Abstract

Lithium is effective in the prophylaxis of affective disorders^{1 2} and is being increasingly used. Lithium has a narrow therapeutic ratio and the difference between toxic and ineffective plasma concentrations is small. To avoid the fluctuations in plasma level which occur with the conventional lithium carbonate tablets (Camcolit - Camden) two sustained-release preparations Priadel (Delandale) and Phasal (Pharmax) have been introduced. In vitro, both Phasal and Priadel are released much more slowly than Camcolit into simulated gastric and intestinal fluids.³ In order to determine the appropriate dosage schedules, the bioavailabilities of these preparations should be established and constant for all patients. Regular estimations of serum lithium concentration are essential; to ensure the best therapeutic effect the level should be between 0.8 and 1.4mmol/litre in samples taken 12 hours after the last dose of lithium.⁴