Effects of interaction with surfactants, adsorbents, and other substances on the permeation of chlorpromazine through a dimethyl polysiloxane membrane

Safety of surfactant excipients in oral drug formulations

Surfactants are a diverse group of compounds that share the capacity to adsorb at the boundary between distinct phases of matter. They are used as pharmaceutical excipients, food additives, emulsifiers in cosmetics, and as household/industrial detergents. This review outlines the interaction of surfactant-type excipients present in oral pharmaceutical dosage forms with the intestinal epithelium of the gastrointestinal (GI) tract. Many surfactants permitted for human consumption in oral products reduce intestinal epithelial cell viability in vitro and alter barrier integrity in epithelial cell monolayers, isolated GI tissue mucosae, and in animal models. This suggests a degree of mis-match for predicting safety issues in humans from such models. Recent controversial preclinical research also infers that some widely used emulsifiers used in oral products may be linked to ulcerative colitis, some metabolic disorders, and cancers. We review a wide range of surfactant excipients in oral dosage forms regarding their interactions with the GI tract. Safety data is reviewed across in vitro, ex vivo, pre-clinical animal, and human studies. The factors that may mitigate against some of the potentially abrasive effects of surfactants on GI epithelia observed in pre-clinical studies are summarised. We conclude with a perspective on the overall safety of surfactants in oral pharmaceutical dosage forms, which has relevance for delivery system development.

Effect of excipients on oral absorption process according to the different gastrointestinal segments

INTRODUCTION

Excipients are necessary to develop oral dosage forms of any Active Pharmaceutical Ingredient (API). Traditionally, excipients have been considered inactive and inert substances, but, over the years, numerous studies have contradicted this belief. This review focuses on the effect of excipients on the physiological variables affecting oral absorption along the different segments of the gastrointestinal tract. The effect of excipients on the segmental absorption variables are illustrated with examples to help understand the complexity of predicting their in vivo effects.

AREAS COVERED

The effects of excipients on disintegration, solubility and dissolution, transit time, and absorption are analyzed in the context of the different gastrointestinal segments and the physiological factors affecting release and membrane permeation. The experimental techniques used to study excipient effects and their human predictive ability are reviewed.

EXPERT OPINION

The observed effects of excipient in oral absorption process have been characterized in the past, mainly in vitro (i.e. in dissolution studies, in vitro cell culture methods or in situ animal studies). Unfortunately, a clear link with their effects in vivo, i.e. their impact on Cmax or AUC, which need a mechanistic approach is still missing. The information compiled in this review leads to the conclusion that the effect of excipients in API oral absorption and bioavailability is undeniable and shows the need of implementing standardized and reproducible preclinical tools coupled with mechanistic and predictive physiological-based models to improve the current empirical retrospective approach.

A systematic and mechanistic evaluation of aspartic acid as filler for directly compressed tablets containing trimethoprim and trimethoprim aspartate

The generally accepted paradigm of 'inert' and 'mono functional' excipient in dosage form has been recently challenged with the development of individual excipients capable of exhibiting multiple functions (e.g. binder-disintegrants, surfactant which affect P-gp function). The proposed study has been designed within the realm of multifunctionality and is the first and novel investigation towards evaluation of aspartic acid as a filler and disintegration enhancing agent for the delivery of biopharmaceutical class IV model drug trimethoprim. The study investigated powder characteristics using angle of repose, laser diffractometry and scanning electron microscopy (SEM). The prepared tablets were characterised using Heckel analysis, disintegration time and tensile strength measurements. Although Heckel analysis revealed that both TMP and TMP aspartate salt have high elasticity, the salt form produced a stronger compact which was attributed to the formation of agglomerates. Aspartic acid was found to have high plasticity, but its incorporation into the formulations was found to have a negative impact on the compaction properties of TMP and its salt. Surface morphology investigations showed that mechanical interlocking plays a vital role in binding TMP crystals together during compaction, while the small particle size of TMP aspartate agglomerates was found to have significant impact on the tensile strength of the tablets. The study concluded that aspartic acid can be employed as filler and disintegrant and that compactability within tablets was independent of the surface charge of the excipients.

From Physical Pharmacy to Clinical Pharmacology

Research works on molecular interactions in solutions were carried out at School of Pharmacy, the University of Wisconsin under the direction of Prof. T. Higuchi and at Faculty of Pharmaceutical Sciences, Kyoto University under the direction of Prof. H. Sezaki. Studies on permeation of drugs through polymer membranes were carried out at Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Canada and at Pharmaceutical Chemistry Research Laboratories at Food and Drug Directorate, Department of Health and Welfare, Canada. Studies on modification of delivery patterns by means of pharmaceutical approaches were carried out at Faculty of Pharmaceutical Sciences, Hokkaido University. Topics related to modification of drug delivery patterns include employment of amorphous forms such as ground mixture with micro-crystalline cellulose and coprecipitate with polyvinylpyrrolidone, use of biodegradable polymers such as polylactic acid and polycarbonates, gel-forming materials such as konjac, agar and hydroxypropylcellulose, and physicochemical systems such as complexation. Works related to drug delivery and disposition of drugs in humans were carried out at Department of Pharmacy, Kumamoto University Hospital. Topics related to drug delivery in humans include injections containing anticancer drugs for intra-arterial administration, lidocaine gels for dermal anesthesia, glucagon solution for nasal administration. Topics related to disposition of drugs in humans include clinical pharmacokinetic studies in infants and elderly and medical uses of adsorbents.

Drug-excipient interactions and their affect on absorption

Excipient(s) are traditionally thought of as inert but they can have a tremendous impact on the ultimate pharmacological availability of a drug substance when added to a formulation. The magnitude of this effect will depend on the characteristics of the drug and on the quantity and properties of the excipients. The aim of this article is to identify the various physicochemical and physiological processes that can be altered by drug-excipient interactions and to explore mechanisms by which they might occur. The regulatory implications of drug-excipient interactions will also be discussed.

Mechanisms to control drug release from pellets coated with a silicone elastomer aqueous dispersion

The mass transport of two different compounds through polydimethylsiloxane (PDMS)-silica films was investigated to demonstrate qualitatively how this coating system can alter the release of various compounds. Various ratios of PDMS elastomer and silica were used to coat monodisperse particle-sized pellets layered with an ionizable compound (tartrazine) and a nonionized compound (acetaminophen). The 2:1 PDMS-silica composition containing the polyethylene glycol (PEG) 8000 pore former allowed mainly pore transport through void spaces in the PDMS films. Both compounds rapidly diffused through the film as a result of the solubilization and subsequent removal of the PEG 8000 from the film matrix. As the PDMS-silica ratios in the films changed from a 1:1 to a 2:1 to a 4:1 (all without polyethylene glycol 8000) coating formulation, the differences in release rate between acetaminophen and tartrazine changed. The lower ratio of PDMS-silica allowed much faster tartrazine diffusion compared to acetaminophen. As the ratio increased from 1:1 to 2:1, the two compounds were released at similar rates. When the ratio reached 4:1, acetaminophen was released significantly faster than tartrazine. Explanations for these differences and the mechanisms controlling the drug release are discussed in the text. In some circumstances, osmolality and pH affected drug release from dosage forms coated with this polymer system. This study demonstrated that utilization of this polymer system offers a useful tool for the formulation scientist to modify release rates of ionic and nonionic drug substances.

Effect of carboxylic acids on permeation of chlorpromazine through dimethyl polysiloxane membrane

The effect of carboxylic acids on the permeation of chlorpromazine was investigated through a dimethyl polysiloxane nonpolar membrane. The permeability of the diffusate, at pH 5.8, increases considerably in the presence of carboxylic acids or phosphate, probably due to an ion-pair formation between the relative anions and chlorpromazine.

A study of the physicochemical interactions between biliary lipids and chlorpromazine hydrochloride. Bile-salt precipitation as a mechanism of phenothiazine-induced bile secretory failure

Since chlorpromazine hydrochloride [2-chloro-10-(3-dimethylaminopropyl)-phenothiazine hydrochloride] is commonly implicated in causing bile-secretory failure in man and is secreted into bile, we have studied the physicochemical interactions of the drug with the major components of bile in vitro. Chlorpromazine hydrochloride molecules are amphiphilic by virtue of possessing a polar tertiary amine group linked by a short paraffin chain to a tricyclic hydrophobic part. At pH values below the apparent pK (pK'a 7.4) the molecules are water-soluble cationic detergents. We show that bile salts in concentrations above their critical micellar concentrations are precipitated from solution by chlorpromazine hydrochloride as insoluble 1:1 salt complexes. In the case of mixed bile-salt/phosphatidylcholine micellar solutions, however, the degree of precipitation is inhibited by the phospholipid in proportion to its mole fraction. With increases in the concentration of chlorpromazine hydrochloride or bile salt, micellar solubilization of the precipitated complexes results. Sonicated dispersions of the negatively charged phospholipid phosphatidylserine were also precipitated, but dispersions of the zwitterionic phospholipid phosphatidylcholine were not. Chlorpromazine hydrochloride efficiently solubilized these membrane phospholipids as mixed micellar solutions when the drug:phospholipid molar ratio reached 4:1. Polarizing-microscopy and X-ray-diffraction studies revealed that the precipitated complexes were amorphous and potentiometric studies confirmed the presence of a salt bond. Some dissociation of the complex occurred in the case of the most polar bile salt (Ks 0.365). As canalicular bile-salt secretion determines much of bile-water flow, we propose that complexing and precipitation of bile salts by chlorpromazine hydrochloride and its metabolites may be physicochemically related to the reversible bile-secretory failure produced by this drug.

Evaluation of a dynamic permeation technique for studying drug-macromolecule interactions

The applicability of a permeation rate technique to the determination of drug-macromolecule interactions was tested by measuring the extent of interaction of methylparaben with polyvinylpyrrolidone and polysorbate 80. Results were in agreement with literature data obtained by other techniques. The present method, although restricted to permeant molecules that diffuse readily through nonporous nylon membranes, is of potential value for investigations of drug binding by macromolecules not retained by porous dialysis membranes.