Drug interactions between phenytoin and Synthroid
Results for the following 2 drugs: |
|
|---|---|
| phenytoin | |
| Synthroid (levothyroxine) | |
Interactions between your selected drugs
phenytoin ⇔ levothyroxine
Applies to: phenytoin and Synthroid (levothyroxine)
MONITOR: Carbamazepine and phenytoin may decrease exogenous thyroid plasma concentrations resulting in elevated thyroid stimulating hormone (TSH) and possible exacerbation of hypothyroidism. The mechanism may be induction of hepatic CYP450 enzymes responsible for thyroxine (T4) and triiodothyronine (T3) metabolism. In addition, T3 and T4 may be displaced from thyroxine binding globulin by phenytoin. Clinical data are limited.
MANAGEMENT: Clinical monitoring of patient response, including laboratory serum TSH concentrations, is recommended. Adjustment of the thyroid replacement dosage may be indicated when initiating or discontinuing phenytoin or carbamazepine therapy.
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