A 73-year-old woman was admitted to hospital for investigation following a short episode of slurred speech which was diagnosed as a transient ischaemic attack. She had a history of paroxysmal atrial fibrillation, transient ischaemic attacks, essential hypertension, duodenal ulcer, chronic hepatitis B infection and acoustic neuroma.
Her drug history found that she had been switched from metoprolol to flecainide 50 mg twice a day for control of her atrial fibrillation three months previously. The only other drug she had been taking was omeprazole 20 mg twice a day for two years.
An incidental finding on admission was a white blood cell count of 2.5 x 109/L, with a neutrophil count of 0.61 x 109/L. Reactive lymphocytes were present. The remaining white cell differential was within normal ranges. Haemoglobin was normal, with a slightly raised mean cell volume. Platelet count was reduced at 127 x 109/L.
Liver function tests were mildly abnormal, consistent with chronic hepatitis B infection. Renal function was normal for age and testing for autoimmune and rheumatoid disorders, HIV and haematological malignancy was negative. C-reactive protein was 15 mg/L and erythrocyte sedimentation rate was 19 mm/hour.
On day two of admission, the neutrophil count dropped to 0.28 x 109/L. Flecainide was ceased on the same day. Five days after stopping flecainide, the neutrophil count had risen to 1.59 x 109/L. Omeprazole was continued throughout and metoprolol reinstated for rate control of her atrial fibrillation.
There was a probable causal association between flecainide and neutropenia. This is a rare adverse reaction associated with some antiarrhythmic drugs and this may be the first such report in Australia.
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