Mechanism of Action and Spectrum of Activity
The antifungal antibiotic griseofulvin has a unique mechanism of action that fundamentally distinguishes it from other classes of antifungals. Chemically, it is not a polyene. While most modern agents disrupt the fungal cell membrane, this antibiotic targets reproductive processes.
Upon entering the pathogen cell, the drug specifically inhibits mitosis. Its primary site of action is the mitotic spindle, the structure of which it irreversibly disrupts. Important for differential diagnosis: the drug does not block ergosterol synthesis and does not form ion channels in the membrane.
Its spectrum of antifungal activity is extremely narrow. It works exclusively against dermatophytes—fungi that infect the stratum corneum of the skin, hair, and nails. Prescribing it for candidiasis or severe systemic mycoses is completely ineffective.
Drug Interactions
A key pharmacological feature of the drug is its ability to act as an inducer of hepatic microsomal enzymes, primarily the cytochrome P-450 system. By upregulating these enzymes, the antibiotic significantly accelerates the metabolism of other concurrently administered medications.
This accelerated clearance leads to a sharp decrease in the clinical efficacy of co-administered therapy. In clinical practice, interactions with the following groups are most critical:
- Oral anticoagulants: their increased clearance raises the risk of thrombosis.
- Glucocorticoids: the anti-inflammatory and immunosuppressive effects of the hormones are diminished.
- Estrogen-containing oral contraceptives: accelerated breakdown of estrogens can lead to unintended pregnancy.
Interaction with ethanol warrants special attention. Combining the drug with alcoholic beverages is strictly contraindicated, as the antibiotic markedly enhances the toxic effects of alcohol on the body.
Side Effects and Risks
Despite its narrow spectrum of activity, the drug exerts systemic effects on the body, resulting in a wide range of adverse reactions. A crucial contraindication/warning is the antibiotic's ability to provoke and exacerbate attacks of acute intermittent porphyria.
Adverse reactions are classified by organ system:
- Central nervous system and special senses: therapy is frequently accompanied by headache and dizziness. In severe cases, confusion and peripheral neuritis occur. Visual disturbances typically manifest as blurred near vision.
- Gastrointestinal tract: mucous membranes may react with dry mouth and stomatitis. Dyspeptic symptoms such as heartburn, nausea, vomiting, and diarrhea are common.
- Hematologic system: toxic effects on the bone marrow manifest as changes in the complete blood count—leukopenia, neutropenia, and compensatory monocytosis.
- Hepatobiliary and urinary systems: the liver responds with elevated hepatic transaminases and jaundice. Renal filtration can be impaired, leading to albuminuria.
- Immune system and skin: allergic reactions range from angioedema and serum sickness-like syndrome to life-threatening dermatoses, such as exfoliative dermatitis and toxic epidermal necrolysis.