A delivery system for sustained release of a calcium-channel blocking agent is adapted for introduction in the cerebrospinal fluid of a subject. The delivery system comprises a solid dispersion product of a calcium-channel blocking agent in a mixture of a (i) first poly(lactide-co-glycolide) having a molecular weight distribution centered around a first number average molecular weight Mn1 and a (ii) second poly(lactide-co-glycolide) having a molecular weight distribution centered around a second number average molecular weight Mn2, wherein Mn1 is in the range of from 2000 to 3000 g/mol and the ratio of Mn1/Mn2 is from 1.8 to 3.5. The delivery system is deposited in the vicinity of or adjacent to a blood vessel showing vasospasm or suspected of developing vasospasm.