AUGUST 01, 2004
Martin A. Erickson, III, RPh

Q I work as a relief pharmacist for a chain drugstore. The pharmacists at 2 stores in the chain compound topical formulations that contain nystatin powder and other ingredients, in different proportions. At one store, the formulation is refrigerated; at the other it is not. Nystatin powder is a refrigerated product. Should both preparations be refrigerated and so labeled once compounded?

A Nystatin USP is sometimes referred to as Nystatin for Extemporaneous Compounding of Oral Suspension and has a specified potency of 5000 units per mg when used in this fashion. It is distinguished from Nystatin for Oral Suspension, which may contain flavoring, preservatives, and the like; and from Nystatin Topical Powder, which contains nystatin diluted with inert material for use in the treatment of dermatologic conditions.

Nystatin degrades rapidly in the presence of moisture; hence the admonition to dispense it as dry powder with "Refrigerate" labeling. (Refrigeration slows degradation; humidity in a refrigerator generally is lower than ambient humidity.) The patient "compounds" the nystatin in water at the time of administration. The material degrades to subpotency within ~90 days after the container is opened. The material reportedly is stable at room temperature (sealed) for ~30 days. When combined with other ingredients in dry form (Nystatin Topical Powder) or in aqueous suspension with sugar, the product is stable. Moreover, in an oilin- water emulsion (Nystatin Cream USP) or in an anhydrous base (Nystatin Ointment USP), the nystatin reportedly is stable for an extended period. The USP Compounding Monograph <795> discusses stability of compounded products where no studies are available and no adequate information on which to make professional judgment can be found. When water is present, the product is assigned a 14-day "beyond-use" date. If the product is anhydrous, the beyond-use date is 30 days. One factor affecting stability, beyond those discussed, is interaction of ingredients in a compounded preparation. The possibility of incompatibilities should be considered when assigning a beyond-use date and specifying storage conditions.

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Mr. Erickson is director of professional affairs at Gallipot Inc.