2015 年 41 巻 5 号 p. 355-359
Lithium carbonate has a narrow therapeutic index. Therapeutic drug monitoring (TDM) is essential for safe and effective lithium therapy. The dose of lithium carbonate administered and renal function were previously suggested to be important variables that affect serum lithium concentrations. Information regarding the co-administration of drugs that may affect serum lithium concentrations is limited. Therefore, the aim of the present drug interaction study was to examine the effects of the co-administration of antipsychotic drugs on serum lithium concentrations. A retrospective analysis was performed on 124 patients prescribed lithium carbonate at the Department of Psychiatry, Shiga University of Medical Science Hospital between January 2013 and March 2014. Serum lithium concentrations were significantly higher in patients co-administered antipsychotic drugs than in those not receiving antipsychotic drugs: 0.95 ± 0.41 mEq/L and 0.79 ± 0.27 mEq/L, respectively (P = 0.012). A multiple linear regression analysis was used to produce the following prediction equation for serum lithium concentrations: serum lithium concentration = 0.001 × lithium carbonate dose (mg) － 0.004 × Creatinine clearance (Ccr) (mL/min) + 0.123 × drug + 0.652 (with the co-administration of antipsychotic drugs:drug = 1, without the co-administration of antipsychotic drugs:drug = 0). R2 was 0.296. These results suggest that the co-administration of antipsychotic drugs is a risk factor for elevated serum lithium concentrations in addition to the dose of lithium carbonate administered and renal function.