Antibiotics

Antifungal Agents - Synthesis and Drug Profile

Antibiotics

1. Amphotericin B

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.

2. Griseofulvin (Fulvicin)

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.

3. Nystatin

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.