Comparative kinetics of digoxin in serum and vitreous humor in a guinea pig model. II. Single oral dose administration.

In a continuation of work previously reported involving the comparative kinetics of digoxin in vitreous humor and serum after an intravenous dose, the present report describes the pharmacokinetics of digoxin in this model following the administration of a single oral dose. Serum and vitreous humor concentrations of digoxin were monitored by radioimmunoassay for 720 min after a single oral dose of 0.1 mg digoxin/kg. Serum concentrations peaked by 60 min and declined over the remaining observation period with a half-life of 360 min. Vitreous humor concentrations lagged behind the serum concentrations, peaked between 60 and 120 min, and then declined at a rate less than that of serum with convergence of concentration occurring in the 720-min samples. The vitreous humor-serum ratios ranged from a low of 0.003 (15 min) to a high of 0.98 at convergence. The impact of these findings upon forensic toxicologic practice is reviewed.

Results of a multilaboratory checksample analysis program for carbon monoxide and cyanide.

A blind check sample analysis program, designed to evaluate global performance in the determination of fire-related analytes (carbon monoxide and cyanide), was implemented and processed using 10 field forensic toxicology laboratories. Each participant received, on a quarterly basis, a set of four calibrators and a set of four unknown check samples. Each participant was asked to determine the presence and quantity of carbon monoxide (carboxyhemoglobin in percent saturation of hemoglobin units) and cyanide (in mg/L units), using the calibrators for reference. The results were to be reported in an anonymous manner. Prior to and during the analysis period all batches of calibrators and check samples were validated for analyte stability using gas chromatography, CO- oximetry, and ion chromatography. The performance of the laboratories in the analysis of carboxyhemoglobin was evaluated over a concentration range of 3 to 40% saturation yielding a correlation with validation concentrations of 0.986. In some cases, false negatives and false positives were reported. The performance of laboratories in the analysis of cyanide was evaluated over a concentration range of 0.1 to 2.5 mg/L. Laboratory results yielded a correlation of 0.443 with validated concentrations. False negatives and false positives were also reported. Based upon the correlation estimates, it was concluded that forensic toxicology laboratories are likely to generate reliable carboxyhemoglobin data.

Comparative kinetics of serum and vitreous humor digoxin concentrations in a guinea pig model. Part I: Intravenous administration of digoxin.

The pharmacokinetics of a single intravenous dose of digoxin in the guinea pig was investigated with emphasis on the penetration of digoxin into the vitreous humor. A controlled study was undertaken and data was collected which indicated that digoxin follows an open, two-compartment pharmacokinetic model with a terminal half-life of 318 minutes. The data indicated that the ratio of vitreous concentrations to serum concentrations were determined to be equal following an initial tissue distribution phase.

An investigation of the toxic effects of combustion products--analysis of smoke components.

A comprehensive experimental design was developed to study the effects of thermal degradation products formed by the combustion of building materials on the behavior of rats. Three materials were studied. They were Douglas fir, wool, and polyvinyl chloride. Each material was tested under both flaming and nonflaming modes of combustion. The smoke and gases produced by each material were analyzed by specific gas detector tubes, gas chromatography/mass spectrometry, and infrared spectroscopy. Products measured during combustion included oxygen, carbon monoxide, carbon dioxide, hydrogen cyanide, and hydrocarbons. Part of a much larger study, this paper will deal with the analytical aspects of the experimental design.

A method to obtain maternal-fetal plasma samples using a microsampling technique in the rat: transplacental passage of cefoxitin.

A microsampling technique that allows taking blood samples from the umbilical vein of the pregnant rat is described. Such techniques are needed in order to allow pharmacokinetic and embryo exposure to be correlated with teratogenic endpoints. Cefoxitin was administered intravenously (300 mg/kg) into tracheotomized, pentobarbital anesthetized dams on day 21 in gestation. Blood samples were collected via the carotid artery from the dam and the umbilical vein of the fetus at designated times. Up to three samples of 20 to 30 microliters each, were taken from individual fetuses at 20-min intervals. With few exceptions, fetal cefoxitin concentrations were homogeneous at each sampling period. Fetal concentrations were low compared to maternal concentrations as seen by the small fetal/maternal area under the curve ratio (0.053 +/- 0.006).

Pharmacokinetics of nalbuphine during parturition.

Nalbuphine hydrochloride (Nubain) is a relatively new agonist-antagonist analgesic, chemically related to both oxymorphone and naloxone, which can be used as a systemic obstetric analgesic. After intravenous administration to six patients in labor at term, serial maternal serum specimens were obtained and assayed for their nalbuphine concentration. The maternal disposition of nalbuphine followed a two-compartment pharmacokinetic model, with an initial distribution phase of 4 to 20 minutes and a terminal elimination half-life of 2.4 +/- 0.4 hours. Measurement of umbilical cord blood nalbuphine concentrations demonstrated that nalbuphine crossed the placenta and entered the fetal circulation. Newborn concentrations varied substantially, ranging from one third to six times the simultaneous maternal concentration.

Measurement of oxygen tension in the ischemic myocardium using encased polargraphic oxygen electrodes.

The ability to continuously monitor the delicate balance between blood flow and oxygen consumption would be a great asset in the study of myocardial ischemia. The present study was performed, in anesthetized dogs, to validate the use of encased polargraphic oxygen electrodes in the study of myocardial ischemia. Polargraphic oxygen electrodes were placed in the area to be rendered ischemic at fixed tissue depths of 3 mm (epicardium) and 9 mm (endocardium). Endocardial and epicardial oxygen tensions as well as the ratio of endocardial to epicardial oxygen tension and left circumflex coronary flow were monitored. Ischemia was induced by decreasing left circumflex coronary flow by 50%. Upon completion of a 20-min poststenotic period, endocardial pO2, endocardial/epicardial ratio, and coronary flow were significantly decreased (59 +/- 7, 52 +/- 7, and 55 +/- 4%, respectively) whereas epicardial pO2 was slightly decreased. Nitroglycerin (10 micrograms/kg, i.v.) markedly increased endocardial pO2 and endocardial/epicardial ratio above poststenotic control (13 +/- 5 mmHg and 64 +/- 10%, respectively) whereas epicardial pO2 was not significantly decreased. The increases in endocardial pO2 occurred at a point where coronary flow and mean arterial pressure were not significantly changed. Conversely, dipyridamole (125 micrograms/kg, i.v.) significantly increased coronary flow (26 +/- 2 ml/min/100 g) although it did not appreciably alter endocardial or epicardial pO2. It is concluded that encased polargraphic oxygen electrodes provide a quantitative method for determination of oxygen tension in the ischemic myocardium.

Effects of nitroglycerin, dipyridamole, nifedipine, verapamil and diltiazem on canine coronary arterial rings contracted with 5-hydroxytryptamine and anoxia.

Anoxia has been shown to potentiate the constrictor effects of 5-hydroxytryptamine (5HT) in isolated vascular tissue. In the present study, canine coronary arterial rings were incubated with various treatments and exposed to 5HT (4 X 10(-7) M) and anoxia (95% N2 and 5% CO2). Developed tension was increased by 250 +/- 40 mg by 5HT alone and 2,000 +/- 90 mg by 5HT and anoxia. Calcium (5 mM) potentiated, while inorganic (lanthanum, 10(-2) M) and organic calcium antagonists (nifedipine, verapamil and diltiazem; IC50 = 7 X 10(-9), 7.3 X 10(-8) and 2.4 X 10(-7) M, respectively) blocked the anoxic potentiation. Anoxia alone decreased resting tension (RT). Methysergide 3 X 10(-5) M inhibited both the 5HT- and anoxia-potentiated responses. Nitroglycerin decreased RT and inhibited the anoxic response (IC50 = 7.6 X 10(-6) M), while dipyridamole decreased RT and did not affect the anoxic response. These data suggest that the potentiation of 5HT contraction by anoxia is dependent upon extracellular calcium influx and is linked to a 5HT receptor. In addition, inhibition of the anoxic response can be achieved at other sites and is not a property common to all coronary vasodilators.

Determination of succinylcholine in tissues by TLC, GC/NPD, and GC/MS.

Succinylcholine, a bis-quaternary ammonium compound, is considered an elusive analyte due to rapid hydrolysis by pseudocholinesterase in plasma. However, tissue acetylcholinesterase is relatively inactive toward this substrate. Hence, analysis of tissues of succinylcholine-treated animals may reveal the presence of unchanged drug. This report describes three chromatographic techniques (TLC, GC/NPD, and GC/MS) which may be applied to the analysis of this substance in human tissues. Validation of the techniques was accomplished using tissues from rats treated with succinylcholine.

Evaluation of the methadone-alcohol interaction. I. Alterations of plasma concentration kinetics.

Clinical anecdotal reports have indicated a probably additive and/or synergistic response to the co-ingestion of ethyl alcohol and methadone. This study investigated the possible explanations for this observations, which may be associated with alterations of the plasma concentration dynamics of methadone and alcohol in the rat. Plasma concentrations of ethanol, methadone or both were followed over an eight hour period following substance administration. GC/FID and GC/MS were employed to quantify ethanol and methadone, respectively. The results of this study indicated that ethyl alcohol significantly increased peak methadone concentrations. Further, methadone significantly depressed late alcohol elimination.

Isolation of drugs from post mortem specimens with the automated sample processor. Part I. Barbiturate derivatives.

Employing an automated sample processor, barbiturate positive tissue homogenates were analyzed to yield gas and liquid chromatographic data. Excellent quality extracts were produced that could be assayed by either GC/NPD or HPLC. Good precision and accuracy was found (CV 2-5%) with approximately 200 mg of tissue sample. The technique has been applied to authentic post mortem tissues and fluids.

Methodology for the detection and measurement of amygdalin in tissues and fluids.

Methods suitable for the demonstration of amygdalin are presented; including an indirect determination (measurement of enzymatically derived benzaldehyde) and several direct methodologies (GC/MS, HPLC, or TLC). Reagents and equipment commonly found in a forensic toxicology laboratory were employed.

Determination of basic drugs in post mortem tissues: a microextraction technique utilizing GLC/NPD of effluents.

A method is described for the estimation of basic drugs and metabolites in post mortem tissues and fluids. The method is based upon the selective extraction of these substances, differential weak acid cleanup, and the final preparation of a microextract that is compatible with the rubidium source found in most nitrogen-phosphorous detectors (NPD). Application of this extract to gas chromatography/NPD allows for the measurement of common basic drugs at subtherapeutic, therapeutic, and toxic concentrations in a variety of tissue matrices (liver, brain, lung, heart, and kidney) using a minimum of sample (less than one gram). Internal standards are used to allow for the quantitative as well as qualitative aspects of the assay. Examples of tissue extract chromatograms containing commonly encountered basic drugs are presented along with precision data.

A rapid isolation technique for drugs from tissues and fluids: use of the Du Pont Prep 1 system.

A microprocessor-controlled, automated extraction/concentration device, the Prep 1 (Du Pont Clinical Systems), was evaluated for application to the isolation of drug substances from postmortem fluids and tissue homogenates. Two classes of materials were investigated: barbiturates and the benzodiazepine, diazepam. With as little as 200 mg of tissue, barbiturate derivatives were successfully isolated and measured by gas chromatography using nitrogen-phosphorus detection with a coefficient of variation of 2 to 5%. Diazepam was measured in a similar fashion with a coefficient of variation of 4.4%. Preliminary investigation indicates that this system is applicable to a wide range of drug substances of toxicological interest.

Respirator toxicology.

A case of delayed death resulting from drowning was investigated. A disparity in the propoxyphene concentrations determined in antemortem and postmortem specimens appeared to exist. The disparity is apparently a product of the fact that cardiopulmonary function had been maintained artificially for 57 h, with subsequent tissue autolysis that was demonstrated microscopically. Interpretation of laboratory findings on postmortem specimens must be done with caution when the interval between drug exposure and death has been interrupted by respiratory therapy.

Immunofluorescence detection of drugs in postmortem tissues: a new technique with potential for assessment of drug influence in cause of death.

This report describes a new technique, immunofluorescence, for the detection and possible characterization of drug content in postmortem tissues. By using antisera generated against a drug-protein conjugate, the stabilization of tissue-sequestered drug is accomplished by incubation of fresh frozen sections of tissue with dilute solutions of rabbit anti-drug antibodies. Secondary incubation with a fluorescence-labeled anti-rabbit immunoglobulin labels these points of sequestration. Tissue sections so stained are examined by fluorescence microscopy. In studies with rats given graded doses of morphine sulfate, there were discernible differences in tissue binding of morphine in brain sections from animals treated "therapeutically," fatally, and chronically. Extension of these studies to human autopsy material is anticipated and potential problems are discussed. This technique offers the forensic toxicologist the potential for evaluating the drug content of tissues in situ.

Rapid determination of serum theophylline levels using the MPLC short column concept.

Many procedures are currently available demonstrating the feasibility of the analysis of serum theophylline concentrations by high performance, high pressure liquid chromatography utilizing chromatographic columns which can only be described by the term "expensive" in terms of column life and cost. We have developed and evaluated a rapid "medium pressure, medium performance" liquid chromatographic (MPLC) method for theophylline in serum utilizing a chromatographic column that costs up to 1/3 the cost of current HPLC columns. Less than 0.2 ml of serum is required for each determination, yet the sensitivity of the method is easily less than 1 mg/liter. The method involves liquid extractive isolation, chromatography on a micro column (4.6mm x 10cm) of RP-18 and provides adequate selectivity, accuracy and precision for routine and non-routine (neonatal) theophylline determinations. We have found no endogenous or exogenous interferences. Reproducibility for the microscale method is controlled through the use of hydroxypropyl theophylline as an internal standard.