Affinity of ocular acid-insoluble melanin for drugs in vitro

The authors examined spectrophotometrically the ability of drugs to bind with ocular acid-insoluble melanin. Each drug, at 5 X 10(-5) M, was incubated at 37 degrees C for 8 hr with 4 mg of melanin in 20 mM potassium phosphate buffer (pH 7.4 and 8.0) or in 20 mM acetate buffer (pH 4.8). The authors findings showed that chloroquine, thioridazine, befunolol, pindolol, daunomycin, and 5-fluorouracil bound to melanin (pH 4.8, 7.4, and 8.0). Methotrexate bound to melanin (pH 4.8 but not at 7.4 and 8.0). Pilocarpine, epinephrine, acyclovir, vincristine, and colchicine did not bind to ocular acid-insoluble melanin.