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A six-year study of therapeutic and toxic drug concentrations in the blood from medical examiner's cases in the State of Maryland is reported. Statistical means, ranges, and number of cases are presented for three categories of cases; single drug deaths (53 drugs and 5 metabolites), multiple drug deaths (40 drugs and 5 drug metabolites), and non-drug related deaths (49 drugs and 5 metabolites). Results are compared to previous studies from the literature to facilitate, augment, and improve the understanding of the concentrations of drugs consistent with therapy or death.

The effects of pulmonary artery infusion of delta-9-tetrahydrocannabinol (delta 9-THC), 0.5 mg/kg, have been studied in four pregnant sheep. Cardiac output (CO) decreased from a baseline of 4.49 +/- 0.91 l/min (mean +/- s.e.m.) to 4.19 +/- 0.87 at 3 min, 3.69 +/- 0.76 at 5 min, and 3.35 +/- 0.77 at 15 min post infusion and returned to baseline by 1 h post infusion. Maternal blood pressure (MBP) decreased from 114 +/- 9 to a nadir of 69 +/- 8 mmHg at 15 min post infusion. Uterine artery blood flow (UTABF) increased from 256 +/- 88 to 317 +/- 132 ml/min at 3 min post infusion, but this was not statistically significant. Maternal acidosis, hypercapnia, and hypoxemia also developed during the first 15 min post infusion. Although fetal blood pressure (FBP) decreased throughout the 1st h post infusion, statistically significant changes in FBP or fetal heart rate (FHR) were not observed. Umbilical artery blood flow (UMABF) increased from 188 +/- 58 to 211 +/- 68 1/min at 5 min post infusion and declined thereafter. This change was also statistically significant. As in the ewe the fetus developed acidosis and hypoxemia, but hypercapnia, although present, was not statistically significant. A single animal was studied following i.v. infusion of delta 9-THC (1 mg/kg). More pronounced effects, including a decrease in UTABF and UMABF, were noted. The sheep were maintained under pentobarbital anesthesia for the duration of the study.

Old mice show an increased sensitivity to parenteral pentobarbitone compared with young adult mice, despite similar plasma concentrations of the drug. One factor may be an alteration in the binding of barbiturate to the plasma protein, perhaps consequent on reduced hepatic synthesis of plasma protein with advancing age. As part of a study of the effect of age upon the pharmacological and adaptive response to barbiturates, binding of pentobarbitone to plasma proteins from mice of different ages was measured by equilibrium dialysis in the presence of a standard concentration of the drug. The total plasma protein concentration was measured and found to be the same in both age groups. The plasma protein binding of pentobarbitone was found to correlate significantly with the plasma albumin concentration, which was lower in the older mice. However, there was no significant overall difference in pentobarbitone binding between old and young mice. Pretreatment of the mice with phenobarbitone for 21 days had no effect upon the capacity for plasma protein binding of pentobarbitone in either age group. Thus, it seems unlikely that the increased sensitivity of older mice to pentobarbitone can be explained in terms of altered plasma protein binding of the drug.

High dose barbiturates were used to treat intracranial hypertension in 15 patients with nontraumatic brain lesions; (3 hypertensive hemorrhage, 4 subarachnoid hemorrhage, 5 infarction, 2 global anoxia-ischemia and 2 encephalitis). All had persistently raised intracranial pressure (ICP) while being treated with aggressive conventional therapy. The addition of barbiturates caused an initial lowering of ICP in 11 patients, but only 5 of these had sustained ICP reductions. Survival of the 5 patients with persistently lowered ICP and death of the remaining 10 may indicate an improvement in outcome attributable to the addition of high dose barbiturates to conventional therapy in non-traumatic brain swelling. Because of the resources required for their prolonged use, randomized studied in patients with intracranial hypertension are required to determine the effect of barbiturates on outcome.

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.

Mouse lines genetically selected for susceptibility [long sleep (LS)] or resistance [short sleep (SS)] to the acute hypnotic effects of ethanol were tested for sensitivity to maximal electroshock seizures. LS mice were slightly more sensitive than SS mice. Ethanol or pentobarbital pretreatment elevated seizure thresholds in both lines. LS and SS mice were approximately equally protected by ethanol, but LS mice were somewhat more protected than SS mice by pentobarbital. These studies do not provide evidence that sensitivity to the anticonvulsant effect of ethanol is mediated by substantially the same genes as those mediating sensitivity to EtOH's hypnotic effects. However, sensitivity to pentobarbital's anticonvulsant effects may be genetically correlated.

1 Total lung resistance (R(L)) and dynamic lung compliance (C(dyn)) were measured in dogs anaesthetized with pentobarbitone or chloralose and subjected to aerosols of histamine during 4 successive inspirations.2 Histamine caused concentration-dependent increases in R(L) and decreases in C(dyn). A significant vagal component was involved, but only when chloralose was employed and then only in the R(L) response.3 The resting values of R(L) and C(dyn) were similar regardless of which anaesthetic was used and remained essentially the same if the vagi were cooled.4 Electrical stimulation of the efferent vagi caused large increases in R(L) of dogs given chloralose and these effects were attenuated by the administration of pentobarbitone. Such stimulation was relatively ineffective in dogs given pentobarbitone alone.5In vitro, electrical field stimulation caused contractions of dog trachealis muscle. The responses were reduced by pentobarbitone in concentrations approximating to plasma levels in the anaesthetized dogs (1 to 5 x 10(-4) M), but the effects of exogenous acetylcholine were unaltered. The inhibition was dose-dependent, reversed by washing and unaltered by hexamethonium.6 The results suggest that pentobarbitone inhibits the vagal component of histamine-induced bronchoconstriction in the dog by an action on the efferent pathway. Furthermore, pentobarbitone acts either by blocking transmission along postganglionic parasympathetic nerves or by preventing the release of acetylcholine from the nerve endings in the lung.

The clinical effects of pentobarbital, 100 mg, and diazepam, 10 mg, given orally as preoperative medications before dental surgery were tested in a double-blind study in 50 adult patients. The concnetrations of pentobarbital and diazepam (plus its three active metabolites) in plasma, measured by gas chromatography, were correlated with their clinical effects as assessed both subjectively and objectively (sedation, apprehension, excitement, dizziness, pre- and post-operative emetic effect, increase or decrease in systolic blood pressure, pulse rate, and ease of venipuncture). No significant difference in the effects of these two agents was observed, nor was there any obvious relationship between the concentration in plasma and clinical effect.

The pharmacokinetics of pentobarbital were studied after i.v. administration of a 30-mg/kg dose to five dogs. Pentobarbital plasma concentrations were measured with a new gas chromatographic method, utilizing on-column methylation of pentobarbital and as a butabarbital internal standard. The kinetics of pentobarbital distribution and elimination were analyzed with a three-compartment open mammillary model. The elimination-phase half-life of pentobarbital was 8.2 +/- 2.2 hr. The steady-state volume of pentobarbital distribution was 1.08 +/- 0.21 liters/kg and the elimination clearance was 0.0013 +/- 0.0004 liters/min X kg. Threshold pentobarbital concentrations required to suppress the corneal reflex and withdrawal response to pain were 26.4 +/- 4.6 and 23.0 +/- 2.9 micrograms/ml, respectively. These results should facilitate the design of i.v. anesthetic regimens with pentobarbital.

Previous studies have indicated that acute exposure to ambient concentrations of ozone (O3) as low as 196 micrograms/m3 (0.1 ppm) increases pentobarbital (PEN)-induced sleeping time in female mice. To elucidate potential mechanisms involved, additional studies were performed. A 3 h exposure to 9800 micrograms O3/m3 (5 ppm) did not affect brain concentrations of PEN at time of awakening, even though sleeping time was increased. Exposure for 3 h to 9800 micrograms O3/m3 (5 ppm) did not alter the pattern of brain or plasma metabolites of PEN. Pentobarbital clearance followed first-order kinetics with a one-compartment model. Mice exposed to 9800 micrograms O3/m3 (5 ppm) for 3 h had a 106% increase in the plasma half-life of pentobarbital; at 1960 micrograms O3/m3 (1 ppm) for 3 h, a 71% increase was observed. It therefore appears possible that PEN-induced sleeping time might be increased due to an decrease in hepatic metabolism of PEN.

The method of "maximally tolerable" dosing technique for establishing a reproducible state of barbiturate dependence in cats was used for the study. The development of tolerance in animals treated by this method has been quantitatively assessed. Sodium pentobarbital was administered morning and evening for 35 days via a plastic tube implanted into the stomach through the abdominal wall. A range of neurological signs of intoxication was scored before and after each dose and during the day at certain preset intervals. Based on the scoring of neurological impairment, each cat was given the maximally tolerable anesthetic dose of sodium pentobarbital. All of the animals treated by this method exhibited severe withdrawal signs upon abrupt withdrawal of the drug. For each cat, blood pentobarbital concentrations were determined every day before and 1 to 11/4 hours after the morning dose. Also, a complete blood pentobarbital elimination study was made on days 1, 7, 14, 21, 28 and 35 of the regimen. These results distinguished between dispositional and functional tolerance. The dispositional tolerance developed maximally within a week and was maintained at that level as long as the treatment was continued. The functional tolerance, on the other hand, developed more gradually and progressed with continued treatment.

The kinetics of thiopentone when administered in high doses were investigated in two patients with elevated intracranial pressure and three patients with focal cerebral ischemia. Initial saturation of the tissues is best achieved by a series of infusions with decreasing infusion rate. Administration of a bolus followed by maintenance doses proved unsuitable. The course of concentration under maintenance dosage was extremely variable, mainly due to interindividual and intraindividual variations in clearance. The apparent distribution volumes in these patients (1.38-3.10 l/kg, mean 2.43 l/kg) corresponded to the volumes determined after bolus administration. The total body clearance was low (45.8-103.4 ml/min, mean 72.3 ml/min) and was the reason for long elimination half-times (15.6-25.0 h, mean 23.2 h). Four patients biotransformed thiopentone regardless of the concentration. In one female patient the biotransforming enzyme systems may have been saturated. While conversion of thiopentone to pentobarbitone is generally only of secondary importance, an unusually high plasma pentobarbitone concentration was observed in one patient, reaching 50% of the concentration of the original substance. On the average, thiopentone was 75-80% proteinbound. The binding rate changed considerably with time. It could not be shown that this was influenced by albumin concentration between 25 and 50 g/l. The thiopentone concentration in the ventricular fluid corresponded approximately to that in the plasma fluid. Owing to the variability of the total body clearance and plasma protein binding, and the possibility of changes in tolerance, thiopentone administration must be controlled individually according to the EEG and intracranial pressure. Monitoring of the drug concentration in plasma is recommended.

The hemodialysis clearance of pentobarbital during continuous infusion was determined in a 34-year-old man in acute renal failure. Pentobarbital specimens were obtained simultaneously from arterial blood entering and leaving the dialysis machine at five 1-h intervals. The mean hemodialysis clearance of pentobarbital was 22.3 ml/min. Pentobarbital concentration was relatively unaffected throughout the dialysis period, because of the high dose and continuous infusion of a drug with low hepatic intrinsic clearance and a short dialysis period. A large contribution to total body clearance was not evident, and dosage adjustment would have been unwarranted.

The morphological and functional alterations of the smooth endoplasmic reticulum of the liver cell related to biliary stasis have brought attention to drug biotransformation during cholestasis. The metabolism of meprobamate, pentobarbital and tolbutamide was assessed in subjects with intrahepatic recurrent cholestasis (3), cholestatic hepatitis (6), extrahepatic biliary obstruction (7) and normal controls (16). In the patients with recurrent intrahepatic cholestasis no differences in drug metabolism were noted as compared to the control group. In cholestatic hepatitis the plasma half-lives of meprobamate (828 +/- 422 min.) and pentobarbital (39+-65) were significantly longer than in in controls (444 +/- 37 and 25.4 +/- 1.1 respectively). Tolbutamide plasma half-life appeared unchanged. The most striking variations were observed in the patients with extrahepatic biliary obstruction. In such cases while meprobamate half-life was unchanged, pentobarbital half-life was significantly prolonged (31.2 +/- 2.5) and the in vitro metabolism of the drug, using liver preparations, was decreased to less than 50% of the control value. In contrast the metabolism of tolbutamide was accelerated as evidenced by a significant decrease of plasma half-life (165 +/- 48 min. versus 384 +/- 76 of the controls) and an enhanced urinary excretion of the drug's metabolites. However the metabolism of tolbutamide in vitro did not show any difference between normal and cholestatic liver. Whatever the mechanism of the peculiar behaviour of tolbutamide in extrahepatic biliary obstruction it seems to be related to the increased bile dalt concentration during cholestasis. In fact the low values of plasma half-life increase significantly either relieving the biliary obstruction or producing a bile salt depletion with cholestyramine. Preliminary results in vitro suggest the bile salt could displace tolbutamide from albumin binding thus increasing the amount of free drug available for biotransformation by the liver. In conclusion cholestasis may affect drug metabolism depending on the degree of biliary stasis, liver cell injury and the type of drug tested. The mechanism could be that of an impaired biotransformation in the smooth endoplasmic reticulum or could involve extrahepatic factors.

The effects of high-dose barbiturates (pentobarbital) on the acoustic reflex, and the auditory brainstem (ABR) and middle-latency (AMR) responses, are illustrated with two case reports. Auditory electrophysiologic data were recorded serially during recovery from therapeutic barbiturate coma. ABR latency remained within normal limits in barbiturate coma, but amplitude of the wave I component was abnormally augmented. Contralateral and ipsilateral acoustic reflex activity, and the Pa component of the AMR, were not observed in barbiturate coma, and reappeared with the emergence of brainstem neurologic signs. These findings suggest a fundamental difference in the neurophysiologic substrate of the ABR vs. acoustic reflex and AMR. Possible mechanisms for the differential influence of barbiturates on these three auditory electrophysiologic measures are offered.

Rats were given pentobarbital by daily intubation. Sleeping times and blood levels of drug at awakening, after intraperitoneal test doses of ethanol, pentobarbital, or barbital, were measured at various times during chronic treatment in order to assess the degree of tolerance developed. No central nervous system (CNS) tolerance to pentobarbital or cross-tolerance to barbital or ethanol occurred on treatment with sodium pentobarbital, 50 mg/kg, daily. However, when the size and frequency of pentobarbital treatment doses were increased (50-80 mg/kg, three times daily) a clear CNS tolerance to barbital occurred. Chronic administration of p-chlorophenylalanine (p-CPA), in a dose previously shown to maintain more than 95% depletion of brain serotonin (5-HT), enhanced the acute hypnotic effect of barbiturates and ethanol. Independently of this effect, p-CPA treatment also resulted in a reduction in the development of CNS tolerance. These results are consistent with earlier findings that brain 5-HT depletion retards tolerance development to central depressant drugs as measured by a variety of unrelated tests.

High hydrostatic pressure has been shown to reverse the anesthetic effects of barbiturates. However, attempts to distinguish between two possible causes of this reversal, changes in drug disposition or changes in drug-receptor interaction, have not been reported. This study examined the possible effects of hyperbaria and hyperbaric hyperoxia on the distribution and clearance of pentobarbital in the dog. The drug was administered to six mixed-breed dogs as a 30 mg/kg i.v. bolus at 1 ATA breathing air, 6 ATA breathing air, and 2.8 ATA breathing 100% oxygen, with serial blood sampling for 12 h. Pharmacokinetic and statistical analyses showed no significant effects of hyperbaria or hyperbaric hyperoxia on the total plasma clearance, volume of distribution or elimination half-life. If pressure reversal of barbiturate anesthesia occurs at these pressures, changes in the disposition of the drug are not the causative factors.

Previous studies have shown that rats with 15% third-degree burns show a severe depression in various in vitro hepatic drug-metabolizing enzymes. This effect was assessed in vivo by measuring the disposition of four liver-metabolized drugs in 16% third-degree burned rats at 7 d postburn. Compared with pair-fed control rats, pentobarbital demonstrated a significantly prolonged clearance and elimination half-life without a change in volume of distribution. Quinidine demonstrated a significantly increased volume of distribution and a significantly decreased clearance without a change in elimination half-life. Lidocaine showed a significantly increased volume of distribution. Theophylline, which is only 50% metabolized in the rat, showed no changes in any pharmacokinetic parameters. The free drug fractions of quinidine and lidocaine were found to be significantly decreased at 1 d postburn and normal at 7 d postburn. These results warrant pharmacokinetic studies in human burn patients.

The mechanism of decreased lymphocyte responsiveness after major surgery is unclear. Because sodium pentobarbital, and intermediately long-acting barbiturate, will reproducibly induce anesthesia in experimental animals, we utilized a canine model to investigate its effect on lymphocyte proliferation induced by the mitogenic lectins erythroagglutinating phytohemagglutinin (E-PHA) and leukoagglutinating phytohemagglutinin (L-PHA). Although no effect was observed at 10 minutes or 1 hour after an anesthetic dose of sodium pentobarbital, after 1 and 3 hours of anesthesia, canine lymphocytes were significantly suppressed, as demonstrated by decreased responsiveness to E-PHA and L-PHA mitogen stimulation. After 3-hours the majority of animals had mitogenesis values of less than 50% of the preanesthetic control values. Recovery, as measured by a return to at least 70% of the preanesthetic mitogenesis value, was noted in the majority of animals at 24, 48, and 72 hours. In order to investigate the machanisms of the in vivo capability of sodium pentobarbital to induce immunosuppression of lymphocyte transformation, in vitro studies were carried out. Sodium pentobarbital was found to significantly inhibit mitogen-induced canine mononuclear cell blastogenesis at anesthetic (1.5 to 3.0 mg%) drug concentrations in vitro. Lymphocytes pretreated with barbiturate and washed prior to plating did not show this inhibiting effect. Our findings suggest that depression of the immune response reported in patients after operation could result from short-acting barbiturates administered during the induction phase of clinical anesthesia. Furthermore, the suppression may involve in vivo metabolism of pentobarbital, hormones or other in vivo factors, since washed lymphocytes from the in vivo but not the in vitro experiments demonstrated suppression. These results indicate that anesthesia may be an important factor in the immunosuppression reported after major surgery.

The commercially available enzyme homogeneous immunoassay (EMIT) method for barbiturates was demonstrated to be useful in the assay for pentobarbital. The method is just as precise as a comparative gas-liquid chromatography (GLC) method but much faster. There appeared to be a slight positive proportional bias with the method when compared to expected values in plasma samples when using aqueous standards. The application of the method is limited to patients receiving pentobarbital as the only barbiturate. Values less than 10 m/L were not quantitated. The enzyme immunoassay in recommended for use in clinical laboratories when a rapid estimation of pentobarbital is required in monitoring patients undergoing high-dose pentobarbital therapy for minimizing brain damage due to head trauma of stroke.

Rats were made dependent on sodium barbital by daily oral administration of the drug over a 4 week period. At the end of this time the animals were switched to sodium pentobarbital, I.P., 30 mg/Kg every 4 hours for 3 days and withdrawn. Mean Plasma pentobarbital concentrations was observed to decline rapidly following peak concentrations which occurred approximately 1 hour after the final dose. The last samples in which pentobarbital was detectable were taken 3 hours after the last dose. Audiogenic seizure susceptibility and intensity peaked at 6 hours following the last dose, suggesting that a low concentration of barbiturate is more important in increasing seizure propensity than a sudden decrease in concentration. No electroencephalographic abnormalities were observed during the withdrawal period.

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.

A simple and relatively quick method of estimating pentobarbitone in plasma samples is reported using an ether extraction and gas-liquid chromatography. Glutethimide was used as the internal standard and proved reliable. Reproducible results were obtained in plasma following 100 mg pentobarbitone given by mouth or intramuscular injection. Evaporation in a heating block at 37 degrees C and storage of samples at -20 degrees C prior to analysis is recommended.

By equilibrium dialysis of human plasma it has been shown that the binding of pentobarbital and diphenylhydantoin to plasma proteins is decreased in uraemic patients (46 and 74 per cent bound, respectively) compared to healthy volunteers (61 and 88 per cent bound). The degree of binding of pentobarbital was significantly correlated with that of diphenylhydantoin and amobarbital, which suggests similarity of their binding sites. Appreciable proportions of the drugs were found in blood cells both in healthy and uraemic subjects. As expected, the distribution of drugs in whole blood was different in the uraemics from healthy subjects, because of the decreased plasma protein binding and the lowered red cell count in uraemia. Analysis of the data showed that the ratio between the concentrations in blood cells and plasma water in uraemic patients was not significantly different from that in healthy subjects.

The pharmacokinetics of intravenously administered pentobarbitol have been studied in heterozygous (non-jaundiced) and homozygous (jaundiced) Gunn rats following single doses of 30 mg/Kg. Plasma pentobarbital concentration time course data from heterozygous animals were fitted to a biexponential equation while a triexponential equation was required to fit the data from homozygous animals. A slower plasma clearance rate and longer elimination half-life were observed in homozygous animals as well as increased overall volumes of pentobarbital distribution. These results suggest a possible effect of bilirubin on the distribution and elimination of pentobarbital. The volume of pentobarbital plasma distribution, however, was approximately equal in heterozygous and homozygous data, suggesting no competition between bilirubin and pentobarbital for serum protein.

Mice continuously exposed to 50% nitrous oxide for 2 weeks or more become tolerant to nitrous oxide, as measured by an 8% to 19% increase in their nitrous oxide ED50 (the dose required to abolish the righting reflex in 50% of the animals). Control mice tolerant to nitrous oxide were given intraperitoneal injections of secobarbital (50 mg/kg), phenobarbital (120 mg/kg), or pentobarbital (55 or 65 mg/kg). Sleep onset times, sleep times, and serum levels of barbiturates upon awakening did not differ between the two groups. These results suggest that nitrous oxide and barbiturates do not share a common mechanism of action.

Factors related to clinical outcome following acute overdosage with pentobarbital or secobarbital were assessed in a series of 162 patients hospitalized during the period 1962 to 1975. The mean ingested dose was 2 Gm (range 0.2 to 10.0 Gm), and plasma barbiturate concentrations ranged from 2.0 to 72.0 microgram/ml. Serious intoxication was common. Intubation and assisted ventilation were required in 59 per cent of patients, and 23 per cent developed clinically important hypotension. Four patients died, all relatively young females. Multiple regression and discriminant function analyses, performed on a subset of 88 patients for whom complete data were available, indicated that plasma barbiturate concentration and/or ingested dose were the most important correlates of serious intoxication among identifiable variables available on admission. Coingestion of other central nervous system depressants, such as ethanol, had no obvious effect on outcome. The present study suggests that measurement of plasma barbiturate concentrations is of value in identifying patients at risk of developing serious intoxication after overdosage with pentobarbital or secobarbital.

A very easy, reliable and specific gas-chromatographic method for identification and dosage of 11 barbiturates in plasma is presented. Methylene unit values determined on two types of column (one polar, one non-polar) allows very accurate identification with a minimum risk of error due to fluctuations in operating conditions. Sensitivity of the method is 0.5 microgram/ml plasma with a flame ionization detector. Derivatization procedure is complete, without any degradation phenomenon as tested by mass spectrometry. Such a method can be easily used as routine procedure for toxicological or pharmacological applications.

In our previous papers, tiopronin (2-mercaptopropionylglycine) and glutathione were reported to suppress the liver damage induced by ethionine. In the damage induced by ethionine. In the present study, we evaluated such suppressive effect from the aspect of drug metabolizing activity. Aniline hydroxylating enzyme activity and aminopyrine N-demethylating enzyme activity of the liver microsome of rats 24 hr after administration of 1 g/kg ethionine were decreased to 53.2% and 61.7% respectively as compared with those of the normal rats. Administration of tiopronin or glutathione to the ethionine treated rats suppressed the decrease of both enzyme activities induced by ethionine. Ethionine did not influence NADH-cytochrome c reductase (fp1) but brought about increase of the activity of NADPH-cytochrome c reductase (fp2) and decrease of the cytochrome P-450 content. These thiol compounds did not influence fp1 and fp2 but tended to suppress the cytochrome P-450 content decreased by administration of ethionine. In particular, tiopronin suppressed the content significantly. Disappearance of aminopyrine, hexobarbital and pentobarbital from the blood was markedly delayed by ethionine administration. It was revealed, however, that such delay was recovered by tiopronin or glutathione. The sleeping time induced by hexobarbital and pentobarbital was also prolonged by ethionine, but this tended to be shortened by tiopronin or glutathione.

Examination of the effect of three doses of pentobarbital on the comparative performance of a complex psychomotor task with two simple neuromotor tasks, i. e., standing steady and pendulum eye tracking, revealed a high correlation. These simple tasks could be used as measures of intoxication since they do not require extensive training. Examination of the complex task impairment blood level ratio revealed that impairment relative to blood level was much greater in the absorption phase. This changing ratio underscores the point that blood levels alone are not an adequate estimate of intoxication.

After "chronically equivalent" barbital and pentobarbital dosing for 5 weeks, treatments were abruptly stopped and the animals were carefully observed for signs of barbiturate withdrawal. The severity of withdrawal was assessed at preset times by counting the number of grand mal type convulsions and subjectively rating 20 additional motor, autonomic and behavioral signs including tremors, twitches, myoclonic jerks, postural disturbances and motor incoordination. Ratings achieved at peak intensity (raw scores) and their incidences were used to compute "total intensity scores" for each graded sign. For all quantitative measures, withdrawal signs were less severe for barbital than for pentobarbital, with strikingly lower (P less than .05) incidences of convulsions (6.3% vs. 100%), bizarre (hallucinatory) behavior (6.3% vs. 41.3), and death (0% vs. 100%). The withdrawal signs for barbital appeared later, developed more slowly and persisted longer than those for pentobarbital. That the onset and then peak of withdrawal signs occurred when the extents of decline from peak blood concentration of barbital and pentobarbital were similiar suggests that the time course of withdrawal might be inversely related to residual concentrations of drug, i.e., negative dose-response.

We describe a liquid-chromatographic method involving a new, nonsilica column (XAD-2, Hamilton Co.) for pentobarbital in plasma. Plasma is extracted with chloroform after addition of the internal standard, 5-ethyl-5-p-tolyl-barbituric acid. Acidic drugs are back-extracted into alkali, then chromatographed on the resin-base reversed-phase column. The use of alkaline mobile phase allows enhanced sensitivity and detection of barbiturates at 240 nm. The within-run CV for 10 samples was 1.9%, the between-run CV 1.8%. Ten commonly used barbiturates are separated isocratically in less than 15 min. Other commonly prescribed acidic drugs do not interfere with determination of pentobarbital.

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.

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.

1. The results of a series of experiments in which anesthetized mongrel dogs were instrumented and preparations for closed-chest partial cardiopulmonary bypass with membrane oxygenation and hemodialysis were made, following which "fatal" barbiturate intoxication was produced by the intravenous route has been presented. 2. Of nine animals, three (33 l/3%) could be removed from cardiopulmonary bypass although postoperative cardiovascular dynamics remained abnormal. 3. The clinical implications of this study in patients with cardiac depression in spite of hemodialysis for barbiturate intoxication seemed promising.

The physical dependence and tolerance characteristics of barbiturates and ethanol were compared. One group of cats was given anesthetic doses of pentobarbital chronically to produce severe physical dependence ("high dose" group). Two other groups of animals were given barbital or ethanol at "chronically equivalent" doses which produced gross ataxia without anesthesia ("low dose" groups). The doses required to produce the preset level of central nervous system depression progressively increased in all three groups during the chronic administration. Functional tolerance estimated by measuring the drug concentration in the blood at the peak of the drug response was demonstrated in all three groups. Drug administration was terminated after various durations and withdrawal was rated. Severity of withdrawal was assessed by monitoring spontaneous convulsions and by rating motor, autonomic and behavioral signs. These ratings were used to compute peak intensity of withdrawal. The number of convulsions, incidence of lethality during withdrawal and peak withdrawal intensity ratings were considerably higher in the ethanol groups than in the low dose barbiturate groups. Similarly, the number of convulsions, incidence of lethality during withdrawal and peak intensity ratings were consistently higher in the high dose barbiturate groups than in the low dose barbiturate groups. The results indicate that ethanol produced more severe withdrawal than barbiturate when the level of chronic intoxication was comparable in the two groups. Also, the level of central nervous system depression during administration was an important factor influencing intensity of barbiturate withdrawal.