Hypothyroidism resulting from generic levothyroxine failure

In today's cost-conscious health care system, generic preparations should be prescribed whenever possible provided that safety and efficacy are not compromised. Several reports, however, suggest that generic levothyroxine may not always be interchangeable with the proprietary preparations. Such interchangeability is critical because patients are likely to receive different brands of levothyroxine during the life of their treatment. We report a case of severe hypothyroidism that developed in a patient who had been well controlled before receiving a generic levothyroxine preparation. Analysis of the patient's tablet by high-pressure liquid chromatography showed that the levothyroxine content was approximately 30 percent less than its labeled content and outside current Food and Drug Administration (FDA) requirements. It is likely that poor tablet bioavailability was a contributory factor. Euthyroidism was achieved with the same dose of a more potent and possibly more bioavailable brand-name product. Until levothyroxine products become more uniform and the FDA confers therapeutic equivalence, product substitution with expense as the principal consideration should be avoided.