Re: Population PKPD using hair drug concentration

Dear Bernard, This looks like really interesting problem. Based on the idea that it should be a long delay, I would start with the transit compartment model (you can google for the references on this type of models) with the input from the plasma compartment. The last compartment will represent a barber shop. The number of transit compartment can be increased until you get a sufficiently long delay. Observation compartment can be either the last one, or the sum of several, depending on how measurements are done (at a particular hair length, or by grinding the hair together before measurement). Depending on whether hair can eliminate the drug (or it happens only in the barber shop), hair clearance can be assigned to all or only to the last of those transit compartments. It could be that a simple effect compartment model with a very slow ke0 could describe it as well but you should be able to see it by increasing or decreasing the number of transit compartments. Regards, Leonid -------------------------------------- Leonid Gibiansky, Ph.D. President, QuantPharm LLC web: www.quantpharm.com e-mail: LGibiansky at quantpharm.com tel: (301) 767 5566