A randomised double-blind, placebo-controlled trial of pramipexole in addition to mood stabilisers for patients with treatment-resistant bipolar depression (the PAX-BD study).

Background: Options for 'treatment-resistant bipolar depression' (TRBD) are limited. Two small, short-term, trials of pramipexole suggest it might be an option.

Aims: To evaluate the clinical effectiveness and safety of pramipexole in the management of TRBD.

Methods: A multi-centre randomised, double-blind controlled trial including participants ⩾18 years old with TRBD (failure to respond, tolerate or clinical contraindication/patient refusal of ⩾2 of quetiapine, olanzapine, lamotrigine or lurasidone) randomised 1:1 to pramipexole (max 2.5 mg/day salt weight) or placebo added to ongoing mood stabiliser (n = 39). Primary outcome: Quick Inventory of Depressive Symptoms, Self-rated (QIDS-SR) at 12 weeks. Up to 48 weeks follow-up.

Results: Pramipexole (n = 18) was associated with a greater reduction in QIDS-SR score at 12 weeks versus placebo (n = 21, 4.4 (4.8) vs 2.1 (5.1)): a medium sized (d = -0.72) but not statistically significant difference (95% CI: -0.4 to 6.3, p = 0.087). Similarly, there was a non-significant approximate 2-point (d = -0.76) improvement in pleasure at 6 weeks (95% CI: -0.11 to 4.20). Significant advantages of pramipexole on QIDS-SR score (6.28 points: 95% CI: 1.85-10.71) and psychosocial function (5.36 points: 95% CI: 0.38-10.35) were seen at 36 weeks post-randomisation, and on the response (46% vs 6%; p = 0.026) and remission (31% vs 0%; p = 0.030) rates at trial exit (48 weeks or last available data after 16 weeks for those affected by the early study closure). Hypomania ratings were significantly higher at 12 weeks. Otherwise, pramipexole was well tolerated.

Conclusions: Clinically large, but statistically non-significant, effects of pramipexole on depression at 12 weeks, with significant longer-term benefits on mood and function were observed. Pramipexole use was complicated by dose titration and increased hypomanic symptoms. The small sample size limits interpretation. Furthermore, larger randomised placebo-controlled trials are warranted.