“…Erythromycin A was purchased from Aldrich Chemical Co., Milwaukee, WI. [1,3,5,7,9,11,13‐ 14 C]erythromycin A (specific activity, 0.327 mCi mmol −1 ) was synthesized with purity >97%[12]. N ‐[ methyl ‐ 14 C]erythromycin A (specific activity, 54 mCi mmol −1 ) with a purity of 98% was purchased from American Radiolabeled Chemicals, St. Louis, MO.…”