Drug reference

thyroxine

Drug monograph

CDSCO approved

EXCRETION

—

not curated

INTERACTIONS

3 major

SEVERE in our sources

PREGNANCY

FDA category + note

Top interactionssee all 12 →

AmiodaroneSevereDatabase
CholestyramineSevereDatabase
ColestipolSevereDatabase

Mechanism

Not yet extracted

Pregnancy & lactation

Pregnancy

Drug interactions

Amiodarone

Severe

Database

Can cause both hypothyroidism and hyperthyroidism. Hypothyroidism is more common.

Monitor thyroid function tests (TSH, free T4, free T3) before and during amiodarone therapy. Adjust thyroxine dose or manage amiodarone-induced thyroid dysfunction as appropriate.

Cholestyramine

Severe

Database

Significantly decreased thyroxine efficacy, leading to severe hypothyroidism symptoms or increased TSH levels

Administer thyroxine at least 4-5 hours before or after cholestyramine. Monitor TSH levels closely and adjust thyroxine dose as needed.

Colestipol

Severe

Database

Significantly decreased thyroxine efficacy, leading to severe hypothyroidism symptoms or increased TSH levels

Administer thyroxine at least 4-5 hours before or after colestipol. Monitor TSH levels closely and adjust thyroxine dose as needed.

Calcium Carbonate

Moderate

Database

Decreased thyroxine efficacy, leading to hypothyroidism symptoms or increased TSH levels

Administer thyroxine at least 4 hours before or after calcium supplements. Monitor TSH levels and adjust thyroxine dose as needed.

Carbamazepine

Moderate

Database

Decreased thyroxine efficacy, leading to hypothyroidism symptoms or increased TSH levels

Monitor TSH and free T4 levels closely when initiating or discontinuing carbamazepine. Adjust thyroxine dose as needed.

Estrogens (oral Contraceptives, Hormone Replacement Therapy)

Moderate

Database

Decreased free thyroxine, potentially leading to hypothyroidism symptoms or increased TSH levels, requiring a higher thyroxine dose.

Monitor TSH levels when initiating or discontinuing estrogen therapy. Adjust thyroxine dose as needed.

Iron Supplements (ferrous Sulfate, Ferrous Fumarate)

Moderate

Database

Decreased thyroxine efficacy, leading to hypothyroidism symptoms or increased TSH levels

Administer thyroxine at least 4 hours before or after iron supplements. Monitor TSH levels and adjust thyroxine dose as needed.

Oral Anticoagulants (e.g., Warfarin)

Moderate

Database

Increased risk of bleeding

Monitor INR closely, especially when initiating or changing thyroxine dose in patients on warfarin. Adjust warfarin dose as needed.

Phenytoin

Moderate

Database

Decreased thyroxine efficacy, leading to hypothyroidism symptoms or increased TSH levels

Monitor TSH and free T4 levels closely when initiating or discontinuing phenytoin. Adjust thyroxine dose as needed.

Proton Pump Inhibitors (e.g., Omeprazole, Pantoprazole)

Moderate

Database

Decreased thyroxine efficacy, leading to hypothyroidism symptoms or increased TSH levels

Administer thyroxine at least 4 hours before or after PPIs. Monitor TSH levels and adjust thyroxine dose as needed.

Rifampicin

Moderate

Database

Decreased thyroxine efficacy, leading to hypothyroidism symptoms or increased TSH levels

Monitor TSH and free T4 levels closely when initiating or discontinuing rifampicin. Adjust thyroxine dose as needed.

Soy Products (high Intake)

Moderate

Database

Decreased thyroxine efficacy, leading to hypothyroidism symptoms or increased TSH levels

Maintain a consistent intake of soy products. Administer thyroxine at least 4 hours before or after soy. Monitor TSH levels and adjust thyroxine dose as needed.