Mechanism of action and pharmacokinetics
Nystatin belongs to natural antibiotics, specifically to the subgroup of polyene antibiotics. The main pharmacokinetic feature of the drug when taken orally is virtually complete absence of absorption. The active substance passes in transit through the gastrointestinal tract (GIT) and is excreted unchanged in the feces.
It is precisely this property (excretion of unabsorbed substances via the intestine) that makes the drug an excellent tool for local therapy within the intestinal lumen. It achieves decontamination without entering the systemic circulation, avoiding systemic adverse effects.
Spectrum of activity and classification
The drug has a narrow, but clinically crucial spectrum of activity. It is most effective against yeast-like fungi of the genus Candida (the most common pathogen being Candida albicans).
The classification of polyene antibiotics includes several key representatives that differ in their clinical application:
- Amphotericin B is the primary drug for treating severe systemic mycoses.
- Nystatin and Levorin are drugs for topical application and GIT decontamination.
- Natamycin.
Unlike amphotericin B, nystatin is not used systemically. This is due to its high toxicity when entering the bloodstream and its pharmacokinetic features. While pharmacologists create complex lipid formulations to reduce the nephrotoxicity of amphotericin B (liposomal Ambisome, lipid complex Abelcet, colloidal dispersion Amphocil), nystatin's safety strategy relies exclusively on its local and enteral administration.
Indications: treatment and prevention of candidiasis
The main indication for prescription is candidiasis. These fungal infections can occur in a superficial form, affecting the oral cavity, intestines, and urogenital tract.
Special attention in clinical pharmacology is paid to the prophylactic use of Nistatinum. Dysbiosis (disruption of the natural balance of mucosal microflora) is a specific adverse effect of antimicrobial pharmacotherapy.
The pathogenesis of fungal superinfection development is as follows:
- Broad-spectrum antibiotics cause the death of beneficial competitive microflora.
- Local mucosal immunity decreases.
- Active proliferation of opportunistic flora begins, specifically Candida fungi.
To prevent this complication, the strategy of rational drug combination is used. The combination of "Broad-spectrum antibiotics + Nystatin (or Levorin)" is considered therapeutically appropriate. In this case, the antifungal drug acts as etiotropic therapy, eliminating the adverse reactions of the antibiotic (prevention of candidiasis).
Dosage forms and administration
To ensure local action in various loci, the drug is available in several dosage forms. Dosage is measured not in grams, but in IU (International Units):
- Tablets: 250,000 and 500,000 IU. Prescribed orally for GIT decontamination.
- Suppositories (rectal and vaginal): 250,000 and 500,000 IU. Used rectally (for lower intestinal candidiasis) and intravaginally (for urogenital candidiasis).
- Ointment: available in 15 and 30 g tubes. Active substance concentration: 1 g of ointment contains 100,000 IU. Used topically for skin and mucosal lesions.
Briefly: answers to topical questions
What is the molecular mechanism of action of nystatin on fungal cells?
The molecular mechanism of action of nystatin, as a representative of polyene antibiotics, involves binding to ergosterol molecules in the fungal cell membrane. This interaction disrupts membrane integrity and leads to pore formation. Through the formed channels, ions ($K^+$, $Mg^{2+}$) and low-molecular-weight substances leave the fungal cell. The loss of intracellular contents causes cell death, providing a pronounced fungicidal effect. The drug has selective action because the primary sterol in mammalian cell membranes is cholesterol, whereas in fungi it is ergosterol.
"Nystatin — GIT transit run." The drug passes straight through the intestine without being absorbed into the blood and destroys Candida right in the lumen.
Class and exam questions
Why is nystatin not used to treat systemic mycoses?
Due to high toxicity upon systemic administration and lack of absorption in the GIT. For systemic infections, the drug of choice from the polyene group is amphotericin B.
What is the rationale for combining broad-spectrum antibiotics and nystatin?
This is an example of rational drug combination. Nystatin prevents the development of candidiasis (superinfection), which occurs due to the death of normal microflora caused by the antibiotic.
How is nystatin excreted when taken orally?
The drug is classified as a non-absorbed substance. It passes in transit through the gastrointestinal tract and is excreted unchanged in the feces.
What else to study on this topic
- Polyene antibiotics: amphotericin B, levorin, natamycin.
- Lipid formulations of amphotericin B and the problem of nephrotoxicity.
- Dysbiosis and superinfections as adverse effects of antibiotic therapy.
- Pseudomembranous colitis (Clostridium difficile) — differential diagnosis of complications.
- Azoles (fluconazole, clotrimazole) as an alternative to polyenes in treating candidiasis.
- Principles of rational drug combinations.
Master the entire topic in the «Pharmacology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Nystatin" and 5,304 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 116 video lessons on the subject
Other topics in the «Drugs and Prescriptions» section
Free video lessons: pharmacologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.