It is the RESULT OF PRESCRIBING OR MIXING TWO OR MORE SUBSTANCES which are ANTAGONIST IN NATURE and an UNDESIRABLE PRODUCT IS FORMED which may affect the safety, purpose or appearance of the preparation. Problems which could ARISE DURING COMPOUNDING DISPENSING of a prescription Arises DURING, BEFORE or AFTER drug administration are usually UNINTENTIONAL It may OCCUR IN VITRO between drugs & other components during preparation, storage or administration .