Today’s USMLE® Step 1 question of the day features a 20-year-old man with schizophrenia who develops involuntary lip, tongue, and limb movements after starting an antipsychotic. Which medication is most likely responsible—and what does its name reveal about atypical antipsychotics?
A 20-year-old man presents to the clinic because he has heard voices for the past nine months. According to his parents, the patient has been acting strangely over the past year. He dropped out of school and broke contact with his friends. He has been increasingly obsessed with government conspiracies and believes the government has placed trackers in his body. The patient is diagnosed with schizophrenia and prescribed an antipsychotic medication. He presents to the clinic again three months later after having developed involuntary and bothersome movements of the lips and tongue and writhing movements of the extremities.
Which of the following medications has the highest risk of causing this side effect?
A. Risperidone
B. Thioridazine
C. Clozapine
D. Aripiprazole
E. Paliperidone
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
B. Thioridazine
Correct: See Main Explanation.
Incorrect Answer Explanations
A. Risperidone
Incorrect: Risperidone is an atypical antipsychotic with a lower risk of tardive dyskinesia when compared to first-generation antipsychotics. Risperidone is associated with symptoms of hyperprolactinemia, such as amenorrhea, galactorrhea, and gynecomastia. Atypical antipsychotics usually end in “-apine” or “-idone”.
C. Clozapine
Incorrect: Clozapine is an atypical antipsychotic with a lower risk of tardive dyskinesia when compared to first-generation antipsychotics. Side effects associated with clozapine include metabolic syndrome, agranulocytosis, and increased seizure risk.
D. Aripiprazole
Incorrect: Aripiprazole is an atypical antipsychotic with a lower risk of tardive dyskinesia when compared to first-generation antipsychotics. Atypical antipsychotics usually end in “-apine” or “-idone”.
E. Paliperidone
Incorrect: Paliperidone is an atypical antipsychotic with a lower risk of tardive dyskinesia. Atypical antipsychotics usually end in “-apine” or “-idone”.
Main Explanation
This patient presents with symptoms of tardive dyskinesia, which are more likely to occur in patients taking first-generation antipsychotics such as thioridazine.
Antipsychotics are used to treat schizophrenia and other psychotic disorders. First-generation antipsychotics, also known as typical antipsychotics, block dopamine D2 receptors in the brain. These include haloperidol, pimozide, trifluoperazine, fluphenazine, thioridazine, and chlorpromazine. They are associated with several side effects, including hyperprolactinemia, metabolic syndrome, QT prolongation, neuroleptic malignant syndrome, and extrapyramidal symptoms (e.g., acute dystonia, akathisia, parkinsonism, tardive dyskinesia). Typical antipsychotics often end in the suffix “-azine”.
Second-generation antipsychotics, also known as atypical antipsychotics, work via inhibition of dopamine D2 receptors in the mesolimbic pathway and inhibition of serotonin 5-HT2A receptors in the mesocortical pathway. Standard atypical antipsychotics include clozapine, olanzapine, quetiapine, paliperidone, risperidone, lurasidone, ziprasidone, and aripiprazole. Per naming convention, atypical antipsychotics usually end in the suffixes “-apine” or “-idone”. Notably, atypical antipsychotics have a lower risk of extrapyramidal symptoms than the typical antipsychotics.
Major Takeaway
Atypical antipsychotics have a lower risk of causing tardive dyskinesia than typical antipsychotics. Per naming convention, atypical antipsychotics usually end in the suffixes “-apine” or “-idone,” whereas typical antipsychotics often end in “-azine”.
Want to learn more about this topic?
Watch this Osmosis video: Typical antipsychotics
References
- Trevor, A.J., Katzung, B.G., Kruidering-Hall, M. (2015) Katzung & Trevor’s pharmacology: Examination & board review (13th ed.). New York, NY: McGraw-Hill. ISBN: 978-0071826358.
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