Ataxia, nystagmus and gum overgrowth after phenytoin dose increase
A pharmacovigilance case for causality assessment: work out which drug is responsible, grade the reaction's severity and seriousness, and defend a causality category using the WHO-UMC causality assessment.
WHO-UMC causality assessment
- Framework
- WHO-UMC causality assessment
- You decide
- Suspect drug, reaction, severity, seriousness, causality
The case
Mr. A, a 35-year-old man, was referred to the neurology clinic with a two-week history of unsteadiness and oscillopsia. He had been diagnosed with epilepsy seven years previously and had been maintained on phenytoin. His usual dose was 300 mg daily in divided doses. Two months ago, he experienced a generalised tonic-clonic seizure and his phenytoin dose was increased to 400 mg daily. He also takes atorvastatin 20 mg daily for hypercholesterolaemia, started one year ago. He reports drinking about two units of alcohol per day.
On examination, he had horizontal nystagmus, an ataxic gait, and mild incoordination in both hands. He also had gingival hyperplasia with overgrowth of the interdental papillae. Blood tests showed a phenytoin total concentration of 24 mg/L (therapeutic range 10-20 mg/L). Other laboratory tests including liver function tests and electrolytes were normal. A CT head was unremarkable.
The patient was advised to reduce his phenytoin back to 300 mg daily. Within three weeks, his ataxia and nystagmus resolved. His gum overgrowth had been noticed for several months and persisted but was not troublesome. He was not rechallenged with the higher dose. The temporal relationship between the dose increase and the onset of ataxia and nystagmus, the elevated phenytoin level, and the improvement after dose reduction are all noteworthy. Alcohol consumption could also cause ataxia and nystagmus, but the gum overgrowth and the elevated phenytoin level are less typical of alcohol.
What you are asked to do
- Identify which of the patient's drugs is the suspect, and say why the others are not.
- Name the reaction and grade its severity.
- Decide whether it is serious by regulatory criteria, which is not the same as severe.
- Assign a causality category under the WHO-UMC causality assessment and justify it from the timeline, the dechallenge and the alternative causes.
- State the management and what should be reported.
The suspect drug and the graded answer are deliberately not on this page: working them out is the exercise.
Log in to assess "Ataxia, nystagmus and gum overgrowth after phenytoin dose increase"
A free account opens the trainer: name the suspect drug, grade the reaction and commit to a causality category, then see how your assessment compares and why.
Taught in
More like this
- Nausea, yellow-tinged vision and bradycardia in an 80-year-old woman on digoxin
- Lithium toxicity after introduction of bendroflumethiazide
- Prescribing case: Urinary sepsis: empirical intravenous antibiotics including gentamicin in an obese patient with renal impairment
- OSCE station: Gentamicin Dose Calculation and Monitoring
- Confusion and Severe Hyponatraemia in an 82-Year-Old Woman on Multiple Medications
- Dry cough and breathlessness in a woman on methotrexate
Educational content for students and clinicians in training. It does not replace professional judgement, local protocols or current prescribing information.