Cocaine users have poorer adherence to HIV pre-exposure prophylaxis (PrEP) and engagement with care, according to research published in the online edition of the Journal of Acquired Immune Deficiency Syndromes. Even light cocaine use doubled the odds of having blood levels of tenofovir, a key PrEP drug, that were insufficient to protect against infection with HIV. Individuals with moderate/heavy cocaine use were three times more likely to drop out of PrEP care than individuals who did not use cocaine.
“These findings underscore the importance of providing comprehensive care at the time of PrEP initiation that includes assessment of cocaine use and other potential barriers to optimal adherence,” comment the investigators. “Expanded efforts are needed to assist persons who use cocaine with completing routine follow-up visits that allow for regular monitoring and present an opportunity to support adherence, discuss risk reduction, and address co-occurring stimulant use.”
Providers have reported that a significant proportion of PrEP users drop out of care. Little is known about the association between the use of stimulant drugs such as cocaine and adherence to PrEP and retention in PrEP programmes. This is an important gap in knowledge as stimulant use is increasing among men who have sex with men (MSM), with a recent study showing that a quarter of MSM in San Francisco used cocaine in the previous three months.
Investigators therefore designed a study which analysed data from 400 MSM and transgender women who took PrEP as part of the iPrEx OLE study.
Cocaine use was measured by establishing measuring concentrations of the drug in hair samples at the first quarterly study visit. Hair analysis indicates drug use in the previous three months. Cocaine levels between 500-3000ph/mg corresponded to light use (perhaps once or twice a month), with concentrations above this level indicating moderate or heavy use of the drug (perhaps weekly to daily use).
Blood concentrations of tenofovir were assessed in the first three months after starting PrEP. The adherence outcome was blood concentration of the medication below the level of quantification. This was selected because levels of tenofovir above this are associated with greater than 90% protection against infection with HIV.
The study population consisted of 358 MSM (90%) and 42 transgender women (10%). Three-quarters were Hispanic/Latino and the median age at PrEP initiation was 29 years.
Just over a fifth (21%) of participants tested positive for recent cocaine use. The median concentration was 2513pg/mg. Of those with evidence of cocaine use, there was an approximately 50-50 split between light (52%) and moderate/heavy (48%) users.
A quarter of participants had blood concentrations of tenofovir below the level of quantification in the first three months of therapy. After taking into account factors such as age, ethnicity and transgender status, individuals with evidence of light (aOR = 2.10; 95% CI, 1.07-4.14) or moderate/heavy (aOR = 2.32; 95% CI, 1.08-5.00) cocaine use were significantly more likely to have undetectable levels of tenofovir than individuals with no evidence of cocaine use.
“We found that cocaine use at any level was associated with lower odds of achieving prevention-effective adherence in the first three months after starting PrEP,” note the authors. “The first few months following PrEP initiation is a particularly critical period as adherence during this time is predictive of future adherence patterns.”
A total of 60 participants (15%) dropped out of care (had a four-month gap in follow-up). In adjusted analysis, individuals with evidence of moderate/heavy cocaine were three times more likely to drop out of care compared to individuals who didn’t use cocaine (aHR = 2.90; 95% CI, 1.48-5.66).
Cocaine use has been associated with kidney damage, which is also a possible side-effect of tenofovir. Creatinine clearance was therefore analysed in participants and compared according to evidence of cocaine use. However, there was no evidence that taking cocaine increased the risk of renal toxicity.