In comparison to levothyroxine (T4), Cytomel has a faster onset of action as well as a shorter biological half-life, which may be due to less plasma protein binding to thyroxine-binding globulin and transthyretin.
Drugs with thyroid hormone activity, alone or together with other therapeutic agents, have been used for the treatment of obesity. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic aminessuch as those used for their anorectic effects.
Physicians can use this instead of or in addition to levothyroxine (T4) for patients undergoing thyroid withdrawal. When a patient has thyroid cancer or Graves' disease, ablation therapy with radioactive iodine (131I) can be used to remove any trace thyroid tissue. For 131I therapy to be effective, the trace thyroid tissue must be avid to iodine. The best method is to starve the tissue of iodine but this can lead to hypothyroid symptoms for the patient. Withdrawal from levothyroxine can be done but it takes six weeks of withdrawal for the remaining thyroid tissue to be completely starved. Six weeks is needed owing to levothyroxine's long half life. Six weeks can be inconvenient for the patient and delay treatment. Cytomel instead can be taken and withdrawn from for two weeks to starve the thyroid tissue. This is much safer and more convenient than levothyroxine.
Cytomel may cause a number of side effects, mostly similar to symptoms of hyperthyroidism, which include:
- weight loss
- upset stomach
- stomach cramps
- excessive sweating
- increased appetite
- changes in menstrual cycle
- sensitivity to heat