FIELD: organic chemistry, chemical technology, pharmacy. SUBSTANCE: invention relates to method of preparing pharmaceutically acceptable clavulanic acid salt of the formula (I) 
by interaction of clavulanic acid or its salt, in part, amine salt with cation source which is able to form a pharmaceutically acceptable clavulanic acid salt, in part, potassium salt in isobutanol (2-methyl-1- propanol) as a solvent in the presence of water. Pharmaceutically acceptable clavulanic acid salt has up to 5 wt. -% or less of isobutanol and water as microimpurities. Mixture eliciting antibiotic action has amoxicillin and clavulanic acid potassium salt containing isobutanol and water. Method of preparing clavulanic acid alkaline metal of the formula (I) from clavulanic acid amine salt by addition of alkaline metal in the presence of isobutanol as a solvent and 2.0-5.0% of water. EFFECT: improved and simplified method of preparing. 19 cl, 9 ex
