COST EFFECTIVENESS ANALYSIS OF A PHARMACEUTICAL CARE SERVICE IN LITHIUM CLINIC FOR PATIENTS WITH BIPOLAR DISORDER

Abstract

Bipolar disorder is a severe long term mental disorder prevalent in up to 2% of the population. Bipolar disorder is reported as the sixth leading cause of worldwide disability among patients ages 15 to 44. The first line pharmacotherapy for treatment of bipolar disorder is lithium. Lithium’s clinical use has an extremely narrow therapeutic range. Therefore, pharmaceutical care in patients using lithium is helpful both in efficacy and safety vigilance. The lithium clinic of Somdet Chaopraya Institute of Psychiatry, the first and only lithium clinic in Thailand, is a pharmacist-run lithium clinic. It has been established for more than 10 years. However, there has been no analysis to date of long-term clinical and economic outcomes of the pharmaceutical care service provided. This study aimed to study the long-term clinical outcomes and cost-effectiveness of a pharmaceutical care service in lithium clinic adjunct to standard care (lithium clinic group) compared with standard care alone (usual care group) for bipolar patients who are treated with lithium as maintenance therapy. Outcomes of this study were long-term clinical outcomes and economic outcomes. Clinical outcomes presented as event rate, relative risk, and time to event. Average study follow-up time was 6.11+3.14 years. Hospitalization rate from all psychiatric causes in lithium clinic group (0.0545+0.170) was significantly less than usual care group (0.1815+0.428). Also, hospitalization rate from manic recurrence and emergency room visit rate in lithium clinic group (0.0449+0.147 and 0.0286+0.13) was significantly lower than usual care group (0.1582+0.392 and 0.1507+0.474), respectively. Also, lithium clinic group had risk of any recurrence (RR= 0.59, 95% CI 0.377-0.923), manic recurrence (RR= 0.459, 95% CI 0.287-0.736) and manic admission (RR= 0.34, 95% CI 0.193-0.600) significantly less than usual care group. Time to manic recurrence was 4.44 years for lithium clinic group, but 3.54 years for usual care group. Time to manic admission was 5.36 and 3.98 years for lithium clinic and usual care groups, respectively. Also, time to emergency room visit was 5.36 years in lithium clinic and 4.09 years in usual care groups. A Markov model was constructed to assess costs, life years, and quality-adjusted life years (QALYs) with lifetime horizon in patients with bipolar disorder, on the basis of provider perspective. Some input parameters were based on data from retrospective cohort study which performed for this current study and from hospital database of Somdet Chaopraya Institute of Psychiatry. Moreover, some parameters which were utility and mortality data were obtained from published articles. Economic outcomes were presented as incremental cost-effectiveness ratios (ICER) of quality-adjusted life expectancy. Deterministic and probabilistic sensitivity analyses were conducted for important variables in the model. Lithium clinic group had life expectancy not differ from usual care group. The quality-adjusted life years (QALYs) increased by 0.62 and incremental cost effectiveness ratio (ICER) was 62,349.04 THB per QALY from adjunct pharmaceutical care service to standard care. Lithium clinic group was more cost effective than usual care group if the willingness-to-pay (WTP) threshold was more than 98,000 THB. Considering the current WTP threshold of Thailand at 160,000 THB/QALY, pharmaceutical care service adjunct to standard care appears to be cost-effective compared to standard care alone.