ABSTRACT
Combination therapy is not a new phenomenon. It has been used in the treatment of diseases such as cancer, cardiovascular disease, infectious diseases, pain, and transplant rejection. Fixed combination drugs are two or more drugs combined in a single dosage form when each component makes a contribution to the claimed effects. Special cases of this are where a component is added to the existing principle active component to enhance the safety or effectiveness and to minimize the potential for abuse of the principle active component. Fixed combination drugs may also help lower the cost and increase the convenience in terms of administration and compliance.1 In settings where combination therapy provides therapeutic advantage, there is growing interest in the development of combinations of investigational drugs not previously developed for any purpose. However, whether it is for the development of a new compound as an add-on to the existing regimen or multiple new compounds as a new combination regimen, there are unique challenges in the drug development process. With two or more active ingredients in the same dosage form, it is important to ensure that these active ingredients are physically and chemically compatible along with their excipients, and do not generate new impurities or raise new drug-drug interactions. General issues relating to the clinical study design should also be addressed when assessing the contribution of each component or the add-on therapy: doses, endpoints, study duration, and data analysis issues.
