Increased lithium dose requirement in a hyperglycemic patient.

Objective: To report a case of apparent increased lithium clearance in a patient with persistent hyperglycemia.

Methods: Lithium doses, blood glucose concentrations, and lithium plasma concentrations were evaluated in a patient during a 53-day inpatient admission for exacerbation of bipolar disorder. The lithium dose required to increase the lithium plasma concentration by 0.1 mEq/L was computed from the lithium dose and corresponding lithium plasma concentration. This value was correlated with the blood glucose concentration.

Results: A plot of the lithium dose required to increase the lithium plasma concentration by 0.1 mEq/L versus the blood glucose concentration exhibited a direct linear relationship (r2 = 0.62). This plot indicates that higher lithium doses are needed during hyperglycemic states compared with euglycemic states to achieve equivalent plasma concentrations.

Conclusions: Glycosuria associated with hyperglycemia induces an osmotic diuresis that increases the renal clearance of lithium, necessitating higher lithium doses to maintain therapeutic lithium plasma concentrations.