Association of Lithium Use and a Higher Serum Concentration of Lithium With the Risk of Declining Renal Function in Older Adults: A Population-Based Cohort Study.

OBJECTIVE: Lithium is an important mood disorder treatment; however, the renal risks of its use in older adults are unclear. We wished to determine in older adults (1) whether lithium is associated with increased risk of renal decline compared to valproate and (2) whether this association differs with higher vs lower baseline serum lithium concentrations. METHOD: We conducted a population-based cohort study using linked health care databases (Ontario, Canada). The cohort consisted of older adults (mean age 71 years) accrued 2007-2015; 3,113 lithium users were propensity-score matched 1:1 to 3,113 valproate users. Users with higher (> 0.7 mmol/L) or lower concentration of serum lithium were further examined. The primary outcome was ≥ 30% loss in estimated glomerular filtration rate from baseline. RESULTS: Matched lithium users and valproate users demonstrated similar indicators of baseline health over a median (maximum) follow-up of 3.1 (8.3) years. Lithium was associated with increased risk of renal function loss compared to valproate (674/3,113 [21.7%] vs 584/3,113 [18.8%]; 6.5 vs 5.7 events per 100 person years; hazard ratio = 1.14 [95% CI = 1.02-1.27]). When baseline serum lithium concentrations were > 0.7 mmol/L, the risk of renal decline compared to valproate use was 1.26 (95% CI = 1.06-1.49); when baseline lithium concentrations were ≤ 0.7 mmol/L, the risk was 1.06 (95% CI = 0.92-1.22). CONCLUSION: In older adults, lithium use is associated with a statistically significant increased risk of renal decline compared to valproate use, although the decline is less than previously reported. Further studies should confirm whether this effect is primarily in patients with higher serum lithium concentrations.