scaling problem??

Dear Group: I hope someone can help me with the following scaling problem. I have data on two groups that I would like to compare the PPK estimates on. The drug is dosed in mg (set amount every 12 hours). The plasma level data is for a surrogate marker and is expressed as iU/mL. What kind of scaling should one use in the $PK block? Thanks in advance. Varsha Varsha Mehta, MS(CRDSA), Pharm.D., FCCP Clinical Associate Professor Pharmacy, Pediatrics and Communicable Diseases Clinical Pharmacist Neonatal Critical Care University of Michigan (O) 734-936-8985 (F) 734-936-6946 [email protected] ********************************************************** Electronic Mail is not secure, may not be read every day, and should not be used for urgent or sensitive issues

Hi Varsha You may use everything in the original variables (dose in mg, conc in iU/mL) but your parameters will be defined up to the transformation Fu=iU/mg (amount of iU in each mg). Without knowing this value, the only thing that you determine from the data is CL/Fu, V/Fu, etc. You may explore the analogy between bioavailability and this unit transformation: if you would know Fu, you could have dose in mg, but use bioavailability-like parameter F1 =Fu (F2=Fu, etc.) thus transforming your dose from mg to iU. Since you do not know Fu, it cannot be (similar to bioavailability, if there is no IV formulation) defined from the data. So the short answer: no transformation is necessary but all the parameters will be defined as CL/Fu, V/Fu, etc. It will not interfere with the group comparison since (CL/Fu)_1/(CL/Fu)_2 = CL_1/CL_2, etc.. Thanks Leonid -------------------------------------- Leonid Gibiansky, Ph.D. President, QuantPharm LLC web: www.quantpharm.com e-mail: LGibiansky at quantpharm.com tel: (301) 767 5566 Varsha Mehta wrote: > Dear Group: > I hope someone can help me with the following scaling problem. > > I have data on two groups that I would like to compare the PPK estimates on. > The drug is dosed in mg (set amount every 12 hours). The plasma level data is > for a surrogate marker and is expressed as iU/mL. > > What kind of scaling should one use in the $PK block? > > Thanks in advance. > Varsha > > Varsha Mehta, MS(CRDSA), Pharm.D., FCCP > Clinical Associate Professor > Pharmacy, Pediatrics and Communicable Diseases > Clinical Pharmacist Neonatal Critical Care > University of Michigan > (O) 734-936-8985 > (F) 734-936-6946 > [email protected] > > ********************************************************** > Electronic Mail is not secure, may not be read every day, and should not be > used for urgent or sensitive issues