Chemical name. Nystatin; CAS Reg. No. 1400-61-9.

Description. A yellow to light brown powder.

Solubility. Very slightly soluble in water; sparingly soluble in ethanol (~750 g/l) TS and methanol R; practically insoluble in ether R.

Category. Antifungal drug.

Storage. Nystatin should be kept in a tightly closed container, protected from light and stored at a temperature not exceeding 5°C.

Additional information. Nystatin is hygroscopic. Even in the absence of light, it is gradually degraded on exposure to a humid atmosphere, the decomposition being faster at higher temperatures. The potency of Nystatin may fall at a rate of 1% per month when it is stored under the conditions mentioned above.

Requirements

Definition. Nystatin is a mixture of substances produced by the growth of certain strains of Streptomyces noursei, the main component of which is nystatin A₁.

Nystatin contains not less than 4400 International Units per mg, calculated with reference to the dried substance.

Identity tests

A. Dissolve 0.10 g in a mixture of 50 mL of methanol R and 5 mL of glacial acetic acid R, add sufficient methanol R to produce 100 mL, and dilute 1 mL to 100 mL with methanol R. The absorption spectrum of the resulting solution, when observed between 240 nm and 350 nm, exhibits three maxima at about 291 nm, 305 nm, and 319 nm; the ratio of the absorbance of a 1-cm layer at 291 nm to that at 305 nm is between 0.61 and 0.73, and the ratio of the absorbance at 319 nm to that at 305 nm is between 0.83 and 0.96.

B. Shake 30 mg with 5 mL of water for 2 minutes, add 2 mL of a solution prepared by dissolving 0.1 g of pyrogallol R in 100 mL of decolorized fuchsin TS, heat on a water-bath until a dark pink colour is produced, cool, and allow to stand for 1 hour; the pink colour is retained.

Loss on drying. Dry to constant weight at 60°C under reduced pressure (not exceeding 0.6 kPa or about 5 mm of mercury); it loses not more than 50 mg/g.

pH value. Shake 0.3 g with 10 mL of carbon-dioxide-free water R; pH of the suspension, 6.5-8.0.

Assay. Carry out the assay as described under 3.1 Microbiological assay of antibiotics, using Petri dishes or rectangular trays filled to a depth of 1-2 mm with culture medium Cm3 having a final pH of 6.0-6.2 and inoculated with Saccharomyces cerevisiae (NCYC 87; ATCC 9763) as the test organism, adding an appropriate concentration of nystatin (usually between 25 and 300 IU per mL) and incubating at a temperature of 29-33°C. Prepare the solutions of the test substance by dissolving 75 mg in sufficient dimethylformamide R to produce 50 mL and dilute 10 mL to 200 mL with sterile phosphate buffer pH 6.0, TS3. Protect the solutions from light throughout the assay. The precision of the assay is such that the fiducial limits of error of the estimated potency (P = 0.95) are not less than 95% and not more than 105% of the estimated potency. The upper fiducial limit of error of the estimated potency (P = 0.95) is not less than 4400 IU of nystatin per mg, calculated with reference to the dried substance.