Mechanism of action and selectivity
The antimicrobial effect of nitrofuran derivatives is dose-dependent: depending on the concentration, they act bacteriostatically or bactericidally. Notably, in an acidic environment (e.g., at low urine pH), the activity of the drugs increases.
The process of microbial cell destruction takes place in several stages:
- Activation. The reduction of the nitro group occurs inside the bacterium.
- Metabolite formation. Highly active amino derivatives appear.
- Target damage. Metabolites disrupt cellular respiration, inhibit RNA replication, destroy the DNA structure, and alter protein conformation (including ribosomal ones).
The basis of safety for humans lies in the speed of reactions: bacterial enzyme systems reduce nitrofurans significantly faster than host (mammalian) cells.
Spectrum of activity and main drugs
The group has a broad spectrum of activity. Gram-positive (staphylococci, streptococci, enterococci) and Gram-negative bacteria (Escherichia coli, Shigella, Salmonella, Vibrio cholerae) are sensitive to nitrofurans. They are also active against protozoa (Giardia, Trichomonas), Chlamydia, and certain viruses. An important advantage is their effectiveness against strains resistant to a number of antibiotics.
Drug classification is based on their pharmacokinetics and primary indications:
- Nitrofural (Furacilin). The most common antiseptic of the group. Used externally (aqueous solutions) for rinsing the mouth and throat in tonsillitis and stomatitis, washing wounds, mucous membranes, and serous and joint cavities. In the form of drops, it is used for conjunctivitis and purulent otitis media. It does not irritate tissues and stimulates regeneration.
- Chinifuryl (Chinifuryl). Available as an ointment. Prescribed for purulent-inflammatory skin lesions: boils, carbuncles, infected burns, and suppuration of postoperative wounds.
- Systemic drugs. These include nitrofurantoin (Furadonin), furazolidone, furazidin (Furagin), and nifuroxazide (Enterofuril).
Safety profile and toxicity
Side effects with systemic administration are characterized by a high incidence of occurrence.
- Gastrointestinal tract: nausea, vomiting, diarrhea. There is a risk of developing pancreatitis and pseudomembranous colitis.
- Neurotoxicity: headache, dizziness, asthenia, peripheral polyneuropathies.
- Hepatotoxicity: chronic hepatitis, cholestatic jaundice.
- Hematologic disorders: granulocytopenia, hemolytic anemia.
- Allergic reactions: from skin manifestations, chills, and myalgia to severe conditions (anaphylactic shock, lupus-like syndrome).
Specific pulmonary toxicity—"nitrofuran lung"—is distinguished separately. The acute reaction manifests as cough, bronchospasm, chest pain, infiltrates, and pulmonary edema. The chronic form leads to interstitial pulmonary fibrosis. The mechanism is associated with the generation of free oxygen radicals during the reduction of the nitro group, which triggers lipid peroxidation and damages alveolar cell membranes.
Resistance and contraindications
Acquired resistance of microorganisms to nitrofurans develops rarely and very slowly. However, there is natural resistance, which is characteristic of anaerobic bacteria, Pseudomonas aeruginosa, Klebsiella, and Enterobacter.
The prescription of nitrofuran derivatives is strictly contraindicated in:
- Genetically determined glucose-6-phosphate dehydrogenase deficiency (high risk of hemolysis).
- Severe impairment of excretory and metabolic organ function (renal and hepatic failure).
- Pregnancy (in the third trimester).
Note: with prolonged use of the drugs, there is a risk of developing malignant renal neoplasms.
Briefly: answers to topical questions
In what conditions and diseases are nitrofuran derivatives absolutely contraindicated?
Nitrofuran derivatives are absolutely contraindicated in a number of genetic and organ pathologies, as well as during certain periods of pregnancy. The main contraindications include:
- Enzymopathies — genetically determined glucose-6-phosphate dehydrogenase deficiency due to the high risk of developing hemolysis.
- Organ failure — severe impairment of excretory and metabolic organ function (renal and hepatic failure).
- Pregnancy — the use of the drugs is contraindicated in the third trimester.
In addition, the use of furazolidone has age restrictions and is contraindicated in children under 3 years of age.
What are the main indications for the clinical use of furazolidone?
The main indications for the use of furazolidone are:
- acute intestinal infections — as an alternative drug for moderate and severe cases, predominantly with the colitic variant;
- shigellosis — in etiotropic therapy regimens for mild forms;
- giardiasis;
- urinary tract infections — as a urinary antiseptic.
What are the features of pharmacokinetics and elimination of nitrofurantoin?
Features of pharmacokinetics and use of nitrofurantoin:
- absorption is improved when taken with food;
- taken orally 3–4 times a day;
- creates high concentrations in urine;
- used as a urinary antiseptic for urinary tract infections.
To memorize the drugs, look for the root -fur-: *Fur*acilin, *Fur*adonin, *Fur*azolidone, *Fur*agin. To recall the mechanism of action, use the acronym DRDB: Dpiration (disruption of cellular respiration), RNA (inhibition of replication), DNA (alteration of structure), Broteins (change in conformation).
Class and exam questions
Why are nitrofurans safe for humans if they damage DNA?
The secret lies in the selectivity of action. Bacterial enzyme systems reduce nitrofurans to active toxic metabolites significantly faster than mammalian cells do.
How to prevent nausea and vomiting during nitrofuran treatment?
Dyspeptic disorders are a frequent side effect of this group. For prevention, the drugs must be taken strictly during or immediately after a meal.
What is the danger of prescribing nitrofurans in glucose-6-phosphate dehydrogenase deficiency?
In patients with a genetic deficiency of this enzyme, the intake of nitrofuran derivatives can provoke a severe hematologic disorder — hemolytic anemia.
What else to study on this topic
- Pharmacokinetics of systemic drugs and the principles of their distribution in the body.
- Mechanisms of development of pseudomembranous colitis during nitrofurans intake.
- Pathogenesis of hemolytic anemia in glucose-6-phosphate dehydrogenase deficiency.
- Features of nitrofurans use depending on the pH of the environment (urine).
- Lupus-like syndrome: severe immunopathological reactions to drugs of this group.
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