ABSTRACT
A gas-liquid chromatographic method for the determination of gabapentin (Neurontin) is described. The method involves extracting 0.5 mL of acidified sample by C18 solid-phase column, derivatization with MTBSTFA plus 1% tBDMCS, and analysis on an HP-1 column with a flame-ionization detector. Quantitation was performed with peak-height ratios of gabapentin to a gabapentin analogue [(1-aminomethyl-1-cycloheptyl) acetic acid] as the internal standard. The assay had a limit of detection of 0.2 mg/L and a linear range from 0.5 to 30.0 mg/L. Several compounds were analyzed for potential interference, and none interfered with the assay.
Subject(s)
Acetates/blood , Amines , Anticonvulsants/blood , Cyclohexanecarboxylic Acids , gamma-Aminobutyric Acid , Acetamides , Calibration , Chromatography, Gas , Cycloheptanes/blood , Flame Ionization , Fluoroacetates , Gabapentin , Humans , Organosilicon Compounds/chemistry , Reference Standards , Reproducibility of Results , Silanes/chemistry , Trifluoroacetic Acid/chemistryABSTRACT
A radioimmunoassay of bencyclane in human serum was developed. Male rabbits were immunized with p-(3-carboxy-propoxy)bencyclane-bovine serum albumin conjugate, giving antisera with high titers. 125I-p-Hydroxybencyclane with a high specific activity was prepared as a labelled antigen by a chloramine-T method. In the radioimmunoassay procedure, a mixture of serum sample, diluted antiserum and 125I-antigen solution were incubated at 4 degrees C for 18 h, and bound-free separation was carried out by a dextran-coated charcoal method. The detection limit of bencyclane in human serum was 1.0 ng/ml, and the cross-reactivity of the antiserum with metabolites was found to be very low. Serum samples from healthy volunteers dosed orally with bencyclane fumarate were analyzed by both of the radioimmunoassay and gas chromatography-mass spectrometric methods. An excellent correlation was observed between the values obtained by both methods.
Subject(s)
Bencyclane/blood , Cycloheptanes/blood , Animals , Cattle , Cross Reactions , Gas Chromatography-Mass Spectrometry , Haptens , Humans , Immunization , Iodine Radioisotopes , Papaverine/pharmacology , Radioimmunoassay , Serum Albumin, Bovine/immunologyABSTRACT
Since 10 years there is a phenomenal increase in the use of mass spectrometry, combined with (capillary-) gas chromatography and dedicated data systems for the rapid, reliable, sensitive and selective determination of xenobiotics (drugs, their degradation/biotransformation products etc.) in biological fluids. This applies especially since the introduction of newer developments in ionization techniques (CI, DCI, FAB) and gas chromatographic column technology (fused silica, bonded phase columns). We employed such a sophisticated method for the quantitative determination of N-[3-(1-benzyl-cycloheptyl-oxy)-propoxy]-N,N'- dimethylammoniumhydrogen fumarate (bencyclane) in human plasma after oral application of a therapeutic doses. Our results clearly show that this approach is the best method available; furthermore the detected plasma levels will lead to discussions with respect to the pharmacokinetic properties of the drug.
Subject(s)
Bencyclane/blood , Cycloheptanes/blood , Gas Chromatography-Mass Spectrometry/methods , Humans , Time FactorsABSTRACT
The quantitative determination of bencyclane from the biological material was carried out with the aid of a combined microchemical method (thin-layer chromatography and measurement of fluorescence) using NBD chloride. The original method [J. Reisch, Z. Analyt. Chemie, 247 (1969) 56; J. Monforte, Clinical Chemistry 18 (1972) 1329; R.S. Fager, Anal. Biochemistry, 53 (1973) 290, etc.] was so modified as to enable attainment of optimal results in respect of sensitivity and accuracy in the determination of bencyclane. The sensitivity of this modified method is 0.1 mug/ml plasma. Volunteer subjects and patients received under standard conditions 2 coated tablets Fludilat (i.e. 200 mg bencyclane hydrogen fumarate) orally as a single dose or repeated 3 times daily over 5 days, or 4 ampoules (= 200 mg) in a single intravenous injection. After a single oral administration, maximum plasma concentrations of approximately 2 mug/ml were attained in about 2 hours. The elimination half-life was about 360-480 min. The appearance of a second peak after about 6-7 hours indicates involvement of several compartments. On intravenous administration, maximum plasma concentrations of above 2 mug/ml were attained. A second peak in the late phase of the elimination was also detected here. The repeated oral administration led to maximum plasma concentrations of above 3 mug/ml without there being any indication of accumulation. Protein binding of about 30% was determined with the aid of the equilibrium dialysis method. A parallel "in vitro" study with 14C-bencyclane (U.R. Kleeberg, 1973, unpublished) showed an approx. 40% protein binding, an approx. 30% erythrocyte binding, and an approx. 10% thrombocyte binding. About 20% bencyclane remain free.
