According to clinical data and drug interaction references (e.g., Lexicomp, Micromedex), there is no direct pharmacokinetic interaction between losartan and levothyroxine. However, timing and absorption are important. Levothyroxine should be taken on an empty stomach, ideally 30–60 minutes before breakfast, to ensure consistent absorption. Losartan, on the other hand, can be taken with or without food. Some reports suggest that levothyroxine may increase metabolism, potentially affecting blood pressure and the effectiveness of antihypertensive drugs like losartan.
Patients stabilized on thyroid replacement therapy may experience blood pressure changes when doses are adjusted. Always inform your doctor of all medications and follow prescribed dosing schedules.
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Levothyroxine
Levothyroxine is prescribed for individuals with an underactive thyroid gland, a condition known as hypothyroidism. It either substitutes or supplements the thyroid hormone that the thyroid gland typically generates. Insufficient thyroid hormone levels can arise naturally or due to injuries caused by radiation/medications or the surgical removal of the thyroid gland. Adequate thyroid hormone levels are crucial for maintaining normal mental and physical functions. In children, proper thyroid hormone levels are essential for typical mental and physical growth. This medication is also effective for managing various other thyroid disorders, such as thyroid cancer. However, it should not be used to address infertility unless the root cause is low thyroid hormone levels.
How to use Levothyroxine
Please read the Patient Information Leaflet and Instructions for Use provided by your pharmacist before starting to take levothyroxine and each time you refill your prescription. If you have any questions, consult your doctor or pharmacist.
Take this medication orally as directed by your doctor, usually once daily on an empty stomach, 30 minutes to 1 hour before breakfast. Some brands may also be taken 15 minutes before breakfast. Confirm with your pharmacist regarding the specific instructions for your brand of levothyroxine.
If you are using the medication from a bottle, use a specialized measuring device/spoon to accurately measure the dose. Avoid using a regular household spoon as it may lead to an incorrect dosage. Consume the medication directly from the measuring device and do not mix it with any other liquid.
If you are using the medication from an ampule, it can be taken by mixing it in water or consumed directly without water. To mix it with water, follow the instructions for opening the ampule and then empty the contents into a glass or cup of water. Gently squeeze the soft part of the ampule repeatedly until no more liquid comes out. Stir the solution and drink it immediately. Rinse the glass or cup with more water to ensure you’ve taken all the medicine. Do not prepare the mixture in advance. To take the medication directly, squeeze the soft part of the open ampule into the mouth or onto a spoon, repeating until all liquid is taken.
The dosage is determined based on factors like age, weight, medical condition, lab test results, response to treatment, and other medications you may be using. Inform your doctor and pharmacist about all products you use, including prescription drugs, nonprescription drugs, and herbal products.
Take this medication regularly at the same time each day to maximize its effectiveness. Do not discontinue this medication without consulting your doctor, as thyroid replacement treatment is typically lifelong.
There are various brands of levothyroxine available; do not switch brands without consulting your doctor or pharmacist.
Symptoms of low thyroid hormone levels include fatigue, muscle aches, constipation, dry skin, weight gain, slow heartbeat, or sensitivity to cold. Inform your doctor if your condition does not improve or worsens after several weeks of taking this medication.
Pros and Cons of losartan and levothyroxine
Losartan:
Pros:
- Effectiveness
- Well-Tolerated
- Kidney Protection
- Heart Health
Cons:
- Hyperkalemia Risk
- Side Effects
- Drug Interactions
Levothyroxine:
Pros:
- Thyroid Hormone Replacement
- Well-Established
- Customizable Dosage
- Disease Management
Cons:
- Absorption Issues
- Side Effects
- Long-Term Use
- Monitoring Needed
Differences Between losartan and levothyroxine
Losartan:
It is an angiotensin II receptor blocker (ARB) used primarily to treat high blood pressure (hypertension) and certain heart conditions like heart failure.
Levothyroxine:
It is a synthetic thyroid hormone used to replace or supplement thyroid hormone in patients with hypothyroidism (underactive thyroid) and other thyroid disorders.
Alternative to losartan and levothyroxine
Losartan Alternatives for Hypertension:
Valsartan:
This is another angiotensin II receptor blocker (ARB) similar to losartan and is often used interchangeably.
Levothyroxine Alternatives for Hypothyroidism:
Synthetic T4 Formulations:
If levothyroxine isn’t suitable, alternative synthetic T4 medications like Liothyronine (T3) or natural desiccated thyroid extract (NDT) may be considered. However, these alternatives are less commonly prescribed and require careful monitoring.
Interactions between your drugs
levothyroxine
Levothyroxine interacts with a total of 211 drugs.
It belongs to the drug class known as thyroid drugs and is used to treat the following conditions:
- Hashimoto’s disease
- Hypothyroidism after thyroid removal
- Myxedema coma
- Thyroid suppression test
- TSH suppression
- Underactive thyroid
losartan
There are a total of 317 drugs known to interact with losartan.
Losartan belongs to the drug class called angiotensin receptor blockers and is used to treat the following conditions:
- Alport Syndrome (off-label use)
- Diabetic Kidney Disease
- High Blood Pressure
Drug and food interactions
levothyroxine food
It’s important to adjust the dosing interval of T4 thyroid hormone (levothyroxine) due to the impact of certain foods and meal timing on its absorption. For instance:
- Increased Absorption: T4 absorption is boosted when taken on an empty stomach (fasting).
- Decreased Absorption: Foods like soybean flour (found in infant formula), cotton seed meal, walnuts, dietary fiber, calcium, and calcium-fortified juices reduce T4 absorption.
- Grapefruit Interaction: Grapefruit or grapefruit juice can delay T4 absorption and lower its bioavailability.
To manage this:
- Administer T4 thyroid hormone consistently at the same time each day and relative to meals to avoid large fluctuations in serum levels.
- Avoid foods that may interfere with T4 absorption within several hours of dosing, if possible.
- For patients on continuous enteral nutrition for over 7 days, consider interrupting tube feeding for at least 1 hour before and after the levothyroxine dose and monitor their thyroid function closely.
