Brain and serum levels of naloxone following peripheral administration.

Striatal, hypothalamic and serum concentrations of naloxone were measured by a new high-performance liquid chromatographic procedure at various time up to 120 min following subcutaneous administration of 1, 5, and 10 mg naloxone hydrochloride/kg to rats. A dose-concentration relationship was evident throughout. Peak levels were observed at the first measurement time (15 min) and tissue values were consistently higher than concentrations in serum. The correlations between serum and brain naloxone levels suggests that in normal rats central concentrations of the drug can be extrapolated from serum concentrations.