Pharmacokinetics of drug overdose

Hepatotoxic assessment in a microphysiological system: Simulation of the drug absorption and toxic process after an overdosed acetaminophen on intestinal-liver-on-chip

To compensate the limitation of animal models, new models were proposed for drug safety evaluation to refine and reduce existing models. To mimic drug absorption and metabolism and predict toxicokinetic and toxic effects in an in vitro intestinal-liver microphysiological system (MPS), we constructed an intestinal-liver-on-chip and detected the acute liver injury process after an overdose of acetaminophen (APAP). Caco-2 and HT29-MTX-E12 cell lines were utilized to establish intestinal equivalents, along with HepG2, HUVEC-T1, and THP-1 induced by PMA and human hepatic stellate cell to establish liver equivalents. The APAP concentration was determined using high-performance liquid chromatography, and the toxicokinetic parameters were fitted using the non-compartmental analysis method by Phoenix. Changes in liver injury biomarkers aspartate aminotransferase and alanine aminotransferase, and liver function marker albumin indicated that the short-term culture of the two organs-on-chip model was stable for 4 days. Reactive oxygen species signaling was enhanced after APAP administration, along with decreased mitochondrial membrane potential, activated caspase-3, and enhanced p53 signaling, indicating a toxic response induced by APAP overdose. In the gut-liver MPS model, we fitted the toxicokinetic parameters and simulated the hepatotoxicity procedure following an APAP overdose, which will facilitate the organ-on-chips application in drug toxicity assays.

Population toxicokinetics of carbamazepine and its metabolite carbamazepine-10,11-epoxide in adults

BACKGROUND

Carbamazepine is one of the most commonly used antiseizure medications. Although carbamazepine pharmacokinetics in epileptic patients is well described, much less is known about these processes in the patients who experienced self-poisoning episode by this drug. Therefore, the aim of our investigation was to perform population toxicokinetics of carbamazepine and its metabolite carbamazepine-10,11-epoxide in adults.

RESEARCH DESIGN AND METHODS

Software program NONMEM and the ADVAN2 TRANS2 subroutine were used for establishing a population toxicokinetic model for the estimation of clearance and volume of distribution based on of the sum values of carbamazepine and carbamazepine-10,11-epoxide concentrations.

RESULTS

Our results indicated that the adult patients' ability to eliminate carbamazepine and carbamazepine-10,11-epoxide following acute carbamazepine self-poisoning was strongly associated with the high levels of CRP and ASP, as well as by the treatment with sedation.

CONCLUSIONS

Our study should provide better understanding of the toxicokinetics of carbamazepine taken in overdose and better management of patient population admitted to hospital.

The Individualized Management Approach for Acute Poisoning

Acute poisoning is a widespread emergency that mandates early management decisions for optimal outcomes. An individualized approach is an ideal way to provide those outcomes. Promoting awareness among healthcare professionals managing acute poisoning about the importance of incorporating the pharmacokinetics and following certain criteria to consider interventions such as activated charcoal, antidote, or specific investigations may improve their risk assessment strategies and management plans. To address the main aspects that should be considered to develop a customized poisoning management plan, we conducted this review based on relevant publications recovered by a careful search in PubMed. Our opinions as experts from the King Saud University (KSU) Drug and Poison Information Center (DPIC) were considered in the review.

Status of Hemodialysis of Drugs in 2002

Hemodialysis is a life-sustaining chronic therapy for individuals with end stage renal disease (ESRD). It is also frequently used for days to weeks for patients with acute renal failure who are awaiting the recovery of their kidneys from the acute toxic or traumatic event. Both populations of patients often require complex pharmacotherapeutic regimens, and it is not uncommon for them to be receiving 10 or more concomitant medications. Optimization of care for these patients is dependent on the selection of the most appropriate drug as well as dosage regimen design, which accounts for the influence of hemodialysis therapy on drug disposition. During the last 10 to 15 years there have been several significant changes in the prescribed dose of dialysis and the composition and size of dialyzers available for use. Furthermore, reuse of dialyzers, which was rare in the early 1980s, is now common; it is employed with over 70% of patients with ESRD. The new synthetic dialyzers, which are now used for over 60% of ESRD patients in the United States, are uniformly associated with dramatic improvements in drug removal; dialysis clearance increases of 3 to 10 fold were common for the few drugs evaluated. The influence of these changes in hemodialysis therapy on drug disposition are discussed in a quantitative fashion, and a conceptual framework for drug therapy regimen decision making is presented. For the majority of the drugs reviewed, however, there were no data in the literature regarding dialyzability with currently available dialyzers. The generation of dialyzability data for old and new pharmacotherapeutic agents with state of the art dialysis procedures is clearly needed.

Extracorporeal Treatment in Phenytoin Poisoning: Systematic Review and Recommendations from the EXTRIP (Extracorporeal Treatments in Poisoning) Workgroup

The Extracorporeal Treatments in Poisoning (EXTRIP) Workgroup conducted a systematic literature review using a standardized process to develop evidence-based recommendations on the use of extracorporeal treatment (ECTR) in patients with phenytoin poisoning. The authors reviewed all articles, extracted data, summarized findings, and proposed structured voting statements following a predetermined format. A 2-round modified Delphi method was used to reach a consensus on voting statements, and the RAND/UCLA Appropriateness Method was used to quantify disagreement. 51 articles met the inclusion criteria. Only case reports, case series, and pharmacokinetic studies were identified, yielding a very low quality of evidence. Clinical data from 31 patients and toxicokinetic grading from 46 patients were abstracted. The workgroup concluded that phenytoin is moderately dialyzable (level of evidence = C) despite its high protein binding and made the following recommendations. ECTR would be reasonable in select cases of severe phenytoin poisoning (neutral recommendation, 3D). ECTR is suggested if prolonged coma is present or expected (graded 2D) and it would be reasonable if prolonged incapacitating ataxia is present or expected (graded 3D). If ECTR is used, it should be discontinued when clinical improvement is apparent (graded 1D). The preferred ECTR modality in phenytoin poisoning is intermittent hemodialysis (graded 1D), but hemoperfusion is an acceptable alternative if hemodialysis is not available (graded 1D). In summary, phenytoin appears to be amenable to extracorporeal removal. However, because of the low incidence of irreversible tissue injury or death related to phenytoin poisoning and the relatively limited effect of ECTR on phenytoin removal, the workgroup proposed the use of ECTR only in very select patients with severe phenytoin poisoning.

Management of the critically poisoned patient

BACKGROUND

Clinicians are often challenged to manage critically ill poison patients. The clinical effects encountered in poisoned patients are dependent on numerous variables, such as the dose, the length of exposure time, and the pre-existing health of the patient. The goal of this article is to introduce the basic concepts for evaluation of poisoned patients and review the appropriate management of such patients based on the currently available literature.

METHODS

An unsystematic review of the medical literature was performed and articles pertaining to human poisoning were obtained. The literature selected was based on the preference and clinical expertise of authors.

DISCUSSION

If a poisoning is recognized early and appropriate testing and supportive care is initiated rapidly, the majority of patient outcomes will be good. Judicious use of antidotes should be practiced and clinicians should clearly understand the indications and contraindications of antidotes prior to administration.

The Management of Tricyclic Antidepressant Poisoning

Although there have been descriptive, uncontrolled clinical reports of removal of tablet debris by gastric lavage, there have been no clinical studies that have demonstrated that this has any impact on outcome in patients with tricyclic antidepressant (TCA) poisoning. There is also the possibility that lavage may increase drug absorption by pushing tablets into the small intestine. Furthermore, gastric lavage in patients with TCA poisoning may induce hypoxia and a tachycardia potentially increasing the risk of severe complications such as arrhythmias and convulsions. In view of the paucity of evidence that gastric lavage removes a significant amount of drug and the risk of complications associated with the procedure, the routine use of gastric lavage in the management of patients with TCA poisoning is not appropriate. Volunteer studies have shown generally that activated charcoal is more likely to reduce drug absorption if it is administered within 1 hour of drug ingestion. In the one volunteer study that looked at later administration of activated charcoal, there was a 37% decrease in plasma concentration associated with administration of activated charcoal at 2 hours post-ingestion. There have been no clinical studies that enable an estimate of the effect of activated charcoal administration on outcome in the management of patients with TCA poisoning. Volunteer studies have shown that multiple-dose activated charcoal increases the elimination of therapeutic doses of amitriptyline and nortriptyline, but not of doxepin or imipramine; however, these studies cannot be directly extrapolated to the management of patients with TCA poisoning. There have been no well designed controlled studies that have assessed the impact of multiple-dose activated charcoal in the management of patients with TCA poisoning. Because of the large volume of distribution of TCAs, it would not be expected that their elimination would be significantly increased by multiple-dose activated charcoal.Haemoperfusion, haemodialysis and the combination of these procedures do not result in significant removal of TCAs and are not recommended in the management of patients with TCA poisoning.

Poisoned patients as potential organ donors: postal survey of transplant centres and intensive care units

BACKGROUND

The number of patients awaiting allograft transplantation in the UK exceeds the number of organs offered for transplantation each year. Most organ donors tend to be young, fit and healthy individuals who die because of trauma or sudden cardiac arrest. Patients who die from drug and poison intoxication tend to have similar characteristics but are less frequently offered as potential organ donors.

METHODS

A postal questionnaire survey of all transplantation centres and an equal number of intensive care units in the UK was undertaken. The use of kidney, heart, lung, liver and pancreas transplants from poisoned patients following deliberate methanol ingestion, cardiac arrest presumed secondary to cocaine overdose, accidental domestic carbon monoxide inhalation and industrial cyanide exposure were used as case scenarios.

RESULTS

Response rates were 70% for transplantation centres and 50% for intensive care unit directors. Over 80% of organs would be offered or discussed with transplant coordinators by intensive care unit directors. Transplantation physicians/surgeons would consider transplanting organs in up to 100% of case scenarios, depending on the organ and poisoning or intoxication involved.

DISCUSSION

The postal survey presented here shows that most transplantation physicians and surgeons and intensive care unit directors would consider those who die following acute drug intoxication and poisoning as potential organ donors. The previously reported literature shows in general that transplanted organs from poisoned patients have good long-term survival, although the number of reports is small. Poisoned patients are another pool of organ donors who at present are probably underused by transplantation services.

Position statement: single-dose activated charcoal. American Academy of Clinical Toxicology; European Association of Poisons Centres and Clinical Toxicologists

In preparing this Position Statement, all relevant scientific literature was identified and reviewed critically by acknowledged experts using agreed criteria. Well-conducted clinical and experimental studies were given precedence over anecdotal case reports and abstracts were not usually considered. A draft Position Statement was then produced and subjected to detailed peer review by an international group of clinical toxicologists chosen by the American Academy of Clinical Toxicology and the European Association of Poisons Centres and Clinical Toxicologists. The Position Statement went through multiple drafts before being approved by the boards of the two societies and being endorsed by other societies. The Position Statement includes a summary statement for ease of use and is supported by detailed documentation which describes the scientific evidence on which the Statement is based. Single-dose activated charcoal should not be administered routinely in the management of poisoned patients. Based on volunteer studies, the effectiveness of activated charcoal decreases with time; the greatest benefit is within 1 hour of ingestion. The administration of activated charcoal may be considered if a patient has ingested a potentially toxic amount of a poison (which is known to be adsorbed to charcoal) up to 1 hour previously; there are insufficient data to support or exclude its use after 1 hour of ingestion. There is no evidence that the administration of activated charcoal improves clinical outcome. Unless a patient has an intact or protected airway, the administration of charcoal is contraindicated.

Correlation of drug pharmacokinetics and effectiveness of multiple-dose activated charcoal therapy

STUDY OBJECTIVE

To evaluate an animal model of multiple-dose activated charcoal (MDAC) therapy and correlate the pharmacokinetic properties of four drugs with the efficacy of MDAC.

DESIGN

Prospective, randomized, controlled, crossover design.

SETTING

A university animal research facility.

PARTICIPANTS

Seven female pigs (15 to 22 kg) with an indwelling central venous line and gastrostomy tube.

INTERVENTIONS

Acetaminophen (30 mg/kg), digoxin (30 micrograms/kg), theophylline (8.9 mg/kg), and valproic acid (18 mg/kg) were simultaneously administered intravenously over 12 minutes. In the experimental arm, 25 g activated charcoal was administered at 0, 2, 4, 6, 12, 18, 24, and 30 hours through the gastric tube. In the control arm, an equal volume of water was given at the same times. Blood specimens were obtained over 36 hours to measure serum drug concentrations.

RESULTS

Each drug exhibited enhanced elimination (P < .01) in the MDAC group except valproic acid. Lower intrinsic clearance was correlated (P < .05) with increased systemic elimination during the charcoal arm. Volume of distribution, half-life, and protein binding were not significantly correlated with charcoal-enhanced systemic drug elimination.

CONCLUSION

The response of a drug to MDAC may be affected by its intrinsic clearance. The restrictive nature of the protein binding of valproic acid may be responsible for its lack of response. Results with the porcine model are consistent with the effects observed in human beings.

Multiple-dose activated charcoal and enhancement of systemic drug clearance: summary of studies in animals and human volunteers

Multiple-dose activated charcoal therapy can enhance the systemic elimination of many drugs. Studies in animals and human volunteers provide a framework for understanding the indications and limitations of multiple-dose activated charcoal therapy. Enterocapillary exsorption creates a compartment for diffusion drugs out of the bloodstream and activated charcoal can augment this process to enhance drug clearance. Once charcoal reaches the intestine, there is a rapid onset of action. Clearance at exsorption sites is limited by blood flow; moreover, the rate of exsorption is related to the dose of charcoal up to a ceiling dose. Drug absorption, distribution, metabolism and elimination dynamically interact with multiple-dose activated charcoal therapy making it difficult to identify a single variable that may predict the success or failure with this therapy. Drug characteristics associated with enhanced systemic clearance with multiple-dose activated charcoal include a low intrinsic clearance, presence in the body for a sufficient time period for charcoal to act, a prolonged distributive phase, non-restrictive protein binding, and a small volume of distribution. Drugs that are unaffected at low doses may respond to multiple doses of activated charcoal when nonlinear kinetics are apparent due to overdose or disease. Although our current understanding is incomplete, multiple-dose activated charcoal therapy will play a role in the future therapy of poisoning patients.

When should dialysis be performed in lithium poisoning? A kinetic study in 14 cases of lithium poisoning

Lithium kinetics were studied in 14 patients with lithium poisoning. Three patients were treated by hemodialysis. Serum lithium peak concentrations ranged between 1.4 and 9.6 mmol/L. The apparent mean serum half-life was 23.16 +/- 9 h, the mean total clearance was 26.5 +/- 13.3 mL/min and the mean renal clearance was 17.2 +/- 5.4 mL/min. The kinetic parameters were dependent on the duration of the study and on the type of the poisoning: acute, acute upon chronic or chronic. During the first 12 h after admission ten patients were in a distribution phase, three were in an elimination phase and one was in an absorption phase. The serum half-life during hemodialysis ranged from 3.6 to 5.7 h and hemodialysis clearance was 63.2 to 114.4 mL/min. The mean volume of distribution calculated in six cases was 0.63 +/- 0.09 L/kg. The evolution of the lithium pools showed a different kinetic pattern between the extra- and the intracellular pool which decreased more slowly. During hemodialysis the decrease of the extracellular pool was about twice that of the cellular pool. Among the factors which may modify lithium toxicity and kinetics, are the type of the poisoning, the presence of an underlying disease and renal impairment. No general and rigid indication for hemodialysis can be set, but the need for hemodialysis should be based on clinical and kinetic data determined during the 12 h following admission.

Pharmacokinetics in acute illness

Severe illness at any age is accompanied by organ dysfunction, the administration of numerous drugs and complex changes in drug absorption, disposition and action. The clinician faced with a seriously ill patient should be aware of the important principles of drug treatment in critical illness. With acute illness of all types, the premature infant and the octogenarian lie at opposite ends of an age spectrum which encompasses the gamut of human disease and changeable organ pathophysiology. The common requirement of this host of variables is a flexible management plan, and careful observation of the patient's response to a therapeutic regimen which has been based on a sound knowledge of drug pharmacokinetics.

Non-linear kinetics of 4-methylpyrazole in healthy human subjects

In order to evaluate the pharmacokinetic profile of the alcohol dehydrogenase inhibitor 4-methylpyrazole 4-MP, a placebo-controlled, double-blind, single-dose, randomized, sequential, ascending-dose "Phase-I study" was performed in healthy male volunteers at dose levels of 10 (n = 4), 20 (n = 4), 50 (n = 4) and 100 mg.kg-1 (n = 3). In the 10 and 20 mg.kg-1 group, the elimination of 4-MP from the plasma followed non-linear kinetics with mean rates of concentration decline of 3.66 and 5.05 mumol.l-1.h-1, respectively. In the two highest dose groups, the elimination also appeared to be non-linear although the patterns were not followed long enough to confirm this. The mean rates of concentration decline at the higher doses were significantly increased, up to 14.9 mumol.l-1.h-1 at 100 mg.kg-1. The average renal clearance of 4-MP was low, 0.016 ml.min-1.kg-1, and only 3% of the administered dose was excreted unchanged in the urine, indicating metabolism as the major route of elimination. Because of the apparently unusual kinetics following single dose treatment, thorough multiple dose studies need to be carried out to determine a safe dosage regimen for 4-MP.

Thermodynamic evaluation of activated charcoal as a poison antidote by high-performance liquid chromatography. II: In vitro method for the evaluation of activated charcoal as a poison antidote

A previous report detailed the derivation and validation of an equation for calculating the Gibbs free energy of liquid-solid adsorption via high-performance liquid chromatography (HPLC). This study utilizes an improved form of that equation in conjunction with an in vitro model of solute adsorption to give an ordered listing of the antidotal activity of activated charcoal towards different drugs and other chemicals. The in vitro model consists of an activated charcoal column with a nominal particle diameter of 15 micron and a surface area of 447 x 10(4) cm2/g, together with a series of acetonitrile:water mobile phases at pH 3. A simple and efficient procedure was developed for ranking the solutes. First, each compound was run in an acetonitrile(ACN):water mobile phase chosen to give a convenient retention time and ideal chromatographic response. The capacity factor for this mobile phase was extrapolated to give a predicted capacity factor for a 35:65 (v/v) ACN:water mobile phase using an empirical equation developed from the exhaustive chromatography of four standard compounds (phenobarbital, strychnine, cyclohexanone, methyl ethyl ketone) in a variety of ACN:water mobile phases. In addition to the standards, 12 other compounds (glutethimide, chlordiazepoxide, quinine, brucine, d-propoxyphene, pentobarbital, methyprylon, methadone, meperidine, codeine, antipyrine, morphine) were evaluated. Based on these data, the Gibbs free energies of liquid-solid adsorption for these compounds were calculated and used to evaluate activated charcoal as a poison antidote for them. The results indicate that a rapid and accurate estimation of the utility of activated charcoal as an antidote for drugs and toxic substances can be obtained from a single chromatographic run of the test compound.

Oral activated charcoal in the treatment of intoxications. Role of single and repeated doses

Activated charcoal has an ability to adsorb a wide variety of substances. This property can be applied to prevent the gastrointestinal absorption of various drugs and toxins and to increase their elimination, even after systemic absorption. Single doses of oral activated charcoal effectively prevent the gastrointestinal absorption of most drugs and toxins present in the stomach at the time of charcoal administration. Known exceptions are alcohols, cyanide, and metals such as iron and lithium. In general, activated charcoal is more effective than gastric emptying. However, if the amount of drug or poison ingested is very large or if its affinity to charcoal is poor, the adsorption capacity of activated charcoal can be saturated. In such cases properly performed gastric emptying is likely to be more effective than charcoal alone. Repeated dosing with oral activated charcoal enhances the elimination of many toxicologically significant agents, e.g. aspirin, carbamazepine, dapsone, dextropropoxyphene, cardiac glycosides, meprobamate, phenobarbitone, phenytoin and theophylline. It also accelerates the elimination of many industrial and environmental intoxicants. In acute intoxications 50 to 100g activated charcoal should be administered to adult patients (to children, about 1 g/kg) as soon as possible. The exceptions are patients poisoned with caustic alkalis or acids which will immediately cause local tissue damages. To avoid delays in charcoal administration, activated charcoal should be a part of first-aid kits both at home and at work. The 'blind' administration of charcoal neither prevents later gastric emptying nor does it cause serious adverse effects provided that pulmonary aspiration in obtunded patients is prevented. In severe acute poisonings oral activated charcoal should be administered repeatedly, e.g. 20 to 50g at intervals of 4 to 6 hours, until recovery or until plasma drug concentrations have fallen to non-toxic levels. In addition to increasing the elimination of many drugs and toxins even after their systemic absorption, repeated doses of charcoal also reduce the risk of desorbing from the charcoal-toxin complex as the complex passes through the gastrointestinal tract. Charcoal will not increase the elimination of all substances taken. However, as the drug history in acute intoxications is often unreliable, repeated doses of oral activated charcoal in severe intoxications seem to be justified unless the toxicological laboratory has identified the causative agent as not being prone to adsorption by charcoal. The role of repeated doses of oral activated charcoal in chronic intoxication has not been clearly defined.(ABSTRACT TRUNCATED AT 400 WORDS)

Lithium intoxication: pharmacokinetics during and after terminated hemodialysis in acute intoxications

Pharmacokinetics of lithium were studied in 4 females acutely intoxicated with lithium with maximal plasma concentrations of 8.7, 4.0, 3.4 and 1.3 mmol/l. Mean plasma dialysance values were 103, 105, 102 and 89 ml/min compared to mean renal clearance values of 13, 16, 20 and 30 ml/min, respectively. A rebound effect in plasma concentration suggested that the sum of the dialysance and renal clearance overestimated the total body clearance of lithium during hemodialysis. During hemodialysis the measured half-lives of the plasma lithium levels in three cases were 4.8, 3.4 and 2.3 hours compared to the corrected values of 12.0, 7.3 and 6.2 hours respectively, when this rebound effect was taken into consideration. These corrected half-lives were 30-66% of the control half-lives recorded later when each patient served as her own control, thus illustrating the effectiveness of hemodialysis in removing lithium. Forced diuresis with sodium chloride did not significantly increase renal lithium elimination.

Efficacy of gastric emptying: gastric lavage versus emesis induced with ipecac

A prospective study was done to compare the efficacy of gastric emptying achieved by gastric lavage (GL) with that of ipecac-induced emesis (IE) in victims of drug overdose. Thiamine was used as a marker of recovery in gastric samples, as measured by ion exchange/ion pair high-performance liquid chromatography. There were 51 patients in the IE group and 37 in the GL group. GL produced a higher mean per cent recovery of thiamine than did IE (90% +/- 34% compared with 50% +/- 35%). There was a significant difference between the two groups (P less than .001). Recovery of thiamine was more than 70% in 28% of the IE patients, and exceeded 70% in 75% of GL patients. When gastric emptying is desired for management of the adult overdose victim, the use of GL maximizes the chance of recovering unabsorbed liquid drugs from the stomach.

Toxicokinetics of lithium intoxication treated by hemodialysis

A 66-year old female on long-term lithium therapy, developed neurologic toxicity with coma and convulsions. The treatment consisted artificial ventilation, fluid and electrolyte infusions and a six hour hemodialysis (HD) on days 2, 3 and 4. The convulsions disappeared on day 4; the patient regained consciousness on day l2 and recovered with slight sequelae. Toxicokinetic studies were conducted for a period of 12 days. The lithium (Li) serum concentration fell from 4.4 mmol/l on admission to 2.16 before HD and 0.35 after three HD. Li serum half life was 54 hours before HD, 25 hours during the three days on which HD was carried out and 106 hours thereafter. The Li cerebrospinal fluid/Li serum ratio ranged between 0.4 and 0.6 and was not influenced by HD. Mean renal clearance was 10.6 ml per min. During hemodialysis, Li serum half life decreased to 3.5 - 4.9 hours and clearance was 108 ml/min. A total amount of l28.6 mmol lithium was excreted; 84.3 mmol by HD and 44.3 mmol in urine. Patient's clinical course and electroencephalographic signs were correlated with the calculated cellular pool of Li but not with Li serum concentrations. This study confirms the effectiveness of HD to decrease the cellular pool of lithium. However, rather than considering only the absolute Li serum concentration, the presence of a rebound peak after HD may be viewed as indication for further hemodialysis.

Pharmacokinetics of methyprylon following a single oral dose

Single oral doses of 300 mg of methyprylon were administered to 10 healthy volunteers. Plasma concentrations of methyprylon and its dehydro metabolite were measured using a recently developed HPLC assay. Plasma concentration-time data were fitted to a two-compartment model with either first-order absorption, zero-order absorption, or two consecutive, discontinuous, first-order absorption rate constants. Based on the criteria of visual inspection, the correlation coefficient, standard deviations of the parameter estimates, and the residual sum of squares, it was concluded that the zero-order absorption model fit the data best. Mean (+/- SD) values for the half-life (9.2 +/- 2.2 h), apparent clearance, (11.91 +/- 4.42 mL/h/kg) and apparent steady-state volume of distribution, (0.97 +/- 0.33 L/kg) were found.

The effects of dopamine on central hemodynamics and myocardial metabolism in experimental propoxyphene-induced shock

The hemodynamic and cardiometabolic effects of dopamine were evaluated in propoxyphene-induced circulatory shock in eight pentobarbital anesthetized pigs. Circulatory shock was induced by an infusion of propoxyphene chloride 15 mg . min-1 i.v. At shock, i.e. CI less than or equal to 2.0 l . min-1 . m-2 and/or MAP less than or equal to 60 mmHg, dopamine was infused at 10, 20, 40, 80 and 160 micrograms . kg-1 . min-1 with an interval between increments of 8 min. After 30 min at 160 micrograms . kg-1 . min-1, the infusion rate was reversibly decreased. The propoxyphene infusion of 15 mg . min-1 was continued throughout the study. Dopamine improved the circulation in seven animals; one animal died in refractory shock during dopamine infusion. Dopamine infusion at shock level resulted in an increase of the following variables (% of baseline value): MAP (69%), HR (109%), CI (138%) and SVI (129%). Normalisation was seen in MRAP (120%) and in MPAOP (100%). A profound decrease in systemic vascular resistance was unchanged. Increases were seen in left and right ventricular stroke work index, to 88% and 176% of baseline, respectively. Left ventricular dP/dt increased (170%). In the coronary circulation myocardial blood flow increased (133%) as did myocardial oxygen consumption (65%) concomitant with a decrease in myocardial oxygen uptake (41%), but coronary vascular resistance progressively decreased (38%). The myocardial propoxyphene extraction changed from +54% to -86% during peak dopamine infusion. In conclusion, dopamine reversed cardiac failure in propoxyphene overdose by a marked positive inotropic stimulation restoring contractility. A marked positive chronotropic stimulation maintained a sufficient cardiac index and a normal blood pressure in spite of a profound vasodilatation which was unresponsive to dopamine.

Acute propoxyphene self-poisoning in 222 consecutive patients

The course of severe propoxyphene self-poisoning in 222 consecutive patients is presented. On admission, 73% of the patients had neurological symptoms, 10% had convulsions, 45% were in respiratory failure, and impaired circulation was present in 48%. A mortality rate of 8% was observed. Twelve patients arrived in asystole of whom six were resuscitated without sequelae. The overdose was accidental in 13 patients, one of whom died. Early medical intensive care was found mandatory for a good prognosis. Before discharge from the ICU we recommend an observation-period free of cardiovascular symptoms for 24 h.

Acute self-poisoning with tricyclic antidepressants in 295 consecutive patients treated in an ICU

Clinical findings on admission to hospital and outcome in 295 consecutive patients with severe tricyclic antidepressant self-poisoning treated in an ICU are presented. Cerebral depression was observed in 92%, convulsions in 23% and respiratory failure was present in 72%. Cardiovascular function was impaired in 44% and an abnormal ECG was found in 57%. Cardiac arrest was treated in 14 patients (6%) of whom seven were resuscitated. The mortality rate was 2%. All patients were artificially ventilated. A beneficial effect of respiratory alkalosis on cardiac arrhythmias is supported.

Drug prescribing in renal failure: dosing guidelines for adults

The data base for rational guidelines to safe, efficacious drug prescribing in adults with renal insufficiency are presented in tabular form. Current medical literature was extensively surveyed to provide as much specific information as possible. When information is lacking, however, recommendations are based on pharmacokinetic variables in normal subjects. Nephrotoxicity, important adverse effects, and special considerations in renal patients are noted. Adjustments are suggested for hemodialysis and peritoneal dialysis when appropriate.

Pharmacokinetic aspects of carbamazepine and its two major metabolites in plasma during overdosage

In 10 out of 25 patients admitted with carbamazepine overdosage to local teaching hospitals sufficient plasma level data of carbamazepine and two of its main metabolites (epoxide and dihydroxy) were obtained to characterize their terminal elimination kinetics. Some other pharmacokinetic aspects which could be useful in extrapolating to the amount and time of ingestion of the overdose are discussed.

The assessment of fractional drug removal by extracorporeal dialysis

It is generally concurred that the effectiveness of extracorporeal dialysis is best evaluated by fractional drug removal, i.e. the proportion of body burden of drug removed during the period of dialysis treatment. Two equations reported in the literature and five equations proposed in this article are examined for their validity in the assessment of fractional drug removal. Potential limitations and applicable conditions of these equations are discussed and compared. Calculations of fractional drug removal are demonstrated using both simulated and experimental data of ethambutol. Depending on the available kinetic measurements during dialysis and post dialysis, one may apply each equation separately or in conjunction with others to the calculation of fractional drug removal.

Impaired metabolism of methylphenobarbital after a combined drug overdose: treatment by resin hemoperfusion

A 38-yr-old woman who by history ingested 13 g methylphenobarbital, alcohol, and 6 g acetaminophen became comatose slowly over 4 d. Acute hepatic injury appeared to impair the oxidative N-demethylation of methylphenobarbital to its product, phenobarbital. On the eighth day after ingestion she was treated because of protracted coma with Amberlite XAD-4 resin hemoperfusion. Hemoperfusion, which removed 0.83 g methylphenobarbital and 2.10 g phenobarbital, led to transient clinical improvement. When supportive patient management fails to produce a satisfactory clinical course in a methylphenobarbital-intoxicated patient, hemoperfusion could be a useful adjunct to therapy.