Interventional psychiatry (Part 1)
For some patients, IV medications, blocks, and injections could be effective treatments.
The efficacy of oral magnesium is not robust. However, IV administration has a pronounced beneficial effect as an abortive and preventative treatment in many patients with anxiety.44
IV administration of magnesium can produce adverse effects, including flushing, sweating, hypotension, depressed reflexes, flaccid paralysis, hypothermia, circulatory collapse, and cardiac and CNS depression. These complications are very rare and dose-dependent.45 Magnesium is excreted by the kidneys, and dosing must be decreased in patients with kidney failure. The most common adverse effect is local burning along the vein upon infusion; small doses of IV lidocaine can remedy this. Hot flashes are also common.45
Various dosing strategies are available. In patients with anxiety, application dosing is based on the recommended preeclampsia IV dose of 4 g diluted in 250 mL of 5% dextrose. Much higher doses may be used in obstetrics. Unlike in obstetrics, for psychiatric indications, magnesium is administered over 60 to 90 minutes. Heart monitoring is recommended.
Scopolamine
Scopolamine is primarily used to relieve nausea, vomiting, and dizziness associated with motion sickness and recovery from anesthesia. It is also used in ophthalmology and in patients with excessive sweating. In off-label and experimental applications, scopolamine has been used in patients with TRD.46
Scopolamine is an anticholinergic medication. It is a nonselective antagonist at muscarinic receptors.47 Tricyclic antidepressants (TCAs) possess strong anticholinergic function. Newer generations of antidepressants were designed specifically not to have this function because it was believed to be an unwanted and potentially dangerous adverse effect. However, data suggest that anticholinergic action is important in decreasing depressive symptoms. Several hypotheses of anticholinergic effects on depression have been published since the 1970s. They include the cholinergic-adrenergic hypothesis,48 acetylcholine predominance relative to adrenergic action hypothesis,49 and insecticide poisoning observations.50 Centrally acting physostigmine (but not peripherally acting neostigmine) was reported to control mania.48,51 A genetic connection between the M2acetylcholine receptor in patients with major depressive disorder (MDD) and alcohol use disorder is also suggestive.52
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