Acute effects of lithium augmentation on the kidney in geriatric compared with non‐geriatric patients with treatment‐resistant depression

Introduction Lithium augmentation (LA) of antidepressants is a first‐line therapy option for treatment‐resistant depression (TRD). Nevertheless, it is rarely used in geriatric patients mostly because of the fear of kidney toxicity. The purpose of this study is to investigate estimated glomerular filtration rate (eGFR) changes and number of acute kidney injuries (AKI) using LA in geriatric compared with non‐geriatric patients. Methods In a prospective multicenter cohort study, eGFR changes were measured in 201 patients with unipolar depression ( n age≥65years  = 29; n age<65years  = 172) at baseline and over 2–6 weeks of LA. We used linear mixed models to investigate changes in eGFR upon LA and assessed the number of AKIs, according to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines. Results Both age groups showed a significant eGFR decline over the course of treatment with lower eGFR in geriatric patients. The lithium serum level (interpretable as “effect of LA”) had a significant effect on eGFR decline. Both effects (age group and lithium serum level) on eGFR decline did not influence each other, meaning the effect of LA on eGFR decline did not differ between age groups. Two AKIs were observed in the geriatric age group when serum lithium levels exceeded the therapeutic range of >0.8 mmol/L. Conclusion This is the first study investigating eGFR change and AKI upon LA for TRD in geriatric compared with non‐geriatric patients. Our data suggest that LA, as an effective treatment option in geriatric patients, should be closely monitored to avoid AKIs.