Is rat a good model for assessment of particulate-based taste-masked formulations?

Recently there has been an increased interest to develop specialised dosage forms that are better suited to specific patient populations, such as paediatrics and geriatrics. In these patient populations the acceptability of the oral dosage form can be paramount to the products success. However, many Active Pharmaceutical Ingredients (APIs) are known to cause an aversive taste response. One way to increase the acceptability and to enhance the palatability of the formulation is to design coated taste-masked particulate-based dosage forms. The masking of poorly tasting drugs with physical barriers such as polymer coatings can be utilised to prevent the release of drug within the oral cavity, thus preventing a taste response. However, currently, there are few assessment tools and models available to test the efficiency of these particulate-based taste-masked formulations. The rat brief access taste aversion model has been shown to be useful in assessment of taste for liquid dosage forms. However, the applicability of the rat model for particulate-based taste masked formulations is yet to be assessed. It is not understood whether dissolution, solubility and thus exposure of the drug to taste receptors would be the same in rat and human. Therefore, rat saliva must be compared to human saliva to determine the likelihood that drug release would be similar within the oral cavity for both species. In this study rat saliva was characterised for parameters known to be important for drug dissolution, such as pH, buffer capacity, surface tension, and viscosity. Subsequently dissolution of model bitter tasting compounds, sildenafil citrate and efavirenz, in rat saliva was compared to dissolution in human saliva. For all parameters characterised and for the dissolution of both drugs in rat saliva, a substantial difference was observed when compared to human saliva. This discrepancy in saliva parameters and dissolution of model drugs suggests that preclinical taste evaluation of particulate-based taste-masked formulations suggests rat is not a good model for predicting taste of solid dosage forms or undissolved drug where dissolution is required. Alternative preclinical in vivo models in other species, or improved biorelevant in vitro models should be considered instead.

Attainment of target rifampicin concentrations in cerebrospinal fluid during treatment of tuberculous meningitis.

OBJECTIVE: There is considerable uncertainty regarding the optimal use of rifampicin for the treatment of tuberculous (TB) meningitis. A pharmacokinetic modeling and simulation study of rifampicin concentrations in cerebrospinal fluid (CSF) during TB meningitis treatment was performed in this study. METHODS: Parameters for rifampicin pharmacokinetics in CSF were estimated using individual-level rifampicin pharmacokinetic data, and the model was externally validated in three separate patient cohorts. Monte Carlo simulations of rifampicin serum and CSF concentrations were performed. The area under the rifampicin CSF concentration-versus-time curve during 24 h (AUC0-24) relative to the minimum inhibitory concentration (MIC) served as the pharmacodynamic target. RESULTS: Across all simulated patients on the first treatment day, 85% attained the target AUC0-24/MIC ratio of 30 under a weight-based dosing scheme approximating 10 mg/kg. At the rifampicin MIC of 0.5 mg/l, the probability of AUC0-24/MIC target attainment was 26%. With an intensified dosing strategy corresponding to 20 mg/kg, target attainment increased to 99%, including 93% with a MIC of 0.5 mg/l. CONCLUSIONS: Under standard dosing guidelines, few TB meningitis patients would be expected to attain therapeutic rifampicin exposures in CSF when the MIC is ≥0.5 mg/l. Either downward adjustment of the rifampicin MIC breakpoint in the context of TB meningitis, or intensified rifampicin dosing upwards of 20 mg/kg/day, would reflect the likelihood of pharmacodynamic target attainment in CSF.

A novel sustained-release clotrimazole varnish for local treatment of oral candidiasis.

The use of dental varnish for therapeutic purposes has been reported for fluoride or antibacterial drugs. Our objectives were to develop a sustained-release varnish containing an antifungal drug (clotrimazole) for topical application and to evaluate the release rate of the drug in human saliva in comparison with an available commercial troche and their acceptance by healthy volunteers. Following in vitro optimization of the release rate from the varnish, we have embarked on a crossover comparative study assessing the oral sensations and pharmacokinetics of a 10-mg clotrimazole oral troche versus a 10-mg sustained-release clotrimazole varnish in 14 human volunteers over a period of 5 h. Saliva samples were assessed for clotrimazole concentration by high performance liquid chromatography analysis. The volunteers' evaluation of the varnish and troche (taste, other sensory changes, convenience, and oral suitability) were recorded. At all time points, salivary clotrimazole concentrations were higher, and the terminal half-life was significantly prolonged in the varnish group in comparison to the control group. This can be attributed to continuous release of clotrimazole from the varnish formulation. The duration of the drug over the minimal inhibitory concentration, following application of the varnish, was more than threefold longer than following administration of the troche. The developed sustained-release varnish can be applied in patients at a lower frequency than troches, thus, achieving higher patient compliance and efficacy. This novel varnish application can serve as the basis for a new treatment approach to oral candidiasis, a very common chronic opportunistic infection with improved clinical outcome.

Subcutaneous and intraperitoneal lipogranulomas following subcutaneous injection of olive oil in Sprague-Dawley rats.

Olive oil is commonly employed as a solubilizing agent for lipophilic materials in preclinical studies in rodents. Here we report that following subcutaneous (SC) injection of olive oil to Sprague-Dawley (SD) rats, local SC lipogranulomas formed, which were associated with an unusual location of the same changes in the peritoneum. Macroscopically, multifocal white spots were found over the liver and mesentery. Histologically, lipid granulomas were seen in the SC injection site, as well as on the capsular or serosal surface of the abdominal organs. No abnormal clinical signs were noted except for swelling at the injection site. The olive oil may have reached the peritoneal cavity from the SC tissue passively via the lymphatic vessels or actively after engulfment by antigen-presenting cells via the lymphatic or blood vessels. These findings are of particular importance for drug safety assessments, as the occurrence of lipogranulomas in locations distant from the site of administration may lead to misinterpretation of histological results. We suggest that these aberrations may be induced by the administration of olive oil as a vehicle.

Selection of drug candidates for gastroretentive dosage forms: pharmacokinetics following continuous intragastric mode of administration in a rat model.

The purpose of the study was to evaluate the pharmacokinetic effects obtained by gastroretentive dosage form (GRDF) for drugs absorbed by passive paracellular diffusion (atenolol, acyclovir) or active transport (valacyclovir). Model drugs were delivered as gastric infusion (GInf) through an implanted catheter (resembling GRDF), intravenous, oral (PO), and colonic administration to rats. For atenolol (highly soluble drug), GInf resulted in a prolonged Tmax and reduced Cmax in comparison to PO, whereas bioavailability was similar. Bioavailability after colonic bolus was significantly lower. Results were also simulated by a pharmacokinetic model. For acyclovir, GInf and PO demonstrated almost the same pharmacokinetic profile with low bioavailability, most probably due to the solubility-limited absorption. Valacyclovir demonstrated the significant change in the shape of pharmacokinetic profile as a function of the rate of gastric delivery, without variation in bioavailability. Valacyclovir was not absorbed from colon. Experimental and theoretical methodologies to assess the pharmacokinetic influences of GRDF mode of administration were developed, avoiding the need to compound the drug in a dosage form. GRDF provides a mean for controlled release of compounds that are absorbed by active transport in the upper intestine. It also enables controlled delivery for paracellularly absorbed drugs without a decrease in bioavailability.