Understanding the mechanism of action (MOA) of a medication can prove beneficial in understanding how the drug will behave. It also helps determine the potential for drug interactions. On occassion we use the MOA to assist in determining cause and effect in a patient experiencing an ADR.

Having a working knowledge of how the medication works proves beneficial when there is no direct cause and effect or when the effect does not always result. An example might occur when a known drug interaction is associated with an event which is in turn associated with yet another event. In other words, “A” causes “B” which in turn causes “C”. In some instances A can cause B but B does not cause C. In other words, we administer two drugs that have the potential to cause a drug interaction, but in a specific patient, no such interaction occurs or does not present itself at a level that is considered clinically significant.

But now let’s take a look at a very interesting scenario where there exist an A and C without a B. We know that A causes B and B causes C but can A cause C without B? This is where the MOA becomes important. If the only known mechanism for A to cause C, is by first causing B, then A cannot cause C without B. In other words, our known drug interaction which is A, must present itself in such a manner that is demonstrated as B before we can make the indirect connection between A and C. This is especially true if there are other variables that can cause C.

A specific example might occur if our drug interaction A, causes anemia B, which in turn results in an infection C. So understanding how the drug interaction A occurs helps us determine the liklihood that A caused C. Thus, the MOA can be beneficial in determining the probability of an ADR in a medication event.