Aim. Polypharmacy may increase the prevalence of potential multidrug
interactions (pMDIs), where one drug interacts with two or more other
drugs, possibly amplifying the risk of a potential adverse drug event
(pADE). The major goal of this study was to estimate the prevalence of
amplifying pMDIs in an ambulatory cohort of older patients. Methods.
Current medication lists of 22033 randomly chosen outpatients ≥50 years
old were extracted from the New York Presbyterian Hospital (NYP) data
warehouse. Network analysis identified patients prescribed three or more
interacting drugs from their current medication lists. Potentially
harmful interactions were identified from the NYP drug-drug interaction
alerting system. pMDIs were considered amplifying if the interactions
increased the probability of a pADE through pharmacokinetic,
pharmacodynamic or conditional mechanisms. Results. pMDIs were
identified in 5.1% of the medication lists; 3.4% were three-drug and
1.1% were four-drug pMDIs. The most common drugs involved were
psychotropic, comprising 23.3% of the total drugs. The most common
pADEs associated with the interactions were serotonin syndrome (17.2%),
seizures (14.4%), prolonged QT interval (15.8%) and bleeding (14.4%).
pADE amplification risk was identified in 71.8% of three-drug pMDIs
when one drug interacted with two others, 97.8% when all three
interacted with each other, and 93% for four-drug pMDIs. Conclusion.
Our data suggest that approximately 5% of elderly ambulatory patients
may be exposed to pMDIs which amplify the probability of associated
adverse drug events. The recent and persistent rise in polypharmacy will
likely increase the prevalence of pMDIs and potential exposure to
serious adverse events.