Stability of Levothyroxine in Aliquots and Capsules Prepared by Extemporaneous Compounding

Abstract

Levothyroxine (T4) is commonly used to supplement low levels of endogenous thyroid hormones in patients with thyroid hormone deficiency. Dosing of T4 is highly individualized and therefore is often compounded extemporaneously by pharmacists. Extemporaneous preparation of T4 involves preparing a ready to use aliquot of T4 in an inert excipient which is then used to prepare the capsules dispensed to the patients. Aliquots and capsules of T4 were assessed for content over a four month span to determine an appropriate beyond use dating for capsules prepared by a local compounding pharmacy, Central Iowa Compounding (CIC). CIC provided a 1:100 T4 aliquot and 95 μg T4 capsules for the study. Stability of T4 was assessed by high pressure liquid chromatography (HPLC) developed to detect T4 and its solid state oxidized degradation product using UV detection. Stability was assessed on days 1, 7, 14, 21, 30, 45, 60, 90, and 120. As of day 120 of the stability study, the average content of T4 in the aliquot was 87.09% ± 4.04 of the original concentration. The 95 mcg T4 capsule retained full activity (100%) over the four month period. Based on the results thus far T4 content in aliquot is statistically significantly lower for day 120 only while capsule content of T4 is maintained over 120 days.