Dissolution and bioavailability of the anhydrate and trihydrate forms of ampicillin

The solubilities and intrinsic dissolution rates of ampicillin anhydrate and trihydrate in distilled water and dilute hydrochloric acid at 37 degrees have been measured. The dissolution rates of these materials from loose filled hard gelatin capsules were determined and the in vivo bioavailabilities of the compounds compared. Small differences in the in vitro behaviour of the anhydrate and trihydrate forms were recorded but the in vivo availability of the two compounds was the same.