Hydroquinone tolerance

The tolerance of the strains to high concentrations of pentachlorophenol—S. chlorophenolica appears to be less sensitive than M. chlorophenolicus (Miethling and Karlson 1996). This may be attribnted to the ability of the cells to adapt their metabolism to avoid synthesis of toxic concentrations of chlorinated hydroquinones, and is consistent with the low levels of these metabolites measnred in the cytoplasm of cells metabolizing pentachlorophenol (McCarthy et al. 1997). Inocnla have also been immobilized on polyurethane that, in addition, ameliorates the toxicity of chlorophenols (Valo et al. 1990). 

Recently Yamaguchi and Mizuno[ 113] reported ruthenium on alumina to be a powerful and recyclable catalyst for selective alcohol oxidation. This method displayed a large substrate scope (Eq. 29, Table 4) and tolerates the presence of sulfur and nitrogen groups. Only primary aliphatic alcohols required the addition of hydroquinone. TOFs in the range from 4 h 1 (for secondary allylic alcohols) to 18 h 1 (for 2-octanol) were obtained in trifluorotoluene, while in the solvent-free oxidation at 150 °C a TOF of 300 h 1 was observed for 2-octanol. 

Monitoring the preparation process can give an idea of how reactive and sensitive the skin is. Thus, a patient who cannot tolerate hydroquinone during pre-peel preparation will tolerate it even less in the days following the treatment as the skin becomes more sensitive to any irritant. Similarly, if the patient develops an allergy to one of the products used in the preparation, it can be isolated and avoided after the peel. 

Gels are more active and better tolerated by oily skins, while the most suitable galenical form for dry skins is cream. Kojic acid (2-5%) can also be added gradually to the combined glycolic acid plus hydroquinone formulation to enhance its action. 

Kojic acid (5-hydroxy-4 pyran 4-1-2 methyl) is a fungal derivative which inactivates tyrosinase via chelation of copper. Concentrations range from 2% to 4%. It can be used for monotherapy or in combination with retinoids or other cosmeceutical products such as glycolic acid. Compared to hydroquinone, these kojic acid formulations usually show less efficacy however, they may be effective in patients who do not tolerate hydroquinone. In addition, they can be used as maintenance therapies for treatment of hyperpigmentation following 4-6 months of hydroquinone treatment. Use of kojic acid has been associated with contact dermatitis in sensitized individuals, however [41 3]. 

Cook-Bolden FE, Hamdton SF (2008) An open-label study of the efficacy and tolerability of microencapsulated hydroquinone 4% and retinol 0.15% with antioxidants for the treatment of hyperpigmentation. Cutis 81 365-371... 

Ennes SBP, PaschoaUck RC, De Avelar M et al (2000) A double-blind, comparative, placebo-controUed study of the efficacy and tolerability of 4% hydroquinone as a depig-menting agent in melasma. J Dermatol Treat 11 173-179... 

Cook-Bolden FE (2004) The efficacy and tolerability of a combination cream containing 4% hydroquinone in the treatment of postinflammatory hyperpigmentation in skin types IV-VI. J Cosmet Dermatol 17(3) 149-155... 

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