The Clinical Side: The drug interactions maze

Many types of drug interactions can occur within the human body. Having a good working knowledge of this complex subject represents a huge opportunity for pharmaceutical representatives both to educate their customers and to better present their products.

A drug interaction can be defined as an increase or decrease in the available amount -- and therefore the effect -- of a medication caused by another medication, food or chemical that is simultaneously present in the body.

Sites of interaction

There are four main sites of interaction in the body.

The gastrointestinal tract. The gastrointestinal tract plays an important role in drug interactions. Some medications, such as cisapride, increase GI motility and therefore decrease the time other medications spend in contact with the lining of the stomach or intestines. This causes decreased absorption of those medications and an effective reduction in dose. Another interaction that can occur at the GI level is when some medications combine with ions found in foods and, as a result, form poorly absorbed complexes. This is why many antibiotics should not be taken with milk. Some medications bind to each other in the GI tract and thus decrease the availability of either or both drugs. Such drugs (like cholestyramine and warfarin) must be dosed several hours apart.

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