digoxin and norverapamil

Digoxin is the recommended substrate for assessment of P-glycoprotein (P-gp)-mediated drug-drug interactions (DDIs) in vivo. The overall aim of our study was to investigate the inhibitory potential of both verapamil and norverapamil on the P-gp-mediated efflux of digoxin in both gut and liver. Therefore, a physiologically-based pharmacokinetic (PBPK) model for verapamil and its primary metabolite was developed and validated through the recovery of observed clinical plasma concentration data for both moieties and the reported interaction with midazolam, albeit a cytochrome P450 3A4-mediated DDI. The validated inhibitor model was then used in conjunction with the model developed previously for digoxin. The range of values obtained for the 10 trials indicated that increases in area under the plasma concentration-time curve (AUC) profiles and maximum plasma concentration observed (Cmax ) values of digoxin following administration of verapamil were more comparable with in vivo observations, when P-gp inhibition by the metabolite, norverapamil, was considered as well. The predicted decrease in AUC and Cmax values of digoxin following administration of rifampicin because of P-gp induction was 1.57- (range: 1.42-1.77) and 1.62-fold (range: 1.53-1.70), which were reasonably consistent with observed values of 1.4- and 2.2-fold, respectively. This study demonstrates the application of permeability-limited models of absorption and distribution within a PBPK framework together with relevant in vitro data on transporters to assess the clinical impact of modulated P-gp-mediated efflux by drugs in development.

Topics: Adjuvants, Anesthesia; Anti-Arrhythmia Agents; ATP Binding Cassette Transporter, Subfamily B; Computer Simulation; Digoxin; Drug Interactions; Enzyme Inhibitors; Humans; Midazolam; Models, Biological; Permeability; Rifampin; Verapamil

The Biopharmaceutics Drug Disposition Classification System (BDDCS) predicts intestinal transporter effects to be clinically insignificant following oral dosing for highly soluble and highly permeable/metabolized drugs (class 1 drugs). We investigated the effect of inhibiting P-glycoprotein (P-gp) on the in vitro rat intestinal permeability (Papp) and metabolism of the class 1 drug verapamil. Jejunal segments from Sprague-Dawley rats fasted overnight were mounted in Ussing chambers filled with 10 mL of Krebs-Ringer buffer (KRB). For P-gp inhibition studies, GG918 0.5 μM was added to the KRB solution. The experiment started by the addition of verapamil (1 or 10 μM) to either apical or basolateral sides. Samples from verapamil donor and receiver compartments were collected at 30 s and 0.166, 0.5, 1, 1.83 and 3 h after the start of the experiment. Analysis of verapamil and its major metabolite, norverapamil, in the samples and intracellularly at 3 h was performed by HPLC. The same experiment was repeated with norverapamil 10 μM (verapamil metabolite), digoxin 100 nM (positive control for P-gp activity) and atorvastatin 1 and 10 μM (example of a class 2 drug). For 1 μM verapamil, efflux ratio (B to A Papp/A to B Papp) was 4.6 and markedly decreased by GG918 (efflux ratio = 1.1). For 10 μM verapamil efflux ratio was 4.1 (control) vs 1.8 (GG918), comparable to the change seen for digoxin 100 nM with an efflux ratio of 3.6 (control) vs 1.6 (with GG918) and atorvastatin (efflux ratio of 5.2 and 3.0 for atorvastatin 1.0 and 10 μM, respectively, changed to 1.0 and 0.65 with GG918). The changes observed in the norverapamil 10 μM experiment were also significant, where efflux ratio decreased from 13.5 (control) to 1.5 (GG918). The extraction ratio (ER) of 10 μM verapamil to norverapamil decreased from 0.41 after an apical dose to 0.21 after a basolateral dose, but was unaffected by the incubation with GG918. The results suggest that P-gp inhibition has an effect on class 1 drug verapamil and class 2 drug atorvastatin Papp in the rat intestine. Moreover, a stronger P-gp effect on the Papp of the more polar norverapamil metabolite was observed. Papp changes caused by the P-gp inhibitor GG918 do not affect the extent of verapamil metabolism.

Topics: Animals; Atorvastatin; ATP Binding Cassette Transporter, Subfamily B, Member 1; Digoxin; Heptanoic Acids; Intestinal Absorption; Pyrroles; Rats; Rats, Sprague-Dawley; Verapamil

Verapamil is subject to extensive oxidative metabolism mediated by cytochrome P450 enzymes with less than 5% of an oral dose being excreted unchanged in urine. Furthermore, verapamil is known to be a potent inhibitor of P-glycoprotein function. There is evidence from in vivo investigations that some verapamil metabolites might be actively transported. The aim of the present study was to investigate P-glycoprotein-mediated transport and inhibition properties of verapamil and its metabolites norverapamil, D-620, D-617, and D-703. Polarized transport of these compounds was assessed in P-glycoprotein-expressing Caco-2 and L-MDR1 cells (LLC-PK1 cells stably transfected with human MDR1-P-glycoprotein). Inhibition of P-glycoprotein-mediated transport by these compounds was determined using digoxin as P-glycoprotein substrate. At concentrations of 5 microM, significant differences between basal-to-apical and apical-to-basal apparent permeability coefficients were observed for D-617 and D-620 in all P-glycoprotein-expressing cell monolayers, indicating that both are P-glycoprotein substrates. In contrast, no P-glycoprotein-dependent transport was found for verapamil, norverapamil, and D-703 in Caco-2 cells and for D-703 in L-MDR1 cells. Moreover, verapamil, norverapamil, and D-703 inhibited P-glycoprotein-mediated digoxin transport with IC(50) values of 1.1, 0.3, and 1.6 microM, respectively, whereas D-617 and D-620 did not (at concentrations up to 100 microM). We conclude that verapamil phase I metabolites exhibit different P-glycoprotein substrate and inhibition characteristics, with the N-dealkylated metabolites D-617 and D-620 being P-glycoprotein substrates and norverapamil and D-703 being inhibitors of P-glycoprotein function, which may influence P-glycoprotein-dependent drug disposition and elimination.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Biological Transport, Active; Caco-2 Cells; Calcium Channel Blockers; Cardiotonic Agents; Cell Line; Digoxin; Epithelial Cells; Humans; Kinetics; LLC-PK1 Cells; Nitriles; Swine; Verapamil

Concentrations of verapamil and norverapamil were measured in the plasma and breast milk of a woman receiving 120 mg verapamil three times daily. Whilst the concentrations of verapamil in breast milk averaged about 64% of those in maternal plasma no drug could be detected in the plasma of the infant. It is concluded that maternal therapy with verapamil does not pose a hazard to the suckling infant.

Topics: Adult; Breast Feeding; Digoxin; Female; Humans; Milk, Human; Verapamil