Jordan Journal of Pharmaceutical Sciences, Volume 7, No. 2, 2014 - 144 - © 2014 DAR Publishers/The University of Jordan. All Rights Reserved. * shahalamkhan@yahoo.com Received on 8/9/2013 and Accepted for Publication on 16/3/2014. Comparative in-vitro Pharmaceutical Evaluation of Four Brands of Metronidazole Tablets Marketed in Gulf Region Reem Khamis Al Naimi and Shah Alam Khan 1 * 1 Department of Pharmacy, Oman Medical College, Muscat, Sultanate of Oman ABSTRACT Metronidazole is an antiprotozoal drug which is also effective against anaerobic bacteria. It exhibits pronounced in-vitro and in-vivo activity against Trichomonas vaginalis and E. histolytica. Many different brands and dosage forms of Metronidazole are available in the gulf countries that place physicians and pharmacists in a dilemma of drug substitution in case of non availability of a particular brand. The present study was aimed to evaluate the pharmaceutical equivalence of four brands of 250 mg Metronidazole tablets marketed in Middle East countries. Four brands of Metronidazole tablets were purchased locally from the retail pharmacy outlets in Muscat, Oman and their solubility, partition coefficient (log P) and pharmaceutical quality were assessed by using in-vitro tests as per the United States Pharmacopoeia (USP) and unofficial standards as recommended by the manufacturers. Selected brands of Metronidazole were found to be highly soluble, highly permeable and also passed all the official and unofficial in- vitro quality control tests prescribed for the tablets except hardness test. All brands of Metronidazole tablets released more than 70% of their drug content within 45 minutes. Thus, based on the above results, it can be concluded that tested brands of Metronidazole tablets being eligible for biowaiver, are pharmaceutically equivalent and therefore can be considered for drug substitution for each other. Keywords: Metronidazole Tablets, Antiprotozoal, Pharmaceutical Equivalence, Dissolution. INTRODUCTION Metronidazole is an antiprotozoal and antiparasitic agent commonly used to treat amoebiasis, giardiasis, trichomoniasis and other microbial diseases caused by anaerobic bacteria. 1 It is also listed in the important WHO essential medicine list. 2 Metronidazole in combination with other drugs is quite effective and beneficial therapy in the management of H. pylori infection. 3 Chemically it is 2-(2-methyl-5-nitro-1H-imidazol-1-yl) ethanol (Fig. 1) and occurs as white to pale yellow microcrystalline powder, slightly soluble in water and alcohol. 4 However, it dissolves readily in dilute hydrochloric acid solution. It is a prodrug that requires reductive activation of the nitro group by susceptible organisms. It is usually completely and promptly absorbed after oral intake, reaching concentrations in plasma of 8 - 13 mg within 0.25 - 4 h after a single 500 mg dose. 5 Therefore, it can be inferred that slight change in the physicochemical characteristics and dissolution will affect its biopharmaceutics and thus its quality and efficacy. There are many multinational brands and dosage forms of Metronidazole available in the market of gulf countries. Some of these brands are manufactured in Middle East countries such as Saudi Arabia, Jordan, UAE, Oman and some are imported from other parts of the world. Various brands available in the market are considered pharmaceutically equivalent if they contain the same amount of active ingredient in the identical dosage form and meet the same compendial or other