Melanin binding affinity

Melanin-binding studies have shown that the affinity of salbutamol for melanin-containing tissues should be lower than that of clenbuterol (40, 23). A residue depletion study in calves orally treated with 1 mg salbutamol/kg bw/day for 7 days showed that liver residues of salbutamol were almost 4 ppm at 0 withdrawal, falling to about 0.11 ppb after a 7 day withdrawal period (37). 

Eye. Several drugs have an affinity for the retinal pigment melanin and thus may accumulate in the eye. Chlorpromazine and other phe-nothiazines bind to melanin and accumulate in the uveal tract, where they may cause retino-toxicity. Chloroquine concentration in the eye can be approximately 100 times that found in the liver. 

QSRR analysis of HPLC data determined on an immobilized human serum albumin (HSA) column helped to propose the topography of two binding sites of different affinity to benzodiazepine enantiomers 1143.163). Also, the mechanism of interaction of phenothiazine neuroleptics with melanin was rationalized by means of QSRR analysis of HPLC retention data [132,164]. Another QSRR study concerned the interactions of drugs with immobilized keratin and collagen [ 165). 

Selective distribution within the body occurs because of special affinity between particular drugs and particular body constituents. Many drugs bind to proteins in the plasma phenothiazines and chloro-quine bind to melanin-containing tissues, including the retina, which may explain the occurrence of retinopathy. Drugs may also concentrate selectively in a particular tissue because of specialised transport mechanisms, e.g. iodine in the thyroid. 

Manganese has been found to have an affinity for melanin (it was found to bind to beef eye, human hair, and synthetic dopamine melanin) although functional damage has not been reported (Lyd6n et al. 

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