Studies on development of insoluble drugs as pharmaceutical suspensions by response surface methodology

The preformulation of insoluble drugs, trimethoprim and nitrofurantoin, was studied in order to achieve a suspension with desirable requirements. The objective of the formulator is to avoid the irreversible aggregation called “caking”, and to obtain a suspension with an airy, large volume sediment easily redispersible and with suitable rheological properties. An experimental design useful to determine optimal properties is a Box-Behnken design. The surfactant, thickener and electrolyte at different proportions were the three factors studied. This strategy allows to point on the main significant effect and to determine the concentrations of each product leading to optimal properties of the suspensions.