DIFFERENTIATION OF GUT AND HEPATIC FIRST-PASS LOSS OF VERAPAMIL IN INTESTINAL AND VASCULAR ACCESS-PORTED (IVAP) RABBITS

Superhydrophobic Substrates for Ultrahigh Encapsulation of Hydrophilic Drug into Controlled-Release Polyelectrolyte Complex Beads: Statistical Optimization and In Vivo Evaluation

: In this work, ultrahigh drug-loaded chitosan (Ch)/K-carrageenan (Kc) polyelectrolyte complex (PEC) beads were formed in situ by cross-linking in a glutaraldehyde-saturated atmosphere and were prepared on superhydrophobic substrates fabricated by spraying glass surfaces with ready-made spray for domestic use (NeverWet^®). Verapamil hydrochloride (VP), a highly hydrophilic drug with a short biological half-life, was incorporated into a series of Ch-based and/or Ch/Kc-PEC-based beads to control its release profile in vivo. The formulation of VP-loaded beads was optimized using stepwise statistical designs based on a prespecified criterion. Several characteristics of the prepared beads, such as entrapment efficiency (EE%), in vitro drug release, swelling ratio, size and surface microstructure as well as molecular interactions between the drug and formulation ingredients, were investigated. In vivo pharmacokinetic (PK) studies were carried out using the rabbit model to study the ability of the optimized VP-loaded beads to control the absorption rate of VP. Results revealed that the prepared superhydrophobic substrates were able to fabricate VP-loaded beads with extremely high EE exceeding 90% w/w compared to only 27.80% when using conventional ionotropic gelation technique. PK results showed that the rate of VP absorption was well controlled following oral administration of the optimized beads to six rabbits compared to a marketed VP immediate release (IR) tablet, as evidenced by a 2.2-fold increase in mean residence time (MRT) and 5.24-fold extension in half value duration (HVD) over the marketed product without any observed reduction in the relative oral bioavailability.

Mechanism of Reductive Metabolism and Chiral Inversion of Proton Pump Inhibitors

Racemic proton pump inhibitors (PPIs) have been developed into pure enantiomers given superior pharmacokinetic profiles. However, after doses of single enantiomer PPIs, different degrees of chiral inversion were observed. We investigated the relationship between chiral inversion and reductive metabolism of PPIs, as well as the mechanism of reductive metabolism. In liver microsomes and Sprague-Dawley rats, PPI thioethers were stereoselectively oxidized to (R)- and (S)-PPIs, indicating that thioethers could be the intermediates of chiral inversion. By comparing the area under the plasma concentration-time curve ratios of thioether to rabeprazole under different routes of administration and blood sampling site, it was determined that thioether was mainly formed in the liver rather than the intestine. The formation rate of PPI thioethers in liver subcellular fractions was significantly higher than that in buffers. Sulfhydryl-blocking agents, such as N-ethylmaleimide, menadione, and ethacrynic acid, inhibited the reductive metabolism of PPIs in vitro, and their corresponding glutathione conjugates were observed. Similar amounts of thioethers were formed in glutathione solutions as in liver subcellular fractions, indicating that biologic reducing agents, instead of reductases, accelerated the reductive metabolism of PPIs. The reduction rates in glutathione solutions were ordered as follows: rabeprazole > omeprazole > lansoprazole > pantoprazole, which was consistent with the natural bond orbital charges of sulfur atoms in these compounds. In conclusion, PPIs were transformed into thioethers by biologic reducing agents in liver, and thioethers continued to be oxidized to two enantiomers, leading to chiral inversion. Furthermore, inhibiting oxidative metabolism of PPIs enhanced reductive metabolism and chiral inversion.

Ultrahigh verapamil-loaded controlled release polymeric beads using superamphiphobic substrate: D-optimal statistical design, in vitro and in vivo performance

Controlled-release multiparticulate systems of hydrophilic drugs usually suffer from poor encapsulation and rapid-release rate. In the present study, ultra-high loaded controlled release polymeric beads containing verapamil hydrochloride (VP) as hydrophilic model drug were efficiently prepared using superamphiphobic substrates aiming to improve patient compliance by reducing dosing frequency. Superamphiphobic substrates were fabricated using clean aluminum sheets etched with ammonia solution and were treated with 1.5% (w/v) perfluorodecyltriethoxysilane (PFDTS) alcoholic solution. The effect of the main polymer type (lactide/glycolide (PLGA) 5004A, PLGA 5010, and polycaprolactone (PCL)), copolymer (Eudragit RS100) content together with the effect of drug load on encapsulation efficiency (EE%) and in vitro drug release was statistically studied and optimized via D-optimal statistical design. In vivo pharmacokinetic study was carried out to compare the optimized system relative to the market product (Isoptin®). Results revealed that superamphiphobic substrates were successfully prepared showing a rough micro-sized hierarchical structured surface upon observing with scanning electron microscope and were confirmed by high contact angles of 151.60 ± 2.42 and 142.80°±05.23° for water and olive oil, respectively. The fabricated VP-loaded beads showed extremely high encapsulation efficiency exceeding 92.31% w/w. All the prepared systems exhibited a controlled release behavior with Q12 h ranging between 5.46 and 95.90%w/w. The optimized VP-loaded system composed of 150 mg (1.5% w/v) PCL without Eudragit RS100 together with 160 mg VP showed 2.7-folds mean residence time compared to the market product allowing once daily administration instead of three times per day.

Effect of P-glycoprotein on the rat intestinal permeability and metabolism of the BDDCS class 1 drug 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.

Dalcetrapib pharmacokinetics and metabolism in the cynomolgus monkey

The thioester dalcetrapib is undergoing Phase III clinical evaluation for the prevention and regression of atherosclerosis and the prevention of cardiovascular events through targeting cholesteryl ester transfer protein and increasing high-density lipoprotein cholesterol levels. Dalcetrapib undergoes rapid hydrolysis to generate the pharmacologically active form (dalcetrapib-thiol), which undergoes extensive metabolism via glucuronic acid conjugation, methylation, and hydroxylation, predominately forming the pharmacologically inactive S-methyl (dalcetrapib-S-Me) and S-glucuronide (dalcetrapib-S-Glu) metabolites. The purpose of this study was to characterize the absorption and disposition of dalcetrapib-thiol and its primary metabolites in cynomolgus monkeys following first pass through the intestines and liver using an in vivo dual portal and peripheral vein cannulation. Results showed the high influence of glucuronidation of dalcetrapib-thiol on the first-pass effect. Following passage through the primate intestinal wall, area under the plasma concentration-time curve indicated a marked loss (by ~85%) of active compound and formation of dalcetrapib-S-Glu and dalcetrapib-S-Me. Based on time to maximum drug concentrations (T(max)) values in the portal vein, metabolism of dalcetrapib-thiol to dalcetrapib-S-Glu appears to occur almost instantly (median T(max) 6.0 and 5.5 h, respectively), whereas methylation to dalcetrapib-S-Me occurs much more slowly (median T(max), 24 h). A relatively modest impact on systemic exposure followed hepatic first pass, with a further decrease in dalcetrapib-thiol exposure of 58% (AUC), a 3-fold reduction in exposure levels of dalcetrapib-S-Me and near-complete decrease in exposure of dalcetrapib-S-Glu. Passage of drug-related material through the intestinal wall and the liver results in an overall decrease of exposure to dalcetrapib-thiol of >90%.

Involvement of cytochrome P450 3A4 and P-glycoprotein in first-pass intestinal extraction of omeprazole in rabbits

AIM

To quantitatively evaluate in vivo first-pass intestinal extraction of omeprazole and to investigate the possible involvement of cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp) in this process in rabbits.

METHODS

Pharmacokinetic parameters were examined after intraduodenal (id), intraportal venous (ipv), and intravenous (iv) administration of omeprazole at various doses to intestinal and vascular access-ported rabbits. Extraction ratios in the liver and intestinal tract were determined from the area under the plasma concentration-time curve (AUC). In addition, omeprazole was administered by id or iv to rabbits alone or 30 min after the id administration of CYP3A4 or P-gp inhibitors (ketoconazole or verapamil, respectively).

RESULTS

Pharmacokinetic parameters of omeprazole were dose-dependent after id, ipv, and iv administration at various doses. After id administration of 3 mg/kg omeprazole, the hepatic and intestinal extraction ratio was 57.18%+/-2.73% and 54.94%+/-1.85%, while the value was 59.29%+/-3.14% and 54.20%+/-1.53% after given 6 mg/kg, respectively. Compared with the control group, the presence of ketoconazole (60 mg/kg) or verapamil (9 mg/kg) significantly increased the area under the plasma concentration time curve (AUC) and the peak concentration (C(max)) of id-administered omeprazole, while it had no significant effect on omeprazole administered by iv.

CONCLUSION

Oral omeprazole undergoes marked extraction in the small intestine, and increased bioavailability of the drug after id administration of ketoconazole and verapamil suggests that this increase results from inhibition of CYP3A4 and P-gp function in the intestine rather than the liver.

Species Differences in In Vitro and In Vivo Small Intestinal Metabolism of CYP3A Substrates

Intestinal first-pass metabolism has a great impact on the bioavailability of CYP3A substrates in humans, and the in vivo impact has quantitatively been evaluated using CYP3A inhibitors or inducers. In vitro and in vivo preclinical investigations for intestinal metabolism are essential in clarifying pharmacokinetic behavior in animal species and predicting the effect of intestinal metabolism in the human. In this review, we will discuss species differences in intestinal CYP3A enzymes, and CYP3A-mdediated intestinal elimination. Identical CYP3A4 enzyme is expressed in human intestine and liver, but different CYP3A enzymes in both tissues of the mouse and rat are found, that is, respective intestinal enzyme is considered as cyp3a13 and CYP3A62. There is little information on CYP3A enzymes in the monkey and dog intestine, unlike the liver. In vitro metabolic activities of midazolam and nisoldipine are higher in the human and monkey than in the rat. In vivo assessment of cyclosporine, midazolam, nifedipine, tacrolimus, and verapamil has been reported in various species (monkey, rat, mouse, and/or dog) including the human. For midazolam, the monkey shows significant in vivo intestinal metabolism, as evidenced in the human. The monkey might be an appropriate animal model for evaluating small intestinal first-pass metabolism of CYP3A substrates.

Risk factors associated with surgical site infection and the development of short-term complications in macaques undergoing indwelling vascular access port placement

BACKGROUND

Risk factors associated with surgical site infection (SSI) and the development of short-term complications in macaques undergoing vascular access port (VAP) placement are evaluated in this study.

METHODS

Records from 80 macaques with VAPs were retrospectively reviewed. Logistic regression was used to identify factors associated with short-term post-operative complications.

RESULTS

The primary outcome was SSI, which occurred in 21.6% (52.6% in the first 12 months vs. 13% thereafter) of procedures. SSI was associated with major secondary complications including VAP removal (11.4%), wound dehiscence (5.7%), and mechanical catheter occlusion (5.7%). In multivariate modeling, only surgical program progress was a statistically significant predictor of SSI, while animal compliance had a slightly protective effect.

CONCLUSIONS

Vascular access ports have a moderate risk of complications, provided the surgical program optimizes best practices. Under complex experimental conditions, VAPs represent an important refinement, both improving animals' overall well-being and environment and reducing stress.

Effects of naringin on the pharmacokinetics of verapamil and one of its metabolites, norverapamil, in rabbits

It was reported that verapamil is metabolized via hepatic microsomal cytochrome P450 (CYP) 3A4 and that naringin (a component of grapefruit juice) inhibits CYP3A4 in humans. Hence, after oral administration of verapamil, the total area under the plasma concentration-time curve from time zero to time infinity (AUC) of verapamil and the AUC(verapamil)/AUC(D-617 (a metabolite of verapamil)) ratio were significantly greater after oral grapefruit juice in humans. The aim of this study was to determine whether similar results could be obtained from rabbits. The pharmacokinetics of verapamil and one of its metabolites, norverapamil, were investigated after oral administration of verapamil at a dose of 9 mg/kg without or with oral naringin at a dose of 7.5 mg/kg in rabbits. With naringin, the AUC of verapamil was significantly greater (28.4 versus 18.4 microg min/ml). Although, the AUC values of norverapamil were not significantly different between groups without and with naringin, the AUC(verapamil)/AUC(norverapamil) ratio was considerably greater (1.49 versus 1.11) with naringin. The above data suggested that the metabolism of verapamil and the formation of norverapamil was inhibited by naringin possibly by inhibition of CYP3A in rabbits.