Proliposomes as a drug delivery system to decrease the hepatic first-pass metabolism: case study using a model drug.

Objective of the present study was to develop a proliposomal formulation to decrease the hepatic first-pass metabolism of a highly metabolized drug. Lovastatin was chosen as the model drug. Proliposomes were prepared by mixing different ratios of phospholipids such as soy phosphatidylcholine (SPC), hydrogenated egg phosphatidylcholine (HEPC) and dimyristoyl phosphatidylglycerol (DMPG) individually with drug and cholesterol in an organic solvent. Proliposomal powder was obtained following evaporation of the solvent. The proliposomal powder was either filled into capsules or compressed into tablets. Physical characterization, in vitro drug transport studies and in vitro dissolution of formulations and pure drug was carried out. In vitro transport across the membrane was evaluated using parallel artificial membrane permeability assay (PAMPA). The extent of drug released from various proliposomal formulations in the first 30 min was 85%, 87% and 96% with DMPG, SPC and HEPC containing formulations respectively, while the pure drug formulation showed 48% drug release in the same period. In vivo studies were carried out in male Sprague-Dawley rats. Following single oral administration of the selected formulation (F9), a relative bioavailability of 162% was achieved compared to pure lovastatin. The study demonstrated that proliposomes can be used as a drug delivery system to decrease the hepatic first-pass metabolism.

Contrary to adult, neonatal rats show pronounced brain uptake of corticosteroids.

Neurotoxic adverse effects after systemic corticosteroid administration are elevated in preterm infants. To test whether this might be related to an immature blood-brain barrier (BBB) that permits corticosteroids to enter the brain and induce neurotoxic effects, this study assessed the differences in brain permeability of triamcinolone acetonide after intratracheal administration to neonatal (10- to 11-day-old) and adult rats. Triamcinolone acetonide (or the phosphate prodrug in the case of neonatal rats) was administered intratracheally to neonatal rats at doses of 2.5, 25, or 50 microg/kg and to adult rats at 100 microg/kg. An ex vivo receptor binding assay was used to monitor the cumulative brain and liver glucocorticoid receptor occupancies over 6 h. Brain and liver receptor occupancies in neonates were similar for the 25 and 50 microg/kg triamcinolone acetonide phosphate (brain/liver receptor occupancy ratio, 1.10 +/- 0.14 and 0.87 +/- 0.13, respectively), whereas some reduction in the brain permeability was seen at the lower dose. After intratracheal administration of 100 microg/kg triamcinolone acetonide to adult rats, receptor occupancies in the brain were significantly lower (brain/liver ratio, 0.21 +/- 0.14; p < 0.001). The study demonstrated that glucocorticoids enter the brain of neonatal rats because of an immature BBB. The results of this study support the hypothesis that neurotoxic adverse effects in preterm infants after systemic corticosteroid administration might be related to an immature BBB.

Brain permeability of inhaled corticosteroids.

The aim of this study was to evaluate if the permeability of inhaled corticosteroids entering the brain is reduced and if P-glycoprotein (P-gp) transporters are involved. Currently employed inhaled corticosteroids were given intravenously and intratracheally to rats at a dose of 100 microg kg-1. An ex-vivo receptor binding assay was used to monitor over 12 h the glucocorticoid receptor occupancy in the brain and a systemic reference organ (kidney). The involvement of P-gp in the brain permeability of triamcinolone acetonide was assessed in wild-type mice and mdr1a(-/-) knockout mice (mice lacking the gene for expressing P-gp). After both forms of administration, the average brain receptor occupancies were 20-56% of those of the reference organ, with the more lipophilic drugs showing a more pronounced receptor occupation. While the receptor occupancies in the liver of wild-type and mdr1a(-/-) mice were similar after administration of triamcinolone acetonide, brain receptor occupancies in mdr1a(-/-) mice were significantly greater (mdr1a(-/-): 47.6%, 40.2-55.0%, n=14; 2; wild-type: 11.5+/-33.0%, n=14; 3). Penetration into the brain for inhaled corticosteroids (especially those of lower lipophilicity) is reduced. Experiments in mdr1a(-/-) mice confirmed the involvement of P-gp transporters. Further studies are needed to assess whether potential drug interactions at the transporter level are of pharmacological significance.

Pharmacokinetics, in-situ absorption and protein binding studies of a new neuroleptic agent centbutindole in rats.

The present study reports the absorption kinetics, plasma protein binding and pharmacokinetic profile of the centbutindole (I) after i.v. and oral dosing in rats. In addition, an in-situ absorption study was carried out using a closed-loop technique at pH 2.6 and 7.4. The rate of absorption at pH 2.6 was 5-fold less compared to that observed at pH 7.4. In-vitro and in-vivo protein binding (ultra filtration technique) was independent of substrate concentration over a range of 1.25-10.0 microg/ml. Pharmacokinetic parameters of I were determined in male rats after administering a single 4 mg/kg oral dose and 2 mg/kg intravenous dose. The peak serum concentration of I was found to be 50.1 ng/ml at 30 min after oral administration followed by a secondary Cmax of 43.2 ng/ml at 180 min. For the hydroxy metabolite (II), a Cmax of 6.4 ng/ml was measured at 360 min after oral administration of I. After oral dosing an irregular concentration-time profile with secondary peaks was observed for both I and II. The terminal half-lives for I and II after oral dosing were 163 and 263 min, respectively. After intravenous dosing, the levels of I decreased biexponentially with a distribution (t(1/2) alpha) and elimination (t(1/2) beta) half-lives of 5.7 and 128 min, respectively. Comparison of the AUC after oral and intravenous dosing of I indicates that only about 24% of the oral dose reaches the systemic circulation. The limited bioavailability can either be due to the poor solubility of the compound and/or extensive first pass metabolism in the gastrointestinal (GI) tract. Co-administration of polyethylene glycol (PEG) at oral dosing improves solubilization and increases bioavailability.

A sensitive LC assay for the simultaneous determination of centbutindole and its metabolite in rat serum using fluorescence detection.

Centbutindole (+/-) 2-gamma-[(p-fluorobenzoyl)propyl]-1, 2, 3, 4, 6, 7, 12, 12a-octahydro-pyrazino (2', 1': 6, 1) pyrido [3, 4-b] indole (I), is a new neuroleptic agent developed by Central Drug Research Institute, India. In the present study, a high performance liquid chromatography (HPLC) assay method for the simultaneous assay for I and its metabolite (II) in rat serum was developed and validated. The present method requires only 1 ml of serum with detection levels similar to that reported earlier using 4 ml serum. This assay has been found to be more suited for pre-clinical as well as phase IV studies. Linearity was observed between 1.25 and 40 ng/ml for I and 0.625 and 20 ng/ml for II in rat serum. Recoveries were consistent for both the analytes over the concentration ranges studied. Variation in intra-and inter-batch accuracy and precision were within acceptable limits of +/-20% at lowest limit of quantitation, whereas at higher concentrations it was +/-15%. The assay method was employed for the study of the pharmacokinetics and metabolism of I in rats. The parent compound and its metabolites were quantitated in serum and could be monitored up to 24 h post dose.