For an alternative view on combination drugs, go to With
declining numbers of new chemical entities (NCEs), there is a
new-found aggression for developing differentiated products
using currently approved drugs. Fixed drug combination products
have emerged as a differentiation strategy, as is evident by the
increasing number of such product approvals1 and recent
launches. The strategy involves identifying molecules that, when
combined, will lead to an improved therapeutic outcome compared
with other treatment options. The rationale for such products
are the associated advantages, such as improved patient
compliance, complementary pharmacodynamic effect and improved
bioavailability. Product stability, however, is a common and
significant factor affecting the outcome of the product
development project. (David Gould/Getty Images) What are the
stability issues? Stability problems in combination products can
be attributed to three types of interaction: Drug–drug chemical
interaction: two or more drugs interact dire