Journal of Postgraduate Medicine Medknow Publications and Staff Society of Seth GS Medical College and KEM Hospital, Mumbai, India ISSN: 0022-3859 EISSN: 0972-2823 Vol. 48, Num. 1, 2002, pp. 78

Journal of Postgraduate Medicine, Vol. 48, Issue 1, 2002 pp. 78

Answer to question asked in previous Drug Watch section

Code Number: jp02028

Trimethoprim is active against E. coli, Klebsiella, and Proteus, while nitrofurantoin is active chiefly against E.coli and enterococci. Trimethoprim can cause side-effects such as skin reactions, gastro-intestinal disturbances and bone marrow depression,while nitrofurantoin use is associated with gastro-intestinal disturbances, peripheral neuropathy, hypersensitivity reactions and acute or chronic pulmonary reactions. It must be noted that fixed-dose drug combinations are considered to be appropriate when they are used to achieve a synergistic effect, to minimize adverse effects or to increase the concentration of the drug at the site of action. The combination of trimethoprim and nitrofurantoin does not fulfil any of the criteria. Besides, both the drugs are bacteriostatic and have no synergistic effect when given in combination. Also, trimethoprim requires an alkaline urinary pH for it's action and at this pH, the anti-bacterial activity of nitrofurantoin is lost .At the acidic pH favourable for nitrofurantoin activity, trimethoprim, which is a weak base is ionized and excreted rapidly. Thus, during therapy, it will be very difficult to adjust a pH which will favour the anti-bacterial activity of both compounds. For all these reasons, the combination of trimethoprim and nitrofurantoin has been banned.

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