Antifungal Agents - Antibiotics : 1. Amphotericin B 2. Griseofulvin (Fulvicin) 3. Nystatin
Antibiotics
Mode of action: The antifungal activity of this drug depends, at
least, in part, on its binding to a sterol moiety. Primarily, ergosterol that
is present in the membrane of sensitive fungi, by virtue of their interaction
with the sterols of cell membranes and polyenes, appear to form pores or
channels. The result is an increase in the permeability of the membrane,
allowing leakage of a variety of small molecules, such as intracellular
potassium, magnesium, sugars, and metabolites leading to cellular death.
Properties and uses: It is polyene antibiotic obtained from Streptomyces nodosus. It is an
amphoteric compound that consists of seven-conjugated double bond, an internal
ester, a free carbonyl group, and a glycoside side chain with a primary amino
group. The carbohydrate moiety is D-mycosamine. The conjugated
systems are usually of all trans configurations,
so that the ring contains a planner lipophilic segment and a less rigid
hydrophilic portion. Amphotericin B is an amphoteric, forming soluble salts in
both basic and acidic environments, and due to extensive unsaturation, it is
unstable, primarily used as antifungal agents.
Mode of action: Griseofulvin is a fungi-static drug that causes
disruption of the mitotic spindle by interacting with polymerized microtubules.
Properties and uses: Griseofulvin is a white or yellowish-white
microfine powder, practically insoluble in water, freely soluble in
dimethylformamide and tetrachloroethane, slightly soluble in ethanol and
methanol. Used as an antifungal agent.
Synthesis
Assay: Dissolve the sample in ethanol and measure the absorbance after
dilution with ethanol at the maxima of 291 nm using ultraviolet
spectrophotometer.
Dose: As an oral suspension, the administered dose is 125 mg/5 ml; as
capsules, 250 or 500 mg as tablets. For adults, in divided doses, the dose is
500 mg/day.
Dosage forms: Griseofulvin tablets I.P., B.P.
Mode of action: It is a polyene antibiotic isolated from Streptomyces noursei. It is structurally
similar to amphotericin B and has the same mechanism of action.
Properties and uses: Nystatin is a yellow or slightly brownish
hygroscopic powder, practically insoluble in water and in alcohol, freely
soluble in dimethylformamide and in dimethyl sulphoxide, and slightly soluble
in methanol. It is used as an antifungal agent.
Assay: It is assayed by adopting microbiological assay method.
Dosage forms: Nystatin tablets I.P., B.P., Nystatin ointment I.P., B.P.,
Nystatin oral suspension B.P., Nystatin pastilles B.P., Nystatin pessaries B.P.
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