Erythromycin Carbimazole

Clinically important, potentially hazardous interactions with adenosine, arformoterol, BCG vaccine, capsicum, carbimazole, cimetidine, ciprofloxacin, clorazepate, cocoa, erythromycin, eucalyptus, fluvoxamine, halothane, influenza vaccines, mebendazole, methylprednisolone, nilutamide, oral contraceptives, prednisolone, prednisone, rasagiline, raspberry leaf, roxithromycin, St John s wort, torasemide, torsemide... 

Clinically important, potentially hazardous interactions with alprazolam, amiodarone, amphotericin B, arbutamine, bendroflumethiazide, benzthiazide, bisacodyl, bumetanide, carbimazole, chlorothiazide, chlorthalidone, cholestyramine, clarithromycin, conivaptan, cyclosporine, cyclothiazide, dan-shen, demeclocycline, devil s claw, dexmedetomidine, doxycycline, erythromycin, esomeprazole, ethacrynic acid, flunisolide, furosemide, ginseng, glycopyrrolate, glycopyrronium, hawthorn (fruit, leaf, flower extract), horsetail, hydrochlorothiazide, hydroflumethiazide, indapamide, licorice, lopinavir, mepenzolate, methyclothiazide, metolazone, minocycline, mistletoe, oxprenolol, oxytetracycline, paroxetine, phenylbutazone, polythiazide, propafenone, propantheline, quinethazone, quinidine, rabeprazole, rifampin, roxithromycin, sarsaparilla, senna, Siberian ginseng, squill, St John s wort, telithromycin, teriparatide, tetracycline, thiazide diuretics, tolvaptan, trichlormethiazide, verapamil... 

An isolated case describes torsade de pointes in an elderly patient taking carbimazole and oral erythromycin. 

Intravenous erythromycin may cause QT prolongation and torsade de pointes. It is rare with oral erythromycin. Carbimazole is rapidly metabolised to thiamazole which is the active form of the drug. Thiamazole inhibits cytochrome P450 isoenzymes including CYP3A4 and it may therefore have inhibited the metabolism of erythromycin resulting in higher than normal levels. In addition, hypothyroidism can cause torsade de pointes, and therefore mild hypothyroidism induced by carbimazole could have contributed. Furthermore, bradycardia (heart rate less than 60 bpm) may also have contributed. 

It was suggested that the combination of oral erythromycin and carbimazole could lead to torsade de pointes in susceptible individuals. In this case, female sex, presence of valvular heart disease, bradycardia, hypoka-laemia, and hypothyroidism may all have been contributory factors. See also, Drugs that prolong the QT interval + Other drugs that prolong the QT interval , p.257. 

Koh TW, Risk of torsades de pointes from oral erythromycin with concomitant carbimazole (methimazole) administration. PACE (2001) 24,1575-6. 

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