The stability of levothyroxine sodium in oral liquid dosage forms compounded from commercially available tablets was studied. Levothyroxine sodium oral liquids (25 micrograms/mL) were prepared from tablets and from powder with and without methylparaben preservative and transferred to amber, high-density polyethylene bottles. Five bottles of each tablet-based formulation were stored at 2-8 degrees C, 23-27 degrees C, and 38-42 degrees C, and five bottles of each powder-based formulation were stored at 38-42 degrees C. On days 3, 8, 14, 22, 31, 61, and 90, samples were taken from each bottle and analyzed for drug concentration by stability-indicating high-performance liquid chromatography. There was significant degradation of levothyroxine sodium in all the formulations. However, the tablet-based formulation without preservative stored at 4 degrees C retained at least 90% of its initial concentration for eight days after compounding. Degradation occurred faster in the tablet-based formulation with preservative. None of the formulations retained > or = 90% initial potency by day 14. An extemporaneous oral liquid formulation of levothyroxine sodium 25 micrograms/mL compounded from crushed tablets was stable for eight days when stored in amber bottles at 4 degrees C.