The results of a comprehensive study of the dissolution of the calcium antagonist nimodipine in aqueous solutions of nine cyclodextrins are reported. The used cyclodextrins were native β-cyclodextrin (β-CD), its derivatives hydroxyethyl-β-CD (HE-β-CD), three hydroxypropyl-β-CD (HP-β-CD) with various degree of substitution and methyl-β-CD (M-β-CD), native α-cyclodextrin (α-CD), hydroxypropyl-α-CD (HP-α-CD) and hydroxypropyl-γ-CD (HP-γ-CD). The nimodipine dissolution was studied as a function of time (up to 14 days) and cyclodextrin concentration up to 0.07 mol/l, excepting the less soluble β-CD. In this range of cyclodextrin concentration, linear phase diagrams of nimodipine solubility in the cyclodextrin solutions were observed. From them we derived the stability constants of the inclusions complexes nimodipine – cyclodextrin (1:1) as well as the empirical linear equations for the calculation of the saturated nimodipine concentration at a given cyclodextrin concentration. The most efficient solubiliser of nimodipine was M-β-CD, a good solubilizing efficiency was also shown by HE-β-CD and HP-β-CDs (with a low degree of substitution), which may be acceptable for the preparation of parenteral nimodipine solutions.

        Key words: nimodipine – calcium antagonist – cyclodextrins – inclusion complexes – solubilization – dissolution