C(16)-methyl corticosteroids are far less allergenic than the non-methylated molecules

It has been confirmed that binding to amino acids in skin proteins takes place at C(21) after oxidation of the corticosteroid molecule, which gives to the constituents of the D-ring an essential role in cross-reactivity patterns. In 2000, Matura et al. subdivided the corticosteroid esters of the D-group into two subgroups: D1, the 'stable' esters; and D2, the 'labile' esters. Recent data have indicated that non-methylated corticosteroids selectively react with arginine to form stable cyclic adducts, which are probably implicated in sensitization to corticosteroids.

To compare the patch test results and reactivity of C(16)-methylated and non-methylated corticosteroids.

Three hundred and fifteen subjects with a proven corticosteroid contact allergy underwent patch testing with an extended corticosteroid series. Statistical analysis was performed with the Wilcoxon signed rank test to compare the number of reactions to molecules with and without C(16)-methyl substitution.

Positive patch test reactions to corticosteroid molecules without C(16)-methyl substitution groups A and D2, were, with statistical significance, much more frequently observed than to those with a C(16)-methyl group, groups D1 and C.

C(16)-methyl substitution, interfering with protein binding, and halogenation, seem to reduce the allergenicity of corticosteroid molecules. Hence, when indicated, C(16)-methylated corticosteroids should be preferentially prescribed.