Polypharmacy, ADRs

Drug/food/chemical interactions which enhance action of drug/reduce clearance. Polypharmacy increases the chance of interactions. About 4—5% of prescription drugs used in hospital have the potential for interaction. About 7% of ADRs may be due to interaction, and up to 1% of hospital admissions are due to interaction. The more drugs, the more interactions are likely. With up to 5 drugs, the chance is about 4%. With 16-20 drugs the chance is up to 54%. 

It is often difficult to assess causality or treatment association. For individual patients, factors such as polypharmacy and multiple events occurring during therapy can interfere with the causality assessment of ADRs. In one study, three clinical pharmacologists independently evaluated 500 untoward clinical events. There were broad differences in interpretation in causality of adverse events (Koch-Weser et al., 1977). 

It has been suggested that the more medications used, the higher the risk for ADRs (27). Consistent drug regimen reviews by healthcare providers in order to reduce polypharmacy may decrease the risk of ADRs. 

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