Endocrine Abstracts

Introduction: Most brand-name drugs do not differ that much from their generic counterparts, so switching between the two is not an issue. Levothyroxine, however, is an exception. The question of generic equivalency of levothyroxine products has remained unanswered for several decades. The purpose of the present study was to learn whether there is a difference of dosage between brand-name and generic levothyroxine in patient with well controlled primary hypothyroidism

Methods: We performed a cross-sectional study in our outpatient consultation, including the patients presenting a well-controlled primary hypothyroidism. The patients were assigned into two groups, those already taking Levothyrox® (G1) and those already taking Berlthyrox® (G2). All patients were taking the same formulation during the three months preceding the study. Pregnant women were excluded. We assessed the duration of treatment, the age and weight, the cause of hypothyroidism, the levothyroxine dose, the adherence to the treatment and the TSH levels (N : 0,27 - 4,2µUI/ml).

Results: We included 46 patients, 16 patients under Levothyrox® and 30 patients under Berlthyrox®. The median age was 52 years, and the median duration of treatment was eight years. The cause of the hypothyroidism was an auto-immune hypothyroidism in 32 cases (70%), thyroidectomy in 5 cases (11%) and iodine therapy in 9 cases (19%). The levothyroxine dosage ranged from 25 to 200µg/day with a median of 100µg/day. TSH levels ranged from 0,29 to 4,27µUI/ml with a median of 2µUI/ml. The median dosage of levothyroxine in the group 1 was 75µg [25-125µg], and the median dosage of levothyroxine in the group 2 was 100µg [50-200µg]. The difference between the two groups was significant (P=0,039). There wasn’t a significant difference between the two groups concerning the age (P=0,772), the weight (P=0,94), the duration of treatment (P=0,224), the cause of the hypothyroidism (P=0,147), the adherence to the treatment (P=0,576) and TSH levels (P=0,368).

Conclusion: Generic and brand-name levothyroxine showed a comparative effectiveness to achieve normal TSH levels. But our study showed that the dosage required to obtain normal TSH levels was significantly different between the two groups. Therefore, the switch between formulations should be monitored for the risk of under or over treatment. It causes concerns in our practice with some patients taking the formulation available, as episodes of shortage have been noted for both formulations.