Physiologically based pharmacokinetic modeling and simulation of topiramate in populations with renal and hepatic impairment and considerations for drug-drug interactions

Topiramate (TPM) is a broad-spectrum antiepileptic drug (AED) commonly prescribed for approved and off-label uses. Routine monitoring is suggested for clinical usage of TPM in special population due to its broad side effect profile. Therefore, it is crucial to further explore its pharmacokinetic characteristics. Physio-chemical properties of TPM were initially determined from online database and further optimized while establishing the PBPK model for healthy adults using the PK-Sim software. The model was then extrapolated to patients with renal impairment and patients who were hepatically impaired. A drug-drug interaction (DDI) model was also built to simulate plasma TPM concentrations while concomitantly used with carbamazepine (CBZ). The goodness-of-fit method and average fold error (AFE) method were used to compare the differences between predicted and observed values to assess the accuracy of the PBPK model. Almost all of the predicted concentration fell within twofold error range of corresponding observed concentrations. The AFE ratio of predicted to observed values of Cmax and AUC0-inf was all within 0.5 and 2. It is recommended that the doses be reduced to 70%, 50%, and 40% of the healthy adult dose for the chronic kidney disease (CKD) stage 3, stage 4, and stage 5 patients, respectively, and reduced to ~70%, and 35% for the Child-Pugh-B, and Child-Pugh C scored patient with hepatic impairment, respectively. If TPM is co-administered with CBZ, increasing TPM doses to 150%-175% of the monotherapy dose is recommended according to model simulation.