Stability Studies of Ampicillin Trihydrate in Suspensions and Acidic Aqueous Solutions

Background: Ampicillin in trihydrate form is a b-lactamine antibiotic frequently used in therapy as suspensions and capsules. Because of the low stability only dry suspensions are sold, and also the low stability in acidic environment is source of unwanted side effects and bioavailability variations.
Aim: Our goal was to stabilize ampicillin so that a better stability can be obtained both in water suspensions and acidic solutions. This way misuse due to faulty preparation, side effects and bioavailability problems can be avoided.
Methods: In order to assess the changes in the ampicillin concentration high performance liquid chromatography (HPLC) and thin layer chromatography (TLC) methods have been used.
Results: None of the tried excipients improved stability of ampicillin suspensions. In contrast cyclodextrins and magnesium salts of glutamic and aspartic acid greatly improved the stability of ampicillin acidic solutions. In high amounts cyclodextrins also change the decomposition kinetic of ampicillin, which is usually a first order kinetic process.
Conclusions: Cyclodextrins and magnesium salts of glutamic and aspartic acid have the potential to be used in ampicillin containing formulations in order to increase its stability, bioavailability and to reduce adverse effects.