Adverse drug reactions leading to hospitalization among older outpatient Veterans

Marcum ZA, Amuan ME, Hanlon JT, Aspinall SL, Handler SM, Ruby CM, Pugh MJ. Adverse drug reactions leading to hospitalization among older outpatient Veterans. Poster session presented at: American Geriatrics Society Annual Meeting; 2011 May 12; National Harbor, MD.

Purpose: To describe the prevalence of adverse drug reactions (ADRs) leading to hospitalization among older outpatient veterans and examine their relationship with suboptimal prescribing measures. Methods: This cohort study included 1000 randomly selected hospitalizations of older outpatient veterans between 10/01/03 and 09/30/06. Study charts derived from electronic medical records were screened for potential ADRs. Charts that screened positive for a potential ADR were evaluated by two separate clinical pharmacists for causality using the Naranjo algorithm and for preventability (i.e., medical error). Evaluation discordances were resolved by consensus. The suboptimal prescribing measures included drugs to avoid, drug-disease interactions and polypharmacy (9+ and 5-8 vs. 0-4 drugs). Results: The sample consisted of 678/1000 (67.8%) patients with unplanned admissions. Overall, 35.4% took 9+ outpatient medications and 44.8% took 5-8. Seventy ADRs involving 113 drugs occurred in 68 (10%) veterans; of these, 38.6% were preventable. The most common ADRs that occurred were bradycardia (n = 6; beta blockers, digoxin), hypoglycemia (n = 6; sulfonylureas, insulin), falls (n = 6; antidepressants, ACE-inhibitors), and mental status changes (n = 6; anticonvulsants, benzodiazepines). Four potential drug-disease interactions (i.e., diltiazem/heart failure, terazosin and nortriptyline/pre-syncope, lorazepam/dementia, and hyoscyamine/constipation) were found involving 5 drugs, of which 1 was a high-risk drug to avoid (i.e., hyoscyamine). Using multivariable logistic regression and controlling for demographic and health status factors, polypharmacy (9+ and 5-8) was associated with an increased risk of ADRs (AOR 3.72, 95% CI 1.37-10.1 and AOR 2.8, 95% CI 0.99-7.60, respectively). Conclusions: ADRs are a common cause of hospitalization among older outpatient veterans, are frequently preventable and are associated with polypharmacy.