Comparative brain levels of phenylpropanolamine and amphetamine in rats

The CNS penetration by phenylpropanolamine (PPA) [(+/-)-norephedrine] was examined and compared to that of (+/-)-amphetamine in the rat. Brain and blood levels of the drugs were measured 1 hr after injection of 0.025, 0.05 or 0.1 mmol/kg doses. Brain levels of both drugs were proportional to dose and were several-fold higher than blood levels. Phenylpropanolamine levels in brain and brain:blood concentration ratios were only slightly lower than those of amphetamine at equimolar doses. The results suggest that phenylpropanolamine penetrates the blood:brain barrier almost as well as amphetamine and that different central actions of the two drugs are probably related to pharmacodynamic differences since they could not be accounted for by the small differences in drug concentrations in brain.