FUSIDIC ACID

C31H48O6, 1/2H2O                      Mol. Wt. 525.73

Fusidic Acid is (17Z)-16 -acetoxy-3a ,11a -dihydroxy- 17(20),24-fusidadien-21-oic acid hemihydrate, an anti- microbial substance produced by the growth of certain strains of Fusidium coccineum or by any other means.

Category: Antibacterial.

Dose: 500 mg to 1 g every 8 hours.

Description: White, crystalline powder.

Solubility: Freely soluble in ethanol (95%) and in chloroform; sparingly soluble in ether; practically insoluble in water.

Storage: Store in well-closed, light-resistant containers.

 

STANDARDS

Fusidic Acid contains not less than 97.5 per cent and not more than 101.0 per cent of C31H48O6, calculated with reference to the anhydrous substance.

Identification: A: The infra-red absorption spectrum, Appendix 5.4, is concordant with the reference spectrum of fusidic acid or with the spectrum obtained from fusidic acid RS.

B: Carry out the method for thin-layer chromatography, Appendix 4.6, using silica gel G as the coating substance and a mixture of 80 volumes of chloroform, 10 volumes of glacial acetic acid, 10 volumes of cyclohexane and 2.5 volumes of methanol as the mobile phase. Apply separately to the plate 5 l of each of two solutions in ethanol (95%) containing (1) 0.20% w/v of the substance being examined, (2) 0.24% w/v of diethanolamine fusidate RS. After removal of the plate, dry it at 105o for 10 minutes and examine under ultra-violet light (365 nm). The principal spot in the chromatogram obtained with solution (1) corresponds to that in the chromatogram obtained with solution (2).

Related substances: Carry out the method for high performance liquid chromatography, Appendix 4.3, using the following solutions. Solution (1) is a 0.5% w/v of the substance being examined in the mobile phase. For solution (2) dissolve 5 mg of 3-ketofusidic acid RS in 5 ml of the mobile phase. To 1 ml of this solution add 0.2 ml of solution (1) and dilute to 20 ml with the mobile phase. For solution (3) dilute 2.0 ml ml (ammendment 6) of solution (1) to 10.0 ml with the mobile phase.

The chromatographic procedure may be carried out using (a) a stainless steel column (12.5 cm x 4 mm) packed with stationary phase LC1 (5 m), (b) a mixture of 50 volumes of acetonitrile, 20 volumes of water, 20 volumes of 1% w/v solution of phosphoric acid and 10 volumes of methanol as the mobile phase with a flow rate of 2 ml per minute, (c) a detection wavelength of about 235 nm and (d) a 20- l loop injector.

Continue the chromatography for at least 3.5 times the retention time of the principal peak. In the chromatogram obtained with solution (1) the sum of the areas of any secondary peaks is not greater than 4 times the area of the peak corresponding to fusidic acid in the chromatogram obtained with solution (2). Ignore any peak with an area less than that of the principal peak in the chromatogram obtained with solution (3). The test is not valid unless the resolution factor between the peaks corresponding to 3-ketofusidic acid and fusidic acid in the chromatogram obtained with solution (2) is not less than 2.5 and unless the principal peak in the chromatogram obtained with solution (3) has a signal-to-noise ratio of not less than 3.

Sulphated ash: Not more than 0.2%, Appendix 3.22.

Water: Between 1.4 and 2.0% w/w, determined on 0.5 g, Appendix 3.24.

Assay: Weigh accurately about 0.5 g and dissolve in 10 ml of ethanol (95%). Titrate with 0.1M sodium hydroxide using phenolphthalein solution as indicator. Each ml of 0.1M sodium hydroxide is equivalent to 0.05167 g of C31H48O6.