[Renal clearance technic for individualizing lithium dosage in routine hospital care]

Lithium has a narrow therapeutic index and exhibits a wide pharmacokinetic variability. Individual dosage regimen adjustment is necessary to warrant the efficacy and safety of long-term treatment. We propose the "renal clearance method" for rapid determination of the lithium carbonate daily dose for chronic therapy. After the first intake of drug by a manic-depressive patient, a four-hour trial is performed. It involves two blood samplings and two urine collections, in which lithium and creatine are assayed. Comparison of observed creatinine with a value predicted according to age, morphological characteristics, sex and serum creatinine of the patients allows the interpretation of conflicting results. The estimation of lithium and creatinine clearances of each patient is performed using a computerized or manual method which unfolds a decision procedure. The daily dosage (1.5 to 6 250 mg tablets in two or three daily intakes) is deduced from the according lithium renal clearance (0.4 to over 2 l/h) by means of a nomogram established in previous studies on about 50 patients. The clearance method has been investigated in routine hospital care on a 40 patients sample. The range of satisfactory lithium serum levels during patients monitoring was 0.6-0.9 mmol/l. Accurate dosage regimen forecasting is obtained in 92% of the patients. The percentage observed in a subset of 13 patients with the C24 method, which relies on a unique blood sample 24 hours after the first dose, was much lower (54%). The renal clearance method appears as a robust and reliable technique for individual lithium dosage regimen adjustment in routine care.