Hydroquinone is used extensively as a photographic developer. The metabolic fate and percutaneous absorption of [U-14C]HQ was determined in male Beagle dogs. The excretion of 14C was determined after dermal exposure, intravenous (iv) and gavage administrations. For iv studies, 1 or 10 mg/kg of [14C]HQ was injected and blood, urine and breath were collected for 8-12 hours in anesthetized dogs. After recovery from the anesthetic, dogs were housed in metabolism cages for 6 to 7 days for collection of blood, urine and feces. Blood 14C concentrations declined slowly, with 2 apparent phases. Half-life values for the α and β phases were 1.3 and 7.2 hours for the 1 mg/kg dose and 1.0 and 8.0 hours for the 10 mg/kg dose, respectively. Excretion of 14C was rapid initially, with 14.6% and 42.4% of the 14C being excreted in 4 hours for the 1 and 10 mg/kg doses, respectively. Values for urine, feces and total recovery of 14C at 4 to 7 days were 34.5%, 7.1%, and 41.6% for a 1 mg/kg dose and 65.7%, 6.1%, and 71.8% for a 10 mg/kg dose. No 14C was detected in the expired air. The concentration of 14C in the skin 24 hours after iv dosing of 1 mg/kg [14C]HQ was about 10.4% of the dose. The other tissues showed low concentrations of 14C. After the oral administration of 50 mg/kg [14C]HQ to dogs, blood 14C concentrations declined slowly. Half-life values for the α and β phases were 0.85 and 12.5 hr, respectively. The urinary excretion pattern was similar to that seen after iv administration, with 62.5% of the dose being excreted after 4 hours. Values for urine, feces, blood, tissue, and total recovery of 14C at 5 to 7 days were 80.4%, 3.7%, 0.15%, 2.2%, and 86.5%. Analysis for urinary metabolites indicated that the urine of iv and orally-treated dogs did not contain sulfates or glucuronides of HQ as was reported elsewhere for rats dosed orally with [14C]HQ. After dermal application of [14C]HQ, no 14C was detected in the blood. Urinary excretion of 14C accounted for only 0.03% of the applied radioactivity at 2 days and 0.04% at 5 days. Urinary 14C was still detectable at 5 days. The percutaneous absorption rate was about 0.16 nmol/cm2/min (1.1 µg/cm2/hr). Using these data to estimate human uptake, assuming immersion of both hands into a photographic developer solution containing HQ for 1 hour, about 0.8 mg of HQ would be absorbed through the skin. These studies compare the metabolic fate of HQ by different routes of administration and show that HQ is poorly absorbed through the skin.
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Hamilton, Marva Louisa, "Percutaneous absorption and metabolic fate of [14C]hydroquinone in the dog" (1985). Thesis. Rochester Institute of Technology. Accessed from
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