Levothyroxine (Synthroid) has been prescribed for a patient with hypothyroidism. The nurse reviews the patient's current medications for potential interactions. Which of these drugs or drug classes interact with levothyroxine? (Select all that apply.)
a. Phenytoin (Dilantin)
b. Estrogens
c. Beta blockers
d. Warfarin (Coumadin)
e. Penicillins
f. Iron supplements