concentration-response curves for the drugs indicated that the melanin-aggregating effects of alpha 2 adrenergic agonists , naphazoline , tramazoline and clonidine , were more than 100-fold greater than that of alpha 1 agonists , phenylpropanolamine , phenylephrine , oxymetazoline and methoxamine .
C1373110
alpha 2 adrenergic agonists
C0009014
clonidine