Using sparse data to develop Population PK model for pediatrics

Dear all, I would like to develop a population PK model for a drug used in pediatrics. We got drug concentrations from 15 patients. The drug was given 3 times a day. Only one plasma sample were drawn every week for 4 weeks. They record the exact sampling time after drug was given. So for each patient, we had 4 concentrations from 4 weeks. I assumed all the 4 samples were from one dose and developed a Pop PK model. This assumption did not consider disease progress and drug accumulation. The result was still comparable with literature. I will be very appreciated your comments and suggestions for this model. Regards -- Daping Zhang Ph.D. Candidate University of Houston