Carbimazole Digoxin

Clinically important, potentially hazardous interactions with abarelix, acenocoumarol, amisulpride, amprenavir, anisindione, anticoagulants, arsenic, astemizole, carbimazole, celiprolol, ciprofloxacin, dabigatran, degarelix, dicumarol, digoxin, diltiazem, enoxacin, fentanyl, fosamprenavir, gatifloxacin, grapefruit juice, lomefloxacin, methotrexate, moxifloxacin, nilotinib, norfloxacin, ofloxacin, oxprenolol, quinidine, quinolones, rifabutin, rifampin, rifapentine, ritonavir, simvastatin, sparfloxacin, sulpiride, tacrolimus, tipranavir, verapamil, warfarin, zuclopenthixol... 

Noninterfering albuterol, allopurinol, alprenolol, aspirin, atenolol, captopril, carbimazole, clonidine, coloxyl, danthron, diazepam, digoxin, doxepin, glibenclamide, hydralazine, in-domethacin, labetalol, metformin, methyldopa, metoprolol, mianserin, minoxidil, nifedipine, nitrazepam, oxazepam, oxprenolol, pindolol, prazosin, propranolol, senokot, theophylline, trifluoperazine... 

The observation of relatively low plasma digoxin levels in a patient taking carbimazole prompted a further study in 10 healthy subjects. In 9 out of the 10, steady-state peak serum digoxin levels were reduced by 23% (from 1.72 to 1.33 nanograms/mL) by a single 60-mg dose of carbimazole, but in the other subject the serum digoxin levels were increased. Other pharmacokinetic parameters were unaffected. 

Carbimazole abolished the systolic blood pressure decrease seen in the first 3 hours with digoxin, and also reduced the duration of the digoxin-induced diastolic blood pressure fall from 12 to 6 hours. The changes in heart rates, cardiac output and stroke volumes were not statistically significant, but inter-individual differences were large. " ... 

One explanation for the changed response to digitalis with carbimazole is that there is a direct and altered response of the heart due to the raised or lowered thyroid hormone levels. Another is that changes in glomerular filtration rate associated with hypo- or hyperthyroidism result in increased or decreased serum digoxin, respectively. Why carbimazole reduced serum digoxin in healthy subjects (normal thyroid status) is not known. 

---