up to nine months, meaning the interaction risk with Viagra or other CYP3A4-metabolized medications may continue long after the last dose.
Lenacapavir has also been shown to be safe for use in pregnant and breastfeeding women, supporting Kenya’s ongoing efforts to reduce mother-to-child HIV transmission.
Health authorities continue to stress the importance of careful patient counseling, adherence to dosing schedules, and awareness of potential drug interactions. Patients taking Viagra alongside Lenacapavir should consult their healthcare providers before starting or adjusting their dosage to minimize risks.
