Plasma and cerebrospinal fluid concentrations of pentazocine in patients: assay by mass fragmentography

Mass fragmentography has been used for the determination of low concentrations of pentazocine in blood plasma and cerebrospinal fluid (csf) after intravenous administration of a 30 mg dose to eight patients undergoing neurosurgery under general anaesthesia. A pharmacokinetic analysis based upon mean plasma levels indicated a half-life of 134 min. Lumbar csf levels of pentazocine increased rapidly with mean values from about 3 ng ml−1 at 5 min to 10 ng ml−1 at 30 min and to about 15 ng ml−1 at 90–120 min. The possibility of repeated analyses of drug concentrations in the csf represents an important step towards the correlation of chemical data with clinical effects for centrally acting drugs.