Side effects of nitrofurantoin

The sole use of this drug is in the treatment of urinary tract infections, as after oral or intravenous (i.v.). administration, therapeutically active concentrations are attained only in urine. The drug has been available for clinical use in a crystalline formulation since 1953 and is marketed as Furadantin. Subsequently, a macrocrystalline form was developed, which may induce fewer gastrointestinal sideeffects. It is marketed under the trade name of Macrodantin. More recently a modified-release nitrofurantoin, which consists of 25% macrocrystalline nitrofurantoin and 75% nitrofurantoin monohydrate, has also been developed (nitrofurantoin MR). This product is suitable for a twice-daily dosage regimen.

Mechanism of action

The precise mode of action of nitrofurantoin is not known, but it has several mechanisms of action on bacteria and this may explain why bacterial resistance to this drug is uncommon. The drug inhibits a number of bacterial enzymes. It attacks bacterial ribosomal proteins and this causes complete inhibition of bacterial protein synthesis. Nitrofurantoin may also damage DNA. 

Side effects

The most common side effects with nitrofurantoin are nausea, headache, and flatulence. Less common adverse events (occurring in less than 1% of those taking the drug) include: 

Gastrointestinal: diarrhea, dyspepsia, abdominal pain, constipation, emesis Neurologic: dizziness, drowsiness, amblyopia Respiratory: acute pulmonary hypersensitivity reaction Allergic: pruritus, urticaria Dermatologic: hair loss Miscellaneous: fever, chills, malaise Patients should be informed that nitrofurantoin colours urine brown; this is completely harmless.Some of the more serious but rare side effects of nitrofurantoin have been a cause of concern. These include pulmonary reactions, hepatotoxicity, and neuropathy.

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