Levothyroxine Warfarin

The absorption of some drugs may also be reduced if they are given with adsorbents such as charcoal or kaolin, or anionic exchange resins such as colestyramine or colestipol. The absorption of propranolol, digoxin, warfarin, tricyclic antidepressants, ciclosporin and levothyroxine is reduced by colestyramine. 

Noninterfering acetaminophen, N-acetylprocainamide, amikacin, amitriptyline, amlodi-pine, carbamazepine, cefotaxime, ceftazidime, chloramphenicol, ciprofloxacin, cisapride, clindamycin, clonidine, codeine, cyclosporine, digoxin, diphenhydramine, disopyramide, ethosuximide, fluconazole, gentamicin, gentamicin, heparin, labetalol, levothyroxine, li-docaine, lithium, methotrexate, metronidazole, minoxidil, nafcillin, nifedipine, phenobar-bital, phenobarbital, phenytoin, phenytoin, primidone, procainamide, propranolol, quini-dine, ranitidine, salicylic acid, theophylline, tobramycin, tobramycin, valproic acid, warfarin... 

A 47-year-old woman with multiple medical problems stabilised on warfarin (and also taking azathioprine, captopril, furosemide, insulin, capto-pril, prednisone, levothyroxine, valproic acid and zolpidem) had all her teeth removed under general anaesthetic. Sixteen days later she needed a dental abscess drained and was given oral clindamycin 300 mg four times daily with ibuprofen 600 mg for any discomfort. On day 17 she needed a suture to stop some bleeding and her INR was found to be 3.5. By day 20 she had developed more severe oral bleeding, which needed emergency room treatment. Her INR was found to have risen to 13 and her haemat-ocrit decreased to 18%. She was treated successfully with a blood transfusion and vitamin K. ... 

A woman taking warfarin, insulin, levothyroxine and digoxin complained of menorrhagia at a routine follow up. Investigations revealed that her British Corrected Ratio had risen to 4.1 (normal range 2.3 to 2.8), and that one month previously she had started to take low-dose piracetam 200 mg three times daily. Within 2 days of withdrawing both the warfarin and piracetam her BCR had fallen to 2.07, and the original dose of warfarin was restarted. ... 

A 69-year-old woman developed confusion and paranoia over several days. She was taking carvedilol 12 mg bd, warfarin 2 mg/day, folic add 1 mg/day, levothyroxine 100 micro-grams/day, pantoprazole 40 mg/day, paroxetine 40 mg/day, and flecainide 100 mg bd. The flecainide had been started 2 weeks before. The plasma flecainide concentration was 1.36 mg/1. Paroxetine was withdrawn and the dosage of flecainide was reduced to 50 mg bd. Her delirium resolved 3 days later. 

Drug interaction Warfarin and thyroxine are frequently taken togetirer especially in elderly patients. This combination is thought to be a source of adverse bleeding due to the thyroxine-dependent potentiation of warfarin effects. The results of a 16-year-population-based nested case-control study in which 10,532 patients hospitalised for haemorrhage were matched with 40,595 controls could not substantiate this interaction. There was no increased risk of haemorrhage in warfarin-treated patients receiving levothyroxine up to 30 days (odds ratio (OR) of 1.11,95% Cl of 0.67-1.86), 60 days (OR of 0.76) or 90 days (OR of 0.67) prior to hospitalisation [13 ]. 

Pincus D, Gomes T, HelHngs C, Zheng H, Paterson JM, Mamdani MM, et al. A population-based assessment of the drug interaction between levothyroxine and warfarin. Clin Pharmacol Ther 2012 92(6) 766-70. 

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