Polypharmacy in bipolar I disorder

There are currently three mood stabilizers available for the maintenance treatment of patients with bipolar I disorder: lithium, valproate, and carbamazepine. Unfortunately, monotherapy with each of these conventional agents often fails. To improve outcome, clinicians utilize polypharmacy. Although the efficacy of this practice is largely unknown, because of the lack of controlled studies, data from the United States and Europe indicate polypharmacy is the rule rather than the exception. The few controlled trials that have been conducted indicate that (1) the specific combination of lithium plus imipramine provides no advantage over lithium monotherapy (notwithstanding the inadequacy of lithium monotherapy); (2) the specific combination of lithium and the depot neuroleptic flupenthixol provides no advantage over lithium monotherapy; and (3) the combination of lithium plus carbamazepine may be as effective as lithium plus haloperidol for acute and continuation treatment. Most of the literature on polypharmacy consists of case reports, retrospective chart reviews, and open-label prospective studies, and describes the use of numerous combinations of medications, including lithium plus valproate, lithium plus carbamazepine, and valproate plus carbamazepine. Preliminary findings suggest these combinations may be effective, and that clozapine and high-dose levothyroxine may each be useful as well when combined with other drugs. Further research is necessary to formally evaluate whether these drug combinations are more effective than monotherapy. Until such studies are completed, certain general principles regarding side effects, pharmacodynamics, and pharmacokinetics should be kept in mind when prescribing two or more medications concurrently.