Pharmacokinetic and pharmacodynamic alterations in the Roux-en-Y gastric bypass recipients.

OBJECTIVE: We conducted a pharmacokinetic (PK) study and a pharmacodynamic (PD) study to assess whether Roux-en-Y gastric bypass (RYGB) surgery is associated with significant changes to PK and PD of oral medications. BACKGROUND: The effect of RYGB on oral drug disposition is not well understood. METHODS: An oral cocktail of probe drugs for major drug-metabolizing enzymes (caffeine, tolbutamide, omeprazole, dextromethorphan, and oral and intravenous midazolam) was administered to 18 RYGB recipients and 18 controls. Timed blood and urine samples were obtained for PK analyses. Forty mg of oral furosemide was administered to 13 RYGB recipients and 14 controls, and urine and blood samples were collected for assessing furosemidePK, and urine volume and urine sodium excretion for PD analyses. RESULTS: Compared with controls, the RYGB group had significantly lower time to maximum plasma concentration (tmax) for caffeine (0.58 ± 0.5 vs 2.1 ± 2.2 hours, P < 0.0001), tolbutamide (1.4 ± 1.8 vs 2.1 ± 2.2 hours, P = 0.0001), omeprazole (1.1 ± 1.1 vs 4.4 ± 1.3 hours, P < 0.0001), and oral midazolam (0.5 ± 0.2 vs 0.7 ± 0.4 hours, P < 0.01). However, maximum plasma concentration, half-life, area under the curve, and oral bioavailability were not different. Compared with controls, the RYGB group had brisk natriuresis, with significantly lower tmax for urine sodium (1.3 ± 0.5 vs 3.1 ± 2.3 hours, P < 0.02) and correspondingly lower tmax for furosemide (1.8 ± 0.3 vs 4.2 ± 1.2 hours, P = 0.006). However, 6-hour urine sodium and 6-hour urine volume were not different between the two groups. CONCLUSIONS: RYGB recipients have significantly shorter tmax for the studied orally administered medications, but otherwise no other significant changes in PK were reported.

A study of the potential confounding effects of diet, caffeine, nicotine and lorazepam on the stability of plasma and urinary homovanillic acid levels in patients with schizophrenia.

Ten men inpatients who met DSM-III-R criteria for schizophrenia participated. On five occasions at least one week apart, each subject had an intravenous line placed at 0730 after an overnight fast. On each occasion blood samples were drawn at 0800 and hourly thereafter through 1200 noon for measurement of plasma homovanillic acid (HVA). Total four-hour urine collections were obtained for measurement of urinary HVA. Subjects received five experimental conditions, in randomized sequence: no intervention, smoking one cigarette per hour, drinking one caffeinated cola per hour, lorazepam 2 mg IV push, or a high monoamine meal. Baseline (0800) plasma HVA measures showed only minor intrinsic variability. The average standard deviation in baseline plasma HVA over five occasions of measurement was low relative to the changes in HVA produced during treatment with antipsychotic medications. The high monoamine meal significantly elevated plasma HVA, with a similar trend for urinary HVA. Neither caffeine, nicotine, nor lorazepam significantly affected plasma or urinary HVA.

Postmortem distribution and redistribution of nitrobenzodiazepines in man.

The distribution of the nitrobenzodiazepines, flunitrazepam, clonazepam and nitrazepam, and their respective 7-amino metabolites were examined in blood, serum, vitreous humor, liver, bile and urine of decedents taking these drugs. Peripheral blood, serum and liver concentrations were not significantly different to each other. However, vitreous concentrations were one-third of blood, while bile concentrations were 5-12 fold higher. Blood, serum and vitreous contained predominantly the 7-amino metabolite, liver contained only the metabolite, while bile contained significant concentrations of both the parent drug and the 7-amino metabolite. Urine contained only small concentrations of parent drug, however, as expected a number of metabolites were detected. Redistribution studies compared the drug concentrations of femoral blood, taken at body admission to the mortuary, with femoral blood taken at autopsy approximately 39 h later in 48 cases. The concentrations of 7-amino metabolites were not significantly different, however the concentrations of parent nitrobenzodiazepines were significantly higher in the admission specimens. In 6 cases in which subclavian blood was taken, the concentrations were not significantly different to the concentrations in admission blood. Similar findings were observed when femoral and subclavian blood concentrations were compared in 6 cases. There was also no apparent difference in total blood concentrations of nitrobenzodiazepines when blood concentrations taken in hospital shortly prior to death were compared to postmortem blood. Postmortem diffusion into peripheral blood is therefore not a confounding factor in the interpretation of nitrobenzodiazepine concentrations.

Prolonged excretion of 7-aminoclonazepam in urine after repeated ingestion of clonazepam: a case report.

Urinary analyses of the metabolite 7-aminoclonazepam (7-AC) can be helpful in monitoring drug abuse and in the context of suspected drug-facilitated sexual assaults (DFSA). Only two studies have reported detection times of 7-AC in urine after a single dose of clonazepam, and no previous studies have reported detection times after repeated ingestions of clonazepam. This report describes along detection time of 7-AC in urine in the case of a 28-year-old woman with a two year history of daily drug abuse of heroin and clonazepam, who was admitted to a detoxification unit. Urinary samples were delivered every morning for 9 days. Screening analysis in urine was performed by immunoassay, and confirmation analysis by LC-MS/MS. 7-AC was detected for 9 days, and the concentration at day 9 was still high (97 ng/ml), compared to previously reported data. These results indicate that after repeated ingestions of clonazepam, 7-AC can possibly be detected for about 2-3 weeks after cessation, applying cut-off levels commonly used in drug testing programs and DFSA cases.

Comparison of clonazepam compliance by measurement of urinary concentration by immunoassay and LC-MS/MS in pain management population.

BACKGROUND: Physicians determine patient compliance with their medications by use of urine drug testing. It is known that measurement of benzodiazepines is limited by immunoassay specificity and cutoff limits and therefore does not offer physicians an accurate picture of their patients' compliance with these medications. A few studies have used lower cutoffs to demonstrate patient compliance. OBJECTIVES: To define more appropriate cutoffs for compliance monitoring of patients prescribed clonazepam as determined using immunoassay and liquid chromatography-tandem mass spectrometry (LC-MS/MS). STUDY DESIGN: A diagnostic accuracy study of the urinary excretion of clonazepam. METHODS: Millennium Laboratories performed measurements on the urinary excretion of pain patients prescribed clonazepam as the indicator test. This benzodiazepine was chosen because it forms one major metabolite, 7-aminoclonazepam which is specific for that drug. Patients whose only benzodiazepine medication was clonazepam were selected as the test population. The Millennium Laboratories test database was filtered first to select patients on clonazepam, then a second filter was used to eliminate patients with any other listed benzodiazepine medications. Samples were tested using the Microgenics DRI benzodiazepine assay with a 200 ng/mL cutoff. The same samples were quantitatively assessed for 7-aminoclonazepam by LC-MS/MS with a cutoff of 40 ng/mL. The results from the immunoassay were scored as positive or negative while the quantitative results from the LC-MS/MS were also scored as positive or negative depending upon their concentration. RESULTS: Samples from 180 patients met these medication criteria. The positivity rates were 21% (38 samples) by immunoassay. The positivity rate was 70% (126 samples) if the LC-MS/MS cutoff was set at 200 ng/mL. However, the positivity rate was 87% (157 samples) if the LC-MS/MS was set at 40 ng/mL. Concentration distributions revealed a significant fraction (7%) in the 40 - 100 ng/mL range. LIMITATIONS: A limitation of the study was the inability to measure lower than 40 ng/mL. There may be another fraction of the population that was positive below the cutoff value. CONCLUSIONS: The difference in positivity rate between the immunoassay and the LC-MS/MS result showed that the nominal 200 ng/mL cutoff of the immunoassay did not apply to 7-aminoclonazepam. This low immunoassay positivity rate is inconsistent with the manufacturer's published cross reactivity data for clonazepam and 7-aminoclonazepam. These data illustrate the limitations of using a 200 ng/mL cutoff to monitor clonazepam compliance and suggest that a cutoff of 40 ng/mL or less is needed to reliably monitor use of this drug.