Nitrofurantoin, often known by the brand names Macrobid or Macrodantin, is an antibacterial agent prescribed for treating and preventing urinary tract infections (UTIs). It targets and eliminates bacteria by concentrating in the urine after being metabolized. This antibiotic remains a common first-line option for uncomplicated UTIs. Like any medication, it carries a risk of adverse reactions, ranging from common, mild digestive issues to rare, severe effects on major organ systems.
Gastrointestinal and General Common Side Effects
The most frequently reported side effects associated with nitrofurantoin involve the digestive system. Nausea and vomiting are particularly common and are considered dose-related, meaning higher doses increase the severity of these symptoms. Patients may also experience diarrhea, loss of appetite, stomach pain, and flatulence.
These gastrointestinal disturbances are generally mild and temporary, often improving as the body adjusts to the medication. Taking the medication with food or milk is recommended to minimize nausea and stomach upset. In some cases, the macrocrystalline formulation may be better tolerated by patients who experience significant nausea with the microcrystalline form.
Outside of the digestive tract, other common reactions include headache, dizziness, weakness, or drowsiness. A noticeable, though harmless, effect is that the medication can cause the urine to turn a rust-yellow or brownish color. While these reactions are typically not signs of a serious problem, they should be discussed with a healthcare professional if they persist or become severe.
Serious and Systemic Organ Risks
While the majority of side effects are mild, nitrofurantoin is associated with serious adverse reactions affecting the lungs, liver, and nervous system, particularly with long-term use. Pulmonary toxicity is a significant concern, manifesting in two forms: acute or chronic reactions. Acute pulmonary reactions are sudden, developing within hours to a few weeks, and are characterized by fever, chills, cough, and chest pain. These acute reactions are usually reversible once the medication is stopped.
Chronic pulmonary toxicity is more insidious, developing after at least six months of continuous therapy, and can lead to interstitial pneumonitis or irreversible pulmonary fibrosis. Symptoms include a persistent, nonproductive cough and shortness of breath. This condition is serious and requires immediate discontinuation of the medication.
Hepatotoxicity, or drug-induced liver injury, is another rare but serious risk that can present as either acute or chronic hepatitis. Acute liver injury may occur within weeks of starting the drug, while chronic active hepatitis is more commonly seen after months or years of use. Symptoms of liver damage include jaundice, dark urine, pale stools, and pain in the upper right abdomen.
Peripheral neuropathy, which is nerve damage outside the brain and spinal cord, is also a risk, especially with prolonged use. This nerve damage typically begins as numbness, tingling, or a burning sensation in the extremities. In severe cases, the neuropathy can progress to muscle weakness and may become irreversible even after the drug is stopped.
Specific Patient Contraindications
For certain individuals, the risk of serious side effects is heightened, making nitrofurantoin use inappropriate. A major contraindication is severe kidney impairment, generally defined as a creatinine clearance below 30 mL/min. When kidney function is poor, the drug is not effectively cleared from the bloodstream. This accumulation increases the risk of systemic toxicity, particularly peripheral neuropathy.
The medication is also contraindicated in pregnant women near term or during labor and delivery. The concern is the risk of hemolytic anemia in the newborn. This same risk extends to individuals with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency, a genetic condition that makes red blood cells vulnerable to damage from certain medications.
Nitrofurantoin can interact with certain other medications, potentially reducing its effectiveness. Antacids that contain magnesium trisilicate, for example, should be avoided because the magnesium binds to the antibiotic in the gut. This binding significantly reduces the absorption of nitrofurantoin.
Managing Side Effects and When to Contact a Doctor
Managing the mild, common side effects of nitrofurantoin often involves minor adjustments to the drug regimen. To help with nausea, vomiting, and stomach discomfort, taking the dose immediately after a meal or snack can help coat the stomach. Staying well-hydrated is also important, especially if diarrhea occurs, to prevent dehydration.
The occurrence of certain symptoms warrants immediate medical attention or discontinuation of the drug. Any sign of a serious reaction, such as a persistent cough, unexpected shortness of breath, or chest pain, requires urgent contact with a healthcare provider. Symptoms pointing to liver damage, like yellowing of the skin or eyes, dark urine, or upper abdominal tenderness, must be reported right away. The development of numbness, tingling, or burning pain in the hands or feet signals peripheral neuropathy and requires the medication to be stopped to prevent irreversible nerve damage.