Improvement in somastatins

PURPOSE: To obtain a medicine composition for treating breast cancer, etc., in a fixed acidic pH range, excellent in durability of pharmacodynamic effects, containing a somastatin analog and lactic acid in a specific ratio. CONSTITUTION: This medicine composition comprises (A) lactic acid and (B) a somastatin analog such as a compound of the formula [Y is S or (CH3 )t ((t) is 0-2); R1 and R2 are each a 1-5C alkyl, benzyl, etc.; R3 is a (substituted) 3-indolylmethyl; R4 is a 1-5C alkyl, a 1-5C hydroxyalkyl, benzyl, etc.; R5 is a 1-5C alkyl, benzyl, etc.] in the ratio of the component A to B of 1/1 to 40/1 and has pH 4-4.5. Preferably the composition contains sodium hydrogencarbonate or sodium hydroxide and an isotonic modifier in amounts enough to make pH 4.2. Preferably the composition contains 0.05-1 mg of the somastatin analog and 2-4 mg of lactic acid based on 1 mL.