Block and replace therapy (hyperthyroidism)

                                                        
                                                          

Dear Readers,
       Hyperthyroidism is a condition where your T3 and T4 level is higher than required. What is T3 and T4? T3 known as triiodothyronine and T4 as thyroxine. What make them different? The only different is the Iodine attached the main chain. T3 with 3 Iodine meanwhile T4 with 4 Iodine. T3 is 4times more potent than T4. T.levothyroxine is synthetic version of T4 and T.liothyronine is synthetic version of T3. T.liothyronine not known by alot of people due to availability. T.liothyronine sold in the brand name cytomel and availability asian region is less.

  Titration method majorly used to treat Hyperthyroidism, where increase according to patient response for 1 year period. The drugs used in this threapy is is Carbimazole, Methimazole and propylthiouracyl (PTU). PTU is favorite is pregnancy and thryrothoxicosis. First trimester PTU is the safest and after that period can me converted to Carbimazole. Why is PTU is favored in thyrotoxicosis compared to Carbimazole? PTU"s MOA almost same as Carbimazole BUT PTU have one extra advantage where PTU block a certain amount of T4 convert to T3. Why is important block the conversion? Because all T4 will change in to T3 when reaches the active site. T3 is the major culprit. By blocking T4 to T3 we cn control the situation more better.

Block-and-replace regimen PO; Carbimazole 20-60mg daily (together with levothyroxine 50-150 mcg dailiy for 6-18 month. Carbimazole can be replaced by PTU 200-400mg daily in this regimen. The block-and-replace method uses persistently high ATD doses in association with L-thyroxine replacement to avoid hypothyroidism; treatment lasts 6-18 months. This method has advantages and disadvantages over the titration method. Higher doses of ATDs may have a greater immunosuppressive action useful for a permanent remission of hyperthyroidism, but this putative effect remains to be demonstrated. Avoidance of hypothyroidism or ‘escape’ of hyperthyroidism seems easier than with the titration method; treatment is shorter, and the number of visits lower. On the other hand, the much higher number of tablets taken every day may create problems of poor compliance. The block-and-replace method should not be used during pregnancy.

Thank you