Development of amorphous solid dispersion formulations of a poorly water-soluble drug, MK-0364.

The goal of this study was to demonstrate that MK-0364 solid dispersions can be developed as a means to increase the solubility and bioavailability of a poorly water-soluble drug, MK-0364. The potential solid dispersions would enable an oral solid dosage form as a monotherapy or combination product of MK-0364. Preliminary screening included sample preparation via a solvent casting method, physical characterization, and in vitro dissolution testing. Lead formulations were subsequently manufactured using hot melt extrusion (HME) and spray-drying (SD). All HME (without polyvinyl pyrrolidone) and SD formulations exhibit characteristics of a single phase glass including an amorphous halo when analyzed with X-ray powder diffraction (XRPD), a single glass transition temperature (Tg) measured with differential scanning calorimetry (DSC), and supersaturation when dissolved in dissolution media. The oral absorption of MK-0364 from selected HME and SD formulations in monkeys results in marginally greater exposure with a consistently longer Tmax relative to a liquid filled capsule reference. Based on the processability, physical characterization, in vitro dissolution, and animal pharmacokinetic results, copovidone- and hydroxypropyl methylcellulose acetate succinate (HPMCAS)-based solid dispersion formulations are viable product concepts. The physical stability of both the solid dispersion formulations was also evaluated for 54 weeks under different conditions. The copovidone-based solid dispersion requires protection from moisture.

An open-label, parallel, multiple-dose study comparing the pharmacokinetics and gastric acid suppression of rabeprazole extended-release with esomeprazole 40 mg and rabeprazole delayed-release 20 mg in healthy volunteers.

BACKGROUND: Novel rabeprazole extended-release (ER) formulations were developed to provide prolonged gastric acid suppression and potentially improved clinical outcomes in GERD patients. AIM: To evaluate the pharmacodynamics and pharmacokinetics of six rabeprazole-ER formulations vs. esomeprazole 40 mg and rabeprazole delayed-release (DR) 20 mg. METHODS: Helicobacter pylori-negative healthy subjects were randomised to receive one of eight treatments once daily for 5 days. Twenty-four-hour intragastric pH was monitored on days -1, 1 and 5. Rabeprazole plasma concentrations were measured on day 5. RESULTS: A total of 248 subjects (N=31/group) were enrolled in the study. On day 5, rabeprazole-ER groups provided mean durations of 18.5-20.2 h (77.0-84.1% of 24-h) with intragastric pH >4.0 vs. esomeprazole 40 mg (15.9 h/66.1% of 24-h) and rabeprazole-DR 20 mg (15.2 h/63.2% of 24-h). A similar increase was observed on day 1. While percentage of daytime (8 am-10 pm) with intragastric pH >4.0 on day 5 was overall similar across the groups, percentage of night-time (10 pm-8 am) with intragastric pH >4.0 was higher with the rabeprazole-ER groups (57.0-72.4%) vs. esomeprazole 40 mg (32.8%) and rabeprazole-DR 20 mg (34.0%). CONCLUSION: Rabeprazole-ER once daily for 5 days demonstrated a significantly longer duration of gastric acid suppression in 24 h vs. esomeprazole 40 mg and rabeprazole-DR 20 mg. The increase in acid suppression was predominantly due to prolonged acid suppression during the night-time; this was supported by the extended-release pharmacokinetic characteristics.

Irreversible inhibition of CYP2D6 by (-)-chloroephedrine, a possible impurity in methamphetamine.

(+)- and (-)-Chloroephedrine, and their respective aziridines, cis- and trans-1,2-dimethyl-3-phenylaziridine, have been reported present in clandestinely synthesized methamphetamine. Since methamphetamine and structurally related compounds are potential substrates for human liver CYP2D6, the possible interaction of the chloroephedrines with human liver CYP2D6 was evaluated. Computational methods (using Flexidock and HINT in SYBYL) were used to determine the feasibility of (+)- or (-)-chloroephedrine and cis- or trans-1,2-dimethyl-3-phenylaziridine binding in the active site of a three dimensional CYP2D6 molecular model. Although modeling indicates both (+)- and (-)-chloroephedrine would bind comparably to methamphetamine, the binding energies of cis- or trans-1,2-dimethyl-3-phenylaziridine products indicate a preference for trans-1,2-dimethyl-3-phenylaziridine, the product formed from (-)-chloroephedrine. The effects of (+)- and (-)-chloroephedrine on the metabolism of dextromethorphan in human liver microsomes were then experimentally evaluated. (+)-Chloroephedrine (50 micro M) had no effect on human CYP2D6. (-)-Chloroephedrine appeared to be selective for human CYP2D6 versus CYP1A2 and CYP3A4/5. The inhibition of CYP2D6 was time-dependent, not dependent on metabolic activation, and irreversible. It appeared to bind at the active site of CYP2D6 with an apparent K(i) of 226 micro M, with a k(int) of 0.039 min(-1), and a t(1/2) of 23 min. Due to the irreversible nature of this inhibition, this impurity in clandestinely synthesized methamphetamine may be important and warrant further study.

Effect of common excipients on Caco-2 transport of low-permeability drugs.

The Biopharmaceutics Classification System (BCS) allows waivers of in vivo bioequivalence for rapidly dissolving immediate-release (IR) formulations of drugs with high solubility and high permeability. One potential issue in possibly extending BCS biowaivers to low-permeability drugs is the potential for excipients to modulate the intestinal permeability of the drug. The objective of this work was to evaluate the effect of nine individual excipients on the Caco-2 permeability of seven low-permeable compounds that differ in their physiochemical properties. Generally, most excipients had no influence on drug permeability. With the exception of sodium lauryl sulfate, no excipient affected Caco-2 monolayer integrity. Sodium lauryl sulfate moderately increased the permeability of almost all the drugs. Tween 80 significantly increased the apical-to-basolateral direction permeability of furosemide, cimetidine, and hydrochlorothiazide, presumably by inhibiting their active efflux, without affecting mannitol permeability. Additionally, docusate sodium moderately increased cimetidine permeability. Other excipients did not have significant effect on the permeability of these three drugs. Further work is needed to interpret the in vivo consequences of these observations from cell culture.

Targeted drug delivery systems 6: Intracellular bioreductive activation, uptake and transport of an anticancer drug delivery system across intestinal Caco-2 cell monolayers.

We demonstrate transport across, intracellular accumulation and bioreductive activation of a conformationally constrained, anticancer drug delivery system (the CH(3)-TDDS) using Caco-2 cell monolayers (CCMs) as an in vitro model of the human intestinal mucosa. Reverse-phase High Performance Liquid Chromatography (HPLC) coupled with UV detection was used to detect CH(3)-TDDS, the bioreduction product (lactone) and the released drug (melphalan methyl ester; MME). Upon incubation of the CH(3)-TDDS with the apical (AP) surface of 21-day-old CCM, we observed rapid decrease in the AP concentration of the CH(3)-TDDS (60%/hr) as a result of cellular uptake. Rapid intracellular accumulation of the CH(3)-TDDS was followed by bioreductive activation to deplete the cellular levels of CH(3)-TDDS. The drug part (MME) and lactone, as well as CH(3)-TDDS, were detected in the basolateral (BL) chamber. Intracellular Caco-2 levels of TDDS and lactone were also detectable. Bioreductive activation of the CH(3)-TDDS was additionally confirmed by formation of lactone after incubation of the CH(3)-TDDS in the presence of freshly prepared Caco-2 cell homogenates. During transport studies of melphalan or MME alone (as control), the intact drug was not detected in the intracellular compartment or in the BL chamber. These observations demonstrate that CH(3)-TDDS has potential for improving intestinal delivery of MME. TDDS could be useful in facilitating oral absorption of MME as well as the oral delivery of other agents.

Transport of poly amidoamine dendrimers across Madin-Darby canine kidney cells.

The objective of this study was to determine the permeability of a series of poly amidoamine (PAMAM) dendrimers of generations 0-4 (G0-G4) across MDCK (Madin-Darby Canine Kidney) cell line. PAMAM dendrimers with incremental increase in size and molecular weight were labeled by fluorescein isothiocyanate (FITC) and the least polydisperse fractions were collected by size exclusion chromatography. MDCK cells were grown on Transwell filters for four days. The conjugates were detected by HPLC equipped with fluorescence detector. The permeability of the dendrimers across MDCK cells was determined in the apical to basolateral direction. The rank-order permeability of the PAMAM dendrimers was G4 >> G1 approximately G0 > G3 > G2. The permeability of mannitol in the presence of G4 increased by nine-fold. Results suggest that the transepithelial transport of PAMAM dendrimers is effected by both the polymer size, and the modulation of the cell membrane by the cationic dendrimers.