Influence of pigmentation on the codeine content of hair fibers in guinea pigs.

Tortoise shell guinea pigs (n = 7) were administered codeine (1 mg/mL codeine-base) in their drinking water for 3 weeks. Black, reddish-brown and white hair was collected separately from each animal before and after treatment. The hair samples were analyzed by GC/MS. The experiment showed positive results for all hair fibers with large individual variability of drug incorporation. Low drug intake resulted in small differences of the drug content in hair fibers different in color, whereas in cases of high drug intake a strong influence of hair pigmentation on the analytical results was observed. The highest drug content was always found in black hair samples, non-pigmented hair showed the lowest drug concentrations and the drug content in reddish-brown fibers was less than in black hair samples from the same animal. From the results it was concluded, that eumelanins rather than phenomelanins are the decisive factor for codeine-melanin binding in hair and the amount of drug intake was suggested to determine the relevance of hair pigmentation on the analytical results.