Review Question - QID 109086

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Muscarinic Antagonists Therapeutic Actions for Muscarinic Antagonists QID: 109086 (M1.PH.17.4767)

QID 109086 (Type "109086" in App Search)

A 22-year-old male presents to the emergency room complaining of neck stiffness. He reports that his neck started “locking” three hours ago. He is now unable to move it. His past medical history is notable for schizophrenia and asthma and he currently takes albuterol as well as another medication whose name he does not remember. His temperature is 99.0°F (37.2°C), blood pressure is 130/90 mmHg, pulse is 105/min, and respirations are 18/min. On physical examination, the patient appears anxious and diaphoretic. He speaks in full sentences and is oriented to person, place, and time. The patient’s neck is flexed and rotated to the right approximately 40 degrees. The right sternocleidomastoid and trapezius are firm and contracted. Extraocular movements are full and intact. Upon further questioning, he reports that he took more medication four hours ago because he was hearing voices. Which of the following should most likely be administered to this patient?

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Glycopyrrolate

43/488

Benztropine

37%

179/488

Levodopa

11%

55/488

Dantrolene

33%

159/488

Propranolol

22/488

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The patient in this vignette presents with a neck spasm suggestive of antipsychotic-induced acute dystonia. Acute dystonia is treated with anticholinergic agents such as benztropine or diphenhydramine.

The use of typical antipsychotics (e.g., haloperidol and fluphenazine) is associated with extrapyramidal symptoms due to strong dopamine (D2 receptor) antagonism. Extrapyramidal symptoms, specifically acute dystonia and secondary parkinsonism, are treated with anticholinergic agents to restore the cholinergic balance associated with dopamine antagonism. Benztropine is an anticholinergic agent that can cross the blood brain barrier and is a first-line agent in the management of acute dystonia. It is also used as an adjunct therapy in the treatment of Parkinson’s disease.

Incorrect Answers:
Answer 1: Glycopyrrolate is an antimuscarinic agent. It is not used in the treatment of acute dystonia because it is unable to cross the blood-brain barrier.

Answer 3: Levodopa is a catecholamine precursor that that is converted to dopamine via DOPA decarboxylase. It is used in the treatment of Parkinson’s disease to increase dopamine availability. It is not used to treat extrapyramidal symptoms.

Answer 4: Dantrolene is a ryanodine receptor blocker that decreases excitation-contraction coupling in skeletal muscle. It is used to treat malignant hyperthermia and neuroleptic malignant syndrome (NMS). NMS is characterized by hyperthermia, confusion, rigidity, and autonomic dysfunction. This patient’s presentation is more consistent with acute dystonia.

Answer 5: Propranolol is a non-selective β-blocker that can be used to treat antipsychotic-mediated akathisia. Akathisia is characterized by a feeling of restlessness and a compulsion to constantly be in motion over a period of several months. This patient’s presentation is more consistent with acute dystonia.

Bullet Summary:
Benztropine is a muscarinic antagonist that is used in the treatment of Parkinson’s disease and antipsychotic-mediated acute dystonia.

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