Forensic toxicology findings in deaths involving gamma-hydroxybutyrate

Concentrations of the illicit drug gamma-hydroxybutyrate (GHB) were determined in femoral venous blood and urine obtained at autopsy in a series of GHB-related deaths (N = 49). The analysis of GHB was done by gas chromatography after conversion to gamma-butyrolactone and quantitation of the latter with a flame ionization detector. The cutoff concentration of GHB in femoral blood or urine for reporting positive results was 30 mg/L. The deceased were mainly young men (86%) aged 26.5 +/- 7.2 years (mean +/- SD), and the women (14%) were about 5 years younger at 21.4 +/- 5.0 years. The mean, median, and highest concentrations of GHB in femoral blood (N = 37) were 294, 190, and 2,200 mg/L, respectively. The mean urine-to-blood ratio of GHB was 8.8, and the median was 5.2 (N = 28). In 12 cases, the concentrations of GHB in blood were negative (<30 mg/L) when the urine contained 350 mg/L on average (range 31-1,100 mg/L). Considerable poly-drug use was evident in these GHB-related deaths: ethanol (18 cases), amphetamine (12 cases), and various prescription medications (benzodizepines, opiates, and antidepressants) in other cases. Interpreting the concentrations of GHB in postmortem blood is complicated because of concomitant use of other psychoactive substances, variable degree of tolerance to centrally acting drugs, and the lack of reliable information about survival time after use of the drug.

Itraconazole, a potent inhibitor of P-glycoprotein, moderately increases plasma concentrations of oral morphine

BACKGROUND

Individual variation in opioid response is considerable, partly due to pharmacokinetic factors. Transporter proteins are becoming increasingly interesting also in the pharmacokinetics of opioids. The efflux transporter P-glycoprotein can affect gastrointestinal absorption and tissue distribution, particularly brain access of many opioids. The aim of this study was to evaluate whether itraconazole, which is a potent inhibitor of P-glycoprotein and CYP3A4, would change the pharmacokinetics or the pharmacodynamics of oral morphine.

METHODS

Twelve healthy male volunteers ingested, in a randomized crossover study, once daily 200 mg itraconazole or placebo for 4 days. On day 4, 1 h after the last pre-treatment dose, the subjects ingested 0.3 mg/kg morphine. Blood samples for the determination of plasma morphine, morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G) and itraconazole concentrations were drawn up to 48 h after morphine ingestion. Pharmacodynamic effects were evaluated using a questionnaire, visual analogue scales, a reaction time test, the Digit Symbol Substitution Test and the Critical Flicker Fusion Test.

RESULTS

Itraconazole increased the mean area under the plasma concentration-time curve [AUC (0-9)] of morphine by 29% (P=0.002), its AUC (0-48) by 22% (P=0.013) and its peak plasma concentration by 28% (P=0.035). Itraconazole did not significantly affect the pharmacokinetic variables of M3G or M6G or the pharmacodynamic effects of morphine.

CONCLUSIONS

Itraconazole moderately increases plasma concentrations of oral morphine, probably by enhancing its absorption by inhibiting intestinal wall P-glycoprotein. A possible improvement of morphine penetration to the brain could not be observed.

Pain management in chronic kidney disease: the pharmacokinetics and pharmacodynamics of hydromorphone and hydromorphone-3-glucuronide in hemodialysis patients

OBJECTIVE

To describe the pharmacokinetics of hydromorphone (HM) and its primary metabolite hydromorphone-3-glucuronide (H3G) both on and off dialysis in relation to the pharmacodynamic measurements of pain.

DESIGN

Prospective, open-label, observational study.

SETTING

Canadian, university-based renal program.

PARTICIPANTS

Twelve anuric hemodialysis patients with chronic pain, established on immediate-release HM.

MAIN OUTCOME MEASURES

HM and H3G plasma concentrations were measured during and between hemodialysis treatments using a reverse-phase high-performance liquid chromatography assay with liquid chromatography/mass spectrometer/mass spectrometer detection. The McGill Pain Questionnaire (MPQ) and a Visual Analogue Scale (VAS) were used to measure pain. Noncompartmental analyses were conducted. Adverse effects were recorded.

RESULTS

HM did not substantially accumulate (accumulation factor R = 2.7 (1.6)), most likely due to the rapid conversion to H3G. Conversely, H3G accumulated between dialysis treatments (R = 12.5 (12.1)) but appeared to be effectively removed during hemodialysis (1.8 (0.7), p = 0.03). HM resulted in > 65 percent reduction in pain over dosing intervals. Mean MPQ pain scores decreased from 39.8 (18.2) to 12.3 (16.2) on dialysis and from 35.0 (18.5) to 15.5 (13.6) between dialysis treatments. Mean VAS pain scores decreased from 7.5 (2.5) to 3.0 (1.5) on dialysis and from 5.9 (3.2) to 4.4 (1.6) between dialysis treatments. No clinically significant opioid toxicity was observed. The accumulation of H3G between hemodialysis treatments was associated with greater sensory-type pain (r = 0.76, p < 0.0001) and reduced duration of analgesia.

CONCLUSIONS

HM may be a safe and effective opioid for use in selected hemodialysis patients.

[The development and application of an immunoenzyme assay kit for the detection of compounds of the opiate family in human biological liquids]

Monoclonal antimorphine antibodies both free and conjugated with horse- radish peroxidase have been raised and used to develop an assay kit for the detection of narcotic opiate-based drugs by an immuno-enzyme assay (IEA). The kit contains all ingredients necessary for the enzymatic reaction. A total of 215 urine and blood samples were analysed using the new kit. The results were compared with the data obtained by thin layer chromatography and high-performance liquid chromatography. False negative results were absent while false positive (inconclusive) results were recorded in three cases, probably due to the fact that sensitivity of IEA is higher than that of control methods. It is concluded that the kit may be used in laboratory screening studies for detecting opiates in biological fluids.

P-glycoprotein mediates brain-to-blood efflux transport of buprenorphine across the blood–brain barrier

The involvement of P-glycoprotein (P-gp) in buprenorphine (BNP) transport at the blood-brain barrier (BBB) in rats was investigated in vivo by means of both the brain uptake index technique and the brain efflux index technique. P-gp inhibitors, such as cyclosporin A, quinidine and verapamil, enhanced the apparent brain uptake of [3H]BNP by 1.5-fold. The increment of the BNP uptake by the brain suggests the involvement of a P-gp efflux mechanism of BNP transport at the BBB. [3H]BNP was eliminated with an apparent elimination half-life of 27.5 min after microinjection into the parietal cortex area 2 regions of the rat brain. The apparent efflux clearance of [3H]BNP across the BBB was 0.154 ml/min/g brain, which was calculated from the elimination rate constant (2.52 x 10- 2 min- 1) and the distribution volume in the brain (6.11 ml/g brain). The efflux transport of [3H]BNP was inhibited by range from 32 to 64% in the presence of P-gp inhibitors. The present results suggest that BNP is transported from the brain across the BBB via a P-gp-mediated efflux transport system, at least in part.

Determining plasma morphine levels using GC-MS after solid phase extraction to monitor drug levels in the postoperative period

OBJECTIVE

To implement a selective and sensitive analytical method to quantify morphine in small volumes of plasma by gas-liquid chromatography-mass spectrometry (GC-MS), aimed at post-operatively monitoring the drug.

METHOD

A gas-liquid chromatographic method with mass detection has been developed to determine morphine concentration in plasma after solid phase extraction. Morphine-d3 was used as an internal standard. Only 0.5 mL of plasma is required for the drug solid-phase extraction in the Bond Elut-Certify, followed by the quantification of morphine derivative by GC-MS using a linear temperature program, a capillary fused silica column, and helium as the carrier and make-up gas. The method was applied to determine morphine content in plasma samples of four patients during the postoperative period of cardiac surgery. Patient-controlled analgesia with morphine was performed by a venous catheter, and a series of venous blood samples were collected. After the oro-After the orotracheal extubation, morphine plasma levels were monitored for up to 36 hours.

RESULTS

The run time was 16 minutes because morphine and the internal standard were eluted after 8.8 minutes. The GC-MS method had 0.5 -1000 ng/mL linearity range (r(2)=0.9995), 0.1 ng/mL limit of detection, intraday and interday precision equivalent to 1.9% and 6.8%, and 0.1% and 0.8% systematic error (intraday and interday, respectively). The analytical method showed optimal absolute (98%) and relative (100.7%) recoveries. Morphine dose requirements and plasma levels are discussed.

CONCLUSION

The analytical gas-liquid chromatography-mass spectrometry method is selective and adequate for morphine measurements in plasma for applications in clinical studies.

[Importance of the formulation for a chronopharmacologically optimised way of pain therapy. Results of a comparative bioavailability study of tramadol extended-release capsules after single-dose evening versus morning administration]

Objective of this study was to investigate the rate and extent of tramadol bioavailability following evening versus morning administration.

METHODS

The study was performed following an open, randomised, cross-over study-design. 18 male and female volunteers were enrolled into the study and treated with 200 mg tramadol extended-release capsules (T-long), which were to be taken either in the morning or in the evening.

RESULTS

Plasma concentration versus time profiles obtained after morning and evening administration were almost superimposable for both, tramadol and its active metabolite. Maximum exposure of tramadol and O-desmethyltramadol (geometric means of c(max)-values) as well as extent of exposure (geometric means of AUC(0-48)-values) were comparable after morning and eveningadministration.

CONCLUSIONS

Time-point of administration does not have any relevant impact on the rate and extent of absorption in the investigated dosage form. Thus, time-point of administration may be adjusted to the patient's need in a chronopharmacologically optimised way for pain therapy.

[Chemical-toxicological analysis of butorphanol]

The conditions of butorphanol isolation from biological fluids were studied. The method of its extraction with the mix of organic solvents by pH 12 was proposed. How to identify butorphanol with the methods of thin-layer chromatography, ultraviolet spectrometry, high-performance liquid chromatography, gas chromatography with a detector of electron capture, chromato-mass spectrometry was developed. Possibility of use ultraviolet spectrometry for quantitative assessment of butorphanol was shown.

Pharmacokinetics of buccal mucosal administration of fentanyl in a carboxymethylcellulose gel compared with IV administration in dogs

The pharmacokinetics of fentanyl administrated IV (0.01 mg/kg) and in a carboxymethylcellulose gel (0.05 mg/kg) applied to the buccal mucosa of six healthy adult medium- to large-breed dogs was evaluated. At 5 minutes after transmucosal (TM) administration, serum fentanyl levels above the therapeutic target (0.95 ng/ml) were achieved in all dogs. Except for the longer duration of serum fentanyl concentrations above the therapeutic target associated with TM administration, no significant pharmacokinetic differences were found between IV and TM fentanyl. TM fentanyl may be considered a noninvasive alternative to IV administration with rapid achievement of serum fentanyl concentrations.

Pharmacokinetics of buprenorphine following intravenous and oral transmucosal administration in dogs

Pharmacokinetic analysis of buprenorphine administered to six healthy dogs via the oral transmucosal (OTM) route at doses of 20 and 120 microg/kg was conducted using liquid chromatography-electrospray ionization-tandem mass spectroscopy (LC-ESI-MS/MS). Bioavailability was 38% plus or minus 12% for the 20 microg/kg dose and 47%+/-16% for the 120 microg/kg dose. Maximum plasma concentrations were similar for buprenorphine doses of 20 microg/kg IV and 120 microg/kg OTM. Sedation and salivation were common side effects, but no bradycardia, apnea, or cardiorespiratory depressive effects were seen. When the two OTM dosing rates were normalized to dose, LC-ESI-MS/MS analysis of buprenorphine and its metabolites detected no significant difference (P>.05), indicating dose proportionality. The results of this study suggest that OTM buprenorphine may be an alternative for pain management in dogs.

Fatal unintentional intoxications with tramadol during 1995–2005

Tramadol is an extensively used centrally acting analgesic and is considered a safe drug devoid of many serious adverse effects of traditional opioids. However, recently, toxicity and an abuse potential of tramadol have been reported. This study examined fatal unintentional tramadol intoxications among Swedish forensic autopsy cases between 1995 and 2005. All fatal intoxications were selected, in which toxic concentrations of tramadol (>1 microg/g femoral blood) had been detected, and where the forensic pathologist considered the intoxication unintentional and the fatal outcome at least partly explained by tramadol. Toxicology analyses, police reports, autopsy protocols and medical records were scrutinized. A total of 17 cases (eleven men and six women) of fatal unintentional tramadol intoxications were identified. For these cases the median age was 44 years (range 18-78 years) and the median tramadol concentration was 2.0 microg/g (range 1.1-12.0 microg/g). Other pharmaceutical substances, illicit drugs or ethanol were detected in addition to tramadol in all of these cases. In fact, intoxication with multiple drugs was considered the cause of death in 10 (59%) cases. However, in seven cases tramadol was the only substance present in toxic concentrations. A history of substance abuse was identified in 14 (82%) subjects and a present tramadol abuse in 8 (47%). These results suggest that fatal intoxications with tramadol may occur unintentionally and that subjects with a history of substance abuse may be at certain risk. Precaution is therefore warranted when prescribing tramadol in such patients.

Lack of influence of CYP2D6 genotype on the clearance of (R)-, (S)- and racemic-methadone

OBJECTIVE

To investigate the influence of CYP2D6 genotype on the oral clearance of (R)-, (S)- and rac-methadone.

METHODS

In this retrospective study, CYP2D6 genotypes were identified in 56 methadone maintained subjects. Plasma concentrations of (R)-, (S)- and rac-methadone were determined by stereoselective HPLC and sufficient data were available to estimate the apparent oral clearances of (R)-, (S)- and rac-methadone using a population kinetic model in 37 of the genotyped subjects.

RESULTS

The CYP2D6 allele frequencies were similar to those previously reported in Caucasians, the most common being: CYP2D6*1 (35.2%), CYP2D6*2 (12.0%) and CYP2D6*4 (22.2%). Three unknown SNPs were found in four subjects: 1811G > A (n = 1), 1834C > T (n = 1) and 2720G > C (n = 2). The oral clearances of (R)-, (S)- and rac-methadone varied 5.4-, 6.8- and 6.1-fold, respectively. No significant differences in methadone oral clearance were found between CYP2D6 genotypic PM, IM and EM (p = 0.57, 0.40 and 0.43 for (R)-, (S)- and rac-methadone, respectively). Only 1 subject had duplication of functional CYP2D6 alleles and the oral clearance of the three analytes was not markedly altered.

CONCLUSIONS

CYP2D6 poor, intermediate and extensive metabolizer genotypes did not appear to impact on the oral clearance of (R)-, (S)- or rac-methadone. In addition, methadone dosage requirements were not influenced by CYP2D6 genotypes in these subjects. However, the impact of duplication of functional CYP2D6 alleles on oral clearance and dosage requirements requires further investigation.

[Pharmacokinetic simulations of remifentanil]

Remifentanil has short half-lives: the values of alpha and beta decay are about 2 and 15 min, respectively. Therefore, the time for remifentanil concentration to reach its steady state concentration (Css) is shorter than those of other anesthetic drugs such as propofol and fentanyl. The Css and the time course of plasma concentration as well as effect-site concentration (Ce) during the continuous infusion of remifentanil could be helpful in our clinical practice. Css is strongly affected by weight and age with Minto's pharmacokinetic parameters of remifentanil. Css increases by a factor of 1.8 when the weight doubles, and Css in a 75-year-old is 1.5 times higher than Css in a 25-year-old. We tried to simulate the time courses of remifentanil Ce and fentanyl Ce during induction, maintenance, and emergence phases of anesthesia. Because of the short half-lives, remifentanil concentration could be well-controlled. However, remifentanil concentration does not reach the Css immediately with constant rate infusion. For example, it will take about 5 min for remifentanil effect-site concentration to decrease from Css to a half of Css. It is considered that anesthetic management with remifentanil is superior to that without it.

Oxycodone as a component of multimodal analgesia for lactating mothers after Caesarean section: relationships between maternal plasma, breast milk and neonatal plasma levels

BACKGROUND

Oxycodone has become popular for post-Caesarean section (CS) analgesia yet it is not currently recommended for use in breast-feeding mothers because of limited information on its excretion into breast milk.

AIM

To investigate the relationship between maternal ingestion of oxycodone after CS and the resultant maternal plasma, breast milk and neonatal plasma drug levels up to 72-h post-partum.

METHODS

Fifty breast-feeding mothers taking oxycodone had blood and breast milk samples analysed for oxycodone levels at 24 h intervals after CS. Forty-one neonates had blood samples taken at 48 h.

RESULTS

Oxycodone was detected in the milk of mothers who had taken any dose in a 24-h period, with significant correlation between maternal plasma and milk levels (R(2) = 0.81). The median milk:plasma (M:P) ratio for the same period was 3.2:1. Over the subsequent 48 h, the relationship between plasma and milk levels was less strong (R(2) = 0.59) and there was a larger range of M:P levels with evidence of persistence of oxycodone in the breast milk of some mothers. Oxycodone levels up to 168 ng/mL were detected in breast milk (20% > 100 ng/mL). Oxycodone was detected in the plasma of one infant.

CONCLUSIONS

Oxycodone is concentrated in human breast milk up to 72-h post-partum. Breastfed infants may receive > 10% of a therapeutic infant dose. However, maternal oxycodone intake up to 72-h post-CS poses only minimal risk to the breast-feeding infant as low volumes of breast milk are ingested during this period.

Fatal intoxication due to tramadol alone: case report and review of the literature

Poisoning may also lead to both coma and multiple organ failure, also in youngsters without a known major medical history. As not all toxic agents are routinely screened when a poisoning is suspected, it is useful to consider less frequently encountered poisons in certain cases. We describe the occurrence of asystole and multiple organ failure which occurred in a young man after a suspected tramadol overdose. The tramadol concentration on admission in the ICU was indeed 8 microg/ml (mg/l), far above the therapeutic range. Subsequently, the patient developed severe acute liver failure, finally leading to death. Post-mortem toxicology did not reveal any other poison responsible for this unfavourable course as only very high serum and tissue tramadol and desmethyltramadol concentrations were found. Only a few fatal poisonings attributable to tramadol alone, as observed in our case, have been reported. An overview of these cases is presented.

Population pharmacokinetics of buprenorphine following a two-stage intravenous infusion in healthy volunteers

OBJECTIVE

The aim of this investigation was to characterize the pharmacokinetics of buprenorphine following administration of an intravenous (i.v.) infusion. To date, the population kinetics of buprenorphine has been described for bolus administration only.

METHODS

Twenty-three healthy male volunteers aged 21-40 years received 0.6 mg buprenorphine by means of an i.v. infusion over a 150-min period. The plasma concentration-time profiles up to 24 h post-administration of the infusion were subjected to population pharmacokinetic modelling using NONMEM: software.

RESULTS

A three-compartment model best described the plasma concentration-time course. Body weight was found to be a significant covariate for elimination clearance in a linear fashion. Inter-individual variability (coefficient of variation) was estimable for apparent clearance (CL, 23.5%), central distribution volume (V(1), 81.8%), peripheral distribution volume 1 (V(2), 23.7%) and inter-compartmental clearances between V(1) and V(2) (Q(2), 34.8%). Models using parameters derived from previous published data obtained after an i.v. bolus of buprenorphine were found to overestimate the measured buprenorphine concentrations during the course of the i.v. infusion and to underpredict those following the end of the infusion.

CONCLUSION

Most parameters describing the disposition of buprenorphine in the volunteers showed only moderate inter-subject variability. However, the parameters differed from those previously reported for i.v. bolus administration. We conclude that pharmacokinetic parameter estimates obtained from the appropriate study in accordance to the mode of administration should be used in the design of dose regimens of buprenorphine.

[Pharmacokinetics of controlled-release oxycodone in patients with cancer pain]

Oxycodone is a useful analgesic for cancer patients in pain. However, its pharmacokinetics have not been sufficiently examined and there is a lack of information, with very few reports on pharmacokinetics concerning the absorption process in particular. With this in mind, we studied the pharmacokinetics of controlled-release oxycodone (Oxy contin). We measured its serum concentration in patients with cancer pain, and calculated parameters derived using the nonlinear least-squared method program (MULTI). In the result, pharmacokinetic parameters calculated at CL/F were: 45.6+/-22.0 L/hr (Mean+/-SD), Vd/F: 473.0+/-19 6.7 L, t(1/2): 7.2+/- 6.2 hr, kel: 0.103+/-0.034, kal: 1.082+/-0.604, Lag time: 0.9 9+/-0.40 hr. In addition, the serum oxycodone concentration hardly rose until 1 hour after and just before medication, whereupon a rapid increase was evident after 1 hour. The pharmacokinetics of controlled-release oxycodone in patients with cancer pain were clarified in this study. Especially during the absorption process, the lag time was calculated specifically at about 1 hour, making it approximately equal to MS contin.

Method for Quantification of Opioids and their Metabolites in Autopsy Blood by Liquid Chromatography-Tandem Mass Spectrometry

A method using liquid chromatography-electrospray ionization-tandem mass spectrometry was developed and validated for the determination of morphine, codeine, hydromorphone, dihydrocodeine, oxycodone, buprenorphine, and naloxone with their metabolites morphine-3-glucuronide, morphine-6-glucuronide, normorphine, 6-acetylmorphine, 6-acetylcodeine, codeine-6-glucuronide, norcodeine, hydromorphine-3-glucuronide, dihydrocodeine-6-glucuronide, dihydromorphine, dihydromorphine-3-glucuronide, dihydromorphine-6-glucuronide, oxymorphone, norbuprenorphine, buprenorphine-3-glucuronide, norbuprenorphine-3-glucuronide, and naloxone-3-glucuronide in human whole blood. Polar metabolites (glucuronides) and other analytes were extracted by SPE using Bond Elut C18. Chromatographic separation was performed on a Phenomenex Synergi reversed-phase column with gradient elution based on a mobile phase consisting of 10mM ammonium formate adjusted to pH 3 and acetonitrile. Intraday and interday precision for all analytes were between 0.6% and 13.8%, and recoveries were between 80.3% and 101.4%. Calibration curves were linear for all analytes over the concentration range 5-400 ng/mL, and correlation coefficients (R(2)) were better than 0.999. Limits of detection and quantitation were 0.16-1.2 ng/mL and 0.5-4.09 ng/mL, respectively. The method described consolidates previous work on opioids and their metabolites published in the literature and is the first to include the detection of naloxone-3-glucuronide. The method has been applied in routine postmortem cases after opiate overdose with the threefold purpose of providing interpretive information on the cause and type of death (rapid, sub-acute, or delayed death) and to distinguish heroin, morphine, and codeine users.

Evaluation of the Clearance of a Sublingual Buprenorphine Spray in the Beagle Dog Using Gamma Scintigraphy

PURPOSE

The aim of this study was to evaluate clearance from the buccal cavity and pharmacokinetic profiles of a sublingual spray formulation in the dog, to assist in interpretation of future pharmacokinetic studies.

METHODS

Radiolabelled buprenorphine in a spray formulation (400 microg/100 microl in 30% ethanol) was administered sublingually to four beagle dogs, and the residence in the oral cavity was determined using gamma scintigraphy. Pharmacokinetic sampling was performed to facilitate correlation of location of dose with significant pharmacokinetic events.

RESULTS

Scintigraphic imaging revealed that clearance of the formulation from the oral cavity was rapid, with a mean T 50% clearance of 0.86 +/- 0.46 min, and T 80% clearance of 2.75 +/- 1.52 min. In comparison, absorption of buprenorphine was relatively slow, with a T max of 0.56 +/- 0.13 h. Good buccal absorption despite short residence time can be explained by lipophilicity of buprenorphine enabling rapid sequestration into the oral mucosa, prior to diffusion and absorption directly into systemic circulation.

CONCLUSION

This study demonstrated rapid clearance of a sublingual solution from the canine oral cavity, with T 50% similar to results previously reported in man, providing initial confidence in using a conscious dog model to achieve representative residence times for a sublingual solution.

Improved liquid chromatographic method for the simultaneous determination of tramadol and its three main metabolites in human plasma, urine and saliva

Tramadol, an analgesic agent, and its main metabolites O-desmethyltramadol (M1), N-desmethyltramadol (M2) and O,N-didesmethyltramadol (M5) were determined simultaneously in human plasma, saliva and urine by a rapid and specific HPLC method. The sample preparation was a simple, one-step, extraction with ethyl acetate. Chromatographic separation was achieved with a Chromolith Performance RP-18e 100 mm x 4.6 mm column, using a mixture of methanol:water (19:81, v/v) adjusted to pH 2.5 by phosphoric acid, in an isocratic mode at flow rate of 2 ml/min. Fluorescence detection (lambda(ex) 200 nm/lambda(em) 301 nm) was used. The calibration curves were linear (r(2)>0.996) in the concentration ranges in plasma, saliva and urine. The lower limit of quantification was 2.5 ng/ml for all compounds. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were acceptable in all analyzed body fluids The developed procedure was applied to assess the pharmacokinetics of tramadol and its main metabolites following administration of 100mg single oral dose of tramadol to healthy volunteers.

Quantification of Drugs in Plasma Without Primary Reference Standards by Liquid Chromatography-Chemiluminescence Nitrogen Detection: Application to Tramadol Metabolite Ratios

Lack of availability of reference standards for drug metabolites, newly released drugs, and illicit drugs hinders the analysis of these substances in biologic samples. To counter this problem, an approach is presented here for quantitative drug analysis in plasma without primary reference standards by liquid chromatography-chemiluminescence nitrogen detection (LC-CLND). To demonstrate the feasibility of the method, metabolic ratios of the opioid drug tramadol were determined in the setting of a pharmacogenetic study. Four volunteers were given a single 100-mg oral dose of tramadol, and a blood sample was collected from each subject 1 hour later. Tramadol, O-desmethyltramadol, and nortramadol were determined in plasma by LC-CLND without reference standards and by a gas chromatography-mass spectrometry reference method. In contrast to previous CLND studies lacking an extraction step, a liquid-liquid extraction system was created for 5-mL plasma samples using n-butyl chloride-isopropyl alcohol (98 + 2) at pH 10. Extraction recovery estimation was based on model compounds chosen according to their similar physicochemical characteristics (retention time, pKa, logD). Instrument calibration was performed with a single secondary standard (caffeine) using the equimolar response of the detector to nitrogen. The mean differences between the results of the LC-CLND and gas chromatography-mass spectrometry methods for tramadol, O-desmethyltramadol, and nortramadol were 8%, 32%, and 19%, respectively. The sensitivity of LC-CLND was sufficient for therapeutic concentrations of tramadol and metabolites. A good correlation was obtained between genotype, expressed by the number of functional genes, and the plasma metabolite ratios. This experiment suggests that a recovery-corrected LC-CLND analysis produces sufficiently accurate results to be useful in a clinical context, particularly in instances in which reference standards are not readily accessible.