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                      Levothyroxine Substitution Update

 
In Texas, two drugs are considered generically equivalent and thus interchangeable with one another if both drugs are therapeutically and pharmaceutically equivalent. To be therapeutically equivalent, two drugs must have identical therapeutic ratings in the Orange Book.

On July 28, 2004, therapeutic ratings for levothyroxine sodium products were updated in the Orange Book. Many of these products have been given a “three-character code” (AB1, AB2, or AB3). Drugs coded with a three-character code are considered therapeutically equivalent only to other drugs coded with the same three-character code. For example: 

n          Synthroid® 0.05 mg is now coded AB2. Pharmacists may use Synthroid® 0.05 as a substitute for any levothyroxine sodium 0.05mg that is also coded AB2.  

n          Levoxyl® 0.05mg is coded AB1, AB3. Pharmacists may use Levoxyl® as a substitute for any levothyroxine sodium 0.05mg that is coded also AB1 or AB3. (Please note that Synthroid® 0.05mg could not be substituted for Levoxyl® 0.05mg since Synthroid is coded AB2). 

n          Levo-T® 0.05mg is coded AB2, AB3. Pharmacists may use Levo-T® 0.05 as a substitute for any levothyroxine sodium 0.05mg that is also coded AB2 or AB3. (Since Levo-T® 0.05mg is coded AB2 and AB3 it could be substituted for either Synthroid® 0.05 or Levoxyl® 0.05).  

n          Levothyroxine Sodium 0.05 by Mylan is coded AB1, AB2, AB3. Pharmacists may use Mylan’s levothyroxine sodium 0.05 as a substitute for any levothyroxine sodium 0.05 that is also coded AB1, AB2, or AB3. ((Since Mylan’s levothyroxine sodium  0.05mg is coded AB1, AB2, and AB3 it could be substituted for either Synthroid® 0.05, Levoxyl® 0.05, or Levo-T).


For a full listing of the ratings for levothyroxine sodium, please consult the Electronic Orange book at www.fda.gov/cder/ob.

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