How nitrofurantoin works
The antibiotic nitrofurantoin is a so-called prodrug. It is only converted into its active form at the site of action (in the urinary tract). The conversion occurs through bacterial enzymes after the active ingredient has been absorbed from the intestine into the blood and passes through the kidneys into the urine.
Because the active form of nitrofurantoin has many different points of attack in the bacterial cell, the probability of the bacteria developing resistance to the antibiotic is quite low.
The low resistance rate is the reason for its recommendation as a first-line agent for acute uncomplicated urinary tract infections.
Absorption, degradation and excretion
Nitrofurantoin absorbed via the intestine reaches only very low concentrations in the blood. The highest urine levels are reached about four to five hours after ingestion.
About half of the ingested active ingredient is broken down to ineffective metabolites. These are also excreted in the urine and may cause a harmless brown coloration of the urine.
When is nitrofurantoin used?
In certain cases, such as congenital or acquired narrowing of the urinary tract or repeated, chronic urinary tract infections, preventive treatment with nitrofurantoin may also be considered.
In the case of an acute infection, the duration of use of nitrofurantoin is usually five to seven days. For prevention, it can last up to a maximum of six months – but at a lower dosage.
How nitrofurantoin is used
In the case of an acute infection, the antibiotic should be taken for as long as prescribed by the doctor – even if the symptoms improve beforehand.
For preventive use, lower dosages are chosen, usually one tablet in the evening after the last urination.
What are the side effects of nitrofurantoin?
Other side effects in one in ten to one hundred patients include headache, loss of appetite, nausea, vomiting, pneumonia, cough, and chest pain.
What should be considered when taking nitrofurantoin?
Contraindications
Nitrofurantoin should not be taken in case of:
- impaired kidney function
- Low or absent urinary excretion
- Liver disease with abnormally elevated liver enzymes
- glucose-6-phosphate dehydrogenase deficiency
- Nervous disorders (such as polyneuropathies)
Interactions
In general, there are relatively few interactions between nitrofurantoin and other drugs, since the drug is activated and acts only in the urine. However, some agents may interfere with the absorption of the antibiotic from the intestine, such as agents for heartburn (like magnesium or aluminum salts) and agents for nausea (like metoclopramide).
Drugs and foods that alkalize the urine (such as many vegetables, citrus fruits, or milk) inhibit nitrofurantoin excretion. In contrast, substances that acidify the urine (such as meat) promote excretion.
Age restriction
Infants should receive the active substance in an appropriately reduced dosage after the third month of life at the earliest. Reduction of the dose is also necessary in children and adolescents.
Pregnancy and lactation
As a precaution, nitrofurantoin should not be used in pregnant women and nursing mothers, as there are better studied and better tolerated alternatives. However, use during the first two months of pregnancy is generally possible.
How to obtain medicines with nitrofurantoin
Medicines containing the active ingredient nitrofurantoin are available in Germany, Austria and Switzerland from pharmacies on prescription.
