THEORETICAL LIMITS OF THE EVALUATION OF DRUG CONCENTRATIONS IN HAIR DUE TO IRREGULAR HAIR-GROWTH

When examining concentration relationships of doses it must be taken i nto account that hair growth is irregular. Hair growing from the shave d skin after a single dose of a certain drug cannot possibly contain t he same concentration as hair after the same dose that has not been cu t over a long period. Concentrations can even change during the hair g rowth in cases where the hair had been cut a couple of months before t he hair sample was taken. The variations in the expected concentration s can exceed 20%. On the other hand, the evaluation of a hair tuft whi ch has grown after the last drug consumption may be important in foren sic cases where the hair which has grown earlier is not available. Thi s may lead to misinterpretations at low concentrations. Expected conce ntrations are calculated assuming a telogen part of 10%.