Drugs Binding to Hair

The model of ionic binding was also evaluated by comparing the binding of fluorescein and rhodamine to hair, two molecules of similar shape, size, and fluorescent quantum yield. Rhodamine, being positively charged, is far more efficient at binding to hair compared to fluorescein. The disparity in binding of materials to 

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Although the structures of pheomelanin and eumelanin have not been resolved, melanin is one of several suspected binding sites in hair for metals, chemicals, and drugs of abuse. The quantity and type of melanin in hair should determine the extent to which drugs bind to hair. Melanin is present in several mammalian tissues including the brain, skin, hair, iris of the eye, vas deferens, and cochlea of the inner ear. - Since melanin is present in many human tissues, drug may bind to other bodily tissues as well as hair. 

The drug binds to anionic phospholipids in the proximal tubule, may alter phospholipids metabolism, and cause phospholipidosis. Gentamycin also damages the hair cells in the ear. 

The nature of our concern is best illustrated by a specific example. Blank and Kidwell use a cocaine solution of 100,000 ng/mL for their contamination experiments, to which they add approximately 1 pCi of tritium-labeled cocaine, i.e., approximately one million counts per minute. Therefore, they have approximately a sensitivity of 10 cpm/ng of sample. Decontamination of hair means that residual drug concentration must drop below the endogenous cutoff level of 5 ng/10 mg of hair, i.e., to 50 cpm/10 mg hair. Now if the labeled cocaine has a radiochemical impurity of as little as 0.1%, this corresponds to 1000 cpm or to 100 ng of residual cocaine equivalents. Since self-irradiation of tritium-labeled material tends to form polymeric impurities, and since these are likely to preferentially bind to hair, one incurs a major risk of concluding erroneously that the residual radioactivity represents residual cocaine contamination rather than contamination by polymeric degradation products. 

Our criticism, of course, is not directed at isotope techniques in general, but only to contamination/decontamination studies of hair where only a small fraction of the total isotope binds to hair and where residual drug levels in hair are exceedingly low when compared to those in the contaminating solution. In light of these considerations it is our opinion that there is no excuse for substituting a risky technique, no matter how convenient, for a reliable one involving the direct measurement of analytes. This is particularly true when it is the objective to validate the latter procedure. 

Moreover, multivariate optimization, the simultaneous optimization of several properties, will increasingly come into focus. A drug should have high selectivity in binding to different receptors and minimal toxicity, good solubility and penetration, and so on. A hair color should have a brilliant shine, be absorbed well, not be washed out, not damage the hair, not be toxic, and be stable under sunlight, etc. 

Some possible criticisms of the use of radiotracers for monitoring the uptake and release of cocaine are that the tracer chemically reacts with the hair matrix or contains radiolabeled impurities which show preferential binding. Both criticisms are unlikely because (1) the radiotracer never exceeds 1% of the urdabeled drug, and (2) hair exposed to drugs without the radiotracer and analyzed by GC/MS show the parent drug present in amounts indicated by the radiotracer analysis. 

This review surveys morphological, ultrastructural, and chemical differences between ethnic hair types which may affect the binding of drugs of abuse to hair. Selected studies are discussed regarding the binding of metals, chemicals, and drugs of abuse to different ethnic hair types and the effects of hair color and chemical treatments on drug disposition in hair. A mechanistic discussion of chemical and... 

There are differences in the chemical and physical attributes of ethnic hair types together with considerable intraethnic variation. Table 1 provides a compilation of differences between hair types of three major ethnic groups. Unfortunately, many of these findings are based on small numbers of subjects and are in need of further validation. Despite these limitations, differences between ethnic hair types warrant special attention because of their importance in the binding of drugs to hair. 

Kidwell, D. A. and Blank, D. L., Mechanisms of incorporation of drugs into hair and the interpretation of hair analysis data, in NIDA Research Monograph, Cone, E. J. and Welch, M., Eds., 1994. Su, T. P, Tsai, W. J., Joseph, R., Tsao, L. L, and Cone, E. J., Cocaine binds in a sterospecific, saturable manner to hair a precaution on hair testing for forensic purposes, presented at College on Problems of Drug Dependence, Palm Beach, June 18-23,1994. 

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