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Researchers observed a significant disconnect between self-reported PrEP adherence and laboratory markers of adherence among people who inject drugs.

“Medication adherence monitoring is a complex process that often relies on self-report. Self-reported data is relatively easy to collect but prone to biases, and the size of these biases is often unknown,” Olga Morozova, PhD, explains. “PrEP adherence monitoring is especially challenging because people may be less motivated to adhere to PrEP compared with ART for people with HIV. Laboratory markers offer an objective measure of PrEP adherence that is not susceptible to social desirability or other biases.”

This is important for all PrEP users, Dr. Morozova notes. However, the extent of a potential mismatch between self-reported adherence and objective markers among people who inject drugs was unknown, including in a setting that provided no incentives for adhering to PrEP.

In a study published in the International Journal of Drug Policy, researchers examined whether PrEP adherence among people who inject drugs could be improved with text message reminders. Dr. Morozova and colleagues randomly assigned participants to receive daily oral PrEP with (n=99) or without (n=100) text message reminders. Participants started PrEP at an HIV clinic and attended follow-up visits at months 1, 3, and 6 in a community harm reduction center. Follow-up visits included a structured interview, adherence counseling, PrEP administration, and laboratory testing.

At the 6-month visit, 158 participants remained (79.4%) in the study. Among this group, 84% reported opioid injection drug use within the prior 30 days, while 20% reported stimulant injection drug use in that same period. Most participants (77%) reported taking more than 95% of prescribed PrEP doses within the last month; 87% reported taking the last dose within 2 days of the visit. However, only 3% of participants (5/158) had laboratory markers that indicated consistent PrEP uptake (four or more doses per week). The researchers found no association between the text message intervention and identifying PrEP metabolites.

PW spoke with Dr. Morozova to learn more about what the study results mean for clinicians.

PW: What are this study’s most important findings?

Dr. Morozova: The study was designed to test whether text message reminders could improve PrEP adherence among people who inject drugs and are at high risk for HIV. The question of concordance between the self-reported and objectively measured adherence was secondary at the study design stage, but after we analyzed the data, we realized that the extent of mismatch was the central finding of this study.

PrEP adherence is key for protection from HIV. Previous studies among MSM suggest that four or more doses per week may be sufficient to offer nearly 100% protection. However, these results have not been replicated among people who inject drugs. Our study findings suggest that sufficient PrEP adherence level may not be attainable among active injection drug users.

The consistently high self-reported adherence rates and the extremely low levels of concordance between those reports and laboratory markers were surprising. We hypothesize that social desirability bias may have been a strong incentive for participants to report high adherence, even though they were not penalized for reporting non-adherence.

Can you elaborate on why reminders did little to improve adherence?

The effect of text message reminders on PrEP adherence among people who inject drugs was small because the overall adherence level was very low. In other studies conducted among populations with higher overall adherence, the effect of text message reminders was more substantial. In our study, the non-significant effect of text message reminders suggests that the reasons for nonadherence are unrelated to memory or daily habits, or lack thereof, and are likely related to low-risk perception and motivation.

What are the implications for clinicians?

First, it is important to reconsider the existing guidelines and recommendations for aggressive PrEP scale-up among people who inject drugs because they are based on a single trial that is hardly generalizable to most people who inject drugs and is outdated.

Daily oral PrEP may not work for people who are active injection drug users. Other options—eg, long-acting injectable PrEP—may overcome these concerns, but they must be tested in this population. If clinicians do choose to prescribe daily oral PrEP to people who continue to inject, they should incorporate objective measures of adherence into clinical practice.

People who inject drugs who are prescribed PrEP should receive ongoing counseling, support, and additional interventions to reduce the risk for HIV; PrEP adherence should not be assumed.

Finally, it is vital to ensure regular HIV testing and make sure patients are switched to ART if they contract HIV. Remaining on PrEP after HIV infection poses a risk of antiviral drug resistance.

What would you like future research to focus on?

It is important to design and test novel interventions to improve PrEP adherence using both self-report and biomarkers to measure adherence. Research to test the efficacy of injectable PrEP among people who inject drugs is also needed. Long-acting injectable PrEP holds promise for overcoming medication adherence challenges with a daily pill.

Providers who prescribe PrEP to people who inject drugs should monitor adherence, preferably using laboratory markers. Additionally, people who inject drugs who are prescribed PrEP should be offered continued counseling regarding other measures to reduce HIV risk.