Cyclodextrin

A method of preparing sulphoalkyl ether-β-cyclodextrin, especially sulphobutyl ether-β-cyclodextrin (SBE-β-CD), comprises contacting cyclodextrin with a base to form activated cyclodextrin and reacting the activated cyclodextrin with an alkyl sultone, wherein the sulphoalkylation is performed under continuous flow conditions. Typically, the activation is carried out as a batch process and the molar ratio of base to cyclodextrin may be from 2:1 to 22:1. The alkyl sultone may be 1,4-butane sultone and the base may be an alkali metal hydroxide, such as NaOH. Normally, the activation is performed in a first vessel and the alkyl sultone is kept in a second vessel, not directly connected to the first, thereby avoiding the base and sultone reacting together. The molar ratio of sultone to cyclodextrin may be from 7:1 to 33:1. Use of sodium hydroxide to control the degree of substitution of sulphoalkyl ether-β-cyclodextrin is also disclosed. A composition and a pharmaceutic excipient containing sulphobutyl ether-β-cyclodextrin with a degree of substitution of ≥7.3 is further claimed.