Investigating the effect of complexation with carbonic anhydrase enzymes on the pharmacokinetic profile of methazolamide

Methazolamide (MTZ) is a carbonic anhydrase (CA) inhibitor that accumulates extensively in erythrocytes. Discrepancies between plasma and RBC half-lives of MTZ were previously reported. These discrepancies were attributed to the complexation with the two isozymes found in blood: CA-I and CA-II.; In the current investigation, computer simulations were utilized to predict and explain the clinical profile of MTZ. Simulations were initially performed using previously published pharmacokinetic parameters. Confidence in the simulated concentration-time profiles for MTZ in plasma and erythrocytes was assessed using sensitivity and Monte Carlo analyses. Experiments were then performed to confirm the model parameters describing MTZ complexation with the isozymes. These experiments included characterization of the binding of MTZ to erythrocyte membranes, the equilibrium binding with pure carbonic anhydrase enzymes, and the kinetics of MTZ release from the isozymes.; MTZ was found to bind to the two isozymes in a 1:1 molar ratio. The binding of MTZ to CA-I was characterized as a low affinity and high capacity while CA-II represented the high affinity low capacity site of binding. Maximum binding to CA-I and CA-II was found to be 33.75 μg/ml (±7.61%) and 4.01 μg/ml (±4.00%), respectively. The affinity constant for MTZ complexation with CA-I was 1.65 ml/μg (±40.12%) while for CA-II the estimate was 5.56 ml/μg (±5.10%).; Studies with Franz cells indicated that the release of MTZ bound to CA enzymes is a relatively slow process. The rate constants describing the release of MTZ from CA-I and CA-II were 0.00011 min−1 (±19.46%) and 0.00062 min−1 (±4.50%), respectively.; Finally, computer assisted clinical trial design (CATD) was utilized to design a clinical study that will have a higher chance of success in determining the correct parameter estimates describing the complexation of MTZ with CA isozymes in blood. Given the intersubject variability among the population, this approach would allow for a more accurate characterization of MTZ disposition in vivo.; In conclusion, this dissertation research provided an example of the application of preclinical data to design a potentially informative clinical study. A physiologic based model was successfully used to characterize possible outcomes regarding the pharmacokinetic and pharmacodynamic profile of MTZ in vivo.