["Hypothyroid" goitre in puberty treated with a combined T3/T4 preparation (author's transl)].

After administration of combined T3/T4 preparations (ratio of 4 : 1) to juveniles with goitre, size II-III (WHO), and hypothyroid T4 or PBI levels, the T3 value reached hyperthyroid levels 7-8 hours afterwards. The increased T3 level with normal T4 blood levels can lead to iatrogenic T3 hyperthyroidism. Serial tests demonstrated that at increasing doses a raised T3/T4 ratio, which is observed with low T4 values, can return to normal but with increasing doses this ratio, caused by T3 rise, can again become elevated. For this reason one should reconsider treatment with T3/T4 preparations and, if necessary, replace it by monotherapy with L-thyroxine.