Melatonin administration to dogs

Melatonin concentrations in serum and urine were examined following oral administration of melatonin to dogs. Four different doses of melatonin ranging from 10 to 80 mg per kg of body weight were given. Melatonin was rapidly absorbed and reached a maximum serum level after 20--30 min, with a distribution phase of 3.5 hours and elimination half life (t1/2) of 5 hours. The fraction excreted in the urine was 0.25% of the administrated dose during the first 5 hours. These results as well as the diurnal rhythm of serum melatonin in the dogs are similar to corresponding data reported in the human.