Decreased bioavailability of some antipsychotic phenothiazines due to interactions with adsorbent antacid and antidiarrhoeal mixtures

Montmorillonite-lipid hybrid carriers for ionizable and neutral poorly water-soluble drugs: Formulation, characterization and in vitro lipolysis studies

Lipid-based formulations (LBFs) are a popular strategy for enhancing the gastrointestinal solubilization and absorption of poorly water-soluble drugs. In light of this, montmorillonite-lipid hybrid (MLH) particles, composed of medium-chain triglycerides, lecithin and montmorillonite clay platelets, have been developed as a novel solid-state LBF. Owing to the unique charge properties of montmorillonite, whereby the clay platelet surfaces carry a permanent negative charge and the platelet edges carry a pH-dependent charge, three model poorly water-soluble drugs with different charge properties; blonanserin (weak base, pKa 7.7), ibuprofen (weak acid, pKa 4.5) and fenofibrate (neutral), were formulated as MLH particles and their performance during biorelevant in vitro lipolysis at pH 7.5 was investigated. For blonanserin, drug solubilization during in vitro lipolysis was significantly reduced 3.4-fold and 3.2-fold for MLH particles in comparison to a control lipid solution and silica-lipid hybrid (SLH) particles, respectively. It was hypothesized that strong electrostatic interactions between the anionic montmorillonite platelet surfaces and cationic blonanserin molecules were responsible for the inferior performance of MLH particles. In contrast, no significant influence on drug solubilization was observed for ibuprofen- and fenofibrate-loaded MLH particles. The results of the current study indicate that whilst MLH particles are a promising novel formulation strategy for poorly water-soluble drugs, drug ionization tendency and the potential for drug-clay interactions must be taken into consideration to ensure an appropriate performance.

In vitro adsorption of mebeverine hydrochloride onto kaolin and its relationship to pharmacological effects of the drug in vivo

The in vitro uptake of mebeverine hydrochloride from an initial drug concentration of 0.25-4.25 or 0.2-3.6 g% w/v onto kaolin 5.0 g% w/v at pH 1.8 or 7.5, respectively, at 37 degrees C was represented by a double- layered adsorption isotherm. The calculated data were in accordance with a Langmuir adsorption isotherm for an initial drug concentration up to 2.1 or 2.0 g% w/v when a monolayer was formed at pH 1.8 or 7.5, respectively. The adsorption process is pH dependent, and is affected by the electrolyte concentration and valency. The amount of the drug desorbed (mg% w/v) by washing with different elution media at 37 degrees C followed the sequence 0.1 M hydrochloric acid > 0.1 M magnesium chloride > 0.1 M sodium chloride > simulated intestinal fluid. The results obtained from this study indicate that two mechanisms, ion exchange and physical adsorption, were involved in the uptake of mebeverine hydrochloride by kaolin. The presence of different concentrations of kaolin with the tablets or capsules of the drug, adversely affected the release rate. The in vivo and in vitro studies on guinea pig ileum showed that the presence of kaolin in a mixture with mebeverine hydrochloride did not affect to any significant level the inhibiting effect of the musculotropic drug on carbachol-induced contractions in the isolated guinea pig ileum. In vivo studies showed similar results for barium chloride as well.

High-performance liquid chromatographic determination of perphenazine in plasma

A reversed-phase high-performance liquid chromatographic (HPLC) method for the analysis of perphenazine in rabbit plasma was developed. Amitriptyline HCl was used as the internal standard. The chromatography was performed using a Microsorb-CN column; the mobile phase consisted of 85:15 methanol/0.005 M ammonium acetate buffer; flow rate of 1.6 ml/min; and ultraviolet detection at 254 nm. Retention times were 10.8 and 18.1 min for perphenazine and amitriptyline HCl, respectively. The recovery of perphenazine added to plasma in the concentration range of 0.05-5 micrograms/ml was found to be greater than 80%. This procedure was used for the analysis of plasma samples collected over time following the oral administration of perphenazine tablets in rabbits.