Comparison of drug concentrations in postmortem cerebrospinal fluid and blood specimens

The concentration of drugs and metabolites in cerebrospinal fluid (CSF) and blood were determined in 282 autopsied cases using liquid-liquid extraction techniques and gas chromatographic analyses. All drugs were confirmed in one matrix by gas chromatography-mass spectrometry. CSF/blood ratios were used to compare the two biological fluids. Classes of drugs evaluated in this study included: benzodiazepines, anticonvulsants, sedatives, opioids, antidepressants, anesthetics, and antihistamines. The majority of the drugs tested were readily detected in CSF specimens. The average CSF/blood ratio for most drugs was in the range of 0.05-0.50. Interpretation of these results is difficult because protein binding, half-life, hydrophobic properties, and pKa of a drug, in addition to survival time after drug use, influence the CSF/blood ratio. While CSF specimens do provide a viable alternative testing matrix when blood specimens are not available, they should not be used to estimate blood drug concentrations.