Pharmaceutical dosage forms, physical attributes

The API must possess appropriate chemical and physical attributes to assure that it delivers the intended pharmacological effect. The chemical attributes describe the appropriate purity and impurity limits. Impurity specifications are established from clinical toxicological studies and are also based on reasonable minimums expected from regulatory authorities and consumers. The physical attributes describe the necessary characteristics for reliable pharmaceutical processing into final dosage forms. These attributes are determined by empirical evidence from formulation trials to produce uniform and stable dosage forms of adequate bioavailability. 

Table 12.4 Examples of physical attributes in pharmaceutical dosage forms...

Pharmaceutical scientists have developed improved suspension dosage forms to overcome problems of poor physical stability and patient-perceived discomfort attributed to some active ingredients. An important development aspect of any suspension is the ability to resuspend easily any settled particles prior to instillation in the eye and ensure that a uniform dose is delivered. It would be ideal to formulate a suspension that does not settle since the patient may not always follow the labeled instructions to shake well before using. However, this is usually not feasible or desirable since the viscosity required to retard settling of the insoluble particles completely would likely be excessive for a liquid eyedrop. The opposite extreme, of allowing complete settling between doses, usually leads to a dense layer of agglomerated particles that are difficult to resuspend. 

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