Dopamine receptor blockade can produce symptoms such as dystonia, akathisia, parkinsonism, tardive dyskinesia and neuroleptic malignant syndrome.
Most commonly seen are dose dependent CNS depression, tachycardia, hypotension and anticholinergic effects.
Treatment is generally supportive. Hypotension is common and responds to fluid loading. QT prolongation commonly occurs but arrhythmias are extremely uncommon - see risk assessment.
Dystonic reactions can be treated with benztropine 2 mg IM or IV.
Neuroleptic Malignant Syndrome
A life-threatening idiosyncratic reaction to older neuroleptic drugs, e.g., haloperidol, chlorpromazine, prochlorperazine, metoclopramide - similar to serotonin syndrome, but with a slower onset.
May occur at any time during patient's treatment with these drugs.