Theophylline overdose Hypermagnesaemia following cathartic therapy: case report

An 87-year-old man with a long history of chronic obstructive lung disorder received controlled-release theophylline 300mg bid , inhaled orciprenaline [metaproterenol] O.2ml qid , oral prednisone 20mg every morning and inhaled beclomethasone qid . Digoxin 0.125 mg/day had been presented for atrial flutter 'Maxzide ', [hydrochlorothiazide 50mg + triamterene 75mg] 1 tablet daily for hypertension and oral ranitidine 150mg bid for peptic ulcer disease.

He was hospitalised after anorexia, nausea, vomiting, occasional palpitation, fatigue and irritability for 2 days and bouts of dyspnoea for 1 week. An irregular tachycardia of 140/min with frequent premature beats was present . Respiratory frequency was 26/min and supine BP was 150/80mm Hg. He admitted to taking 'several ' extra theophylline tablets that morning for dyspnoea. His serum theophylline concentration was 75 mg/ L. Serum magnesium was 2.3 mg/dl, creatinine 1.8 mg/dl and BUN 65 mg/dl. Haemodialysis revealed haemoglobin 11 .7 g /dl , haematocrit 34.8% and white blood cell count 25.3 x 109/L. Lactate dehydrogenase and uric acid were both elevated at 276 U/ Land 14.1 mg/dl , respectively . Arterial blood gases on room air were: p02 62mm Hg; pC02 38mm Hg; and pH 748.

Activated charcoal plus magnesium citrate 113g (equivalent to 1 32g of magnesium) was initially given . Repeat doses of activated charcoal 25g every 2 hours and magnesium citrate 113g every 4 hours were given over a 16-hour period , to a total dose of 240 and 565g , respectively . Within 24 hours normal sinus rhythm was restored and serum theophylline concentration was reduced to 10 mg/L. However, serum magnesium peaked at 5.3 mg/dl. The patient was disorientated , less responsive than normal and spent most of the time asleep. Deep tendon reflexes were diminished bilaterally . Over several days serum magnesium gradually fell and renal function improved . By day 4 the patient was easily arousable and deep tendon reflexes were increased.

In conclusion, ' ... the use of sorbitol in place of magnesium citrate, at least in patients at high risk for magnesium toxicity, is recommended'.

Carrelts JC. Watson WA. Holloway KD. Sweet DE Magnesium toxIcit y to ca tharsIs dUring management of theophytline pOIsoning American Journat of Emergency MediCine 7 3 4·37. Jan 1989 8'~8