Effects of charcoal, sodium bicarbonate, and ammonium chloride on chlorpropamide kinetics

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.

Intestinal Excretion, Intestinal Recirculation, and Renal Tubule Reabsorption Are Underappreciated Mechanisms That Drive the Distribution and Pharmacokinetic Behavior of Small Molecule Drugs

Drug reabsorption following biliary excretion is well-known as enterohepatic recirculation (EHR). Renal tubular reabsorption (RTR) following renal excretion is also common but not easily assessed. Intestinal excretion (IE) and enteroenteric recirculation (EER) have not been recognized as common disposition mechanisms for metabolically stable and permeable drugs. IE and intestinal reabsorption (IR:EHR/EER), as well as RTR, are governed by dug concentration gradients, passive diffusion, active transport, and metabolism, and together they markedly impact disposition and pharmacokinetics (PK) of small molecule drugs. Disruption of IE, IR, or RTR through applications of active charcoal (AC), transporter knockout (KO), and transporter inhibitors can lead to changes in PK parameters. The impacts of intestinal and renal reabsorption on PK are under-appreciated. Although IE and EER/RTR can be an intrinsic drug property, there is no apparent strategy to optimize compounds based on this property. This review seeks to improve understanding and applications of IE, IR, and RTR mechanisms.

Mechanistic PBPK Modeling of Urine pH Effect on Renal and Systemic Disposition of Methamphetamine and Amphetamine

The effect of urine pH on renal excretion and systemic disposition has been observed for many drugs and metabolites. When urine pH is altered, tubular ionization, passive reabsorption, renal clearance, and systemic exposure of drugs and metabolites may all change dramatically, raising clinically significant concerns. Surprisingly, the urine pH effect on drug disposition is not routinely explored in humans, and regulatory agencies have neither developed guidance on this issue nor required industry to conduct pertinent human trials. In this study, we hypothesized that physiologically based pharmacokinetic (PBPK) modeling could be used as a cost-effective method to examine potential urine pH effect on drug and metabolite disposition. Our previously developed and verified mechanistic kidney model was integrated with a full-body PBPK model to simulate renal clearance and area under the plasma concentration-time curve (AUC) with varying urine pH statuses using methamphetamine and amphetamine as model compounds. We first developed and verified drug models for methamphetamine and amphetamine under normal urine pH condition [absolute average fold error (AAFE) < 1.25 at study level]. Then, acidic and alkaline urine scenarios were simulated. Our simulation results show that the renal excretion and plasma concentration-time profiles for methamphetamine and amphetamine could be recapitulated under different urine pH (AAFE < 2 at individual level). The methamphetamine-amphetamine parent-metabolite full-body PBPK model also successfully simulated amphetamine plasma concentration-time profiles (AAFE < 1.25 at study level) and amphetamine/methamphetamine urinary concentration ratios (AAFE < 2 at individual level) after dosing methamphetamine. This demonstrates that our mechanistic PBPK model can predict urine pH effect on systemic and urinary disposition of drugs and metabolites. SIGNIFICANCE STATEMENT: Our study shows that integrating mechanistic kidney model with full-body physiologically based pharmacokinetic model can predict the magnitude of alteration in renal excretion and area under the plasma concentration-time curve (AUC) of drugs and metabolites when urine pH is changed. This provides a cost-effective method to evaluate the likelihood of renal and systemic disposition changes due to varying urine pH. This is important because multiple drugs and diseases can alter urine pH, leading to quantitatively and clinically significant changes in drug and metabolite disposition that may require adjustment of therapy.

Toxicity of Oral Agents Used to Treat Diabetes

Oral agents used for the management of type 2 diabetes mellitus include sulfonylureas, biguanides, thiazolidinediones, metglitinides, and/or α -glucosidase inhibitors. These medication classes can be further classified as hypoglycemic and antihyperglycemic agents. Hypoglycemia is a major symptom of toxicity of these agents, particularly with the sulfonylureas, including combination medications that include sulfonylureas. In overdose situations, metformin, a biguanide, can lead to considerable gastrointestinal adverse effects and potentially lactic acidosis in severe cases. Data on the management of toxicities of the other classes are limited. This article will review the treatment modalities that have been used for treating symptomatic hypoglycemia and metformin-induced lactic acidosis.

Enhanced poison elimination in critical care

Nephrologists and critical care physicians are commonly involved in the treatment of severely poisoned patients. Various techniques exist presently to enhance the elimination of poisons. Corporeal treatments occur inside of the body and include multiple-dose activated charcoal, resin binding, forced diuresis, and urinary pH alteration. Extracorporeal treatments include hemodialysis, hemoperfusion, peritoneal dialysis, continuous renal replacement therapy, exchange transfusion, and plasmapheresis. This review illustrates the potential indications and limitations in the application of these modalities as well as the pharmacological characteristics of poisons amenable to enhanced elimination.

Bench-to-bedside review: Antidotal treatment of sulfonylurea-induced hypoglycaemia with octreotide

The major potential adverse effect of use of sulfonylurea agents (SUAs) is a hyperinsulinaemic state that causes hypoglycaemia. It may be observed during chronic therapeutic dosing, even with very low doses of a SUA, and especially in older patients. It may also result from accidental or intentional poisoning in both diabetic and nondiabetic patients. The traditional approach to SUA-induced hypoglycaemia includes administration of glucose, and glucagon or diazoxide in those who remain hypoglycaemic despite repeated or continuous glucose supplementation. However, these antidotal approaches are associated with several shortcomings, including further exacerbation of insulin release by glucose and glucagon, leading only to a temporary beneficial effect and later relapse into hypoglycaemia, as well as the adverse effects of both glucagon and diazoxide. Octreotide inhibits the secretion of several neuropeptides, including insulin, and has successfully been used to control life-threatening hypoglycaemia caused by insulinoma or persistent hyperinsulinaemic hypoglycaemia of infancy. Therefore, this agent should in theory also be useful to decrease glucose requirements and the number of hypoglycaemic episodes in patients with SUA-induced hypoglycaemia. This has apparently been confirmed by experimental data, one retrospective study based on chart review, and several anecdotal case reports. There is thus a need for further prospective studies, which should be adequately powered, randomized and controlled, to confirm the probable beneficial effect of octreotide in this setting.

Position Paper on urine alkalinization

This Position Paper was prepared using the methodology agreed by the American Academy of Clinical Toxicology (AACT) and the European Association of Poisons Centres and Clinical Toxicologists (EAPCCT). All relevant scientific literature was identified and reviewed critically by acknowledged experts using set criteria. Well-conducted clinical and experimental studies were given precedence over anecdotal case reports and abstracts were not considered. A draft Position Paper was then produced and presented at the North American Congress of Clinical Toxicology in October 2001 and at the EAPCCT Congress in May 2002 to allow participants to comment on the draft after which a revised draft was produced. The Position Paper was subjected to detailed peer review by an international group of clinical toxicologists chosen by the AACT and the EAPCCT, and a final draft was approved by the boards of the two societies. The Position Paper includes a summary statement (Position Statement) for ease of use, which will also be published separately, as well as the detailed scientific evidence on which the conclusions of the Position Paper are based. Urine alkalinization is a treatment regimen that increases poison elimination by the administration of intravenous sodium bicarbonate to produce urine with a pH > or = 7.5. The term urine alkalinization emphasizes that urine pH manipulation rather than a diuresis is the prime objective of treatment; the terms forced alkaline diuresis and alkaline diuresis should therefore be discontinued. Urine alkalinization increases the urine elimination of chlorpropamide, 2,4-dichlorophenoxyacetic acid, diflunisal, fluoride, mecoprop, methotrexate, phenobarbital, and salicylate. Based on volunteer and clinical studies, urine alkalinization should be considered as first line treatment for patients with moderately severe salicylate poisoning who do not meet the criteria for hemodialysis. Urine alkalinization cannot be recommended as first line treatment in cases of phenobarbital poisoning as multiple-dose activated charcoal is superior. Supportive care, including the infusion of dextrose, is invariably adequate in chlorpropamide poisoning. A substantial diuresis is required in addition to urine alkalinization in the chlorophenoxy herbicides, 2,4-dichlorophenoxyacetic acid, and mecoprop, if clinically important herbicide elimination is to be achieved. Volunteer studies strongly suggest that urine alkalinization increases fluoride elimination, but this is yet to be confirmed in clinical studies. Although urine alkalinization is employed clinically in methotrexate toxicity, currently there is only one study that supports its use. Urine alkalinization enhances diflunisal excretion, but this technique is unlikely to be of value in diflunisal poisoning. In conclusion, urine alkalinization should be considered first line treatment in patients with moderately severe salicylate poisoning who do not meet the criteria for hemodialysis. Urine alkalinization and high urine flow (approximately 600 mL/h) should also be considered in patients with severe 2,4-dichlorophenoxyacetic acid and mecoprop poisoning. Administration of bicarbonate to alkalinize the urine results in alkalemia (an increase in blood pH or reduction in its hydrogen ion concentration); pH values approaching 7.70 have been recorded. Hypokalemia is the most common complication but can be corrected by giving potassium supplements. Alkalotic tetany occurs occasionally, but hypocalcemia is rare. There is no evidence to suggest that relatively short-duration alkalemia (more than a few hours) poses a risk to life in normal individuals or in those with coronary and cerebral arterial disease.

Position statement and practice guidelines on the use of multi-dose activated charcoal in the treatment of acute poisoning. 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. 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. Although many studies in animals and volunteers have demonstrated that multiple-dose activated charcoal increases drug elimination significantly, this therapy has not yet been shown in a controlled study in poisoned patients to reduce morbidity and mortality. Further studies are required to establish its role and the optimal dosage regimen of charcoal to be administered. Based on experimental and clinical studies, multiple-dose activated charcoal should be considered only if a patient has ingested a life-threatening amount of carbamazepine, dapsone, phenobarbital, quinine, or theophylline. With all of these drugs there are data to confirm enhanced elimination, though no controlled studies have demonstrated clinical benefit. Although volunteer studies have demonstrated that multiple-dose activated charcoal increases the elimination of amitriptyline, dextropropoxyphene, digitoxin, digoxin, disopyramide, nadolol, phenylbutazone, phenytoin, piroxicam, and sotalol, there are insufficient clinical data to support or exclude the use of this therapy. The use of multiple-dose charcoal in salicylate poisoning is controversial. One animal study and 2 of 4 volunteer studies did not demonstrate increased salicylate clearance with multiple-dose charcoal therapy. Data in poisoned patients are insufficient presently to recommend the use of multiple-dose charcoal therapy for salicylate poisoning. Multiple-dose activated charcoal did not increase the elimination of astemizole, chlorpropamide, doxepin, imipramine, meprobamate, methotrexate, phenytoin, sodium valproate, tobramycin, and vancomycin in experimental and/or clinical studies. Unless a patient has an intact or protected airway, the administration of multiple-dose activated charcoal is contraindicated. It should not be used in the presence of an intestinal obstruction. The need for concurrent administration of cathartics remains unproven and is not recommended. In particular, cathartics should not be administered to young children because of the propensity of laxatives to cause fluid and electrolyte imbalance. In conclusion, based on experimental and clinical studies, multiple-dose activated charcoal should be considered only if a patient has ingested a life-threatening amount of carbamazepine, dapsone, phenobarbital, quinine, or theophylline.

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.

Antihyperglycaemic agents. Drug interactions of clinical importance

Non-insulin-dependent (type 2) diabetes mellitus (NIDDM) affects middle-aged or elderly people who frequently have several other concomitant diseases, especially obesity, hypertension, dyslipidaemias, coronary insufficiency, heart failure and arthropathies. Thus, polymedication is the rule in this population, and the risk of drug interactions is important, particularly in elderly patients. The present review is restricted to the interactions of other drugs with antihyperglycaemic compounds, and will not consider the mirror image, i.e. the interactions of antihyperglycaemic agents with other drugs. Oral antihyperglycaemic agents include sulphonylureas, biguanides--essentially metformin since the withdrawn of phenformin and buformin--and alpha-glucosidase inhibitors, acarbose being the only representative on the market. These drugs can be used alone or in combination to obtain better metabolic control, sometimes with insulin. Drug interactions with antihyperglycaemic agents can be divided into pharmacokinetic and pharmacodynamic interactions. Most pharmacokinetic studies concern sulphonylureas, whose action may be enhanced by numerous other drugs, thus increasing the risk of hypoglycaemia. Such an effect may result essentially from protein binding displacement, inhibition of hepatic metabolism and reduction of renal clearance. Reduction of the hypoglycaemic activity of sulphonylureas due to pharmacokinetic interactions with other drugs appears to be much less frequent. Drug interactions leading to an increase in plasma metformin concentrations, mainly by reducing the renal excretion or the hepatic metabolism of the biguanide, should be avoided to limit the risk of hyperlactaemia. Owing to its mode of action, pharmacokinetic interferences with acarbose are limited to the gastrointestinal tract, but have not been extensively studied yet. Pharmacodynamic interactions are quite numerous and may result in a potentiation of the hypoglycaemic action or, conversely, in a deterioration of blood glucose control. Such interactions may be observed whatever the type of antidiabetic treatment. They result from the intrinsic properties of the coprescribed drug on insulin secretion and action, or on a key step of carbohydrate metabolism. Finally, a combination of 2 to 3 antihyperglycaemic agents is common for treating patients with NIDDM to benefit from the synergistic effect of compounds acting on different sites of carbohydrate metabolism. Possible pharmacokinetic interactions between alpha-glucosidase inhibitors and classical antidiabetic oral agents should be better studied in the diabetic population.

Features, prevention and management of acute overdose due to antidiabetic drugs

Hypoglycaemic medication forms a disparate group of therapeutic compounds including insulin, the sulphonylureas and biguanides. They are all designed to prevent hyperglycaemia and in general are well tolerated. Careful prescribing practice and patient education by the physician can do much to reduce the risk of adverse effects from diabetic therapy. However, the presentation of adverse effects, together with accidental and non-accidental overdose, is a frequent clinical problem. Furthermore, the possible impairment of hypoglycaemic awareness in patients prescribed human insulin has added complexity to diabetic management. The cardinal features of insulin overdose are hypoglycaemia and hypokalaemia. The sulphonylureas predominantly cause hypoglycaemia, while the biguanides may precipitate lactataemia and acidosis. Recognition of hypoglycaemia is therefore crucial in avoidance of toxicity. Intravenous dextrose is the mainstay of therapy following gut decontamination (for the oral agents). The efficacy of glucagon is dependent on hepatic glycogen stores and should therefore be used with caution. Diazoxide is not recommended. More recently, octreotide has been shown to be effective in sulphonylurea overdose. Patients should be admitted and monitored with serial blood sugar measurements for a minimum of 1 to 2 days as clinically warranted.

Physicochemical characteristics of drugs and response to repeat-dose activated charcoal

Although the administration of repeated doses of activated charcoal has been advocated to increase the systemic clearance of many drugs, it is unknown whether a drug's physicochemical properties are associated with enhanced removal by repeat-dose activated charcoal. The English language literature was searched to identify clinical studies evaluating repeat-dose activated charcoal. Percent reduction in plasma elimination half-life during repeat-dose activated charcoal was calculated and correlated with the drugs' characteristics. A step-wise multiple regression analysis with the independent variables of the drugs' molecular weight, pKa, plasma protein-binding, intrinsic plasma elimination half-life, and volume of distribution failed to identify potential predictors (P = .1) of effectiveness of repeat-dose activated charcoal. This analysis suggested that charcoal therapy was more effective for drugs with a longer intrinsic half-life (r2 = .24, P = .04). A uniform framework that evaluates the physicochemical characteristics of drugs and their response to repeat-dose activated charcoal is needed to better define which patients would benefit from repeat-dose activated charcoal therapy.

The effect of cholestyramine and activated charcoal on glipizide absorption

1. The interference of cholestyramine and activated charcoal with the absorption of glipizide was studied. 2. In a cross-over study comprising three phases, single doses of cholestyramine (8 g), activated charcoal (8 g) or water only were given to six healthy volunteers together with a single dose of glipizide. 3. The absorption of glipizide was moderately (29%, P less than 0.01) reduced by cholestyramine and greatly reduced (81%, P less than 0.01) by activated charcoal. 4. If cholestyramine and glipizide are used concomitantly, glipizide should be taken 1-2 h beforehand. In acute glipizide overdosage, activated charcoal can be used to reduce absorption.

Pharmacokinetics of midaglizole, a new hypoglycaemic agent, in healthy subjects

The objective of this study was to evaluate the pharmacokinetics of midaglizole, a new orally effective hypoglycaemic agent, in healthy male subjects. In Study I, volunteers were given single oral doses of 150, 200, 300, and 500 mg of midaglizole 20 min before breakfast. In Study II, 200 mg of midaglizole was given 30 min after breakfast. In Study III, multiple oral administration study was carried out at a dose of 200 mg t.i.d. 20 min before meals for 7 days. The disposition of midaglizole was adequately described by a one-compartment open model with first order absorption. It was essentially dose-dependent up to 500 mg given orally. The pharmacokinetic parameters calculated by employing this model indicated that the disposition of this drug was characterized by good absorption from the intestine, a wide distribution in the body, and a rapid excretion via the kidneys. The absorption rate of midaglizole from the intestine was definitely slowed by the presence of food, probably due to a decrease in the rate of gastric emptying. No clinical significant accumulation of midaglizole in the body was observed during or after multiple doses. A linear correlation was found between the area under the curve of plasma concentration of midaglizole versus time and the area calculated from the curve of change in blood glucose level versus time after oral administration of midaglizole.

The relationship between debrisoquine oxidation phenotype and the pharmacokinetics of chlorpropamide

The pharmacokinetics and urinary metabolite pattern of a single oral dose of chlorpropamide 250 mg have been studied in 6 extensive and 5 poor metabolizers of debrisoquine. Ammonium chloride was given orally to acidify the urine in order to make elimination of the parent drug dependent on metabolism alone. The concentration profile in serum and the pharmacokinetic parameters of the parent drug were similar in both groups. However, the ratio in urine of unchanged chlorpropamide to its hydroxylated metabolites was higher in poor than in extensive metabolizers.

Role of repeated doses of oral activated charcoal in the treatment of acute intoxications

While single dose activated charcoal is effective in preventing drug absorption, repeated doses not only prevent absorption but also can increase systemic drug clearance. The mechanism for the latter effect may involve interruption of enterohepatic recycling and/or promotion of drug exsorption from the systemic circulation into the gut lumen. A comprehensive review of reported studies in volunteer subjects and overdose patients showed that repeated dose activated charcoal markedly decreased the half-life and/or increased the clearance of a wide range of drugs. Side-effects of the treatment were infrequent, but included aspiration pneumonia, diarrhoea and constipation. The addition of laxatives to repeated dose charcoal treatment did not offer any significant increase in drug clearance and is not recommended. It is suggested that the optimal regimen for the use of repeat dose activated charcoal in acute drug intoxications is an initial dose of 75-100 g, followed by 50 g every 4 hours until the risks of systemic drug toxicity are reduced to an acceptable level.

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.

Sulphonylurea antidiabetic drugs. An update of their clinical pharmacology and rational therapeutic use

Apart from the amelioration of symptoms, a major aim of the treatment of non-insulin-dependent diabetes mellitus (NIDDM, type 2 diabetes) should be the prevention of cardiovascular complications. These are associated with the chronic hyperglycaemia that is characteristic of NIDDM, and the risk of complications is already increased in subjects with impaired glucose tolerance (IGT). For these reasons, and because hyperglycaemia appears to be a self-perpetuating condition, treatment should be introduced as early as possible and should be aimed at normalisation of blood glucose. To enable early detection and intervention, screening is necessary. As diet regulation alone rarely suffices to normalise blood glucose, addition of sulphonylurea drugs is indicated in many cases. If introduced in the IGT phase, sulphonylureas drugs combined with diet regulation may postpone the development of IGT to manifest NIDDM, and may reduce the increased risk of cardiovascular morbidity and mortality. Sulphonylureas stimulate insulin release, possibly via interaction with receptors in the pancreatic B cells. In addition, such treatment enhances the reduced insulin action. This might be a primary effect but is also a consequence of the increased access to insulin and the subsequent reduction of hyperglycaemia. Sulphonylureas may enhance insulin availability by reducing insulin clearance. Effects on blood lipids are probably secondary phenomena. Fast and short acting sulphonylureas may improve the impaired meal-induced acute insulin release. If combined with weight-reducing diet regulation and introduced early, such treatment can maintain (near) normal blood glucose levels and an improved insulin action for several years without increasing basal insulin secretion, without chronic hyperinsulinaemia, and without weight increase. If not combined with diet regulation, sulphonylurea therapy is likely to fail. If introduced when NIDDM is advanced, the efficacy of these drugs is limited, with secondary failures developing at a rate of 5 to 10% per year. Continuous (24-hour-a-day) exposure to drug treatment could possibly desensitise the B cell to sulphonylurea stimulation. 'Second-generation' sulphonylurea drugs have a higher potency than 'first-generation' drugs, but this need not signify a greater clinical efficacy. The effect of several of these drugs may be increased if they are ingested half an hour before meal(s). Short acting sulphonylureas may be safer than long acting ones, which seem more likely to cause long lasting and fatal hypoglycaemia, at least in elderly patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Stereoselective gastrointestinal clearance of disopyramide in rabbits treated with activated charcoal

The ability of activated charcoal to enhance the drug elimination of two enantiomers, R- and S-disopyramide, was compared in rabbits. Orally administered activated charcoal significantly decreased the area under the serum concentration curve of R-disopyramide, whereas the same treatment had no effect on that of S-disopyramide. The difference could be explained by the difference in the hepatic extraction ratio of two enantiomers in rabbits. S-Disopyramide is a drug of high hepatic extraction ratio in rabbits and R-disopyramide is of intermediate hepatic extraction ratio. Equations were derived to illustrate the influence of the hepatic extraction ratio on the apparent gastrointestinal clearance. A higher hepatic extraction ratio decreases the apparent gastrointestinal clearance of a drug. This phenomenon may explain some unsuccessful experiments of gastrointestinal dialysis. When considering the use of activated charcoal to enhance systemic drug elimination, the hepatic extraction ratio of the drug should be included.

Oral hypoglycemic agents

The sulfonylureas remain the most important oral agents, although their chronic hypoglycemic actions are still unexplained and the evidence on their relative efficacy is inconclusive. Data on relative safety suggest that chlorpropamide is the most toxic sulfonylurea but glyburide causes dangerous hypoglycemia as often as chlorpropamide. For many patients, good blood glucose control will be achieved by taking tolbutamide or another sulfonylurea 30 minutes before breakfast and the main evening meal. The biguanide metformin, which is as safe as glyburide, is of use in treating overweight diabetic patients who do not have cardiovascular, hepatic, or renal dysfunction.

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)

The influence of nutrition on the systemic availability of drugs. Part II: Drug metabolism and renal excretion

Plasma concentrations of an active compound vary between individuals and within a subject, even if the same drug dosage is used. These differences are related to variations of drug absorption from the gastrointestinal tract, of presystemic drug metabolism in the intestine or the liver, and of drug elimination from the systemic circulation, for instance by hepatic metabolism or renal excretion. All of these processes can be modified by nutrition. However it is necessary to emphasize the significance of the pharmaceutical formulation for variations of both drug absorption and elimination. The role of nutrition should receive adequate attention during therapeutic use of drugs as well as in drug disposition studies. Recent guidelines for the assessment of the systemic availability of drugs therefore do recommend nutrition to be controlled.

The relationship between the pharmacokinetics and pharmacodynamic effects of oral hypoglycaemic drugs

Oral hypoglycaemic drugs have widely differing pharmacokinetic properties. Possible pharmacodynamic benefits include greater efficacy and fewer adverse effects. In general, it has not been possible to demonstrate unequivocal differences in clinical efficacy between the sulphonylureas during long term use, although there are clear differences in potency. These differences have been emphasised to the extent that the term 'second-generation' has been used for the most potent sulphonylureas, but there is little to suggest that potency is of any therapeutic significance. Trials to study differences in efficacy have rarely been of acceptable design. They have often used fixed doses of drugs, begging the question of whether true potency ratios have been established for chronic treatment. They have rarely involved substantial numbers of patients in double-blind crossover studies with a suitable washout period. Trials which show that there is a clear relationship between drug concentrations in blood and drug effects (whether therapeutic effects or adverse effects such as severe hypoglycaemia) are generally lacking. Qualitative and semiquantitative analysis of adverse effects supports the concept that drugs with a long half-life (e.g. chlorpropamide), renally excreted active metabolites (e.g. acetohexamide) or unusual properties (e.g. glibenclamide, which accumulates progressively in islet tissue) are more likely to cause prolonged hypoglycaemia, which may be fatal. The major adverse effect of treatment with biguanides is lactic acidosis, and this probably occurs more commonly in patients treated with phenformin than those treated with metformin because of pharmacogenetic variation in phenformin metabolism. The available evidence therefore favours the use of drugs with a short elimination half-life which are extensively metabolised and which have no active metabolites.

Pharmacokinetics of chlorpropamide in epileptic patients: effects of enzyme induction and urine pH on chlorpropamide elimination

The effects of liver enzyme induction and of urine pH on the pharmacokinetics of chlorpropamide have been studied. A single oral dose of chlorpropamide 250 mg was administered to 8 patients on antiepileptic drugs (phenytoin, carbamazepine) and to 8 healthy volunteers. The half-life of chlorpropamide was significantly shorter in the patients (34.4 h) than in the healthy volunteers (50.2 h), but the difference between the groups in the half-life of antipyrine was even more pronounced (5.1 vs 11.4 h). The clearance and volume of distribution of total chlorpropamide were significantly higher in the patients (2.99 ml X h-1 X kg-1 and 126 ml X kg-1) than in the healthy volunteers (1.60 ml X h-1 X kg-1 and 106 ml X kg-1). The unbound fraction of chlorpropamide in serum was also higher in the patients (5.7%) than in the healthy subjects (4.4%). Neither the volume of distribution nor the clearance of the free fraction of chlorpropamide differed significantly between the groups. There was a significant correlation between the half-lives of chlorpropamide and antipyrine, and the half-life of chlorpropamide also had at least as good an inverse correlation with the urinary excretion of unchanged chlorpropamide. The renal clearance of chlorpropamide correlated well with urine pH and was almost 100-fold higher at pH 7 than at pH 5. Both the metabolic and renal clearances of chlorpropamide are important in its elimination. At urine pH higher than 6.5-7, the renal clearance of chlorpropamide represents more than half its total clearance regardless the degree of induction of liver enzymes.

Effect of sucralfate on the absorption and pharmacokinetics of chlorpropamide

This study compared the pharmacokinetics of chlorpropamide (C) when administered alone, or in combination with sucralfate (S) to evaluate whether a drug-drug interaction exists between these two agents in vivo. A two-way, randomized, cross-over study was performed in 12 healthy male volunteers who received 250 mg C alone or were pretreated with S qid for two days and then received a single 250-mg dose of C with S on day 3 and continued to take sucralfate throughout the day while serial blood samples were drawn. High-performance liquid chromatography determination of plasma concentrations found there to be no statistically significant differences in maximum concentration, time to maximum concentration, elimination rate constant, or area under the concentration-time curve from 0 to 96 hours. However, there was a statistically significant difference in the area under the curve from 0 to infinity data (P less than .05). The authors conclude that there appears to be no drug interaction between sucralfate and chlorpropamide when given concurrently; however, a trend towards less drug availability was seen that may warrant a future multiple-dose study to further evaluate the significance of this finding.

Adsorption of sulfonylureas onto activated charcoal in vitro

Adsorption of carbutamide, chlorpropamide, tolazamide, tolbutamide, glibenclamide (glyburide), and glipizide onto activated charcoal was compared in vitro using different charcoal-to-drug ratios. Maximal binding capacities of different sulfonylureas were 0.45-0.52 g/g of charcoal at pH 7.5. The affinity of the second generation derivatives, glibenclamide and glipizide, was considerably higher than that of the first generation derivatives. The affinity of sulfonylureas to charcoal was higher at pH 4.9 than at pH 7.5. Poor water solubility of sulfonylureas at pH 1 prevents the adequate testing in these conditions. Contrary to what has appeared previously, activated charcoal effectively adsorbs different sulfonylureas and can be used to possibly prevent their gastrointestinal absorption.