Acute Dystonic Reaction

An acute dystonic reaction is a sudden extrapyramidal adverse effect caused by dopamine-receptor blockade. When a dopamine D2-blocking drug suppresses dopaminergic activity in the nigrostriatal pathway, cholinergic activity becomes relatively excessive within the basal ganglia. The resulting imbalance produces sustained, involuntary muscle contraction rather than the tremor or weakness a learner might initially expect from a neurological problem. The usual causative drugs are dopamine-receptor-blocking agents: first-generation antipsychotics such as haloperidol, second-generation antipsychotics such as risperidone, and antiemetics or prokinetics such as metoclopramide and prochlorperazine. Higher doses and greater striatal D2-receptor occupancy increase extrapyramidal risk. High-potency first-generation drugs, particularly haloperidol, are especially associated with acute dystonia. The timing is a major diagnostic clue. About half of reactions occur within 48 hours of starting, increasing, or giving a higher dose of the causative medication; approximately 90% occur within five days. Risk is higher in younger patients, males, people who have never previously taken an antipsychotic, those receiving a high dose or parenteral drug, anyone with a previous dystonic reaction, and people with recent cocaine use. Metoclopramide-related dystonia is particularly dose- and age-dependent....