Intestinal secretion of digoxin in the rat. Augmentation by feeding activated charcoal

Systematic review on the use of activated charcoal for gastrointestinal decontamination following acute oral overdose

INTRODUCTION

The use of activated charcoal in poisoning remains both a pillar of modern toxicology and a source of debate. Following the publication of the joint position statements on the use of single-dose and multiple-dose activated charcoal by the American Academy of Clinical Toxicology and the European Association of Poison Centres and Clinical Toxicologists, the routine use of activated charcoal declined. Over subsequent years, many new pharmaceuticals became available in modified or alternative-release formulations and additional data on gastric emptying time in poisoning was published, challenging previous assumptions about absorption kinetics. The American Academy of Clinical Toxicology, the European Association of Poison Centres and Clinical Toxicologists and the Asia Pacific Association of Medical Toxicology founded the Clinical Toxicology Recommendations Collaborative to create a framework for evidence-based recommendations for the management of poisoned patients. The activated charcoal workgroup of the Clinical Toxicology Recommendations Collaborative was tasked with reviewing systematically the evidence pertaining to the use of activated charcoal in poisoning in order to update the previous recommendations.

OBJECTIVES

The main objective was: Does oral activated charcoal given to adults or children prevent toxicity or improve clinical outcome and survival of poisoned patients compared to those who do not receive charcoal?  Secondary objectives were to evaluate pharmacokinetic outcomes, the role of cathartics, and adverse events to charcoal administration. This systematic review summarizes the available evidence on the efficacy of activated charcoal.

METHODS

A medical librarian created a systematic search strategy for Medline (Ovid), subsequently translated for Embase (via Ovid), CINAHL (via EBSCO), BIOSIS Previews (via Ovid), Web of Science, Scopus, and the Cochrane Library/DARE. All databases were searched from inception to December 31, 2019. There were no language limitations.  One author screened all citations identified in the search based on predefined inclusion/exclusion criteria. Excluded citations were confirmed by an additional author and remaining articles were obtained in full text and evaluated by at least two authors for inclusion. All authors cross-referenced full-text articles to identify articles missed in the searches. Data from included articles were extracted by the authors on a standardized spreadsheet and two authors used the GRADE methodology to independently assess the quality and risk of bias of each included study.

RESULTS

From 22,950 titles originally identified, the final data set consisted of 296 human studies, 118 animal studies, and 145 in vitro studies. Also included were 71 human and two animal studies that reported adverse events. The quality was judged to have a Low or Very Low GRADE in 469 (83%) of the studies. Ninety studies were judged to be of Moderate or High GRADE. The higher GRADE studies reported on the following drugs: paracetamol (acetaminophen), phenobarbital, carbamazepine, cardiac glycosides (digoxin and oleander), ethanol, iron, salicylates, theophylline, tricyclic antidepressants, and valproate. Data on newer pharmaceuticals not reviewed in the previous American Academy of Clinical Toxicology/European Association of Poison Centres and Clinical Toxicologists statements such as quetiapine, olanzapine, citalopram, and Factor Xa inhibitors were included. No studies on the optimal dosing for either single-dose or multiple-dose activated charcoal were found. In the reviewed clinical data, the time of administration of the first dose of charcoal was beyond one hour in 97% (n = 1006 individuals), beyond two hours in 36% (n = 491 individuals), and beyond 12 h in 4% (n = 43 individuals) whereas the timing of the first dose in controlled studies was within one hour of ingestion in 48% (n = 2359 individuals) and beyond two hours in 36% (n = 484) of individuals.

CONCLUSIONS

This systematic review found heterogenous data. The higher GRADE data was focused on a few select poisonings, while studies that addressed patients with unknown and or mixed ingestions were hampered by low rates of clinically meaningful toxicity or death.  Despite these limitations, they reported a benefit of activated charcoal beyond one hour in many clinical scenarios.

Cutaneous absorption of Oleander: Fact or fiction

Cardiac conduction disorders following oral ingestion of Oleander plant materials were documented earlier. Transcutaneous absorption of yellow oleander (Thevetia peruviana) leaf extract applied over non intact skin (raw wound) resulting in reversible cardiac conduction disorder observed in four healthy males who were free from any other systemic or electrolyte or metabolic disorders or exposure to pesticide or toxins is reported for the first time. Their hematological, biochemical, clinical, and echocardiogram status were within normal limits and free of any abnormalities. One among the four, presented for weakness and breathlessness (class II). He had bradycardia with Mobitz II block and hypotension without any other demonstrable localizing signs. The other three were identified in the community and without any symptoms. However, their ECG revealed bradycardia with Mobitz I block in two and complete heart block in the other. All of the four recovered well without any untoward events. Hence, it is suggested that physicians and practitioners have to elicit history and route of administration of unconventional therapy, whenever they are confronted with clinical challenges and during medical emergencies before embarking final decision.

P-glycoprotein in intestines, liver, kidney and lymphocytes in horse

P-glycoprotein (P-gp) is an important drug transporter, which is expressed in a variety of cells, such as the intestinal enterocytes, the hepatocytes, the renal tubular cells and the intestinal and peripheral blood lymphocytes. We have studied the localization and the gene and protein expression of P-gp in these cells in horse. In addition we have compared the protein sequence of P-gp in horse with the protein sequences of P-gp in several other species. Real time RT-PCR and Western blot showed gene and protein expression of horse P-gp in all parts of the intestines, but there was no strict correlation between these parameters. Immunohistochemistry showed localization of P-gp in the apical cell membranes of the enterocytes and, in addition, staining was observed in the intestinal intraepithelial and lamina propria lymphocytes. Peripheral blood lymphocytes also stained for P-gp, and gene and protein expression of P-gp were observed in these cells. There was a high gene and protein expression of P-gp in the liver, with P-gp-immunoreactivity in the bile canalicular membranes of the hepatocytes. Gene and protein expression of P-gp were found in the kidney with localization of the protein in different parts of the nephrons. Protein sequence alignment showed that horse P-gp has two amino acid insertions at the N-terminal region of the protein, which are not present in several other species examined. One of these is a 99 amino acid long sequence inserted at amino acid positions 23-121 from the N-terminal. The other is a six amino acid long sequence present at the amino acid positions 140-145 from the N-terminal. The results of the present study indicate that P-gp has an important function for oral bioavailability, distribution and excretion of substrate compounds in horse.

Management of yellow oleander poisoning

BACKGROUND

Poisoning due to deliberate self-harm with the seeds of yellow oleander (Thevetia peruviana) results in significant morbidity and mortality each year in South Asia. Yellow oleander seeds contain highly toxic cardiac glycosides including thevetins A and B and neriifolin. A wide variety of bradyarrhythmias and tachyarrhythmias occur following ingestion. Important epidemiological and clinical differences exist between poisoning due to yellow oleander and digoxin; yellow oleander poisoning is commonly seen in younger patients without preexisting illness or comorbidity. Assessment and initial management. Initial assessment and management is similar to other poisonings. No definite criteria are available for risk stratification. Continuous ECG monitoring for at least 24 h is necessary to detect arrhythmias; longer monitoring is appropriate in patients with severe poisoning. Supportive care. Correction of dehydration with normal saline is necessary, and antiemetics are used to control severe vomiting. Electrolytes. Hypokalemia worsens toxicity due to digitalis glycosides, and hyperkalemia is life-threatening. Both must be corrected. Hyperkalemia is due to extracellular shift of potassium rather than an increase in total body potassium and is best treated with insulin-dextrose infusion. Intravenous calcium increases the risk of cardiac arrhythmias and is not recommended in treating hyperkalemia. Oral or rectal administration of sodium polystyrene sulfonate resin may result in hypokalemia when used together with digoxin-specific antibody fragments. Unlike digoxin toxicity, serum magnesium concentrations are less likely to be affected in yellow oleander poisoning. The effect of magnesium concentrations on toxicity and outcome is not known. Hypomagnesaemia should be corrected as it can worsen cardiac glycoside toxicity. Gastric decontamination. The place of emesis induction and gastric lavage has not been investigated, although they are used in practice. Gastric decontamination by the use of single dose and multiple doses of activated charcoal has been evaluated in two randomized controlled trials, with contradictory results. Methodological differences (severity of poisoning in recruited patients, duration of treatment, compliance) between the two trials, together with differences in mortality rates in control groups, have led to much controversy. No firm recommendation for or against the use of multiple doses of activated charcoal can be made at present, and further studies are needed. Single-dose activated charcoal is probably beneficial. Activated charcoal is clearly safe. Arrhythmia management. Bradyarrhythmias are commonly managed with atropine, isoprenaline, and temporary cardiac pacing in severe cases, although without trial evidence of survival benefit, or adequate evaluation of possible risks. Accelerating the heart rate with atropine or beta-adrenergic agents theoretically increases the risk of tachyarrhythmias, and it has been claimed that atropine increases tachyarrhythmic deaths. Further studies are required. Tachyarrhythmias have a poor prognosis and are more difficult to treat. Lidocaine is the preferred antiarrhythmic; the role of intravenous magnesium is uncertain. Digoxin-specific antibody fragments. Digoxin-specific antibody fragments are effective in reverting life-threatening cardiac arrhythmias; prospective observational studies show a beneficial effect on mortality. High cost and lack of availability limit the widespread use of digoxin-specific antibody fragments in developing countries.

CONCLUSIONS

Digoxin-specific antibody fragments remain the only proven therapy for yellow oleander poisoning. Further studies are needed to determine the place of activated charcoal, the benefits or risks of atropine and isoprenaline, the place and choice of antiarrhythmics, and the effect of intravenous magnesium in yellow oleander poisoning.

Role of P-glycoprotein and the intestine in the excretion of DPC 333 [(2R)-2-{(3R)-3-amino-3-[4-(2-methylquinolin-4-ylmethoxy)phenyl]-2-oxopyrrolidin-1-yl}-N-hydroxy-4-methylpentanamide] in rodents

The role of the intestine in the elimination of (2R)-2-{(3R)-3-amino-3-[4-(2-methylquinolin-4-ylmethoxy)phenyl]-2-oxopyrrolidin-1-yl}-N-hydroxy-4-methylpentanamide (DPC 333), a potent inhibitor of tissue necrosis factor alpha-converting enzyme, was investigated in mice and rats in vivo and in vitro. In Madine-Darby canine kidney cells stably transfected with P-glycoprotein (P-gp) and DPC 333, the transport from B-->A reservoirs exceeded the transport from A-->B by approximately 7-fold. In Caco-2 monolayers and isolated rat ileal mucosa, DPC 333 was transported from basolateral to apical reservoirs in a concentration-dependent, saturable manner, and transport was blocked by N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918), confirming the contribution of P-gp/breast cancer resistance protein in B-->A efflux of DPC 333. In quantitative whole body autoradiography studies with [(14)C]DPC 333 in mice and rats, radioactivity was distributed throughout the small intestine in both species. In GF120918-pretreated bile duct-cannulated rats, radioactivity in feces was reduced 60%. Using the in situ perfused rat intestine model, approximately 20% of an i.v. dose of [(14)C]DPC 333 was measured in the intestinal lumen within 3 h postdose, 12% as parent. Kinetic analysis of data suggested that excreted DPC 333 may be further metabolized in the gut. Intestinal clearance was 0.2 to 0.35 l/h/kg. The above data suggest that in the rodent the intestine serves as an organ of DPC 333 excretion, mediated in part by the transporter P-gp.

Use of plasma proteins as solubilizing agents in in vitro permeability experiments: Correction for unbound drug concentration using the reciprocal permeability approach

The purpose of the present study was to explore the applicability of the reciprocal permeability approach to correct for changes in thermodynamic activity when in vitro permeability data are generated in the presence of plasma proteins. Diazepam (DIA), digoxin (DIG), and propranolol (PRO) permeability was assessed in the presence of bovine serum albumin (BSA) and bovine alpha-1-acid glycoprotein (AAG). The reciprocal permeability approach was subsequently employed to calculate the true permeability coefficient (Papp(corr)) and the operational protein association constant (nK(a)). For BSA binding, good agreement was observed between the Papp(corr) values and Papp values obtained in the absence of protein. For PRO and AAG, where binding affinity was high, deviation in the reciprocal permeability plots was evident suggesting ligand depletion at low drug/high protein concentrations. Bidirectional DIG permeability data in the presence of either BSA or AAG indicated that neither protein had an effect on the efflux transporters involved in DIG permeability. The data suggest that plasma proteins can be utilized in permeability experiments with no adverse effects on transporter function and that the reciprocal permeability approach can be used to correct permeability data for changes in unbound drug concentration.

Pharmacokinetics of digoxin cross-reacting substances in patients with acute yellow Oleander (Thevetia peruviana) poisoning, including the effect of activated charcoal

Intentional self-poisonings with seeds from the yellow oleander tree (Thevetia peruviana) are widely reported. Activated charcoal has been suggested to benefit patients with yellow oleander poisoning by reducing absorption and/or facilitating elimination. Two recent randomized controlled trials (RCTs) assessing the efficacy of activated charcoal yielded conflicting outcomes in terms of mortality. The effect of activated charcoal on the pharmacokinetics of Thevetia cardenolides has not been assessed. This information may be useful for determining whether further studies are necessary. Serial blood samples were obtained from patients enrolled in an RCT assessing the relative efficacy of single-dose and multiple-dose activated charcoal (SDAC and MDAC, respectively) compared with no activated charcoal (NoAC). The concentration of Thevetia cardenolides was estimated with a digoxin immunoassay. The effect of activated charcoal on cardenolide pharmacokinetics was compared between treatment groups by determining the area under the curve for each patient in the 24 hours following admission, the 24-hour mean residence time, and regression lines obtained from serial concentration points, adjusted for exposure. Erratic and prolonged absorption patterns were noted in each patient group. The apparent terminal half-life was highly variable, with a median time of 42.9 hours. There was a reduction in 24-hour mean residence time and in the apparent terminal half-life estimated from linear regression in patients administered activated charcoal, versus the control group (NoAC). This effect was approximately equal in patients administered MDAC or SDAC. Activated charcoal appears to favorably influence the pharmacokinetic profile of Thevetia cardenolides in patients with acute self-poisoning and may have clinical benefits. Given the conflicting clinical outcomes noted in previous RCTs, these mechanistic data support the need for further studies to determine whether a particular subgroup of patients (eg, those presenting soon after poisoning) will benefit from activated charcoal.

Multiple-dose activated charcoal for treatment of yellow oleander poisoning: a single-blind, randomised, placebo-controlled trial

BACKGROUND

Deliberate self-poisoning with yellow oleander seeds is common in Sri Lanka and is associated with severe cardiac toxicity and a mortality rate of about 10%. Specialised treatment with antidigoxin Fab fragments and temporary cardiac pacing is expensive and not widely available. Multiple-dose activated charcoal binds cardiac glycosides in the gut lumen and promotes their elimination. We aimed to assess the efficacy of multiple-dose activated charcoal in the treatment of patients with yellow-oleander poisoning.

METHODS

On admission, participants received one dose of activated charcoal and were then randomly assigned either 50 g of activated charcoal every 6 h for 3 days or sterile water as placebo. A standard treatment protocol was used in all patients. We monitored cardiac rhythm and did 12-lead electocardiographs as needed. Death was the primary endpoint, and secondary endpoints were life-threatening cardiac arrhythmias, dose of atropine used, need for cardiac pacing, admission to intensive care, and number of days in hospital. Analysis was by intention to treat.

FINDINGS

201 patients received multiple-dose activated charcoal and 200 placebo. There were fewer deaths in the treatment group (five [2.5%] vs 16 [8%]; percentage difference 5.5%; 95% CI 0.6-10.3; p=0.025), and we noted difference in favour of the treatment group for all secondary endpoints, apart from number of days in hospital. The drug was safe and well tolerated.

INTERPRETATION

Multiple-dose activated charcoal is effective in reducing deaths and life-threatening cardiac arrhythmias after yellow oleander poisoning and should be considered in all patients. Use of activated charcoal could reduce the cost of treatment.

Digoxin toxicity in chronic renal failure: treatment by multiple dose activated charcoal intestinal dialysis

1. Digoxin toxicity can result from overdose or iatrogenic causes, especially if renal function is impaired. 2. We present a case of digoxin toxicity presenting with severe bradycardia and hypotension in a 66 year old man with chronic renal failure. Regular haemodialysis had, as predicted, failed to reduce his plasma digoxin concentration. Digoxin specific antibody fragments (Fab) were not readily available and their use was probably inappropriate as they are normally renally eliminated. 3. The patient was successfully treated by two prolonged courses of intestinal dialysis with repeated doses of activated charcoal over 48 and 72 h and totaling 400 g and 600 g, respectively. However, the patient found the activated charcoal extremely unpalatable. 4. Multiple dose activated charcoal intestinal dialysis (MDACID) has been recently advocated for use in a wide range of poisonings. The technique takes advantage of the large surface area of the small intestine to eliminate drugs and metabolites, over several days if necessary. The pharmacokinetics of digoxin toxicity in chronic renal failure make intestinal dialysis an appropriate method of treatment but the realisation of the true potential of this technique awaits a more palatable absorbent or formulation.

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.

Gastrointestinal dialysis of digoxin using cholestyramine

The pharmacokinetic parameters of digoxin given intravenously (0.075 mg/kg) alone and following treatment with oral cholestyramine (8 gm in 50 ml water) were studied in rabbits. Pretreatment with cholestyramine produced a significant decrease in the serum concentration of digoxin and significantly enhances its systemic clearance as indicated by a statistically significant decrease in the area under the concentration-time curve (AUC), half time of elimination (t 1/2), and mean residence time (MRT). These findings indicate that the idea of gastrointestinal dialysis, known with activated charcoal, could be extended to ion-exchange resins that could be a potentially useful adjunctive measure in the management of drug overdose especially with commonly used drugs with a low therapeutic index like digoxin.

The influence of cholestyramine on the elimination of tenoxicam and piroxicam

We have studied the influence of multiple oral doses of cholestyramine on the single dose pharmacokinetics of tenoxicam and piroxicam in eight healthy young volunteers. Each subject received on two occasions single intravenous injections of 20 mg tenoxicam and on another two occasions single oral doses of 20 mg piroxicam. Both medications were followed by multiple oral doses of either cholestyramine or plain water (placebo). Compared with placebo cholestyramine accelerated the elimination of both drugs. The average values of half-lives were reduced (tenoxicam: 31.9 h vs 67.4 h; piroxicam: 28.1 h vs 46.8 h) due to increases in clearance. Cholestyramine-mediated enhancement of drug elimination was most pronounced in the subjects with a comparatively low baseline drug clearance. Thus, intersubject variability in clearance was smaller when the drug administrations were followed by the anion-exchange resin. The twofold acceleration of tenoxicam elimination in the present study in man contrasts with a much larger effect (five-fold) seen in experiments with dogs. This points to a much easier access of unchanged tenoxicam to the intestinal lumen in the dogs than in man. Comparing the pharmacokinetics of tenoxicam and piroxicam in the same volunteers revealed a high degree of correlation in clearance and half-lives and similar intersubject variabilities in mean kinetic variables.

The influence of digoxin-specific antibody fragments on digoxin disposition in the rat

Pentobarbitone-anaesthetized bile duct-cannulated female rats were injected intravenously with an equimolar dose of digoxin-specific sheep antibody fragments (DS-Fab) at 2 or 60 min after a dose of [3H]digoxin. The plasma drug levels were promptly elevated by 7-fold or 12-30-fold when the DS-Fab were given at 2 or 60 min respectively. When tissue drug concentrations were measured 2 min after a dose of DS-Fab (given 60 min after digoxin) which caused a 30-fold increase in plasma concentration, reductions could be detected if corrections were made for the presence in the tissues of high plasma concentrations of DS-Fab-bound drug. For instance, reductions in the heart, liver and small intestine were 63, 58 and 48% respectively. However, by 120 min after digoxin injection the only detectable effects on tissue drug concentration were in the kidney, where concentrations had increased 14-fold or 7-fold when the DS-Fab were given at 2 or 60 min respectively. Over the 120 min period the urinary excretion of digoxin-derived radioactivity was enhanced, and in the case where DS-Fab were given at 2 min, a 3-fold increase in urinary excretion was seen, which resulted in a net increase in the overall drug elimination. This greater urinary elimination was accompanied by a marked increase in the amount of bound drug in the urine (control and experimental values were 4 and 36% respectively). The cumulative biliary excretion of radioactivity seemed to be slightly reduced by DS-Fab administration at 2 or 60 min, although this was not statistically significant. A lack of significant drug-specific binding in the bile suggested that the liver is not involved in the elimination of hapten-DS-Fab complexes. There was little effect on the intestinal secretion of the drug.

Quinidine reduces biliary clearance of digoxin in man

Quinidine is known to reduce the renal clearance of digoxin, but this effect does not completely explain the influence of quinidine on the total clearance of digoxin. We therefore studied the effect of quinidine administration on biliary clearance of digoxin in five patients with atrial fibrillation. Biliary clearance of digoxin under steady state conditions before and during treatment with quinidine was investigated using a duodenal-marker-perfusion technique. Quinidine caused an average 42% (range 21-65%, P less than 0.02) reduction of the measured biliary clearance of digoxin. We conclude that the biliary effect adds to the previously demonstrated inhibitory effect of quinidine on the renal clearance of digoxin and helps to explain the decrease in total clearance of the drug. This is the first demonstration in man of a pharmacokinetic drug interaction at the level of biliary excretion.

The effects of activated charcoal on digoxin and digitoxin clearance

The effect of multiple oral doses of activated charcoal on digitalis glycoside kinetics was studied to determine whether an activated charcoal regimen might have utility in treating patients with digitalis toxicity. Normal subjects were given intravenous infusions of digoxin 0.75 mg/70 kg or digitoxin 1 mg/70 kg iv followed by either water alone or water with activated charcoal in divided doses in a randomized crossover design. A subject with chronic renal failure was also given digoxin 0.5 mg/70 kg iv followed by water alone or water with activated charcoal. In six normal subjects, treatment with activated charcoal did not increase digoxin clearance (Cl) significantly (16.79 +/- 1.70 vs. 22.68 +/- 3.51 L/h). However, digitoxin Cl did increase significantly, from 0.24 +/- 0.01 to 0.47 +/- 0.04 L/h. In the renal failure subject, digoxin Cl increased from 3.6 L/h to 10.1 L/h. We conclude that the activated charcoal regimen is probably useful in patients with digitoxin toxicity. Although similar benefit is limited in patients with normal renal function who develop digoxin toxicity, it is possible that activated charcoal will be useful in patients with prolonged digoxin elimination due to renal dysfunction.

Effect of partial jejunectomy and colectomy on the disposition of hexachlorobenzene in rats treated or not treated with hexadecane

The disposition of hexachlorobenzene (HCB) was studied in partially jejunectomized (middle section) or colectomized (excision of cecum and proximal colon) rats after iv or ip dosage (1.5 to 2.0 mg/kg). Excision of about 50% of the jejunum had no effect on body weight, feed intake, volume of urine, weight of feces, or urinary and fecal excretion of HCB as demonstrated by a comparison of sham-operated and jejunectomized animals. Similarly colectomy did not affect body weight, feed intake, volume of urine, or urinary excretion of HCB. However, the wet weight of feces was significantly higher and the amount of HCB in feces significantly lower in colectomized than in sham-operated rats. Hexadecane increased fecal excretion of HCB about two- to threefold without affecting its urinary excretion. The effect of jejunectomy and colectomy was similar in hexadecane-treated animals to that seen in untreated rats. Concentration of HCB in adipose tissue was significantly higher in colectomized rats than in sham-operated controls. Data represent in vivo evidence that the major site of nonbiliary, intestinal excretion of HCB is the large intestine.

Intestinal excretion of toxic substances

Chemicals can be eliminated from body via feces by two major mechanisms, namely biliary and intestinal excretion. The relative importance of these processes in the elimination of a highly lipophilic xenobiotic such as hexachlorobenzene (HCB) has been studied. It has been demonstrated that fecal (90%) rather than urinary (10%) excretion is the major route of elimination of HCB in most species. It has been shown also that the bile of HCB dosed animals contained HCB metabolites only whereas fecal excretion consisted primarily of the parent compound. These findings suggested that the bile could not be the source of fecal HCB. Indeed, bile duct ligation in rats increased rather than decreased the fecal excretion of HCB. Experiments in rhesus monkeys with complete biliary bypass confirmed the conclusion that the source of fecal HCB is not the bile, suggesting that most of the fecal HCB originated from intestinal excretion. Exfoliation of intestinal epithelium and exudation across the intestinal mucosa are the two major nonbiliary mechanisms whereby xenobiotics can enter the intestinal lumen. The contribution of desquamation and exudation to fecal excretion of HCB was estimated in jejunectomized and hemicolectomized rats. Removal of 50% of the jejunum did not influence fecal excretion of HCB, whereas excision of 50% of the large intestine reduced it by 40%. These data suggest that the source of fecal HCB is nonbiliary, intestinal transfer (exudation) from blood into the intestinal contents, which occurs primarily in the large intestine. Fecal elimination of HCB is significantly enhanced by dietary treatments with mineral oil or hexadecane.(ABSTRACT TRUNCATED AT 250 WORDS)

Postmortem digoxin tissue concentration and organ content in infancy and childhood

The concentration of digoxin in tissues and the content of the drug in various organs are reported in 36 infants and children. Sixteen received the drug on a short-term basis and 20 on a long-term basis. The drug was given intravenously to 12, orally to 17, and by intramuscular injection to 7. The study was conducted to determine distribution of digoxin in infants and children and to examine the forensic implications related to digoxin overdosage. Upper therapeutic concentration thresholds for digoxin were established in various tissues. These are different for preterm and full-term neonates than for older children and adults; for example, adult and neonatal values for postmortem blood specimens are 8 and 15 ng/ml, and for ventricular myocardium are 250 and 450 ng/g, respectively. The chronically digitalized premature infant retains in most tissues a considerably larger fraction of digoxin than more mature infants and children. This is in accord with previously demonstrated lower renal digoxin levels in premature infants attributed to their reduced ability to excrete this drug.

Inactivation of digoxin by the gut flora: reversal by antibiotic therapy

In approximately 10 per cent of patients given digoxin, substantial conversion of the drug to cardioinactive, reduced metabolites (digoxin reduction products, or DRPs) occurs. The site and clinical importance of this conversion is unknown. In four normal volunteers taking digoxin daily for four weeks, urinary excretion of DRPs was greatest after a poorly absorbed tablet was ingested, and least after intravenous administration, Stool cultures from subjects known to make DRPs in vivo ("excretors") converted digoxin to DRPs; cultures from nonexcretors did not. Three excretors were given tablets for 22 to 29 days. A five-day course of erythromycin or tetracycline, administered after a base-line period of 10 to 17 days, markedly reduced or eliminated DRP excretion in urine and stool. Serum digoxin concentrations rose as much as twofold after antibiotics were given. We conclude that in some persons digoxin is inactivated by gastrointestinal bacteria. Changes in the enteric flora may markedly alter the state of digitalization.