Page 230 - SAHCS HIVMed Journal Vol 20 No 1 2019

Page 5 of 6 Original Research

200 a drug exposure and are also subject to ‘white coat effects’
(good adherence around the time of clinic visit). As a result,
23
it is suggested in the literature that hair ARV concentrations
150 might be of more value than single plasma concentrations
when measuring adherence. 3,22,24 Because virologic failure was
% Adherence 100 uncommon in our study, we were unable to evaluate either

adherence measure as a predictor of virologic outcomes.

50 Hair EFV concentrations were found to have a non-significant
association with adherence measured by the EAMD (Figure 3).
These results suggest that, for this study, no significant
0 correlation between adherence and EFV concentrations in
0.1 1 10 100
hair exists. Even though the median adherence measured by
Hair EFV concentra on (log 10 of ng/mg)
the EAMD was 100% at weeks 16 and 32 (IQR: 92–100 and
200 b 92–103, respectively) and 101% (IQR: 96–107) at week 48, the
concentration of EFV in the hair samples varied, most likely
because of the different metaboliser genotypes present in the
150 subset. While hair ARV concentrations have previously been
8,24,25,26,27,28
shown to correlate well with virological suppression,
% Adherence 100 this has not been the case when the relationship between hair
concentrations and measures of adherence such as self-report

the low occurrence of virological failures in this subset did not
50 and EAMD have been assessed. 11,29,30 As previously discussed,
allow for hair EFV concentrations to be associated with
virologic outcomes for this study. The relationship between
0 hair EFV concentrations and virologic outcomes needs to be
0.1 1 10 100
further explored in a cohort with a higher rate of virological
Hair EFV concentra on (log 10 of ng/mg) failures.
200 c
The study was limited by the study design, in that the
participants who provided hair samples were predominantly
150 female, had higher levels of adherence compared to the rest
of the cohort and were mostly virologically suppressed. This
% Adherence 100 did not allow for certain associations to be investigated. The
limited the extent to which the data could be analysed and
collection of head hair samples was also challenging as many
50 women were reluctant to donate a braid and most men had
shaved heads. Only 135 (59%) of the 230 participants that
were enrolled in the parent study provided hair samples.
0
Conclusion
0.1 1 10 100
Hair EFV concentra on (log 10 of ng/mg)
In conclusion, we have shown that a strong correlation
FIGURE 3: Scatterplots showing the relationship of adherence assessed by exists between EFV concentrations measured in plasma and
electronic adherence monitoring device (EAMD) (represented as a percentage) hair samples collected from participants with good ARV
to concentrations of efavirenz (EFV) in hair at weeks 16 (a), 32 (b) and 48 (c).
adherence. In addition, patient metaboliser status was
study also showed increased concentrations of EFV in hair observed to have a significant effect on long-term exposure to
samples from individuals with the slow metaboliser EFV. However, because of the low rates of virologic failure in
genotype. 14 our cohort, we were unable to assess the ability of EFV
concentrations in hair to predict outcomes. The challenges
we experienced in collecting hair from our cohort suggest
Plasma and hair EFV concentrations were strongly correlated that this adherence measure may have limited utility in an
throughout the 48-week study period (Figure 2), which African population.
suggests that, for our cohort with very high virologic
suppression, a single plasma concentration was as good an Acknowledgements
adherence measure as a single hair concentration. This is an
interesting result as hair concentrations provide an average The authors thank Jennifer Norman and the team at the
level of drug exposure over the last 30 days or so, whereas Clinical Pharmacology Laboratory, Division of Clinical
22
single plasma concentrations represent a brief snapshot of Pharmacology, Department of Medicine, University of

http://www.sajhivmed.org.za 223 Open Access