Sampling and sample size for pkpd analysis

Dear all I would like to apply pkpd-vd analysis to quantify the impact of HAART(based) prophylaxis to the rate of mother to child transimission and progression of HIV-1 in mother and child pairs expected to be followed up for a minimum of 2 years. Can you please assist me on the following issues: 1. What are the methods to use for determining the minimum number of mother and newborn pairs to be included for pkpd-vd analysis? 2. What are the minimum number of blood samples and optimal sampling times should i collect from both mother and newborn pairs to obtain an accurate measure of the drug and viral load levels over the 2-year period? Primary covariates to be included in the analysis are CYP2B6, CYP3A4 and ABCB1. Your comments and suggestions are welcome. Regards Bernard PhD Student, University of Zimbabwe -- Bernard Ngara Trainee Biostatistician Africa Institute of Biomedical Science and Technology P. O Box 2294 Harare Zimbabwe +263 772 160 896