Solutions drug product, physical stability

If the drug is insufficiently soluble to allow delivery of the required dose as a solution (the maximum delivered dose for each nostril is 200 p,L), then a suspension formulation will be required. There are additional issues for suspension products, for example crystal growth, physical stability, resuspension, homogeneity and dose uniformity. Suspension products will also require information on density, particle size distribution, particle morphology, solvates and hydrates, polymorphs, amorphous forms, moisture and/or residual solvent content and microbial quality (sterile filtration of the bulk liquid during manufacture is not feasible). 

By this we mean interactions that occur after the medicine has been administered to the patient. For the most part, they are physical interactions. However, the major distinctions are that the interaction is between the medicine (including excipients) and the body fluids, primarily comprising aqueous solutions, and that they have the potential to influence the rate of absorption of the drug. They will vary depending on the route of administration. Because physiological and biopharmaceutical interactions are so important, and they are not specifically linked, for example, to the stability of the medicinal product, and also because they occur after the medicine has been administered to the patient, they have been included as a special category for the purposes of this discussion. The importance and potential impact of biopharmaceutical interactions of excipients has been recognized for some years (see for example Ref. 29). 

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