CYP2C19 genetics in fatal carisoprodol intoxications.

INTRODUCTION: Carisoprodol, a frequently used muscle relaxant, can cause potentially fatal intoxications. Conversion to its active metabolite meprobamate is almost solely mediated by cytochrome P450 2C19 (CYP2C19), and mutations in this enzyme could have significant effects on serum concentrations. The objective of this study was to investigate the role of CYP2C19 genetics in mortalities due to carisoprodol intoxication. METHODS: The frequencies of CYP2C19 variant alleles were compared between the study group (n = 75) and two control groups, i.e. (1) deaths where carisoprodol was detected in the blood of the deceased, but intoxication was not the cause of death (control group A, n = 38), and (2) a healthy population not using carisoprodol (control group B, n = 185). In the study group and control A, the concentrations of carisoprodol and meprobamate were compared between the different genotype subgroups. RESULTS: The variant allele frequencies of CYP2C19 did not differ significantly between the study group and control groups. Moreover, no statistically significant difference in the concentrations of carisoprodol and meprobamate between the different genotype subgroups was found. CONCLUSIONS: This study finds no evidence for an important association between CYP2C19 genetics and mortality risk of carisoprodol. Other factors, such as co-administration with other drugs, likely play a more important role.

Quantitative analysis of carisoprodol and meprobamate in whole blood using benzylcarbamate and deuterated meprobamate as internal standards.

Carisoprodol and meprobamate are frequently encountered drugs in impaired driving casework. Deuterated internal standards, although preferred, were not available until recently. Earlier published studies report the use of a variety of non-deuterated internal standards, many of which lack the chemical and physical similarities that are desired for quantitative analysis. Carisoprodol and meprobamate were determined in whole blood using solid-phase extraction and gas chromatography-mass spectrometry with benzylcarbamate and meprobamate-d(7) as internal standards. When benzylcarbamate was used as internal standard, the linear ranges for carisoprodol and meprobamate were 0-20 mg/L and 0-40 mg/L, respectively. The linear range increased to 100 mg/L when meprobamate-d(7) was used. Limits of detection for carisoprodol and meprobamate were 0.2 and 0.4 mg/L, respectively, regardless of the internal standard selection. The limit of quantitation for both drugs using either internal standard was 0.4 mg/L. Accuracies using benzylcarbamate and meprobamate-d(7) were 100-106% and 91-100%, respectively. Corresponding values for precision indicated intra-assay coefficients of variation of 2.6-4.3% for benzylcarbamate and 1.0-2.3% for meprobamate-d(7). No carryover was evident at 100 mg/L, the highest concentration tested, and no interferences were observed. Results indicated that either benzylcarbamate or meprobamate-d(7) is a suitable internal standard for quantitative determination of carisoprodol or meprobamate from whole blood.

Impact of Expanding ELISA Screening in DUID Investigations to Include Carisoprodol/Meprobamate and Zolpidem.

In 2013, the National Safety Council's Alcohol Drugs and Impairment Division added zolpidem and carisoprodol and its metabolite meprobamate to the list of Tier 1 drugs that should be tested for in all suspected drug impaired driving and motor vehicle fatality investigations. We describe the validation of an enzyme linked immunosorbent assays (ELISA) for both drugs in whole blood, and the utilization of the ELISA to assess their positivity in a sample of 322 suspected impaired driving cases that was retrospectively screened using the validated assays. The occurrence of carisoprodol/meprobamate was found to be 1.2%, and for zolpidem, 1.6%. In addition, we analyzed a large dataset (n = 1,672) of Driving Under the Influence of Drugs (DUID) test results from a laboratory performing high volume DUID testing to assess the frequency of detection of both drugs after implementing the expanded NSC scope. Carisoprodol or meprobamate were found positive in 5.9% (n = 99) of these samples, while zolpidem was found positive in 5.3% (n = 89) in drivers who in many cases had been found to be negative for other drugs. Carisoprodol and zolpidem are both potent CNS depressants and are appropriate additions to the recommended NSC scope of testing.

A one-step and sensitive GC-MS assay for meprobamate determination in emergency situations.

A rapid, sensitive, and ready-to-use gas chromatography-mass spectrometry method for meprobamate assay using carisoprodol as internal standard is described. The method involves extracting a 0.2-mL sample with chloroform, previously acidified with HCl 0.2N. For the quantitative analysis, we used selected-ion monitoring mode, selecting the ion m/z 144 for quantification of meprobamate and m/z 245 for carisoprodol. Excellent linearity was found between 0 and 200 mg/L plasma. The limit of detection was 0.58 mg/L, and the limit of quantification was 1.93 mg/L. A high reproducibility [intra-assay coefficient of variation (CV) range of 2.3-4.3% and interassay CV range of 5.5-12.3%] and accuracy (intra-assay range of 96.8-112.3% and interassay range of 85.5-99.3%) were observed. Recoveries were concentration-independent (87.0%, 76.2%, and 81.2% for 20, 75 and 150 mg/L, respectively). No interference from endogenous compounds, other metabolites of meprobamate, or frequently coadministered drugs was detected. This sensitive, simple assay for meprobamate in plasma, whole blood, and urine meets the current requirements for bioanalytical assays in overdose cases.

Quantitation of Carisoprodol and Meprobamate in Urine and Plasma Using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

Carisoprodol and meprobamate are centrally acting muscle relaxant/anxiolytic drugs that can exist in a parent-metabolite relationship (carisoprodol → meprobamate) or as a separate pharmaceutical preparation (meprobamate aka Equanil, others). The monitoring of the use of these drugs has both clinical and forensic applications in pain management applications and in overdose situations. LC-MS/MS is used to analyze urine or plasma/serum extracts with deuterated analogs of each analyte as internal standards to ensure accurate quantitation and control for any potential matrix effects. Positive ion electrospray is used to introduce the analytes into the mass spectrometer. Selected reaction monitoring of two product ions for each analyte allows for the calculation of ion ratios which ensures correct identification of each analyte, while a matrix-matched calibration curve is used for quantitation.

Incidence, causes and prognosis of hypotension related to meprobamate poisoning.

OBJECTIVE: Meprobamate self-poisoning has been reported as potentially inducing hypotension. We examined the incidence and causes of hypotension induced by this poisoning and its prognosis. DESIGN AND SETTING: Retrospective observational study conducted in a medical ICU between June 1997 and October 2003. Seventy-four patients admitted for meprobamate poisoning and needing mechanical ventilation were included. Demographic, clinical, and laboratory data were compared between patients with and without hypotension. All echocardiograms recorded in patients with hypotension were reviewed, and left ventricular (LV) and right ventricular (RV) functions were assessed. RESULTS: Twenty-nine (40%) patients exhibited hypotension without any significant difference in age, gender, cardiac history, or meprobamate concentration in blood when compared to patients without hypotension. Base excess was significantly lower in patients with hypotension. Echocardiography demonstrated a hypokinetic state, associating decreased LV ejection fraction (45+/-15%) and cardiac index (2+/-0.7 l min(-1) m(-2)), and increased inferior vena cava diameter. Most patients with hypotension received inotropic drugs by infusion, and were ventilated for significantly longer. CONCLUSIONS: Meprobamate self-poisoning induces hypotension, notably related to cardiac failure, in about 40% of cases. This has important therapeutic consequences, as frequent inotropic drug infusion. The mechanisms of cardiac toxicity remain largely unknown, and no predictive factor could be isolated.

Multidrug toxicity involving sumatriptan.

A multidrug fatality involving sumatriptan is reported. Sumatriptan is a tryptamine derivative that acts at 5-HT(1B/1D) receptors and is used for the treatment of migraines. The decedent was a 21-year-old white female found dead in bed by her spouse. No signs of physical trauma were observed and a large number of prescription medications were discovered at the scene. Toxicological analysis of the central blood revealed sumatriptan at a concentration of 1.03 mg/L. Following therapeutic dosing guidelines, sumatriptan concentrations do not exceed 0.095 mg/L. Sumatriptan was isolated by solid-phase extraction and analyzed using liquid chromatography-tandem mass spectrometry in multiple reaction monitoring mode. A tissue distribution study was completed with the following concentrations measured: 0.61 mg/L in femoral blood, 0.56 mg/L in iliac blood, 5.01 mg/L in urine, 0.51 mg/kg in liver, 3.66 mg/kg in kidney, 0.09 mg/kg in heart, 0.32 mg/kg in spleen, 0.01 mg/kg in brain, 15.99 mg/kg in lung and 78.54 mg/45 mL in the stomach contents. Carisoprodol, meprobamate, fluoxetine, doxylamine, orphenadrine, dextromethorphan and hydroxyzine were also present in the blood at the following concentrations: 3.35, 2.36, 0.63, 0.19, 0.06, 0.55 and 0.16 mg/L. The medical examiner ruled the cause of death as acute mixed drug toxicity and the manner of death as accident.

Association between blood carisoprodol:meprobamate concentration ratios and CYP2C19 genotype in carisoprodol-drugged drivers: decreased metabolic capacity in heterozygous CYP2C19*1/CYP2C19*2 subjects?

Carisoprodol is metabolized to meprobamate by the cytochrome P450 enzyme CYP2C19, encoded by the polymorphic CYP2C19 gene. Most studies on carisoprodol metabolism have been carried out on individuals phenotyped for CYP2C19 activity using the probe drug S-mephenytoin. We aimed to investigate whether the ratio of carisoprodol to meprobamate in a 'real life' setting could be predicted by CYP2C19 genotype or, more specifically, if high carisoprodol : meprobamate ratios in drugged drivers could be ascribed to the presence of mutant CYP2C19 alleles. From original material comprising 358 blood samples from apprehended drivers, two polarized groups were selected; a high-ratio group of 11 subjects where the carisoprodol : meprobamate ratio was >1 and a low-ratio control group of 23 subjects where the ratio was <0.31. Genotyping was carried out for the CYP2C19*2, CYP2C19*3 and CYP2C19*4 alleles. DNA samples from 94 healthy blood donors were used as reference material. The number of mutant alleles in the high-ratio and low-ratio groups was significantly higher and lower, respectively, than in the reference material. The increased number of mutant alleles in the high-ratio group was not due to the presence of many poor metabolizers, but to a high number of heterozygous individuals with the genotype CYP2C19*1/*2. This result indicates a gene dosage effect where the carisoprodol : meprobamate ratio reflects the number of active CYP2C19 alleles. The metabolism of carisoprodol to meprobamate is dependent on CYP2C19 genotype. Heterozygous individuals with the CYP2C19*1/*2 genotype have a reduced capacity for metabolizing carisoprodol, and should probably be regarded as intermediate metabolizers of this drug.

The present status of meprobamate ingestion. A five-year review of cases with serum concentrations and clinical findings.

Fifty-seven cases of meprobamate ingestion from 1974 through 1979 were reviewed. Serum meprobamate concentrations, clinical findings, and epidemiologic data were studied to determine the present status of the abuse of this compound. The average patient was a 37-year-old woman who ingested meprobamate and at least one other drug (usually a benzodiazepine, a barbiturate, ethanol, or an opiate) in a suicide attempt of gesture. She arrived at the hospital either alert or lethargic with equal frequency. Half of the time she was seen only in the emergency room, and half of the time she was hospitalized. She was usually treated with supportive care alone and survived the ingestion. Serum meprobamate concentrations exceeding 12 mg/dl were consistent with coma. Dysarthria, hypotension, tachycardia, and ataxia were the most common physical findings. Meprobamate addiction was present in six patients.

Stimulant and relaxant drugs combined with stimulant and relaxant information: a study of active placebo.

RATIONALE: The active placebo hypothesis states that placebo effects are potentiated when an active drug is administered. OBJECTIVE: This hypothesis was tested in an experiment where information about the effect of a drug was combined with administration of an active drug or placebo. METHODS: Information that a drug acted as a relaxant, a stimulant, or as a placebo was crossed with oral administration of a relaxant drug (700 mg carisoprodol), a stimulant drug (400 mg caffeine) or placebo (lactose) in healthy volunteers ( n=94). Dependent variables were subjective and physiological measures of arousal, as well as serum carisoprodol and caffeine levels. Data were collected from 15 to 280 min after administration of drug or placebo. RESULTS: Caffeine increased alertness, systolic and diastolic blood pressure, startle blink reflexes, and skin conductance responses. Subjects were calmer after carisoprodol, and heart rate was increased. There was a positive correlation between increased arousal and carisoprodol levels when stimulant information had been provided. However, this was only seen when carisoprodol levels were very low. There was no evidence that caffeine modulated the placebo response. CONCLUSIONS: Active placebo responses were seen only transiently when carisoprodol levels were low, and only in the subjective arousal data. Caffeine did not support active placebo responses. The overall findings did not favour the active placebo hypothesis.

A system of screening for the presence of a number of common drugs.

A method is described to provide a rapid screening technique for the presence of barbiturates, glutethimide, carbromal, meprobamate, salicylate, phenothiazine derivatives, bromide, carbon monoxide, and alcohol. Phenothiazines are detected by a spot urine test. The first four drugs are identified, within 60 minutes of blood collection, on thin-layer chromatoplates of microscope slide dimensions. The estimations of bromide, salicylate, carbon monoxide, and of alcohol levels are started in that period so the overall time for the screening is less than two hours, and the amount of blood required is only 10 ml.

Impairment due to intake of carisoprodol.

BACKGROUND: Carisoprodol is a centrally acting muscle relaxant commonly used for lower back pain. It is a drug of abuse and has been detected among impaired drivers. Carisoprodol's active metabolite meprobamate is thought to act through the GABA(A) receptor complex and produces a well-known impairing effect. It is unclear whether therapeutic intake of carisoprodol leads to impairment, and the effect of supratherapeutic doses has not been investigated. Possible impairment could further be a product of the parent drug and/or the metabolite meprobamate. The present study aimed to investigate if carisoprodol had an impairing effect by it self. METHODS: From the database at the Norwegian Institute of Public Health, Division for Forensic Toxicology and Drug Abuse 62 cases containing carisoprodol and meprobamate as only drugs were identified. These cases constituted our material. RESULTS: Impaired drivers (73%) had higher blood carisoprodol concentration than not impaired drivers (27%), but no difference in blood meprobamate concentration was found for all the drivers viewed together. Amongst occasional users of carisoprodol, however, there was difference in blood meprobamate concentration between not impaired and impaired drivers. The risk of being judged impaired rose with increasing blood carisoprodol concentration, but not with increasing blood meprobamate concentration. The clinical effects of carisoprodol as measured by the clinical test for impairment (CTI) resembled those of benzodiazepines with some important differences such as tachycardia, involuntary movements, hand tremor and horizontal gaze nystagmus, which may be specific carisoprodol effects. CONCLUSION: Carisoprodol probably has an impairing effect by itself, at least at blood concentration levels above which can be seen after therapeutic intake of the drug.

Relative bioavailability of meprobamate tablets in humans.

The relative bioavailability of 400-mg meprobamate tablets manufactured by 11 different firms was evaluated in two groups of healthy male subjects. Each group of six subjects received a reference standard product and five test products given at 1-week intervals. Plasma meprobamate concentrations at 1, 2, 3, 4, 6, 8, 10, 24, and 32 hr after dosing were determined using a GLC assay. Analysis of variance of the plasma level--time profiles revealed no statistically significant differences between any of the products in terms of plasma levels at the various sample times, time of peak plasma level, peak plasma level, and area under the plasma level--time curve. It was concluded that the 11 400-mg products could be considered bioequivalent.

Wall-coated open tubular column coupled with nitrogen-selective detector for routine GLC determination of diazepam, meprobamate, phenylbutazone, and thioridazine in serum.

The selectivity and sensitivity provided by a wall-coated open tubular column coupled with a nitrogen-selective detector allowed rapid, accurate determination of diazepam, meprobamate, phenylbutazone, and thioridazine in serum in the same chromatographic system using 100--200 microliters of sample.

Drug interactions: the effects of alcohol and meprobamate applied singly and jointly in human subjects. IV. The concentrations of alcohol and meprobamate in the blood.

The absorption and elimination of alcohol and meprobamate from the blood during Experiments IV (E-IV) and V (E-V) of Carpenter et al. [J. Stud. Alc., Suppl. No. 7, pp. 54-139, 1975] were studied by means of mathematical models representing the relation between doses, concentration in the blood and time elapsing since drug ingestion. The blood concentrations of samples taken 2 and 5.5 hr after beginning to drink in E-IV and 1, 1.5, 2, 2.5, 3.5 and 4.5 hr in E-V were analyzed. The presence of meprobamate did not affect blood alcohol concentration (BAC) in either experiment. At 2 hr the mean BACS after 0.25, 0.50, 0.75 and 1.00 g of alcohol per kg were 6.8, 20.9, 37.7 and 53.7 mg per 100 ml in E-IV; 5.0, 34.1, 42.0 and 72.0 mg per 100 ml in E-V; and 8.1, 32.6, 41.3 and 71.3 mg per 100 ml when calculated by regression from E-V data. The calculated elimination rate of the 2 highest doses of alcohol in E-IV was 6.0 and 7.1 mg per 100 ml per hr; in E-V the mean calculated rates after 0.25-0.75 and after 1.00 g of alcohol per kg were 6.6 and 11.0 mg per 100 ml per hr. The blood meprobamate concentrations (BMC) in E-IV were not affected by alcohol. In E-V, 2.5 and 5.5 hr after meprobamate administration, the combination of 28 mg of meprobamate per kg and 0.75 g of alcohol per kg resulted in significantly lower BMC (7.83 and 12.63 mug per 100 ml) than after same dose of meprobamate with the other doses of alcohol (14.23 and 20.02 mug per 100 ml). The differences between these results and the findings of Carpenter et al. are discussed.

Drug interactions: the effects of alcohol and meprobamate applied singly and jointly in human subjects. II. Five experiments.

Five experiments were conducted to study the effects of alcohol and meprobamate, administered singly and in combination, at doses up to 1.20 g of alcohol per kg of body weight and up to 30 mg of meprobamate per kg. Most of the 158 men were of college age (range, 21-49). In all experiments it appeared to the subjects that both drugs were administered, alcohol as a 25% solution in orange juice and meprobamate as 10 tablets. One hour after the men took the meprobamate they had 1 hr to drink the beverage. Before and at 1/2 hr intervals after administration of the drugs blood samples were taken and behavioral response measured by means of a visual-motor coordination tracking task (Stressalyzer). An experimental session lasted 6 hr. In Experiment I (E-I) each of 12 men was tested on 2 days, after 0, 1.00 or 1.20 g of alcohol per kg and 0 or 25 mg of meprobamate per kg. In Experiment II (E-II) 56 men were tested (8 per group) after 0, 5, 10, 15, 20, 25 or 30 mg of meprobamate per kg and alcohol placebo. In Experiment III (E-III) 40 men were tested (8 per group) after 0, 0.25, 0.50, 0.75, or 1.00 g of alcohol per kg and meprobamate placebo. In Experiment IV (E-IV) 25 men (5 per group) received meprobamate 3 times a day (total daily dosage, 0, 7, 14, 21 or 28 mg per kg) for 12 days. On days 8 to 12 all subjects drank alcohol, as in E-III. In Experiment V (E-V) 25 subjects (5 per group) were tested on 5 days, drinking each day the same doses of alcohol as in E-III and all received the same doses of meprobamate as in E-IV.

Drug interactions: the effects of alcohol and meprobamate applied singly and jointly in human subjects. III. The concentrations of alcohol and meprobamate in the blood and their effects on performance; application of mathematical models.

The relations between the levels of alcohol and meprobamate in the blood and performance on a visual-motor coordination tracking task were analyzed by a general system of mathematical models, using data from Experiment V by Carpenter et al. [J. Stud. Alc., Suppl. No. 7, pp. 54-139, 1975]. The derivation of the models is described. In general, the relationship between blood alcohol concentration (BAC) and performance was nonmonotonic: best performance occurred at BACS of 10 to 20 mg per 100 ml. The relationship between meprobamate concentration (BMC) and performance was monotonic: performance deteriorated with increasing BMC. The results of the reaction latency measure, howevr, showed no consistent relationship with BAC or BMC. The action of alcohol can be represented by a model which involves 2 distinct sites of action; that of meprobamate, 1 site. It could not be determined whether the site of action of meprobamate is distinct from those of alcohol because the blood levels of the drugs were not high enough. The implications of the results are discussed, with particular reference to the quantitative description of the joint action of drugs and the design of future experiments.

Drug interactions: the effect of alcohol and meprobamate applied singly and jointly in human subjects. V. Summary and conclusions.

The design, analysis and conclusions of the series of experiments by Carpenter et al., Ashford and Cobby, and Cobby and Ashford [J. Stud. Alc., Suppl. No. 7, pp. 54-176, 1975] are reviewed. Mathematical models of the joint action of drugs were developed and data obtained to test the models by studying the action of alcohol and meprobamate singly and in combination in human subjects. The data proved to be too limited in the range of drug concentrations in the blood necessary to identify the single most appropriate model. Carpenter et al. analyzed the data by analysis of variance, which involves assumptions about the structure of the observation and the form of the distribution of the error terms. The analyses of Ashford and Cobby and Cobby and Ashford used the mathematical models, which represented pharmacological and physiological actions of the drugs. The majority of the results of the two analyses agreed; however in Experiment V Carpenter et al. combined drugs, doses and blood samples in one analysis anf found a significant influence of meprobamate dose on blood alcohol concentration (BAC) and homogeneous error terms. Cobby and Ashford analyzed absorption and elimination phases of each alcohol dose separately and found no influence of meprobamate on BAC and significant heterogeneity in the residual error terms. Both sets of analyses found a complex interaction between the pattern of abosorption and elimination of meprobamate and dose of alcohol. Carpenter et al. related the results of behavioral measures to drug doses, Ashford and Cobby to the concentrations of the drugs in the blood. Theoretically the models can analyze the pattern of behavioral results at each combination of doses but the data available were insufficient for the purpose. The modifications in experimental design and analytical techniques necessary to continue research in developing mathematical models are discussed.

Use of hemodialysis in meprobamate overdosage.

A case of meprobamate overdosage successfully treated with hemodialysis is described. The patient was admitted 4 hours after an overdosage of meprobamate (30-40 g) deeply unconscious, hypotensive, in respiratory failure and with a serum meprobamate level of 50 mg/100 ml. Hemodialysis was instituted using a Gambro parallel flow dialyzer and a portable re-circulating dialyzate delivery system (Redy, CCi Life Systems). Meprobamate removal with hemodialysis was 672+/-167 mg/hr with a corresponding clearance of 61.97+/-9.9 ml/min. Drug removal with forced diuresis was 177+/-23.4 mg/hr. Metabolic degradation of the drug was approximately 482 mg/hr with a plasma disappearance rate of 5.2%/hr. No drug could be detected in the dialyzate fluid after its passage through the Redy re-circulating dialyzate system. Because of the rapidity of metabolic degradation of meprobamate, we feel that hemodialysis should be reserved for severe clinical intoxication and either compromised normal excretory routes or progressive clinical deterioration.