Several double-blind RCTs of patients with unipolar or bipolar depression that used 3 pulsed IV infusions (4.0 mcg/kg) over 15 minutes found a rapid, robust antidepressant effect with scopolamine vs placebo.8,9 The oral formulation might also be effective, but would not have a rapid onset.
Common adverse effects of scopolamine include agitation, dry mouth, urinary retention, and cognitive clouding. Given scopolamine’s substantial AE profile, it should be considered only for patients with TRD who could also benefit from the oral formulation for the medical indications noted above, should generally be avoided in older patients, and should be prescribed in consultation with the patient’s PCP.
Botulinum toxin. This neurotoxin inhibits acetylcholine release. It is used to treat disorders characterized by abnormal muscular contraction, such as strabismus, blepharospasm, and chronic pain syndromes. Its MOA for depression may involve its paralytic effects after injection into the glabella forehead muscle (based on the facial feedback hypothesis), as well as modulation of neurotransmitters implicated in the pathophysiology of depression.
In several small trials, injectable botulinum toxin type A (BTA) (29 units) demonstrated antidepressant effects. A recent review that considered 6 trials (N = 235; 4 of the 6 studies were RCTs, 3 of which were rated as high quality) concluded that BTA may be a promising treatment for MDD.10 Limitations of this review included lack of a priori hypotheses, small sample sizes, gender bias, and difficulty in blinding.
In clinical trials, the most common AEs included local irritation at the injection site and transient headache. This agent’s relatively mild AE profile and possible overlap when used for some of the medical indications noted above opens its potential use as an adjunct in patients with comorbid TRD.
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