Stability and consistency of compounded oral liquid levothyroxine formulations

With consideration of the narrow therapeutic index of levothyroxine (LT4), the objective of this study was to investigate the stability and consistency of compounded oral liquid formulations of LT4.

Six pharmacies and 6 student pharmacists provided compounded oral liquid formulations of LT4. Pharmacies used their standard compounding best practice including addition of excipients, labeling, and storage instructions. The student pharmacists were required to have completed all academic compounding training and were provided instructions and materials. All analyses were performed at the Pharmaceutical Education and Research Center, a Food and Drug Administration-registered pharmaceutical sciences laboratory. The compounded products were assayed for percent of labeled strength (%LS) of LT4 on days 3, 6, 13, 20, 27, and 34. Each compounding pharmacy and student pharmacist subsequently prepared a second compounded product sample approximately 30 days later to simulate a refill prescription.

Individual product assays on days 3, 6, 13, 20, 27, and 34 demonstrated a range in variation of %LS from 12% to 47% (mean 26.5%). Wide variations of %LS of LT4 were observed between compounding sources. The assays for all products on day 3 demonstrated a range for %LS of LT4 from 77% to 113%, and those on day 34 ranged from 30% to 97%. Assay comparison of the original compounded product (month 1) to the refill compounded product (month 2) varied from 1% to 58%. Variations in excipients and flavorings were also present. One sample contained liothyronine and was not used for evaluation. These variations may be secondary to aliquot sampling of a suspension or product degradation.

Compounded oral liquid LT4 products are unlikely to deliver the precise prescribed dosage and reliable product performance when administered to patients.