71 - 75 Pharmacology SBAs for the Primary FRCA
Question 71
You're on labour ward and one of the midwives has asked you to sign for the premeds for a patient on the elective caesarean section list.
- Omeprazole 20 mg
- Metoclopramide 10mg
An hour later you hear the patient has started having strange neck and eye spasms. Her other observations are unremarkable
Which of the following is the most appropriate course of action?
- Dantrolene 2.5 mg/kg IV titrated to clinical effect
- Naloxone 200-400 mcg IV titrated to clinical effect
- Midazolam 1-2 mg IV titrated to clinical effect
- Procyclidine 5-10 mg IV
- Activated charcoal PO
Answer
- Procyclidine 5-10 mg IV
This is a classic description of acute extrapyramidal dystonia as a result of central D2 blockade by metoclopramide.
It crosses the blood brain barrier, blocks the D2 receptors in the nigrostriatal pathway, reduces dopaminergic inhibition and leads to a relative excess of striatal acetylcholine.
This leads to acute extrapyramidal motor side effects.
The treatment is to give an anticholinergic (procyclidine) to counteract the relative cholinergic hyperactivity.
That oculogyric crisis we learned about in medical school is defined as 'sustained, upward conjugate deviation of the eyes'.
- Dantrolene is fabulous for malignant hyperthermia but would not help here
- Naloxone would ensure the patient is in as much discomfort as possible while continuing to have her horrible muscle spasms
- Midazolam would provide amnesia and anxiolysis but wouldn't undo the central mechanism causing the dystonia
- Activated charcoal is a good idea for anticholinergic toxicity but isn't going to do much more than create a huge mess here.
"Could I just use atropine instead?"
While we're taught that atropine crosses the blood brain barrier, it doesn't have the right selectivity profile to adequately hit the striatal receptors at clinical doses.