Direct preparation of solid particulates of aminopyrine-barbital complex (pyrabital) from droplets by a spray-drying technique.

Aqueous slurries of aminopyrine and barbital (molecular ratio 2:1) containing various excipients such as colloidal silica, synthetic aluminum silicate, montmorillonite clay, corn starch, microcrystalline cellulose, hydroxypropylcellulose, methylcellulose, gelatin, and chitosan were spray-dried by a centrifugal wheel atomizer with various rotation speeds (10,000-40,000 rpm) at various temperatures (85-145 +/- 5 degrees). The spray-dried products were a mixture of aminopyrine-barbital complex (molecular ratio 1:1), aminopyrine, and the excipient used. The flowability and the packing property of the products were improved by compounding colloidal silica into the formulation used for spray-drying. The products with montmorillonite clay, chitosan, and a corn starch-colloidal silica mixture were compressed directly into tablets. It was found that aminopyrine in the products was oxidized during spray-drying. The oxidation products were assumed to be a trace mixture of 5-oxo-2-methyl-4-dimethylamino-1-phenyl-3-pyrazoline carboxyaldehyde and miscellaneous oxidation products. Montmorillonite clay compounded in the formulation considerably prevented the oxidation of aminopyrine during spray-drying. The present study proposes an improved method for the preparation of solid particulates of aminopyrine-barbital complex for tableting, which combines the synthesis, drying, and agglomeration processes into a single process.