Sodium Novobiocin: Stability Aspects

Abstract

The stability of monosodium novobiocin has been examined. The solid antibiotic has been shown to be sensitive to light, but if properly protected, to be stable for a period of 2 years at 20". In aqueous solution and suspension it is affected by increase of temperature, pH and certain heavy metals. Phosphate, and possibly sulphate, also cause decomposition. Concentrated solutions of novobiocin become coloured, particularly above 20" and in the presence of air. Light has little effect on potency but irradiation with ultra-violet light accelerates potency loss in solution. There appears to be no difference in the potency stability of three different batches of sodium novobiocin. Ultra-violet spectrophotometry cannot be used as a method of assay.NOVOBIOCIN is a dibasic acidic antibiotic produced by the actinomycete Streptomyces niveus. In neutral to slightly alkaline solutions it exists as the monosodium salt (I), the disodium salt being formed in strongly alkaline solution. OGNH, ONa M e(1)The acidic form of novobiocin has been reported almost insoluble in water, but it is soluble at pH values between 7.5 and 9.Y. There are only few references in the literature to the stability of novobiocin. Stability in aqueous solution is said to be a function of pH and temperature; dilute solutions at pH 2 are stable at 24", but a half-life of about 60 days is observed at pH values between 7 and 10. A 10 per cent solution of sodium novobiocin at pH 7.5 is said to have a half-life of 30 days a t 24" and of several months at 4". Mention is made of the light sensitivity of the dry antibiotic2. METHODS A large plate microbiological method was employed for determinations of potency. The unit of activity of novobiocin is defined as one microgram of pure novobiocin acid. The designs used were 8 x 8 Quasi-Latin squares capable of yielding results with a standard error of 1 7 per cent (P = 0.95) from the means of duplicate assays by separate operators. The test organism was B. subtilis (MB.32) seeded into neutral agar medium at pH 7.0 and incubated for 18 hours at 30". The reference standard was sodium novobiocin of high potency and low moisture content, previously 250 T