A single measurement of the indinavir level in a sample of human hair was able to predict virological response to an indinavir-containing regimen, French researchers reported this week in the Annals of Internal Medicine.
The authors suggest that the method may be a non-invasive method that could be used to measure drug levels, and that it may prove more reliable than patient reports for monitoring adherence.
The researchers recruited 104 consecutive patients at seven French and Swiss clinics, and took a small sample of hair from the neck at least three months after individuals had started treatment. Using liquid chromatography, they measured levels of indinavir and correlated these to viral load measurements taken on the same day. Patients with undetectable viral load were classified as responders, whilst those with undetectable viral load were classified as non-responders.
Samples from 13 patients were excluded because their hair samples were too short (
The mean indinavir concentration was significantly higher in responders compared to non-responders (24.4ug vs 12.9ug; p=0.016). Amongst non-responders, the patients with the higher indinavir concentrations had indinavir-associated resistance mutations. The study found that the mean concentration of indinavir was lower in hair samples taken further from the scalp (i.e. the tips of the hairs).
Professor David Back of Liverpool University Department of Pharmacology, one of the leading authorities on therapeutic drug monitoring of HIV treatment expressed caution about the findings.
“Whilst the results are interesting, more data are needed. I’m not convinced that adequate validation has been provided. For example, hair samples taken from different parts of a person’s scalp have not been compared. Also, this is a retrospective measure, given the rate at which hair grows. Potentially it may tell us if a patient was adherent one, two or three months ago.”
The size of hair samples needed may not make it a practical method for use among many HIV patients, given the popularity of very short hair and the inevitable loss of hair among older male patients.
Bernard L et al. Relationship between levels of indinavir in hair and virologic response to highly active antiretroviral therapy. Annals of Internal Medicine 137: 656-659, 2002.