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Differing drug distribution in penis and rectum of men taking TDF/FTC PrEP
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19th International Workshop on Clinical Pharmacology of Antiviral Therapy
Mark Mascolini
Men using tenofovir/emtricitabine (TDF/FTC) for preexposure prophylaxis (PrEP) had detectable drug levels in the urethra more often than on the glans penis, according to results of an 18-man study [1]. FTC concentrations proved similar on urethral and rectal swabs, but tenofovir (TFV) levels were lower on urethral specimens than on rectal swabs.
Researchers from the Centers for Disease Control and Prevention (CDC) and Emory University noted that men account of almost half of new HIV infections globally, and penile exposure during sex puts them at risk. Yet studies of mucosal HIV acquisition focus mainly on the rectum and vagina. The CDC/Emory team planned this study to measure TFV and FTC penetration of penile tissues in men taking TDF/FTC PrEP.
The study involved 18 HIV-negative gay or bisexual men 18 to 49 years old, including 9 who took a single dose of TDF/FTC and had samples collected 4 and 24 hours later, and 9 who took daily TDF/FTC for 10 days and had samples collected after 4 and 10 days. Samples came from swabs inserted in the urethra, swabs rolled along the surface of the glans penis, swabs collected from the rectal mucosa via rigid sigmoidoscopy, and blood samples.
TFV could be detected on 18 of 36 urethral swabs (50%) and FTC on 27 of 36 urethral swabs (75%). In contrast, TFV could be detected on 11 of 36 glans swabs (30.5%) and FTC on 19 of 36 glans swabs (53%). TFV and FTC concentrations varied widely in urethral and glans swabs, yet urethral TFV and FTC levels correlated strongly with each other (r = 0.659, P < 0.013).
TFV concentrations on urethral swabs proved lower than those on rectal swabs, but FTC levels were similar on urethral and rectal swabs. Both TFV and FTC concentrations on urethral specimens significantly exceeded TFV and FTC levels in plasma.
The CDC/Emory investigators believe their findings "point to the possible role of urethral TFV and FTC in PrEP protection of men against penile HIV acquisition."
Reference
1. Haaland R, Fountain J, Dinh C, et al. Evaluation of tenofovir and emtricitabine in the penile compartment of men receiving oral pre-exposure prophylaxis for HIV prevention. 19th International Workshop on Clinical Pharmacology of Antiviral Therapy. May 22-24, 2018. Baltimore. Abstract 39.
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