Can you take Coumadin and Synthroid together

Coumadin and Synthroid Drug Interactions

What is Coumadin

Coumadin is a Brand name for an anticoagulant (or blood thinner) drug that contains warfarin as an active ingredient. Warfarin prevents the formation of blood clots as well as their migration by inhibiting vitamin K-dependent coagulation factors. Coumadin is indicated for: treatment and prophylaxis of venous thrombosis and pulmonary embolism as its extension, treatment and prophylaxis of thromboembolic complications associated with atrial fibrillation and/or cardiac valve replacement, reduction of recurrent myocardial infarction and thromboembolic events (such as stroke or systemic embolization) after myocardial infarction and therefore the reduction the risk of death.

Coumadin has no effects on an established thrombus, and can’t reverse ischemic tissue damage. The main targets of anticoagulant therapy are to prevent further extension of the formed blood clot and to prevent the risk of secondary thromboembolic complications that may result in serious and possibly fatal outcomes. Despite its effectiveness, warfarin therapy has several issues. Many drugs interact with warfarin, as well as some foods (such as leaf vegetable foods because they typically contain large amounts of vitamin K1) and its activity has to be monitored by blood testing for parameter INR – International Normalized Ratio to be ensured that adequate safe dose is taken. If INR value is high, patients are predisposed to an increased risk of bleeding, while low INR values indicates that the dose of warfarin is uneffective to protect against thromboembolic events.

Other Brand names for warfarin products on the market are: Jantoven, Marevan, Waran and Warfant.


What is Synthroid

Synthroid is a Brand name for drug containing Levothyroxine (also known as L-thyroxine), a synthetic form of thyroid hormone, as an active ingredient. Chemically it is a chiral molecule in the L-form which is identical to natural thyroid prohormone thyroxine – T4. Thyroxine is naturally secreted by the follicular cells of the thyroid gland. Levothyroxine is used for the treatment of thyroid hormone deficiency, and rarely for the prevention of thyroid cancer recurrence. In the past, its related compound Dextrothyroxine was used for the treatment of hypercholesterolemia but it was withdrawn due to cardiac side effects. Synthroids indication are: Hypothyroidism, Pituitary TSH Suppression and Adjunct therapy for surgery and radioiodine therapy in the treatment of thyrotropin-dependent well-differentiated thyroid cancer. It is also used for the treatment of decompensated hypothyroidism or myxedema coma and stupor.

Other Brand names on the market are: Most common Brand names are: Euthyrox, Levothroid, Levoxyl, Levoxine, Levothyrox, Letrox, Tirosint, and Unithroid.


How does Coumadin and Synthroid work in the body

Warfarin works by inhibiting the enzyme activity of vitamin K reductase, which results in depletion of vitamin KH2 – the reduced form of vitamin K. Vitamin K is a cofactor for the carboxylation reactions of glutamate residues of vitamin K-dependent proteins, so this inhibition limits the gamma-carboxylation reactions and activation of the vitamin K-dependent coagulant proteins. Therefore, the synthesis of vitamin K-dependent coagulation factors II, VII, IX, and X and anticoagulant proteins S and C is inhibited. Decreased levels of 3 of the 4 vitamin K-dependent coagulation factors (II, VII, and X) results in decreased prothrombin levels in blood and a decrease in the amount of thrombin generated and bound to fibrin. This reduces the thrombogenicity of clots.

Levothyroxine acts by imitating the effects of body thyroid hormone thyroxine – T4, (tetra-iodinated tyrosine derivative). T4 is converted to T3 (the active metabolite) in the liver and kidney. Thyroid hormones attach to thyroid hormone binding proteins, thyroxin-binding globulin, and thyroxin-binding prealbumin in order to increase solubility. After that, protein complex is transported to cytoplasm and nucleus of the cell where complex is binding to the thyroid hormone receptors. So by levothyroxine acting as a replacement for natural thyroxine, deficiency symptoms are relieved.

Can patients take Coumadin and Synthroid together

Coumadin and Synthroid Drug Interactions: If patients are currently being treated with Coumadin, they should let their doctor know before they are start taking Synthroid. Increased thyroid hormone levels can sensitize effects of warfarin, which may increase the risk of bleeding. Patients may need a dose adjustment or more frequent monitoring by their doctor or specialist to safely use both medicines. However, no special precautions are necessary if patients have been stable on levothyroxine therapy and are currently starting therapy with warfarin. It is very important to tell doctor about all other medications administration, including vitamins and herbs.

Prothrombin time or INR should be monitored closely when initiating, discontinuing, or changing the dosage of thyroid hormone therapy in patients stabilized on their oral anticoagulant regimen. Patients should be advised to contact their doctor if they develop signs and symptoms of excessive anticoagulation, such as: bruising, vomiting, unusual or prolonged bleeding, headache, dizziness, change in stool or urine color, or weakness.

The table below shows the incidence of side effects after Coumadin and Synthroid administration in recommendable doses. The incidence can be increased if these drugs are taken together or overdosed.

Frequency not defined Angina pectoris, Myocardial infarction, Palpitations, Abdominal pain, Congestive heart failure, Flushing, Increased pulse, Choking sensation, Emotional lability, Headache, Heat intolerance, Arrhythmias, Arthralgia, Alopecia, Weight loss, Infertility, Dyspnea, Tremor, Fever, Tachycardia, Nervousness, Anxiety, Myasthenia, Pseudomotor cerebri, Cramps, Diarrhea, Insomnia, Decreased bone mineral density, Cholesterol embolus syndrome, Intraocular hemorrhage, Flatulence, Pruritus, Rash, Dizziness, Hematuria, Respiratory tract bleeding, Hypersensitivity reaction, Hemorrhage, Blood dyscrasias, Taste disturbance, Tissue necrosis, Anemia, Fever, “Purple toe” syndrome

Special precautions and warnings during Coumadin and Synthroid administration:

  • Patients should tell their doctor and pharmacist if they are allergic to Coumadine or Synthroid, or any other medications, or any of the ingredients that can be found in these products.
  • Patients should tell their doctor and pharmacist what prescription and nonprescription medicines, nutritional supplements, vitamins and herbal preparations they are taking or plan to take. There are many drugs that have interaction with warfarin and those interactions can cause serious side effects.
  • Patients should tell their doctor and pharmacist if they have or have ever had diseases such as: diabetes; atherosclerosis, some liver or kidney disease; bleeding problems; porphyria, cardiovascular disease such as chest pain (angina), arrhythmias, high blood pressure or heart attack; an underactive adrenal or pituitary gland, or any condition that makes swallow difficult.
  • Patients using Coumadin should tell thir doctor and pharmacist what herbal or botanical products they are taking, especially if they are using coenzyme Q10 prparation, Echinacea, Ginkgo biloba, garlic, goldenseal, ginseng, and St. John’s wort. There are also many other herbal or botanical products which might affect body’s response to Coumadin.
  • Patients should tell their doctor if they have or have ever had diabetes. Also they should tell their doctor if they have an infection, a gastrointestinal illness such as diarrhea, or sprue or an indwelling catheter.
  • Patients should also tell their doctor if they are pregnant or plan to become pregnant or if they are breast-feeding. If they become pregnant while using these drugs they should call their doctor immediately. Pregnant women should not take warfarin unless they have a mechanical heart valve. Coumadin may harm the fetus.
  • If patients should have surgery, including dental surgery, they should tell their doctor or dentist that they are using these drugs. Doctor may tell to stop taking Coumadin before the surgery or procedure or change your dosage of Coumadin before the surgery or procedure.
  • Cigarette smoking may decrease the effectiveness of Coumadin
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About Miljan Krcobic 78 Articles
My name is Miljan Krčobić. I was born on 14th of November 1989. in Negotin, Serbia, where I finished elementary and high school. In June 2015 I graduated from the Faculty of Pharmacy in Belgrade and thus acquired the title Master of Pharmacy. From the July of 2015 to January 2016 I worked in a pharmaceutical company Hemofarm a.d.(Member of STADA group) based in Vrsac, Serbia, as an expert associate for GMP compliance within the sector Quality Assurance. I am currently working in a pharmacy called Zivkovic in Negotin. As a freelancer I write medical articles on Elance and Upwork.