Prophylactic, by intramuscular injection, 900 mg (1,200,000 Units) every 2 or 3 weeks [900 mg of Benzthine Penicillin

[300,000 Units) to 750 mg (1,000,000 Units). Prophylactic, by intramuscular injection, 900 mg (1,200,000 Units) every 2 or 3 weeks [900 mg of Benzthine Penicillin is approximately equivalenl lo 720 mg of benzylpenicillm (1,200,000 Unils of penicillin)]. Description: White, crystalline powder, almost odourless. Solubility: Freely soluble in formamide. and dimethylformamide, slightly soluble in ethanol (95%); very slightly soluble in chloroform and in water, practically insoluble in ether. Storage: Store in lightly-closed containers in a cool, dry place. If the material is intended for use in the manufacture of injectable preparations the container should be sterile and sealed so as to exclude micro-organisms. Labelling: The label states whether or not the contents are intended for use in the manufacture of injectable preparations. STANDARDSBenzathine Penicillin contains not less than 96.0 per cent and not more than 100.5 per cent of penicillins, calculated as C16H20N2(C16H18N2O4S)2 and not less than 24,0 per cent and not more than 27.0 per cent ofN.N'-dibenzylethylenediamineC16H20N2 both calculated with reference to the anhydrous substance. Identification: Test A may be omitted if tests B, C and D are carried out. Tests B, C and D may be omitted if test A is carried out. A: The infra-red absorption spectrum, Appendix 5.4, is concordant with the reference spectrum of benzathine penicillin or with spectrum obtained from benzathine penicillin RS. B: Shake 0.1 g with 1 ml of 1M sodium hydroxide for 2 minutes, add 2 ml of ether, shake for 1 minute and allow to separate Evaporate 1 ml of the ether layer to dryness, dissolve the residue in 2 ml of glacial acetic acid and add 1 ml of potassium dichromate solution; a golden yellow precipitate is formed. C: Shake 0.1 g with 2 ml of 1M sodium hydroxide for 2 minutes, extract the mixture with two quantities, each of 3 ml, of ether, evaporate the combined extracts and dissolve the residue in 1 ml of ethanol (50%) Add 5 ml of picric acid solution, heat at 90° for 5 minutes and allow to cool slowly, the precipitale, after recrystall isation from ethanol (25%) containing a small quantity of picric acid melts at about 214° Appendix 8.8.D: Gives the reactions of penicillins and cephalosporins, Appendix 3.1 pH: Between 5.0 and 7.5, determined in a saturated solution, Appendix 8.11. Water: Between 5.0 and 8.0% w/w, determined on 0.3 g, Appendix 3.24. Assay