(PL27) RETROSPECTIVE OBSERVATION OF TENOFOVIR DRUG LEVELS IN DRY BLOOD SPOT SPECIMENS IN TRUVADA AND DESCOVY PATIENTS

Background:
The utility of dried blood spots (DBS) for measuring tenofovir diphosphate (TFV-DP) concentrations has been well-documented. However, large-scale observational studies based on diagnostic labs' retrospective analyses are lacking. This study aims to fill that gap by providing comprehensive data on TFV concentrations in a large cohort.

Methods:
TFV-DP, creatinine, and HIV ELISA assays using DBS were developed and validated according to CLIA and CAP guidelines. The lower limit of quantification of TFV-DP in DBS was 100 fmol/punch. Clinically collected TFV-DP test samples analyzed in 2023 were curated from the Laboratory Information System (LIS) and analyzed.

Results:
A total of 11,298 specimens were successfully tested for TFV-DP, with male samples comprising 95% of the total TFV-DP test samples. The 20-39 age group represented 66% of the total samples, marking the highest age range for both males and females.  Descovy drug monitoring accounted for 70% of total TFV-DP test samples.  Interestingly, co-testing for creatinine and HIV on DBS was performed on <1% and 5%, respectively, of TFV-DP samples. The Truvada 99th percentile drug concentration range was <100 - 8577 fmol/punch, with a median of 2213 fmol/punch. The Descovy 99th percentile drug concentration range was <100 - 6196 fmol/punch, with a median of 544 fmol/punch.

Conclusion:
This study highlights the observed drug concentrations were similar to the range reported by Gilead (NDA 208215/S-0120.) The high percentage of male samples and the predominant age range of 20-39 reflect the demographic most engaged in PrEP monitoring and HIV prevention. The limited number of patients who tested for creatinine and HIV ELISA underlines areas for improved clinical monitoring, assuming these patients were not tested by other methods. DBS-based TFV-DP drug monitoring, along with creatinine and HIV ELISA, can better support PrEP patients and enhance the effectiveness of PrEP regimens.