A Gas Chromatographic Method for the Determination of Amitriptyline and Nortriptyline in Human Serum

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Abstract
Amitriptyline (AMT) and nortriptyline (NT) were extracted from serum with hexane at pH 9. An internal standard was added and extracted with the drugs. During the concentration of the hexane phase nortriptyline was acetylated to improve separation. One fifth of the final hexane phase was injected into a gas chromatograph equipped with a detector, which was selectively sensitive towards nitrogen. The lower limits of detection were 5 ng/ml for AMT and 10–15 ng/ml for NT. A constant relative standard deviation of 7.6% was found in the concentration interval used for the standard curves. No interference appeared from AMT metabolites and some benzoediazepines. The method has been used for the estimation of AMT after a single dose of this drug to two human volunteers and for the estimation of AMT and NT after repeated administration of amitriptyline to patients. After single dose administration NT was not detectable, while the NT concentration was of the same order as the AMT concentration after repeated administration. A great individual variation in the concentrations of the two drugs was seen after repeated administration.