Objective: To assess if the lithium dosage prescribed according to the Pepi
n method leads to therapeutic serum concentrations of lithium. Methods: For
13 healthy volunteers, the initial daily doses of lithium were calculated
according to the Pepin formula with a view to obtaining a serum lithium lev
el of 0.8 mmol/L. Lithium was administered twice daily for 21 days, and blo
od samples were drawn daily, 12 hours after the last dose was taken. Dosage
was adjusted if serum concentrations were below 0.6 mmol/L or above 1.0 mm
ol/L or if major side effects were reported. Results: Daily lithium doses r
anged from 1050 mg to 1950 mg (mean 1569 mg, standard deviation [SD] 291 mg
), The mean serum lithium concentrations for weeks 1, 2 and 3 were 0.74 mmo
l/L (SD 0.19 mmol/L), 0.67 mmol/L (SD 0.22 mmol/L) and 0.69 mmol/L (SD 0.13
mmol/L), respectively. Within-subject variance was negligible. Sixty-eight
percent of the serum lithium concentration measurements fell between 0.57
mmol/L and 0.83 mmol/L, and 84% fell within the recommended therapeutic ran
ge of 0.60 mmol/L and 1.20 mmol/L. Conclusions: The Pepin method is a. safe
but conservative method for predicting the appropriate daily dose of lithi
um.