In vitro dissolution of sustained-release Nifedipine brands marketed in the Kumasi Metropolis

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With the advent pattern of generic prescribing and substitution in developing countries like Ghana, there has been an influx of a wide variety of antihypertensive drug brands on the market. The study was aimed at establishing the most prescribed sustained-release (SR) antihypertensive drug in the Kumasi Metropolis and evaluation of the quality of selected brands of this drug by in vitro dissolution studies and to establish whether the selected brands were interchangeable based on analysis of the dissolution patterns. The survey was conducted for 66 doctors in 50 hospitals and 150 patients within the Kumasi metropolis, based on hypertension management. Information gathered from the survey was edited, coded and analyzed using the version 16 of Statistical Package for Social Science, SPSS software. The drug Nifedipine SR ranked first on the list as the most stocked and used SR antihypertensive drug. Twelve brands of Nifedipine SR comprising 20 mg (8 brands) and 30 mg (4 brands) were purchased from randomly selected pharmacies within the Kumasi metropolis and coded as brands A, B, C, D, E, F, G, H, I, J, K and L. On the subject of SR brands interchangeability, 60% of prescribers and 41% of patients were of the opinion that all brands of SR nifedipine brands were indeed interchangeable. Patients’ perception on interchangeability might have been influenced by their experience in the use of the drugs whereas doctors’ perception might have been influenced by their knowledge of drug contents and general experience in practice. The twelve coated tablet brands were analyzed for weight uniformity and content. All the twelve brands passed the BP weight uniformity test and 9 passed the USP test for Assay. Dissolution testing was conducted using the USP dissolution test 2, paddle method at 18 time points to obtain their dissolution profiles which were subjected to analysis involving model-independent methods and model dependent methods. For the in vitro USP dissolution test conducted, 7 out of the 12 brands passed all the 3 time-points specified (3hours, 6hours and 12 hours). Further analysis by fit factors showed that brands B, C and D (30 mg) were interchangeable. However, the pairs of 20 mg brands considered similar included brands E &K, E & L, G&H, G&I, and G &J. Based on the analysis of the release profiles in the light of distinct kinetic models, brands A, B, C, D, E, I and K were considered similar because their drug release kinetic followed Higuchi’s model. Brands H and J were considered similar because their drug release kinetics followed Hixson-Crowell kinetic model. Therefore, few SR nifedipine brands were similar and could be interchanged, whereas majority of the selected brands could not.
A thesis submitted to the School of Graduate Studies in partial fulfilment of the requirement for the Master of Philosophy