Health professionals have raised concerns that Lenacapavir, a long-acting HIV prevention drug administered twice a year, may interact with Viagra (Sildenafil).
Experts explain that Viagra is broken down in the liver by the enzyme CYP3A4, while Lenacapavir slows down this enzyme.
As a result, taking the two drugs together may cause Viagra to remain in the body longer and at higher concentrations than intended.
Additionally, Lenacapavir may increase the blood levels and effects of Viagra. Health experts warn that elevated Viagra levels could heighten the risk of side effects, including severe low blood pressure, dizziness, headaches, vision changes, and priapism (a prolonged painful erection).
Medical professionals are therefore recommending dose adjustments for patients using Viagra. Clinical guidelines now advise a lower starting dose of Viagra when taken alongside Lenacapavir.
Although the Lenacapavir injection is administered once every six months, its inhibitory effect on the CYP3A4 enzyme can persist for up to nine months after the last dose. This means the risk of drug interaction may continue long after the injection is given.
“The Lenacapavir increases the concentration of Viagra, hence it becomes toxic, so you have to start with a lower dose of Viagra,” said Dr. Elizabeth Irungu, Regional Technical Advisor for PrEP at Jhpiego.
Dr. Irungu has urged Kenyans to provide accurate information about their medical history when initiating Lenacapavir, to enable healthcare providers to determine whether dose adjustments are necessary.
She noted that individuals on medication for high cholesterol, erectile dysfunction, and tuberculosis may be particularly affected.
Lenacapavir is strictly administered to individuals who are HIV negative. The injection is given in the abdomen or thighs, where there is more fatty tissue.
“During initiation, a client receives two injections accompanied by two oral tablets on the first day and two oral tablets the following day. Thereafter, the client waits six months for the next dose,” Dr. Irungu explained.
However, if a client fails to return within two weeks after the six-month period, they will be required to restart the dosing process.
In efforts to reduce mother-to-child transmission of HIV, Lenacapavir has also been proven safe for use among pregnant and breastfeeding mothers.
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