Treatment adherence and tolerability of immediate- and prolonged-release lithium formulations in a sample of bipolar patients: a prospective naturalistic study.

The aim of this study was to compare treatment adherence and tolerability of different lithium formulations in 70 bipolar patients receiving lithium therapy for the first time. During the 1-year follow-up, information was collected regarding patient's clinical course, therapeutic adherence, side effects of the treatment and serum levels of lithium, creatinine and thyroid-stimulating hormone. At baseline, 30 patients (43%) were on prolonged-release lithium formulations and 40 (57%) on immediate-release formulations. At the final evaluation, 37 patients (53%) were considered lost to follow-up. Both prolonged- and immediate-release patients showed significant improvement in the Functioning Assessment Short Test and in the Clinical Global Impressions for Bipolar Disorder scores during the follow-up. At the first follow-up visit, the mean plasma lithium level of prolonged-release patients was higher than immediate-release patients (0.61 vs. 0.47, respectively; P = 0.063), as well as the therapeutic adherence (85 vs. 64%, respectively; P = 0.089). Fine tremor and gastrointestinal symptoms were more frequent in immediate-release patients than in prolonged-release patients at each follow-up visit, with the sole exception of gastrointestinal symptoms at the last evaluation. Prolonged-release lithium therapy could provide potential advantages over immediate-release formulations. Future naturalistic studies and clinical trials with a longer follow-up duration are needed.