In preparation of pharmaceutical compositions, a spray dry method is often used. Japanese Patent Publication Kokai 1988-20302 discloses a spray dry method which comprises spraying an acidic solution of chitosan. Japanese Patent Publication Kokai 1988-210101 discloses a method which comprises spraying an acidic solution of chitosan followed by neutralization with a basic solution. These methods are used for reducing or adjusting the particle size of chitosan and characterized in using an acidic solution of chitosan. These documents do not disclose or indicate the utility and dispersion of a suspension.
In preparation of pharmaceutical compositions comprising a hydrophobic medical compounds, an aqueous suspension must be prepared when a spray dry method is used. The preparation of the above suspension is often difficult because a direct addition of the hydrophobic compound to water generates micro foams to form a foaming layer. The foaming layer is not easily degassed due to its stability.
As a method for suspending a hydrophobic medical compound without generating foams, the following methods are known; (1) a method for suspending under reduced pressure, and (2) a method using organic solvents.
The above method (1) requires special equipment. The above method (2) is accompanied with problems such as the danger of explosion and the residual solvents.