PrEParing for the unexpected: mechanisms and management of HIV pre-exposure prophylaxis failure

Determinants of adherence to daily PrEP measured as intracellular tenofovir diphosphate concentrations over 24 months of follow-up among men who have sex with men

OBJECTIVES

Adherence is key to the effectiveness of oral pre-exposure prophylaxis (PrEP) to prevent HIV. Therefore, we aimed to explore factors associated with adherence to daily PrEP (dPrEP).

METHODS

Men who have sex with men (MSM) using dPrEP (emtricitabine/tenofovir disoproxil) within the Amsterdam PrEP demonstration project at the Public Health Service of Amsterdam, provided dried blood spots (DBS) 12 and 24 months after PrEP initiation. From DBS, we determined intracellular tenofovir diphosphate (TFV-DP) concentrations to assess adherence; TFV-DP ≥700 fmol/punch was considered adequate. We assessed associations of sociodemographic, clinical and behavioural characteristics with TFV-DP concentrations using multivariable linear regression.

RESULTS

Of 263 participants who attended 12-month or 24-month study visits while on dPrEP, 257 (97.7%) provided DBS at one or both visits (492 DBS in total). Median TFV-DP concentration was 1299 (IQR 1021-1627) fmol/punch (12 months: 1332 (1087-1687); 24 months: 1248 (929-1590]). Higher TFV-DP concentrations were associated with: older age (p=0.0008), condomless anal sex with a casual partner in 6 months preceding PrEP initiation (+166 fmol/punch; 95% CI 36.5 to 296) and using a mobile application providing visualised feedback on PrEP use and sexual behaviour (+146 fmol/punch; 95% CI 28.1 to 263). Lower TFV-DP concentrations were associated with longer duration of PrEP use (24 vs 12 months; -91.5 fmol/punch; 95% CI -155 to -28.1). Time-updated number of sex partners, diagnosed STIs and chemsex were not associated with TFV-DP concentrations.

CONCLUSIONS

Overall, TFV-DP concentrations were high among MSM using dPrEP, indicating excellent adherence. Especially older participants, those who reported condomless anal sex with a casual partner prior to PrEP initiation and those who used an app with visualised feedback showed higher levels of adherence. As TFV-DP concentrations had decreased slightly at 2 years of PrEP use when compared with 1 year, we emphasise the importance of adherence counselling to those who continue using PrEP.

TRIAL REGISTRATION NUMBER

NL5413.

Acquisition of tenofovir-susceptible, emtricitabine-resistant HIV despite high adherence to daily pre-exposure prophylaxis: a case report

BACKGROUND

Pre-exposure prophylaxis (PrEP) with emtricitabine and tenofovir disoproxil fumarate is highly protective against HIV infection. We report a case of tenofovir-susceptible, emtricitabine-resistant HIV acquisition despite high adherence to daily PrEP.

METHODS

Adherence to PrEP was assessed by measuring concentrations of emtricitabine and tenofovir disoproxil fumarate or their metabolites in plasma, dried blood spots, and hair. After seroconversion, genotypic and phenotypic resistance of the acquired virus was determined by standard clinical tests and by single-genome sequencing of proviral genomes. HIV partner services identified the likely transmission partner.

FINDINGS

A 21-year-old Latino man tested positive for HIV infection 13 months after PrEP initiation. He had a negative HIV antibody test, but detectable HIV RNA with 559 copies per mL. He reported good adherence to daily PrEP. He was linked to care and immediately started antiretroviral therapy, at which point his RNA was 1544 copies per mL and his HIV antibody test was positive. The HIV genotype revealed Met184Val, Leu74Val, Leu100Ile, and Lys103Asn mutations in reverse transcriptase, and the phenotype showed susceptibility to tenofovir disoproxil fumarate and resistance to emtricitabine. Segmental hair analysis of tenofovir disoproxil fumarate concentrations measured in 1 cm segments of hair from the scalp indicated consistently high adherence to PrEP in each of the 6 months before HIV diagnosis (0·0672-0·0889 ng/mg). Concentrations of tenofovir diphosphate (1012 fmol per punch) and emtricitabine triphosphate (0·266 fmol per punch) in a dried blood spot indicated high adherence over the preceding 6 weeks. Concentrations of emtricitabine (870·5 ng/mL) and tenofovir disoproxil fumarate (188·2 ng/mL) measured in plasma 3 months before HIV seroconversion confirmed adherence in the days preceding that visit. The likely transmission partner was not engaged in HIV primary care and had a similar viral genotype.

INTERPRETATION

Acquisition of HIV virus that is susceptible to tenofovir disoproxil fumarate, but resistant to emtricitabine can occur despite high adherence to PrEP. Quarterly screening for HIV and sexually transmitted diseases facilitates early diagnosis in people on PrEP; when combined with prompt linkage to care and partner services this can prevent onward transmission of HIV.

FUNDING

US National Institutes of Health.