Clonazepam acetylation in fast and slow acetylators

Six slow acetylators (SAs) and six rapid acetylators (RAs), as determined by sulfamethazine (SMZ) phenotyping, were each given a 2-mg oral dose of clonazepam. Ninety-six-hour urine collections from these subjects were analyzed for clonazepam, 7-amino clonazepam (7-AM, clonazepam nitroreduced metabolite), and 7-acetamido clonazepam (7-ACT, N-acetylated 7-AM). The SA group excreted more 7-AM and less 7-ACT than the RA group; mean (+/- Sd) recovered as 7-AM was 22.7 +/- 5.0% for the SA group and 13.6 +/- 4.1% for the RA group and mean (+/- SD) recovered as 7-ACT was 1.5 +/- 0.4% for the SA group and 3.9 +/- 1.8% for the RA group. Both differences were substantial (p less than 0.02 by unpaired t test) and indicate that the rate of acetylation of 7-AM to 7-ACT in the biotransformation of clonazepam is determined by the acetylator phenotype.

Determination of an antisecretory trimethyl prostaglandin E2 analog in human plasma by combined capillary column gas chromatography-negative chemical ionization mass spectrometry

A method is described for measuring a trimethyl prostaglandin E2 analog, TM-PGE2, in human plasma. Trideuterated and monofluorinated analogs of TM-PGE2 and added to plasma as internal standard and carrier, respectively. The plasma is adjusted to pH 3.0 and is extracted with a mixture of benzene-dichloromethane (9:1). The residue, following removal of the extracting solvent, is reacted consecutively with pentafluorobenzyl bromide and bistrimethylsilyltrifluoroacetamide. The excess derivatizing reagents are removed by evaporation, and an aliquot of the reconstituted residue is analyzed by capillary column gas chromatography using methane as the carrier gas. A quadrupole mass spectrometer is set to monitor in the gas chromatographic effluent the (M - C7H2F5)-fragment ion of TM-PGE2 (m/e 449) and trideuterated TM-PGE2 (m/e 452) generated by methane negative chemical ionization. Quantitation of unknowns is based on a comparison of the m/e 449 to m/e 452 ion ratio in each unknown to that obtained from the analysis of control plasma spiked with known amounts of TM-PGE2 and fixed amounts of internal standard and carrier. The sensitivity limit of the assay is approximately 100 pg ml-1, which is equivalent to 1 pg injected. The assay was used to measure the concentration of TM-PGE2 in the plasma of two subjects following a single 10 micrograms kg-1 oral dose of the drug.

Influence of phenytoin and phenobarbital on the disposition of a single oral dose of clonazepam

Clonazepam (CZP) was measured in the plasma of eight subjects for 48 hr after a 0.03-mg/kg oral dose. After pretreatment for 19 days with phenytoin (DPH, 4.3 mg/kg/day), plasma CZP concentrations were determined in the same subjects after another 0.03 mg/kg oral dose of CZP. The same protocol was followed in eight additional subjects using phenobarbital (PB, 1.4 mg/kg/day) instead of DPH. DPH pretreatment lowered mean plasma CZP concentration in 8 of the 12 time points. DPH pretreatment increased CZP clearance by 46% to 58% and decreased CZP half-life (t1/2) by 31%. Both changes were statistically significant. After PB pretreatment the mean plasma CZP concentration was lowered by an average of 11%, but the decrease was statistically significant for only 1 of the 12 time points. PB decreased mean CZP t1/2 by 11% and increased CZP clearance by 19% to 24%, but only the increase in clearance was statistically significant. Both DPH and PB increased CZP clearances and decreased the areas under the plasma concentration-time curves without altering the volumes of distribution. This observation is consistent with induction of CZP metabolism. The overall effect of DPH (4.3 mg/kg/day) was greater than the effect of PB (1.4 mg/kg/day). Neither the DPH or PB had a significant effect on the extent of CZP protein binding.

A method for the determination of amitriptyline and its metabolites nortriptyline, 10-hydroxyamitriptyline, and 10-hydroxynortriptyline in human plasma using stable isotope dilution and gas chromatography-chemical ionization mass spectrometry (GC-CIMS)

A gas chromatography--mass spectrometry (GC-MS) method has been developed to measure amitriptyline and its metabolites nortriptyline, 10-hydroxyamitriptyline, and 10-hydroxynortriptyline in human plasma. Deuterated analogs of each compound were synthesized as internal standards. Isobutane was used as both gas chromatography (GC) carrier gas and chemical ionization (CI) reagent gas. In order to obtain compounds with satisfactory GC and mass spectrometry (MS) properties, the two alcohol metabolites were dehydrated without loss of label during sample preparation. Selective ion monitoring of the MH+ ions of the protio- and deuterio- compounds gave ion ratios which were converted to plasma concentrations using standard curves. For amitriptyline and nortriptyline, which are assayed using multiple deuterated analogs as internal standards, the curves are straight lines. For 10-hydroxyamitriptyline and 10-hydroxynortriptyline, which are assayed using monodeuterated analogs as internal standards, the curves are nonlinear and are analyzed using an iterative computer procedure. Assay sensitivity is 0.5 ng/ml for amitriptyline, nortriptyline, and 10-hydroxyamitriptyline and 1 ng/ml for 10-hydroxynortriptyline. Assay precision and accuracy in terms of percent error are both less than 5%. Following oral administration of a single 75-mg dose of amitriptyline to two subjects, the mean plasma levels of amitriptyline, nortriptyline, 10-hydroxyamitriptyline, conjugated 10-hydroxyamitriptyline, 10-hydroxynortriptyline, and conjugated 10-hydroxynortriptyline were 36, 8, 10, 66, 16, and 46 ng/ml, respectively, at 2 hr after dosing and 3, 4, 0.5, 1, 6, and 17 ng/ml, respectively, at 72 hr after dosing. Analyses of plasma samples from 12 subjects who had been receiving 50 mg amitriptyline therapy three times a day for an average +/- SD of 32 +/- 5 days gave a mean concentration of 81 +/- 40 ng/ml for amitriptyline, 71 +/- 57 ng/ml for nortriptyline, 12 +/- 5 ng/ml for 10-hydroxyamitriptyline, 91 +/- 30 ng/ml for conjugated 10-hydroxyamitriptyline, 82 +/- 27 ng/ml for 10-hydroxynortriptyline, and 176 +/- 64 ng/ml for conjugated 10-hydroxynortriptyline.

Determination of clonazepam in human plasma by gas chromatography--negative ion chemical ionization mass spectrometry

Our previously reported gas chromatographic--mass spectrometric assay for clonazepam using positive ion chemical ionization has been modified to employ negative ion chemical ionization. The sensitivity using this technique (less than 0.1 ng/ml) is approximately twenty times better than the positive ion chemical ionization procedure with similar precision. The method was used to determine the clonazepam plasma concentration in one human for 96 h following a single 2-mg dose of clonazepam.

Kinetics of biotransformation of clonazepam to its 7-amino metabolite in the monkey

The pharmacokinetic behavior of the 7-amino metabolite of clonazepam administered exogenously and formed endogenously from the parent drug was studied in a group of rhesus monkeys using constant rate intravenous infusions. Plasma levels of the 7-amino metabolite and/or clonazepam were determined with a GC-CI-MS method. The biological half-life of the 7-amino metabolite (2.2 +/- 1.0 hr) was shorter than that of clonazepam (4.9 +/- 0.2 hr). Total body clearance of the metabolite (0.83 +/- 0.16 liters/hr/kg) was larger than that of the parent drug (0.55 +/- 0.09 liters/hr/kg). The kinetics of in vivo biotransformation were described by a two-compartment model in which formation and disposition of the metabolite follow first-order processes. The fraction of a dose of clonazepam appearing in the systemic circulation as 7-amino metabolite was 0.70 +/- 0.30. This value may underestimate the actual fraction formed, if the metabolite is susceptible to first-pass metabolism following in situ formation.

Determination of clonazepam and its amino and acetamido metaoblites in human plasma by combined gas chromatography chemical ionization mass spectrometry and selected ion monitoring

Our previously published gas chromatography chemical ionization mass spectrometry stable isotope dilution assay for clonazepam and its 7-amino metabolite in plasma has been modified to obtain more consistent recoveries of the amine metabolite and to permit the determination of the 7-acetamido metabolite of clonazepam. In addition, the manuscript describes the details of a method for a least squares analysis of the nonlinear standard curves associated with the use of certain stable isotope labeled analogs as internal standard.

The kinetics of amitriptyline following single oral dose administration to man

Amitriptyline and its metabolite, nortriptyline, were measured in the plasma of eight humans for 96 hours following oral administration of a 75 mg dose of amitriptyline hydrochloride. Based on the 8 to 96 hour post dosing plasma concentration data, the terminal exponential half life of amitriptyline +/- S.D. was 22.4 +/- 4.3 hr. Based on the 24 to 96 hour concentration data, the "apparent" terminal half time of nortriptyline +/- S.D. was 26.0 +/- 7.4 hours for seven subjects. For these same seven subjects the relative area under the plasma concentration time curve of nortriptyline +/- S.D. was only 0.88 +/- 0.34 times that of amitriptyline. One subject whose apparent nortriptyline half time was 108 hours had a nortriptyline bioavailability 3.83 times that of amitriptyline. Average steady state plasma levels for 12 psychiatric patients who had received a 50 mg oral dose of amitriptyline three times a day for an average of 32 days could be predicted from the single dose plasma clearance of amitriptyline.

The developmental biology of induced malignant melanoma in guinea pigs and a comparison with other neoplastic systems

Malignant melanoma has been induced in the Weiser-Maple guinea pig by prolonged application of 7,12-dimethylbenz(a)anthracene. The tumor shows a biphasic growth pattern analogous to the radial and vertical growth phase of human cutaneous malignant melanoma. It evolves through a predictable series of cellular events classified as intraepidermal melanocytic hyperplasia, dermal melanocytosis, dermal melanocytoma, malignant melanoma without intralesional transformation, and, finally, malignant melanoma with intralesional transformation, which is characterized by the appearance of "new kinds of cells" and is associated with widespread metastases and massive lymph node involvement. Clinically, the lesions evolve from diffuse hyper-pigmentation to brown-black macules, to nodules of increasing size, to overt malignant melanoma associated with metastases, wasting, and death. Examples of intralesional transformation analogous to that in guinea pigs are found not only in human malignant melanomas, but in other human neoplastic systems, and such analogous cellular events are discussed in this paper.