Develop an In Vitro Release Testing Method and Calculate Release Rate Comparisons for a Suppository Tablet
Challenge: Diteba's main objective of this study was to develop a simple, reliable and reproducible in vitro quality control method that could be used to discriminate variation in release characteristics of NNRTI solid dose formulations to assure batch-to-batch uniformity. Diteba's scientists attempted to develop a methodology that could be used to discriminate formulation changes, and evaluate the precision, reproducibility and sensitivity for in vitro release rate study (IVRT) experiments.
Solution: Several different technical approaches were evaluated including as a modified paddle and sinker method, a modified basket method and an enhancer cell system method. All methods utilized a High Performance Liquid Chromatography (HPLC) method for quantification of the active in the in vitro samples.
These solid dose suppository products were formulated in such a way that during the contact with receptor fluid, the product easily breaks down into small particles and lipophilic gel (sustained release matrix) which ultimately slowly releases the active drug. After melting, the drug will have to partition between the lipophilic matrix and the receptor fluid. This may lead to distribution equilibrium between the two phases rather than complete dissolution.
In vitro drug release from semi-solid topical dosage form products (creams, ointments, and gels) has been extensively investigated using Franz Diffusion Cell systems with synthetic membranes. In some cases, these experiments have used enhancer cell systems. Comparative studies indicate that the two types of apparatus generate similar data.
In general, compendial apparatus and methods should be used as a first approach for in vitro method development. To avoid unnecessary proliferation of equipment and method design, modification of compendial equipment or development or use of alternative equipment should be considered only when it has been proven that a compendial setup does not provide meaningful data for a given dosage form. Quantification and validation efforts should be demonstrated indicating the suggested method is scientifically sound and guarantees accurate, precise, reproducible data. Such methods would ensure acceptable drug product quality and allows for some interpretation of the product's in vivo performance.
Suppositories have not been investigated to the extent of oral or other topical dosage forms regarding correlation between in vitro dissolution and in vivo absorption. Testing for the rate of in vitro release of drugs from suppositories has always posed a difficult problem, due to melting, deformation, disintegration and dispersion in the dissolution medium. Several techniques have been employed for studying the in vitro drug release from suppositories but none until now, has been recommended by USP as a standard method. The most popular methods are the breaker method, basket method, membrane diffusion method, dialysis method, and continuous flow method or flow-through bead-bed apparatus. Only the European Pharmacopoeia (Ph.Eur.III) and British Pharmacopoeia have introduced a dissolution apparatus for suppositories. This is a modified membrane-free system described in the literature and it is recommended especially for reproducibility of results.
In Diteba's IVRT studies, the drug release testing was accomplished using a paddle/basket small volume dissolution system and Enhancer diffusion cell techniques.
Selection of the receptor medium was investigated in these studies. Selection of the receptor medium is based on the solubility and stability of the drug in that medium. The receptor medium must provide adequate stability and sink conditions ensuring that the drug has sufficient solubility in the receptor medium, such that the receptor medium does not affect the release rate of the drug from the matrix. This will presumably occur if the concentration of drug in the receptor phase (Ct) ≤ 10% of the saturation solubility of the drug in the receptor medium (Cstr) i.e., Ct ≤ 0.1 Cstr.
Selection of artificial membranes, both synthetic and semi-synthetic was also investigated. The membrane selected should provide an inert holding surface for the test formulation, but not a barrier. It is important to confirm that there is no interaction, (physical or chemical) between the membrane and formulation. The excipients present in the formulation may affect the physical integrity of the membrane, or in many cases, the active ingredient may bind to the membrane.
In these studies, a DURAPOR membrane 0.45μm HV was evaluated for the release rate of the drug from the matrix obtained after suppository tablets were softened and completely disintegrated into the receptor solution. An analytical method for determination of the NNRTI drug in suppository tablets was developed and verified by Diteba. Verification parameters included: specificity, system suitability, system precision, linearity and range, accuracy, limit of quantification (LOQ), Stability, and Robustness.
The most reproducible and linear release rate were obtained from the Enhancer cell method using nylon mesh (with 1000 micron of mesh size) as the sample holder, instead of artificial membranes with 0.45μm of pore size. As has been discussed previously, this configuration of diffusion cell allows the receptor medium to freely flow from the vessel to the sample cavity through the nylon mesh, thereby melting and simultaneously releasing the drug from the suppository tablets. The mesh size of 1000 micron is ideal to prevent the penetration of disintegrated small tablet particles and gel droplets into the receiving chamber.
Samples were collected at the six hour time point to meet the sink condition requirements which had been set at less than 30% drug release form the total dosage applied amount. The second requirement for sink conditions also were fulfilled as the saturation solubility of the drug in the receptor medium was 10 times higher than the maximum concentration detected in a vessel during the 3 hour diffusion rate studies. The six hour release rate studies also yielded acceptable results if paddle rotation speed was reduced from 150 rpm to 75 rpm.
Result: Diteba conducted several IVRT studies and statistically compared two different manufactured lots. The test results demonstrated that the formulation applied to the cells fell within the 90% confidence interval (CI). This provided statistical evidence of the "sameness" of suppository tablet lots and demonstrated that the method used in these studies would provide reproducible results when testing different lots of the same formulation.