Our results reveal the high incidence of substandard drugs on some Arab market where several factors might jeopardize the quality status of medicines: lack of effective quality assurance system during manufacture in both Arab and export countries, and uncontrolled storage conditions, especially unsuitable pharmacy premises. Use of substandard antibiotic preparations increases the risk of therapeutic failure and the emergence of drug-resistant microorganisms.

Generic drugs offer a cost-effective alternative to brand-name products. However, the main concern with modified-release formulations is the substitution of one product for another. Accordingly, the first objective of this study was to assess the interchangeability of the available diltiazem extended-release (ER) products on the basis of their in vitro dissolution characteristics using USP Apparatus 2 and 3. The second objective was to compare dissolution profiles in simulated fasted and fed states and determine whether there is a change in the mechanism of drug release. Dissolution profiles characterized using Apparatus 2 or 3 under fasted conditions were similar. However, Apparatus 3 testing provided a more discriminating and comprehensive evaluation of the drug release performance of ER products. Testing using Apparatus 3 in the fed state highlighted some difference in dissolution profiles, suggesting a food effect on drug release. This implies that, depending on the targeted concentration, a patient should be instructed whether to take the medication in fasted or fed state. The study therefore shows the necessity of testing the products in both fasted and fed states to determine their similarity and therapeutic interchangeability. Apparatus 3 testing was also more accurate in determining the release mechanism than the Apparatus 2 method. No change in the mechanism of drug release between fasted and fed state was observed.

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