Colesevelam with Levothyroxine Interaction Details

Brand Names Associated with Colesevelam

Brand Names Associated with Levothyroxine

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Feb 28, 2024

Interaction Effect

Reduced levothyroxine exposure and reduced efficacy of levothyroxine

Interaction Summary

Concurrent use of levothyroxine and colesevelam may result in decreased bioavailability of levothyroxine. In one study, concurrent administration of colesevelam with levothyroxine significantly reduced the absorption of levothyroxine by approximately 96%[1]. Reductions were minimal in another study when the levothyroxine was given 4 hours prior to colesevelam [2]. In patients requiring coadministration of these agents, levothyroxine should be taken at least 4 hours prior to colesevelam [2][3]. Patients should be monitored for an adequate response to levothyroxine therapy and the levothyroxine dose should be adjusted appropriately [2].

Severity

Moderate

Onset

Rapid

Evidence

Probable

How To Manage Interaction

Concomitant use of colesevelam and levothyroxine may cause a reduction in the absorption of levothyroxine. If co-treatment with colesevelam and levothyroxine is necessary, patients should usually take levothyroxine at least 4 hours prior to colesevelam[2][3]. Alternatively, monitor patients for an adequate response to levothyroxine therapy and adjust the levothyroxine dose appropriately [2].

Mechanism Of Interaction

Reduced absorption of levothyroxine by nonspecific binding with colesevelam

Literature Reports

A) Concurrent administration of colesevelam and levothyroxine in participants significantly reduced levels of levothyroxine in one study. Coadministration of levothyroxine 600 micrograms and colesevelam 3.75 grams resulted in a 22% and 33% mean reduction in levothyroxine AUC and Cmax, respectively. Administration of levothyroxine 1 hour prior to colesevelam changed the AUC and Cmax by 6% and -2%, respectively. When levothyroxine was given 4 hours prior to colesevelam, the mean changes in AUC and Cmax were 1% and 8%, respectively [2].

B) There was an approximately 96% reduction in the absorption of levothyroxine when concomitantly administered with colesevelam, according to a study of 6 euthyroid healthy volunteers. Patients age 27 to 40 years, with normal serum thyroxine (T4) and thyrotropin (TSH) levels at baseline were administered levothyroxine sodium 1 mg orally at visit 1, followed by levothyroxine plus colesevelam 3.75 g or lanthanum carbonate 500 mg at 2 subsequent study visits at least 3 weeks apart. The mean increase of T4 AUC when levothyroxine was given alone was 1692 +/-183.5 mcg-min/dL, but the increase was blunted when concomitant colesevelam was administered (107.5 +/- 45.8 mcg min/dL; 3.8% of the area of levothyroxine alone) [1].

C) Elevated TSH level was reported among patients receiving thyroid hormone replacement and colesevelam concomitantly during postmarketing use. Frequency and causality of these events have not been established [2].

References

1 ) Weitzman SP, Ginsburg KC, & Carlson HE: Colesevelam hydrochloride and lanthanum carbonate interfere with the absorption of levothyroxine. Thyroid 2009; 19(1):77-79.PubMed Abstract: http://www.ncbi.nlm.nih.gov/...

2 ) Product Information: WELCHOL oral tablets, colesevelam hcl oral tablets. Daiichi Sankyo Inc, Parsippany, NJ, 2008.

3 ) Product Information: TIROSINT(R)-SOL oral solution, levothyroxine sodium oral solution. IBSA Pharma Inc. (per FDA), Parsippany, NJ, 2023.

Colesevelam Overview

• Colesevelam is used in adults along with diet, weight loss, and exercise to reduce the amount of cholesterol and certain fatty substances in the blood alone or in combination with other cholesterol-lowering medications known as HMG-CoA reductase inhibitors (statins). Colesevelam is also used alone or in combination with HMG-CoA reductase inhibitors in certain boys and in girls, ages 10 to 17, with familial heterozygous hypercholesterolemia (an inherited condition in which cholesterol cannot be removed from the body normally) to decrease the amount of cholesterol and other fatty substances in the blood. Colesevelam is also used along with diet and exercise to control blood sugar levels in adults with type 2 diabetes (condition in which the body does not use insulin normally and therefore cannot control the amount of sugar in the blood). Colesevelam is in a class of medications called bile acid sequestrants. It works by binding bile acids in your intestines to form a product that is removed from the body.

• Bile acids are made when cholesterol is broken down in your body. Removing these bile acids helps to lower your blood cholesterol. Accumulation of cholesterol and fats along the walls of your arteries (a process known as atherosclerosis) decreases blood flow and, therefore, the oxygen supply to your heart, brain, and other parts of your body. Lowering your blood level of cholesterol and fats may help prevent heart disease, angina (chest pain), strokes, and heart attacks.

Levothyroxine Overview

• Levothyroxine is used to treat hypothyroidism (condition where the thyroid gland does not produce enough thyroid hormone). It is also used with surgery and radioactive iodine therapy to treat thyroid cancer. Levothyroxine is in a class of medications called hormones. It works by replacing thyroid hormone that is normally produced by the body.

• Without thyroid hormone, your body cannot function properly, which may result in poor growth, slow speech, lack of energy, excessive tiredness, constipation, weight gain, hair loss, dry, thick skin, increased sensitivity to cold, joint and muscle pain, heavy or irregular menstrual periods, and depression. When taken correctly, levothyroxine reverses these symptoms.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

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Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.