Abstract
The Pharmaceutical industry has become more interested in developing fixed-dose combinations (FDCs) in recent years. FDCs have been used successfully in a variety of clinical areas, including diabetes, HIV/AIDS, and cardiovascular diseases etc. FDCs are intended to extend the product life cycle and enhance patient compliance by decreasing cost. Active Pharmaceutical ingredients are chosen for FDC development based on variety of purposes such as Pharmacokinetic profile, drug-drug interactions, mechanism of action, and manufacturability for successful development. Tablet in tablet technology has gained popularity in recent years for creating modified release products. The compression coating or solvent-free-coating technology is also known as Tablet in Tablet technology. Tablet in Tablet technology is presently the finest alternative technology for the formulation of bilayer tablets for physical separation of active medicines and used to avoid chemical incompatibilities and to produce different drug release patterns such as rapid release, sustained release, controlled release, delayed release, and pulsatile release. This review mainly focuses on combining the techniques of both FDC and Tablet in Tablet formulations which offer a wide variety of benefits such as increased patient compliance, convenience, separation of incompatible ingredients, avoiding close interaction of two drugs, achieving various drug release patterns and maximizing the potency of both drugs over conventional oral dosage forms.

Key words: Fixed dose combinations, Tablet in tablet technology, Compression coated tablet, Bilayer tablet, delayed release.