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Table 3. Potential Concerns About Long-Term Combination
Therapy Use in the General Population With
Hypothyroidism
Area of Concern Implication
Published combination therapy trials are
of short duration (e.g. 5-15 weeks)
Outcomes of long term therapy, including
risks such as cardiac arrhythmias, are not
known
Published combination therapy trials are
very different with respect to dosing, study
methods, and chosen endpoints
Optimal dosing regimen and clinical end
points to monitor in patients are not
known
Studies have very different results (e.g.
better health-related quality of life with
combination therapy in some studies, but
not in others)
Reason for the different study results are
not yet understood
Combination therapy has been mostly
studied in healthy, young-middle aged
women
Outcomes in the elderly and men are less
studied
Data regarding a favorable response to
combination therapy in those with a
specific deiodinase polymorphism was
from a retrospective study
Response to combination therapy based
on genetic characterization has not yet
been reported from a prospectively
conducted study
Studies shown that up to 40% of patients
receiving levothyroxine are under- or
over-treated
e frequency of iatrogenic
hypothyroidism or hyperthyroidism
during combination therapy is not
established
