Nitrofurantoin is a medication that is used primarily to kill the organisms responsible for causing urinary tract infections. Like many other antibiotics, medical professionals recommend the avoidance of alcohol while taking this drug. This warning is due in part to the safety issues surrounding the combination of nitrofurantoin and alcohol, as well as issues with potential diminished efficacy of the antibiotic. Mixing nitrofurantoin with alcohol is not as dangerous as many combinations of alcohol and medications, but there are still safety issues that make this combination undesirable.
Some of the risk factors behind mixing nitrofurantoin and alcohol pertain to the the way that these two substances affect the body. This antibiotic requires high concentrations in order to attack bacteria, which it does by damaging their genetic information within cell structures. For the most part, this drug remains in the gastrointestinal (GI) tract until it is excreted in the urine, and in the urinary tract it reaches sufficient concentrations to kill bacteria. About three-quarters of the ingested medication is broken down in the liver and kidneys before it reaches this point, but enough nitrofurantoin is excreted without being metabolized to kill bacteria in the urinary tract.
This drug does not normally make it into the bloodstream, so most of its side effects are limited to the GI tract. These side effects are caused by slight damage to the rapidly dividing cells of the GI tract, although the lower concentrations of this drug outside of the urinary tract limits their prominence. Adverse effects of nitrofurantoin often include nausea, dyspepsia, or upset stomach, vomiting, and decreased appetite. In the most extreme cases, stomach bleeding and ulcers can even occur.
The combination of nitrofurantoin and alcohol can make these side effects more severe. Alcohol is an irritant to the cells of the GI tract, and can trigger the release of additional stomach acid that can harm the surrounding tissue even more. When combined with the potential for stomach tissue harm from the antibiotic, this combination can lead to side effects that are much more unpleasant, and even painful. The chance of stomach bleeding and severe side effects becomes worse when nitrofurantoin and alcohol are mixed.
Alcohol may also make this antibiotic less effective, which is another source of risk behind mixing the two. This combination can lead to alcohol increasing the metabolism, or breakdown, of nitrofurantoin in the liver and kidneys before excretion. In turn, the antibiotic will not be as effective, and may not be able to successfully treat urinary tract infections.