Pharmacodynamics is the study of the time course of pharmacological effects of drugs. The field of pharmacodynamic modeling has made many advances, due in part to the relatively recent development of basic and extended mechanism-based models. The purpose of this article is to describe the classic as well as contemporary approaches, with an emphasis on pertinent equations and salient model features. In addition, current methods of integrating various system complexities into these models are discussed. Future pharmacodynamic models will most likely reflect an assembly of the basic components outlined in this review.

Objectives Pantoprazole is metabolized by cytochrome P450 2 C19, which shows genetic polymorphism. The effect of CYP2C19 polymorphism on single-dose pharmacokinetics of oral pantoprazole in healthy volunteers was evaluated. Methods Pantoprazole pharmacokinetics was determined in 32 healthy volunteers after a 40-mg single oral dose of the drug. Results Carriers of CYP2C19*2/*2 (n = 2) were characterized by higher, starting from 3.5 h post dose, plasma concentrations of pantoprazole in comparison to wild-type (CYP2C19*1/*1, n = 6) volunteers. In subjects with CYP2C19*17/*17 genotype (n = 6) significantly lower plasma concentrations of the drug vs CYP2C19*1/*1 carriers, were observed from 3.0 h after oral pantoprazole administration. Carriers of CYP2C19*1/*17 (n = 6) and CYP2C19*2/*17 (n = 6) displayed concentration–time profiles comparable to wild-type subjects. CYP2C19*2/*2 volunteers showed a decrease in terminal elimination rate constant (λ_z) by 83.3%, prolongation of terminal half-life (t_½) by 572%, a rise in area under the concentration–time curve (AUC) and mean residence time (MRT) by 506% and 259% respectively. Heterozygotes, i.e.. CYP2C19*1/*2 vs CYP2C19*1/*1 were characterized by higher AUC (4.38 ± 1.00 mg⋅h/L vs 3.00 ± 1.02 mg⋅h/L, p < 0.05) and C_max (2.13 ± 0.42 mg/L vs 1.61 ± 0.35 mg/L, p < 0.05) respectively. A significant reduction in MRT (3.83 ± 0.82 h vs 2.73 ± 0.23 h, p < 0.05) in carriers of CYP2C19*17/*17 vs CYP2C19*1/*1 genotypes was observed. Population modeling confirmed the influence of *1/*2, *2/*2, and *17/*17 genotypes on the pharmacokinetics of pantoprazole. The lowest population oral clearance was assessed in the carriers of genotype *2/*2 (3.68 L/h) and the highest value in subjects with genotype *17/*17 (31.13 L/h). Conclusion These data suggest that CYP2C19 polymorphism is an important determinant of pantoprazole pharmacokinetics.

Introduction: Nowadays, the first-line medications in depression include SSRIs, SNRIs, NDRIs, NaSSAs, SMSs, or a melatonin (M1/M2) receptor agonist and a 5-HT_2C receptor antagonist. These drugs have quite similar antidepressant efficacy and safety profiles, but they differ in chemical structure, receptor affinity, and pharmacokinetics. Areas covered: Pharmacokinetic properties of first-line antidepressant drugs and factors influencing their pharmacokinetic processes are presented. Alterations in pharmacokinetics of newer antidepressants in special populations are summarized. In addition, the significance of therapeutic drug monitoring (TDM) and pharmacogenetic testing in dose optimization for the treatment of depressive disorders using newer antidepressants is discussed. Expert opinion: Due to the fact that 30-40% of depressive patients do not respond to the therapy and that the incidence of depression is constantly growing, the search for new more effective and safer antidepressant therapies is becoming an urgent need. More well-designed clinical studies under naturalistic conditions are needed to establish/refine therapeutic ranges for older and current state-of-the art antidepressant drugs. The pharmacogenetic testing with concomitant application of TDM seems to be the best way for implementing personalized dosing of current state-of-the-art antidepressants metabolized by polymorphic CYPs, especially when co-administered with strong inhibitors or other substrates of CYP2D6 or CYP2C19.