The comparative bioavailability of oral doses of levothyroxine (LT(4)) 
formulation taken as tablets, after being crushed, or chewed before swallowing 
has not been well studied. Three patients with hypothyroidism who showed 
persistent elevation of serum thyrotropin (TSH) despite taking 200, 150, and 125 
microg of LT(4) tablets per day are presented. They did not show signs and 
symptoms of gastrointestinal illness that could interfere with the absorption of 
LT(4) nor history of such a condition. They did not concurrently take 
medications known to affect the absorption of LT(4) from the gut. Their serum 
TSH levels normalized when the tablets were taken after being pulverized. The 
difference appeared attributable to the slow dissolution of the tablets in the 
gut of these patients.