Drug interactions between multivitamin with iron and Synthroid
Results for the following 2 drugs: |
|
|---|---|
| multivitamin with iron | |
| Synthroid (levothyroxine) | |
Interactions between your selected drugs
levothyroxine ⇔ multivitamin with iron
Applies to: Synthroid (levothyroxine) and multivitamin with iron
ADJUST DOSING INTERVAL: Concurrent administration of iron-containing products may decrease the oral bioavailability and pharmacologic effects of levothyroxine. The exact mechanism of interaction is unknown, but in vitro data suggest it may involve nonspecific adsorption of levothyroxine to iron at acidic pH levels, resulting in an insoluble complex that is poorly absorbed from the gastrointestinal tract. In one study, 14 patients with hypothyroidism who were taking a stable long-term regimen of levothyroxine demonstrated an increase in mean serum thyrotropin (thyroid-stimulating hormone, or TSH) level from 1.6 to 5.4 mU/L following the addition of ferrous sulfate (300 mg administered simultaneously with levothyroxine 30 to 60 minutes before breakfast) for 3 months. A total of 11 patients had increases in serum TSH at week 12 compared to baseline, including two that had levels above the upper limit of normal for the assay, indicating the presence of hypothyroidism. Nine of the eleven also had an increase in signs and symptoms of hypothyroidism based on subjective evaluation using a clinical score. It is not known whether this interaction occurs with other thyroid hormone preparations.
MANAGEMENT: Some experts recommend separating the times of administration of levothyroxine and iron-containing preparations by at least 2 to 4 hours. Monitoring of serum TSH levels is recommended. Patients with gastrointestinal or malabsorption disorders may be at a greater risk of developing clinical or subclinical hypothyroidism due to this interaction.
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