Determination of Potency and Quality of Some Selected Penicillins on the Ghanaian Market Using Microbiological and Developed and Validated HPLC Methods

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The use of antibiotics in health delivery is inevitable since it is one of the most prescribed medications. The quality and efficacy of these medications are crucial in health systems since they can affect the quality of healthcare delivery. The study was designed to determine the quality and potency of some penicillins on the Ghanaian market. A total of 54 samples (29 capsules and 25 suspensions), of different brands and batches were sampled from different pharmacies in Accra and Kumasi, Ghana, from October, 2011 to May, 2012. The potency, activity and minimum inhibitory concentration (MIC) of the samples were determined by the agar well diffusion and micro-dilution methods against selected Gram-negative and Gram-positive bacteria (Escherichia coli ATCC 25922,Pseudomonas aeruginosa ATCC 4853, Staphyloccocus aureus ATCC 25923 and Bacillus subtilis NTCC 10073). The quality of the samples was determined quantitatively by developed and validated HPLC method. The MICs of flucloxacillin and cloxacillin samples were ≥ 1400 μg/mL, whiles that of amoxicillin samples were ≥ 200 μg/mL, with reference to the standards which gave MICs of 200 to 800 μg/mL against all the test bacteria with the suspensions exhibiting higher antimicrobial activity. The biological assay results revealed higher MICs for all the various penicillins evaluated but were much higher in flucloxacillin samples. The United State Pharmacopoeia (2011) methods of assay of the selected samples were slightly modified, making use of the available materials in the laboratory. The methods were well validated using the International Conference on Harmonization (ICH) guidelines, British Pharmacopoeia (BP) and USP. Specificity, linearity, precision and accuracy of the HPLC method were determined. HPLC analysis of the samples revealed that 75% of amoxicillin capsule samples and 92.3% of amoxicillin suspension samples contained the right amount of active pharmaceutical ingredient (API) with percentages ranging from 93.2 to 104.3% and 81.0 to 104.1% respectively. For samples of flucloxacillin iv capsules, 62.5% of the samples revealed API’s within 96 to 120.5%. All flucloxacillin suspension samples were below the British Pharmacopoeia (BP) and United State Pharmacopoeia (USP) specifications. None of the cloxacillin capsule samples contained the right active pharmaceutical ingredient and all the suspension samples have their API within BP and USP specification of 114.4 to 120.0%. Variation within same brand was observed in some of the samples but were not significant (p>0.05). For some of the samples, only one batch could be sampled within the period of the study. Consequently, no data from these have been analyzed. Variations in microbiological evaluation and HPLC analysis were observed. In general, 58.6% of the capsules of all the samples contained the right API whereas 64% of them were recorded for suspensions. Out of the 54 samples evaluated, 61.1% were within BP and USP specifications. The biological assay revealed higher MIC values for all the penicillin samples evaluated compared with the reference samples. Among the samples evaluated, amoxicillin showed better quality of 82.8% as compared to flucloxacillin (31.3%) and cloxacillin (44.4%) samples. Efforts should therefore be made to improve the quality and storage conditions of these antibiotics and also constant monitoring and surveillance of activity and potency of these antibiotics should be done. These results suggest the need for increased monitoring and surveillance of these antibiotics by their manufacturers and regulatory bodies.
A Thesis Submitted to the Department of Pharmaceutics, Kwame Nkrumah University of Science and Technology in Partial Fulfilment of the Requirements for the Degree of Master of Philosophy