Haloperidol dystonia caused

Acute dystonic reactions are usually very painful and should be treated immediately with parenteral administration of a muscarinic blocking agent. Adding clozapine will not be protective, and fluphenazine is as likely as haloperidol to cause acute dystonia. Oral administration of diphenhydramine is a possibility, but the patient may find it difficult to swallow and it would take a longer time to act. The answer is (E). 

Side effects can also occur quickly after a single dose of a medication. For example, some antidepressants (e.g., selective serotonin reuptake inhibitors) can cause nausea, stomach upset, loose stools, and even diarrhea. Likewise, some anti-psychotics (e.g., haloperidol (Haldol)) can cause unpleasant or painful muscle spasms called dystonias. All of these side effects can occur within minutes or hours of taking a single dose of the medication. These side effects are also a result of the direct effects of the medication in the synapse. 

Flaherty JA, Lahmeyer HW. Laryngeal-pharyngeal dystonia as a possible cause of asphyxia with haloperidol treatment. Am J Psychiatry 1978 135(ll) 1414-5. 

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