Diclofenac, a phenylacetic acid derivative, is a drug demonstrating high efficacy after oral administration in the treatment of pain and physical disability in rheumatic diseases. In view of the adverse effects associated with using diclofenac, it is necessary to consider all known drug safety information before the drug is selected for therapy and the dosage regimen is set for individual patients. Selecting an oral dosage form with specific properties determined by excipients is a method to improve the availability of the drug substance and, at the same time, minimize adverse drug reactions. An alternative to tablet or capsule dosage forms is diclofenac application to the skin. The proven efficacy of this method is further improved through the use of transdermal penetration enhancers and vehicle ingredients which provide dosage forms with specific physical properties.