Photostability of drugs of abuse in hair irradiated in a solar box

The concentration of drugs in hair may be altered by physical and chemical factors, among which the use of cosmetics or chemical treatments such as dying perming or bleaching, and environmental exposure. Solar light was demonstrated to alter molecular structures of drugs when irradiated in solutions or in biological fluids, decreasing the concentrations of drugs and/or producing new compounds/metabolites. Studies were performed for different classes of compounds by exposure of hair to sun (cannabinoids) or controlled UVA and UVB (cocaine, opiates, methadone) . In order to better understand the role and mechanisms of solar light exposure in decreasing hair concentrations of drugs, and following our previous photodegradation studies on UVA and UVB induced changes (Drug Test Anal 2014 , 6, 78-84), we undertook the present work irradiating true positive hair samples, containing cocaine and metabolites, in a solar box, reproducing the whole spectrum of sunlight. Authentic positive hair was selected from samples routinely tested at the laboratory that had previously tested positive for cocaine. Irradiation was performed in a Suntest CPS+ (Atlas, Linsengericht, Germany) equipped with a 1.8 kW xenon lamp and a glass filter (cut off 310 nm) according to Option 1 of ICH Guideline Q1B (1998). 25 hair samples were collected of different natural colours (blond, brown, dark brown, black). Hairs, 5–7 cm long, were divided into two approximately identical strands: the former was put between two 5 x 5 cm optical glasses and exposed at 765 W/m2 (310-800 nm) for 48 hours to an endpoint corresponding to two months exposure under the sunlight, and the latter was kept as a dark control in the same chamber of irradiation covered with an aluminium foil. Hair samples were washed and 10 mg were extracted and analyzed by a validated method already proposed by Favretto et al. (Drug Test Anal 2014 , 6, 78-84) encompassing micropulverized extraction and liquid chromatography-high accuracy, high resolution mass spectrometry (HPLC-HRMS) detection on an LTQ-Orbitrap (Thermo Fisher Scientific, Bremen, Germany). The % photodegradation was calculated as [100 *(drug concentration in the dark - drug concentration after exposure)/drug concentration in the dark]. The concentration ranges in the intact samples were 0,16 – 40,0 ng/mg and 0,05 - 19 ng/mg respectively for COC and BZE. 69 % of samples exhibited a decrease of COC concentration in post-irradiation samples, with percent reduction from to 6 % to 72 % (mean 37,8 %); in 23 % of samples BZE decreased from 10 to 50 % of its initial concentration; in 46 % of samples BZE increased from 6 to 23 %; in 31 % of samples both COC and BZE contents did not vary. BZE increase was observed only in samples that exhibited COC decrease, suggesting that photodegradation of the parent compound generates BZE that remains incorporated into the hair shaft. If this holds true, for the 6 samples (23 %) that exhibited both COC and BZE decrease, the further degradation of BZE originally formed by photodecomposition of COC can be envisaged. No relation could be found with hair color or hair thickness. The possible contribution of hair damage is under investigation by imaging techniques. Results will be presented also for nor-cocaine and cocaethylene in a smaller group of samples. When compared with our previous studies, when only specific UV components of sunlight (UVB lamp, emitting irradiation with a peak at 311–312 nm and UVA lamp, peaked at 365 nm) were used for irradiation, experiments in the solar box evidenced a similar percent of “degraded” hair samples (69 % solar box vs 62 % UVA/UVB) but a higher photodegradation yield of COC (mean 37 % vs mean 10 % respectively). The increase of concentration of a metabolite upon concomitant degradation of its parent compound highlights the peculiar role of whole sunlight and prompts for further studies, including other classes of compounds.