Comparing adherence to HIV Pre-Exposure Prophylaxis (PrEP) among new, male PrEP users initiating F/TAF vs. F/TDF

BACKGROUND: Pre-exposure prophylaxis (PrEP) with emtricitabine/tenofovir disoproxil fumarate or tenofovir alafenamide (F/TDF or F/TAF) is effective at preventing HIV when used consistently. There are limited real-world data that compare adherence and seroconversion rates for F/TAF and F/TDF over concurrent timeframes. This study compared adherence measures and HIV incidence in new PrEP users initiating either F/TAF or F/TDF using a real-world database.
METHODS: This retrospective longitudinal analysis used PurpleLab, a nationally representative medical and pharmacy claims database (all U.S. payer types). Eligible users were (recorded as) male adults ('¥18 years) with no history of PrEP (variable baseline from 10/1/2015), initiating F/TAF or F/TDF 10/1/2019-1/31/2020 (index date) with '¥1 medical claim 30 days prior (for improved linkage to clinical records). Users with evidence of HIV/HepB treatment or '¥1 HIV/HepB diagnosis (-12 months to +30 days of index date) were excluded. Included users were followed for '¥240 days. Outcomes included: proportion of days covered (PDC), adherence (PDC '¥0.8), and seroconversion ('¥1 claim with HIV diagnosis). Differences in outcomes were assessed using Chi-square and T-tests. Multivariable logistic regression estimated the effect of PrEP regimen on adherence, controlling for age group, geography and type of insurance.
RESULTS: A total of 1,113 F/TAF and 1,961 F/TDF users met study criteria. Adherence dropped over time for both regimens; F/TAF users had significantly higher mean PDC and adherence (PDC '¥0.8) at all time points (Table). In multivariable analyses, F/TAF users had 1.67 higher odds of adherence (PDC'¥0.8) relative to F/TDF (180 days; P<0.0001); adherence odds also increased with older age, private insurance. Differences between seroconversion rates (F/TAF: 1.24/100 person-years; F/TDF: 1.80/100 person-years) were not significant (p>0.05).

Table: Adherence Measures Over Time, by PrEP regimen
Regimen	Mean PDC (180d)	Mean PDC (210d)	Mean PDC (240d)		Adherence (180d)	Adherence (210d)	Adherence (240d)
F/TAF (n=1,113)	0.65**	0.62**	0.58**		47%**	44%**	36%**
F/TDF (n=1,961)	0.57	0.53	0.50		34%	31%	23%
PDC: proportion of days covered; Adherence: proportion of users with PDC '¥0.8; d = days of follow up ** differences significant at p<0.0001 comparing F/TAF to F/TDF over follow up period

CONCLUSIONS: These results are the first to compare adherence to F/TDF and F/TAF over concurrent timeframes, using real-world data. F/TAF users had higher levels of adherence, compared to F/TDF users over the same period. Overall seroconversion rates were low for both F/TDF and F/TAF; the study did not have sufficient power to detect differences between the two cohorts.