Distribution of pentazocine in blood and brain of the baboon following intravenous injection.

1 In the baboon the blood levels of pentazocine between 1 and 60 min after intravenous injection of 0.5 mg/kg were measured by a gas chromatographic technique. From cerebral arteriovenous differences it was shown that the peak of the brain concentration occurred within 15 min and probably within 10 min of intravenous injection. At the time of peak concentration about 10% of the injected dose was in the brain, while the corresponding value at 60 min was 2%.2 The concentration of pentazocine in the brain was an order of magnitude greater than the concentration in cerebral venous blood both at 5 min and 60 min after injection. No major brain interregional differences were demonstrated. Cerebrospinal fluid from the cisterna magna did not yield values from which the cerebral concentration of pentazocine could be predicted.