Serum Pentobarbital Research Articles

Quantitative LC-MS/MS Method for the Simultaneous Measurement of Six Antiepileptics and Pentobarbital in Human Serum.

Antiepileptic drugs (AEDs) are a chemically diverse group of medications that are used to control seizures and different clinical forms of epilepsy. AEDs can be used as single agents but are commonly administered in combination, as a multi-drug regimen. AEDs have narrow therapeutic windows. Therapeutic ranges may not be properly defined, and symptoms of toxic serum concentrations may include increased frequency of seizures, as seen when AED concentrations are subtherapeutic. Pentobarbital, a barbiturate, is a potent anti-seizure medication, but it is also used in the treatment of head injury. Therapeutic drug monitoring (TDM) is required for optimal treatment of epilepsy. The method presented here is designed to measure serum concentrations of six commonly administered antiepileptic drugs (levetiracetam (Keppra), lamotrigine, lacosamide, 10-hydroxycarbazepine (oxcarbazepine metabolite), topiramate, zonisamide) and that of pentobarbital by LC-MS/MS. Liquid-liquid sample extraction is followed by reversed-phase chromatography using biphenyl HPLC column and gradient elution. Two MRM transitions are monitored for each drug, and their heavy isotope labeled internal standards. Six-point calibration curve is generated with each batch of analysis for quantitation of AEDs. The method's AMR covers the clinically relevant concentration range for each AED. The method has <10% CV throughout the AMR, is free of matrix effect commonly found in clinical samples, and is free from cross reactivity by other AEDs.

Pentobarbital suicide attempt in a young pregnant veterinary assistant

We describe a case of pentobarbital (Dolethal®) acute intoxication in a 20 weeks pregnant woman and discuss the intoxication consequences in the mother and in the foetus. We report the case of a 24-year-old pregnant veterinary assistant who attempt to kill herself by ingestion of 9 g of pentobarbital. At the EMS arrival, the patient is in cardio respiratory arrest and an external cardiac massage is undertaken. It permits to restore the cardio respiratory activity without the use of adrenaline or external electrical shock. The patient is then intubated and transferred directly to medical intensive care unit for further management. At the admission, a hypotension and a deep hypothermia at 33.3 °C are observed. The neurological examination also reveals reactive miosis, hypotonia and a Glasgow Coma Scale (GCS) score of 3. A complete blood biological investigation including a screening by LC-MS-MS of pharmaceuticals and drugs of abuse has been performed at the admission. It has been completed by a regular measurement of pentobarbital concentrations by HPLC-DAD in sera samples taken respectively at 3, 11, 30, 50 and 70 ho after the supposed ingestion of pentobarbital. As there are few data in the literature regarding the pentobarbital toxicokinetics in pregnant women, we have conducted a non-compartmental analysis using the PKSolver software to determine the toxicokinetics parameters including elimination half-life (t 1/2 ), total plasma clearance (Cl), volume of distribution (V D ) and area under the curve (AUC). Para clinical exams (an electroencephalogram [EEG]) (on day 1) and multiple foetal ultrasounds (at the admission and on day 2) have also been performed to evaluate the gravity of the intoxication in the mother and in the foetus. At the beginning of her care, the patient shows no alteration of her biological parameters except of hypercapnic acidosis (pH: 7.28, pCO2: 50 mmHg). The toxicological analyses don’t reveal the presence of any drug apart from pentobarbital. The pentobarbital serum concentration measured 3 h after pentobarbital ingestion is very high (68.3 mg/L) and a 6 h continuous veinoveinous haemodiafiltration (CCVHDF) has been quickly set up. The serum pentobarbital concentration measured at the end of the CCVHDF (i.e. 11 h after the pentobarbital ingestion) has been determined at 33.6 mg/L (t 1/2 = 8 h). After the haemodialysis stopping, pentobarbital sera concentrations then slowly decrease and are respectively equal to 28.9, 15.9 and 6.7 mg/L at 30, 50 and 70 h after the overdose (t 1/2 = 19.2 h). The non-compartmental analyse has permit to estimate the pentobarbital toxicokinetics parameters in our pregnant patient. Thus V D , Cl and AUC have been respectively calculated at 126.5 L, 76.7 mL/min and 1782.5 mg/L*h. The decrease in pentobarbital concentrations has been correlated with a progressive improvement of the patient consciousness state (evaluated at the admission by an EEG and by the GCS score and then regularly monitored by the GCS score) and with a recovery of spontaneous foetal movements on day 2. As pentobarbital is exclusively reserved for veterinary use in France, few cases of voluntary acute intoxication have been described in recent years and, to our knowledge, no case has been reported in pregnant woman. In our patient, the initial pentobarbital concentration is very high. The rapid setting up of CVVHDF has allowed the pentobarbital elimination half-life to be divided by 2 and to decrease the intoxication duration. Thus foetal movements, that were absent at admission, have been recovered on day 2. During the end course of the pregnancy, no malformation or any development problem have been observed in the foetus. However, as barbiturates cross the placental barrier and distribute in foetal tissues and especially in the brain, close post-natal monitoring is recommended to evaluate the possible later consequences of this in utero exposure.

Use of Continuous Venovenous Hemodiafiltration to Enhance the Elimination of Serum Pentobarbital before Diagnosis of Brain Death

Continuous venovenous hemodiafiltration (CVVHDF) was used to eliminate pentobarbital from the blood of a 30-year-old potentially brain dead male patient with traumatic intracranial hemorrhage after a motorcycle accident. The Acute Physiology and Chronic Health Evaluation (APACHE) II score of hospital day 1 was 24, but by day 8 it was 36, when the patient was considered to be brain dead. To control seizures and reduce intracranial pressure, pentobarbital had been administered in a continuous flow (2,880 mg/day for 5 days). Coma can be induced by pentobarbital at a serum level of 1∼5 mg/dL. However, drug intoxication should be excluded from a brain death evaluation; therefore, the patient was not given any drug for approximately 88 hrs after ceasing pentobarbital in order for serum level to dip below 0.5 mg/dL (which is the hypnotic level). At 48 hours from CVVHDF, the pentobarbital level was close to the hypnotic level (0.1∼0.5 mg/dL). Before stopping, the serum level of pentobarbital was 3.89 mg/dL and between 48 and 72 hours from CVVHDF, 4 cycles of pentobarbital half-life elimination (0.24 mg/dL) could be measured. Therefore, we suggest that in case of potential brain dead patients who have been administered pentobarbital, CVVHDF can enhance the elimination of pentobarbital from the circulatory system and shorten the waiting time for a brain death evaluation.

Fluoxetine Potentiates Pentobarbital Lethality and Sedation in the Rat

The 5-hydroxytryptamine-transport inhibitor fluoxetine interferes with the hepatic metabolism of many drugs and can potentiate the effects of anaesthetics. Because of the significance of this behaviour and because previous reports are inconsistent, the effect has been further investigated. Rats given fluoxetine (15 mg kg−1, i.p.) for six days did not regain consciousness after sodium pentobarbital anaesthesia (65 mg kg−1, i.p.). Serum pentobarbital levels were increased by 50% by fluoxetine (10 mg kg−1, 24 and 16 h before pentobarbital, 30 mg kg−1), and fluoxetine (0–10 mg kg−1) dose-dependently (ED50 = 2·9±0·5 mg kg−1) increased nocturnal behavioural sedation induced by pentobarbital (50 mg kg−1, 4 h later). Gastrointestinal abnormalities and weight loss also were found after repeated fluoxetine administration, particularly intraperitoneally. These observations indicate that fluoxetine can lethally potentiate pentobarbital anaesthesia, and suggest additional adverse effects of repeated injections of high doses.

Mechanical Ventilation of a Dog with Pentobarbital Intoxication

SummaryA 9‐year old spayed female American bulldog presented 5 hours after ingesting a portion of a recently euthanized sheep carcass. The dog was comatose, intubated and manually ventilated on arrival. On physical examination, the dog had stable cardiovascular parameters but was hypothermic. Cranial nerve reflexes were absent and spinal reflexes were depressed. Mechanical ventilation was initiated and maintained for 18 hours before spontaneous respiration returned. Elevated serum pentobarbital concentration (19.1 mg/ml) confirmed pentobarbital intoxication as the cause of neurological signs. This is the first report of a dog with pentobarbital toxicity that was successfully managed with mechanical ventilation. Neurologic and functional recovery was complete and the dog was discharged 48 hours after admission. (J Vet Emerg Crit Care 2001; 11(1):33–37)

Supercritical fluid extraction and negative ion electrospray liquid chromatography tandem mass spectrometry analysis of phenobarbital, butalbital, pentobarbital and thiopental in human serum.

Four commonly used barbiturates (phenobarbital, butalbital, pentobarbital and thiopental) were analyzed in human serum using supercritical fluid extraction (SFE) and negative ionization LC/ESI-MS/MS. Barbital was used as the internal standard. Carbon dioxide SFE was performed at 40 degrees C and 500 atm, with a total extraction time of 35 min. The analytes were collected off-line in a liquid trap containing absolute methanol. Samples were then concentrated by vacuum centrifugation. The high performance liquid chromatography separation utilized gradient elution with a total analysis time of 21 min. The precursor and major product ions for the four barbiturates were monitored on a triple quadrupole mass spectrometer with negative ion electrospray ionization (ESI) in the multiple reaction monitoring mode as follows: (1) thiopental (m/z 241.20-->58.00), (2) phenobarbital (m/z 231.10-->188.0), (3) pentobarbital (m/z 225.10-->181.90) and (4) butalbital (m/z 222.80-->179.90). In the case of phenobarbital, pentobarbital and butalbital, the most abundant product ion arises from the loss of 43 u (HCNO loss). However, in the case of thiopental, the most abundant product ion was observed at m/z 58.0 (the [M-183]-ion, or NCS-). Mechanisms for the formation of the collision induced dissociation reaction products of these barbiturates are proposed.

Therapeutic Intervention Scoring System used in the care of patients in pentobarbital-induced coma to determine nurse-patient ratios

Critical care patients generally require extensive interventions, thereby consuming a large percentage of healthcare resources. Induced pentobarbital coma for the management of increased intracranial pressure is one such intervention, required to maintain patient stability. Quantification of these interventions, as well as the amount of nursing work required, has not been addressed in the literature. To use the Therapeutic Intervention Scoring System to analyze and quantify how interventions affect nurse-patient ratios in the management of patients in pentobarbital coma for refractory increased intracranial pressure. The medical records of patients with subarachnoid hemorrhage from aneurysmal rupture and subsequent increased intracranial pressure, in whom pentobarbital coma was salvage therapy, were reviewed retrospectively. The Therapeutic Intervention Scoring System was used to quantify the number of interventions required before, during, and after coma induction. The data were analyzed and daily Therapeutic Intervention Scoring System scores correlated with serum pentobarbital levels. Typically, a critical care nurse can manage a patient caseload of 40 to 50 Therapeutic Intervention Scoring System points. By quantifying the interventions, the score reflected the amount of care required to manage the patient in barbiturate coma. The intensity of interventions correlated with the level of coma, length of time in coma, and associated complications. The scores indicated the intensity of interventions used in pentobarbital coma and the use of resources. Nursing care and complications involved with this therapy were quantified and nurse-patient ratios were established.

Serum Pentobarbital Assay by Capillary Electrophoresis

Abstract A simple and rapid assay for pentobarbital in serum based on capillary electrophoresis (CE) is described. Serum is deproteinized with acetonitrile then electrophoresed at 11 KV in 300 mmol/L borate buffer pH 8.5. This method demonstrates the potential of CE for a rapid and simple quantitation of many drugs and small molecules in serum.

Electroencephalographic activity and serum and cerebrospinal fluid pentobarbital levels in determining the therapeutic end point during barbiturate coma

Controversy exists regarding the optimal means for monitoring the patient receiving pentobarbital therapy during medical coma. Serum pentobarbital levels have been used traditionally to gauge cerebral penetration and efficacy of the drug. These peripheral levels have been assumed to reflect pentobarbital concentrations in the cerebrospinal fluid (CSF) and, therefore, the physiological effect on the central nervous system. To determine the relative accuracy of serum versus CSF pentobarbital levels, continuous electroencephalographic (EEG) monitoring in 10 consecutive patients was studied prospectively. Each patient received pentobarbital therapy for cerebral protection in the face of a traumatic injury. Simultaneous serum and CSF pentobarbital levels were obtained 1) before and after the initial barbiturate bolus, 2) every 12 hours during constant infusion therapy, and 3) before and after subsequent boluses necessary because of elevated intracranial pressure (ICP) (ICP greater than 15 mm Hg) or loss of burst suppression by continuous EEG monitoring (defined as greater than five bursts per minute). ICP and relevant clinical events were recorded hourly. Serum and CSF levels ranged from 33 to 74 mg/L and 4 to 54 mg/L, respectively. There was poor correlation between serum and CSF pentobarbital levels at any given time, although patients remained in burst suppression 73% of the time during their therapy. The EEG monitoring not only provided dynamic physiological monitoring, but it also permitted the lowest pentobarbital dose to maintain burst suppression for a specific patient's metabolism, reducing the likelihood of toxicity. In conclusion, CSF pentobarbital levels are of no greater accuracy than serum pentobarbital levels in predicting physiological effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Electroencephalographic Activity and Serum and Cerebrospinal Fluid Pentobarbital Levels in Determining the Therapeutic End Point during Barbiturate Coma

Abstract Controversy exists regarding the optimal means for monitoring the patient receiving pentobarbital therapy during medical coma. Serum pentobarbital levels have been used traditionally to gauge cerebral penetration and efficacy of the drug. These peripheral levels have been assumed to reflect pentobarbital concentrations in the cerebrospinal fluid (CSF) and, therefore, the physiological effect on the central nervous system. To determine the relative accuracy of serum versus CSF pento-barbital levels, continuous electroencephalographic (EEG) monitoring in 10 consecutive patients was studied prospectively. Each patient received pentobarbital therapy for cerebral protection in the face of a traumatic injury. Simultaneous serum and CSF pentobarbital levels were obtained 1) before and after the initial barbiturate bolus, 2) every 12 hours during constant infusion therapy, and 3) before and after subsequent boluses necessary because of elevated intracranial pressure (ICP) (ICP &amp;gt; 15 mm Hg) or loss of burst suppression by continuous EEG monitoring (defined as greater than five bursts per minute). ICP and relevant clinical events were recorded hourly. Serum and CSF levels ranged from 33 to 74 mg/L and 4 to 54 mg/L, respectively. There was poor correlation between serum and CSF pentobarbital levels at any given time, although patients remained in burst suppression 73% of the time during their therapy. The EEG monitoring not only provided dynamic physiological monitoring, but it also permitted the lowest pentobarbital dose to maintain burst suppression for a specific patient's metabolism, reducing the likelihood of toxicity. In conclusion, CSF pentobarbital levels are of no greater accuracy than serum pentobarbital levels in predicting physiological effect. Constant EEG monitoring remains the best modality by showing the presence of burst suppression moment-to-moment and thus establishing the minimal necessary dose.

Treatment of refractory generalized tonic-clonic status epilepticus with pentobarbital anesthesia after high-dose phenytoin.

We report the results of treatment of refractory generalized tonic-clonic status epilepticus in 17 adults. Of 13 patients who received high-dose phenytoin (PHT, mean dose 23.8 mg/kg), seizure control was sustained in five patients. In 12 cases, anesthetic doses of pentobarbital rapidly suppressed convulsions, but sustained control required prolonged treatment. Break-through seizures were, in most cases, explained by inadequate serum pentobarbital concentrations, although we could not establish a therapeutic range of serum concentrations. EEG monitoring is necessary to assess the therapeutic response but is not a reliable index of depth of anesthesia. Some cases developed pharmacodynamic tolerance to pentobarbital. The most serious treatment complications were cardiorespiratory, but the most common and disabling side effects, although reversible, were neurologic. Fifteen patients were discharged from the hospital in stable condition; two patients died, but not as a direct consequence of treatment. Our results suggest a very good outcome of pentobarbital anesthesia for patients in refractory status epilepticus who are a reasonable medical risk and who receive optimal medical management.

Pentobarbital quantitation using immunoassays in Reye's syndrome patient serum.

Analysis of serum pentobarbital concentrations in 28 specimens from Reye's syndrome patients was conducted with modifications of three nonspecific immunoassay procedures originally designed to detect barbiturates in serum or urine. An adaptation of the urine enzyme-multiplied immunoassay technique (EMIT) Dupont aca barbiturate screen to the quantitation of serum pentobarbital is described. Replicate analysis of control specimens containing pentobarbital across a wide spectrum of concentrations revealed a between-day precision of less than 6%. Regression analysis revealed excellent agreement with a high-performance liquid chromatography (HPLC) method: (HPLC) = 0.98 (aca) - 0.07 (r = 0.97). Multiple linear regression analysis with a serum EMIT barbiturate screen and a urine fluorescence polarization immunoassay screen modified to quantitate pentobarbital in serum revealed excellent agreement among all methods, demonstrating that immunoassays offer a reliable approach to pentobarbital quantitation.

Pharmacodynamics and pharmacokinetics of ethanol, diazepam and pentobarbital in young and aged rats.

Sleeping time was measured in groups of old and young rats following the intraperitoneal injection of pentobarbital (39.5 mg.kg-1), diazepam (30 mg.kg-1) and ethanol (3 g.kg-1). Concentrations of pentobarbital, and unbound and total diazepam in serum, and ethanol in breath were quantified; as well as whole brain concentrations of diazepam and N-demethyldiazepam. Healthy old rats slept significantly longer than young rats after receiving diazepam and ethanol but not pentobarbital. There were no significant differences in serum or whole brain concentrations of diazepam or N-demethyldiazepam between healthy young and old rats. There were also no changes in the serum pentobarbital or breath ethanol concentrations between the young and old rats. Increases in pharmacologic effect that occur with aging may be caused by alterations in pharmacokinetic parameters or changes at the site of drug action. The cause of an increased pharmacodynamic effect depends upon the specific drug, possibly because these compounds affect the same receptorionophore complex at different sites.

Evaluation of a rapid immunoassay for monitoring serum pentobarbital concentrations

A modification of the EMIT-Tox qualitative serum barbiturate assay (Syva Company, Palo Alto, CA) was evaluated for measuring pentobarbital concentrations. Pentobarbital calibrator solutions were substituted for the secobarbital calibrators provided with the assay kit, and control solutions of pentobarbital were used to determine the modified assay's precision and accuracy. Specificity for pentobarbital with respect to other barbiturates and assay interference from other drugs were evaluated in vitro. Serum samples obtained from 49 patients receiving intravenous pentobarbital sodium to treat intracranial hypertension were assayed by gas-liquid chromatography (GLC) and by the modified EMIT procedure. Samples from patients who were receiving both phenobarbital and pentobarbital (9 of 49) were assayed for both drugs, interference curves were plotted, and the corrected pentobarbital concentrations were compared with GLC values. The modified assay method provided an accurate measurement of serum pentobarbital concentrations of 1-30 micrograms/ml. Significant cross-reactivity with the pentobarbital assay was present for secobarbital, butabarbital, allobarbital, and phenobarbital. Dexamethasone, dopamine, phenytoin, cimetidine, lidocaine, diazepam, morphine, and several other drugs at concentrations of 1000 micrograms/ml did not interfere with the assay. There was a strong correlation between the GLC reference method and the modified EMIT assay (r = 0.96). Clinically important cross-reactivity with phenobarbital was found; the corrected pentobarbital concentrations for patients who had received phenobarbital strongly correlated with GLC results (r = 0.98). The modified assay appears to be sufficiently reliable for determination of pentobarbital serum concentrations.

Quantitation of pentobarbital in serum by enzyme immunoassay.

Pentobarbital was quantitated in serum by a homogeneous enzyme immunoassay (EMIT), and the method evaluated for accuracy and precision. A comparison was performed against the authors' modified Goldbaum ultraviolet spectrophotometric procedure. The analytical sensitivity was 2 micrograms/mL with a linearity to 10 micrograms/mL and a coefficient of variation of 6.24%. Linear regression analysis revealed a correlation coefficient of 0.977, a slope of 1.05, and an intercept of -0.07. The t test demonstrated no difference between the two methods at a level of P less than 0.01. The enzyme immunoassay also had the advantages of speed and small sample requirement.

Rapid quantification of pentobarbital in serum by fluorescence polarization immunoassay.

The commercially available fluorescence polarization immunoasay (FPIA) method for phenobarbital is demonstrated to be useful in the quantification of pentobarbital in serum. The effective range for the method is 1.0 to 80.0 mg/L. The method is simple, precise, and fast. The application of the method is limited to patients receiving pentobarbital as the only barbiturate. The FPIA is recommended for use in clinical laboratories when a rapid estimation of pentobarbital is required in monitoring patients undergoing high-dose pentobarbital therapy.

Quantitation of barbiturates by a modification of the EMIT-tox serum barbiturate assay.

A modification of the Syva EMIT-tox Serum Barbiturate Assay was developed to provide a rapid and practical method for quantitating serum barbiturates. Standard curves for eight selected barbiturates were run using specific sets of standards for each. Correlation coefficients, slopes, and y-intercepts for the curves of best fit were determined by the least-squares method. Between-run and within-run precision analysis indicated acceptable reproducibility for barbiturate concentrations in high therapeutic to toxic serum levels. A case report describing the use of this method for the determination of serum pentobarbital concentrations during therapy for intracranial hypertension is presented. The modified EMIT assay may be useful for monitoring barbiturate blood levels in overdose, and when used for therapy of ischemic brain damage.

Reversed-phase liquid-chromatographic simultaneous analysis for thiopental and pentobarbital in serum.

We describe a reversed-phase liquid-chromatographic assay suitable for therapeutic monitoring of thiopental and pentobarbital simultaneously in human serum. The drugs are extracted from serum at pH 6.6 into n-butyl chloride containing thiamylal and barbital as the respective internal standards. The compounds are back-extracted into dilute sodium hydroxide, an aliquot of which is submitted to chromatography. The lowest measurable concentrations are 1.0 mg/L for thiopental and 2.0 mg/L for pentobarbital. The standard curve is linear from 0 to 100 mg/L for both. Between-run CVs are: at 25 mg/L, 4.1% (thiopental) and 3.2% (pentobarbital); at 50 mg/L, 2.8% (thiopental) and 3.4% (pentobarbital). Data on patients receiving thiopental and pentobarbital illustrate use of the method.

The effects of deep barbiturate coma on multimodality evoked potentials.

The authors report their investigation of the effects of high-dose barbiturates on the multimodality evoked response in 9 cats. After baseline evoked responses were obtained, boluses of pentobarbital were infused intravenously at regular intervals, amounting to cumulative total doses of 9, 18, 27, 45, 63, 123, and 183 mg/kg at respective infusions. This resulted in gradually increasing serum pentobarbital levels, reaching therapeutic coma levels (4 to 5 mg/dl) after the fifth infusion. At this point, the electroencephalogram was flat, and pressor agents were required to maintain cardiovascular stability. Evoked responses were obtained 15 minutes after each infusion. Brain-stem auditory evoked response (BAER) showed little change in wave latencies at therapeutic coma levels of pentobarbital. Further barbiturates resulted in delay of the late components of this response. In the somatosensory evoked responses (SER), early brain-stem components were relatively unaffected by therapeutic coma levels. Late brain-stem components and the initial cortical response showed progressive latency increase. Late cortical (association cortex) waves were abolished at relatively low doses. The central conduction time was relatively unaffected. The late waves of the visual evoked responses (VER) were abolished with low-dose barbiturates (9 mg/kg). A single positive-negative complex persisted despite massive infusions. It is concluded that evoked responses may prove useful in monitoring patients in deep barbiturate coma, but barbiturate effects must be kept in mind.

Rapid method for screening toxic drugs in serum with liquid chromatography.

We present a method for the simultaneous analysis of a variety of commonly abused drugs (acetaminophen, theophylline, salicylate, primidone, methyprylon, phenobarbital, butabarbital, ethchlorvynol, butalbital, chlordiazepoxide, pentobarbital, amobarbital, phenytoin, glutethimide, secobarbital, flurazepam, nitrazepam, methaqualone, N-desmethyldiazepam, and diazepam) in serum or plasma. Serum proteins are precipitated with an acetonitrile solution containing hexobarbital, the internal standard. The drugs are eluted from a reversed-phase column with a mobile phase consisting of acetonitrile/phosphate buffer (pH 3.2), using a two-step linear gradient, at a flow rate of 3.0 mL/min. The eluted drugs are detected by their absorption at 210 nm; their quantities are estimated from their peak heights. A complete analysis requires no longer than 45 minutes at the optimum column temperature of 50 degree C. A sensitivity of 2 mg/L of serum is attained routinely for most of the hypnotic and analgesic drugs; while methaqualone, chlordiazepoxide, diazepam, and N-desmethyldiazepam can be detected at a concentration of 0.2 mg/L. Analytical recoveries for the twenty drugs varied from 93-112%, with good reproducibility. Of more than forty drugs tested for possible interference, desmethyldoxepin, procainamide, phenylpropanolamine, mesantoin, and phenacetin interfere with the analysis of flurazepam, acetaminophen, ethchlorvynol, and phenobarbital, respectively.