The First International Standard for Somatropin: report of an international collaborative study.

Following an earlier decision to move away from the in vivo bioassay for determination of the potency of therapeutic somatropin (recombinant DNA human growth hormone), 18 laboratories in 12 countries participated in an international collaborative study designed to establish an international standard for somatropin, calibrated both by bioassay and by physicochemical assays of somatropin content. The mean in vivo biological potency of preparation studied, coded 88/624, was 6.75 IU/ampoule (fiducial limits 6.30-7.23). Determination of the protein content by quantitative amino-acid analysis yielded a mean estimate of 1.98 mg protein per ampoule. (Relative standard deviation = 2.88%). Data from the study also yielded mean values of 97.2% +/- 0.8% for the monomer content of the preparation, and 8.18 (RSD = 4.00%) for A1% at 276 nm. At its 45th meeting, in October 1994, the ECBS of WHO formally established the preparation 88/624 as the First International Standard for Somatropin, with a defined content of 2.0 mg protein per ampoule, and a defined specific activity of 3.0 International Units per milligram.