A comparative evaluation of the change in hardness, of two commonly used maxillofacial prosthetic silicone elastomers, as subjected to simulated weathering in tropical climatic conditions.

Silicone elastomers have become the materials of choice for fabrication of facial prostheses. However such prostheses need periodic replacement due to the degradation of their physical properties due to weathering of polymers. The effect of environmental factors, disinfection solutions and skin secretions on weathering of silicones has been reported. However, the literature does not report on the comparative evaluation on the change in hardness of two commonly used maxillofacial prosthetic silicone elastomers, cured by different techniques and subjected to tropical climatic conditions. This study provides improved insight and understanding into the behavior of such materials for better material selection and treatment results.

Bioavailability and in-vitro/in-vivo correlation for propranolol hydrochloride extended-release bead products prepared using aqueous polymeric dispersions.

The influence of formulation and extrinsic factors has been investigated for the in-vitro release of propranolol hydrochloride from controlled-release beads prepared using aqueous polymeric dispersions, Aquacoat and Surelease. A single-dose three-way crossover bioavailability study of two extended-release experimental formulations (80 mg), Inderal LA (80 mg) and an Inderal immediate-release dosage form (2 x 40 mg) was also conducted and a comparative analysis of pharmacokinetic parameters and the in-vitro release profiles was performed to assess in-vitro/in-vivo correlation. Analysis showed that the in-vitro release data appeared to follow zero-order release kinetics. Intensity of agitation and dissolution method were found to have no significant effect on drug release from beads prepared using either of the coating dispersions studied or Inderal LA. Release of drug from beads coated with Aquacoat was faster in basic media than in acidic media; Surelease-coated beads, however, showed release characteristics that were less sensitive to changes in the pH of the dissolution fluid, and Inderal LA beads showed slower release profiles in acidic medium than in other dissolution media studied. Pharmacokinetic analysis of the data revealed sustained-release absorption characteristics without any evidence of dose-dumping from any of the extended-release dosage forms studied. Regression analysis of the fraction of drug absorbed against the percentage of the drug released in-vitro, at the corresponding times, yielded good in-vitro/in-vivo correlation (level A) for all the extended-release formulations studied. The results showed that there was no dose-dumping from any of extended-release formulations and that the relative bioavailabilities of the experimental formulations were superior to that of the marketed formulation.

A fluorimetric liquid chromatographic method for the determination of propranolol in human serum/plasma.

A simple, rapid, and sensitive fluorimetric-high-performance liquid chromatographic method for the determination of propranolol in human serum/plasma has been developed, without the need for solvent extraction. The procedure required 200 microliters of serum/plasma, and the addition of 1 ml of acetonitrile for protein precipitation followed by vortexing and centrifugation at 10 000 g. The clear supernatant was evaporated to dryness under a stream of nitrogen at 50-60 degrees C, the residue was reconstituted in 100 microliters of methanol, and a 90 microliters portion was injected onto the high-performance liquid chromatograph for propranolol quantitation. Chromatography was accomplished using a Hypersil cyano column, a mobile phase of acetonitrile-aqueous acetic acid (1%) containing 0.2% triethylamine (35:65, v/v) (pH 3.6), a flow rate of 1.5 ml min-1, a fluorescence detector set at an excitation wavelength of 230 nm and an emission wavelength of 340 nm, and using pronethalol as the internal standard. Retention times for pronethalol and propranolol were 7.5 min and 9.5 min, respectively. Standard curves were linear in the range 5-200 ng ml-1. Relative standard deviations for both inter-day and intra-day precision analysis were less than 7% for serum. No interference was observed from endogenous serum/plasma components. Specificity was shown for some, but not all, commonly coadministered drugs tested. The advantages of this method include good precision, low sample volume, good reproducibility and recovery, and high sensitivity.

Relationship between planar and all-surface rate constants for drugs formulated in nondisintegrating cylindrical slow-release tablets.

The release of drug through the planar surface of a nondisintegrating tablet with an insoluble matrix has been described mathematically using the Higuchi release rate constant (kH). The release of drug through a similar all-surface tablet has been described by using a cubic equation and the all-surface rate constant (kr). Using sodium salicylate and quinidine sulfate as model drugs, the relationship between kH and kr was verified for cylindrical slow-release tablets. Accordingly, the rate constant obtained from a single exposed planar surface can be used to predict the rate constant (kr) when all surfaces of the tablet are exposed to dissolution fluid.

pH- and flow-rate-independent release of drug from uncoated slow-release tablets.

Slow-release tablets were prepared using a polyvinyl chloride--polyethylene matrix and sodium salicylate as a model drug. The in vitro release of salicylate was described adequately by a previously published equation. The release rate constant was independent of the pH of the dissolution fluid and the flow rate of the fluid past the tablet. Accordingly, the procedures used to test the in vitro drug release from this type of matrix tablet are not as critical as for conventional tablets. It may therefore be postulated that the in vivo performance of the tablet may be less subject to variations in the physiological parameters of the GI tract.