5G-06 - Are Heat-Related Hospitalization Exacerbated by Heat-Sensitizing Medications in Older Adults ?

Background: The US Centers for Disease Control and Prevention advises multiple medication classes can increase the risk of heat-related illnesses. Our prior research found some heat-sensitizing medications elevated the risk of heat-related hospitalization (HRH) in older adults during summer. However, evidence of heat-medication interaction remains limited.

Objectives: To assess the potential effect modification of heat-sensitizing medications on the association between ambient temperature and HRH among older adults.

Methods: We conducted a time-stratified bidirectional case-crossover analysis using a 50% random sample of Medicare Part D beneficiaries (≥65 years) from June to September (2007-2019). Exposure to heat was identified by linking residential ZIP codes to gridded daily temperature data from the Parameter-elevation Relationships on the Independent Slopes model. HRH was defined as inpatient visits with primary or secondary ICD-9/10 codes for heat-related illnesses. Exposure to commonly used heat-sensitizing medications, including antihypertensives (diuretics, beta-blockers, calcium channel blockers, angiotensin-converting enzyme inhibitors, and angiotensin II receptor blockers), anticholinergics, antipsychotics, antidepressants (selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors), and antiseizure medications, was identified using Part D dispensing data. Controls were matched by day of the week and month. Maximum daily temperature (Tmax) was the primary exposure, adjusted for national holidays, PM2.5 level, and green space. Conditional logistic regression estimated the Tmax-HRH relationship by medication use, applying spline transformations for non-linearity. Odds ratios (95% CI) for HRH were calculated using 65°F as the reference and 98°F (95th percentile) as the comparator.

Results: Among 13 million Medicare beneficiaries, 144,905 had at least one HRH (32% male; 82% White; mean age 78 years). Splines showed a non-linear increasing trend between temperature and the odds of HRH, with an odds ratio (95% CI) of 1.3 (1.2-1.4) among anticholinergic users (n = 343,553) and 1.5 (1.4-1.6) among non-users (n = 28,417). Likewise, among diuretic users, the odds ratio was 1.3 (1.2-1.4) for users (n = 132,916) and 1.4 (1.3-1.5) for non-users (n = 247,386). Results for other heat-sensitizing medications were similar.

Conclusions: Higher temperatures were associated with increased HRH risk among older adults, with no evidence of effect modification by medication use. The lack of elevated risk among medication users may reflect differences in underlying health status or reduced heat exposure due to multimorbidities. Identifying suitable active comparators remains challenging.