Drug distribution in dog brain studied by positron emission tomography

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Abstract
We used positron emission tomography to monitor the distribution of radioactivity in dog brain and muscle following i.v. administration of 11C-labelled antipyrine, imipramine, and quinidine. Twenty-five sequential scans of a transaxial slice of the head were performed within 90 min; radioactivity in plasma was measured in a gamma-counter. Following i.v. injection of [11C] antipyrine (50 mg kg−1; 9–68 mCi; n=10), the decay of plasma activity was accompanied by rapid uptake in brain and variable uptake in muscle, immediately followed by a redistribution leading to equalization of the radioactivity in the tissues. Administration of [11C]imipramine (4 mg kg−1; 30–110 mCi; n=8) was followed by a rapid build-up of a sustained gradient between high brain, and low plasma and muscle radioactivity. After i.v. injection of [11C]quinidine (1 mg kg−1; 11–87 mCi; n=10), radioactivity in brain was low, with higher activity in plasma and muscle throughout the experiment. Positron emission tomography thus revealed for each drug a distinct pattern of distribution consistent with established properties of the compounds. This technique seems promising for the study of early drug distribution, notwithstanding certain limitations.