In a recent study from Ontario, Dr. Juurlink performed a retrospective analysis on hospital admissions and determined the odds of elderly patients requiring hospital admission after experiencing known (and therefore preventable) drug interactions.
Juurlink DN, Mamdani M, Kopp A, Laupacis A, Redelmeier DA. Drug-drug interactions among elderly patients hospitalized for drug toxicity. JAMA 2003 Apr 2;289(13):1652-8
“The frequency of significant beneficial or adverse drug interactions is unknown. Surveys that include data obtained in vitro, in animals, and in case reports tend to predict a frequency of interactions that is higher than actually occurs…. Estimates of the incidence of clinical drug-drug interactions range from 3% to 5% in patients taking a few drugs to 20% in patients who are receiving 10-20 drugs.”
(Goodman and Gilman’s The Pharmacological Basis of Therapeutics, Joel G. Hardman, et.al., editors, McGraw-Hill 10^th edition, 2001, pg. 54.)
”Potential risk factors for and the preventability of drug-induced threats to life were studied. Case reports of adverse drug events (ADEs) published in Clin-Alert during 1977-97 were the source of information on drug-induced life threats. Patient, drug, and event variables were identified, and the causality, predictability, and preventability of each case were assessed. Data were entered into a relational database for analysis. The data indicated 846 drug-induced life threats. Seventy-four percent of the cases were assessed as definite or probable. Patients received usual or below-usual dosages in 89% of the cases. Patients tended to be middle-aged and only moderately ill. The drug categories most frequently associated with life threats were antimicrobials and central-nervous-system agents. Plasma drug level monitoring should have been performed in 127 cases but occurred only in 31 cases (24%). Event types were distributed as adverse drug reactions (50%), allergic reactions (35%), drug interactions (11%), and medication errors (4%). A commercial reference classified almost half of the drug interactions associated with a life threat as posing minimal or no potential risk to the patient. Half of the life-threatening events were judged to have been preventable; about half of these could have been prevented by a pharmacist. Litigation was reported for only 1% of the cases of drug-induced threats to life; judgments and settlements averaged $1.2 million. A review of published case reports of ADEs for 1977-97 yielded information on possible risk factors for drug-induced life threats and on which events may have been preventable.
Marcellino K, Kelly WN. Potential risks and prevention, Part 3: Drug-induced threats to life. Am J Health Syst Pharm 2001 Aug 1;58(15):1399-405