Clinical Chemistry - 18 Toxicology

CLINICAL CHEMISTRY 4 MAJOR DISCIPLINES OF TOXICOLOGY TOXICOLOGY MECHANISTIC TOXICOLOGY OUTLINE • Toxicology o 4 Major Disciplines of Toxicology o Exposure to Toxins o Oral Dosage o Acute and Chronic Toxicity o Routes of Exposure & Dose-Response Relationship o Toxicology of Specific Agents o Drug & Toxin Tests TOXICOLOGY • • • • • • • • • • • • • From Greek words, - toxicos “poisonous” and logos “study” Study of substances introduced exogenously into the body o Exogenous - substances from environment/external source; they may be toxic or poisonous Concerned with the determining the presence and levels of natural substances in the body o Determining the presence - qualitative o Determining levels - quantitative o presence (qualitative) is established before determining levels (quantitative) Toxicologist - a person specializes in toxicology, can be a physician, scientist, or medical technologist Any material that will render harm to human are called toxic materials. It forms may include xenobiotics, poisons, and toxins of different degree, found in our sorrounding. Included are food we thought as essential but can be a poison at a certain level. Alcohol that when exposed or ingested when metabolized and converted to a substance that become toxic. How the condition will be managed through the available measurements and assay is being studied in the succeeding modules. Toxicology is the study of toxic drugs or poisons. A toxicant (poison) is any substance that, when taken in sufficient quantity, causes sickness or death. Toxicity is a relative term used to compare one substance with another; a toxic substance is one with a toxicity defined as “extremely” or “super” toxic. Specific drugs considered to be toxicants are composed of several categories. Some of these drugs are also considered to be therapeutic in nature. Absorption of toxins in the GIT is by passive diffusion – this process requires that the substance cross cellular barriers. Toxins that are not absorbed from the GIT – Do not produce systemic effects but may produce local effects (diarrhea, bleeding, and malabsorption of nutrients). Common substances (ACUTE TOXICITY) – alcohol, acetaminophen, salicylate, abuse substance and carbon monoxide. Routes of exposure – ingestion, inhalation and transdermal absorption. • • • • • • • Elucidates the cellular and biochemical effects of toxins Focuses on the mechanism of action/effects of toxins to the cells and biochemical processes and physiology Provide a basis for rational therapy design and the development of tests to assess the degree of exposure of poisoned individuals Useful for therapy design/management Helpful in diagnostic aspects of exposure to toxins Mechanism is important for clinicians to determine what appropriate sample is collected to optimally determine the effects of toxin to the patient Pathophysiology of toxins is a critical aspect for management and therapy DESCRIPTIVE TOXICOLOGY • • • • • • Uses the results from animal experiments to predict what level of exposure will cause harm in human o Animal experiments before clinical trials o Some animals are anatomically comparative to humans Aka risk assessment Assesses risk of substances (cosmetics, drugs) for humans Provides basis for determining if a substance is beneficial or harmful for end user/human consumption o Allows testing to provide information on for allergens, harmful effects (for warning labels) Used for regulation of products (food, cosmetic, vaccines) FDA - regulatory body o Responsible for allowing products to be available for public consumption FORENSIC TOXICOLOGY • • • • Primarily concerned with the medico legal consequences of toxin exposure o Medico legal - legal implications; used for evidence for legal proceedings Under forensic pathology (collects samples from crime scenes/victims for autopsy and testing) Focus on establishing and validating analytic performance of the methods used to generate evidence in legal situations, including the cause of death In PNP Crime Lab, benchworks on testing evidences are preferably done by medical technologists and chemists CLINICAL TOXICOLOGY • • • Study of interrelationships between toxin exposure and disease states o Connection between toxin & pathogenesis/ pathophysiology of diseases Emphasize not only in diagnostic testing but also therapeutic intervention In laboratory, under clinical chemistry o Methods used are best footed in CC area EXPOSURE TO TOXINS CAUSALITY OF EXPOSURE • • • Intentional suicide attempts o Self-exposure to toxins o The person intentionally exposes himself to toxins usually for self-harm o Caused by ▪ Intake of toxic agents (bleach, acid) ▪ Drug overdose (sleeping pills, overmedication) o Suicide - highest mortality rate for toxin exposure Accidental exposure o More frequently occurring among children ▪ Due to lack of knowledge/ignorance on toxins ▪ Impulsive intake of food/materials/substance o Drug overdose can also be accidental in nature ▪ May be due to accidental intake of drug/medicine (overmedication of wrong/same medicine) ▪ High risk for geriatric pxs, sensory-impaired pxs Homicide or Occupational exposure o Homicide - intentional exposure o Occupational - exposure due to occupation ▪ In agriculture industry, exposure to pesticides (organophosphates) ▪ In manufacturing, exposure to potential toxins ▪ In clinical laboratory-histopathology, exposure to various volatile reagents (formalin, chloroform,…) ORAL DOSAGE • • • • ACUTE AND CHRONIC TOXICITY • • • ROUTES OF EXPOSURE • • • Ingestion o Most common route of exposure o Injection - common method o Toxins must be absorbed in the circulation to cause systemic effect on the human body ▪ If toxins are not absorbed in the intestine, it can cause localized effects in GIT (diarrhea, bleeding, malabsorption syndrome) ▪ No absorption in intestine = no systemic effect o Liver - affected by absorption ▪ First pass - whatever is absorbed in the intestine must be absorbed in liver to check for substances ▪ Can detoxify toxins in minimal dose ▪ High doses can destroy the liver ▪ Most abused part of the body • Alcohol - most abused drugs; considered a drug because it can cause alterations to normal body functions Inhalation o Toxic substance must be in gas/volatile form o Small particulate toxins may also enter the body o Respiratory system is affected Transdermal absorption o Through the skin o IV ensure full exposure to toxin due to direct exposure in the circulation of toxin Effective dose (ED50) is the dose of drug in which 50% of treated individuals will experience benefit o Considered as the dose to be predicted to be effective or with therapeutic benefit to 50% of the population Toxic dose (TD50) is the dose of drug in which 50% of individuals will experience toxic adverse effects o Dose predicted to produce a toxic response in 50% of the population Lethal dose (LD50) is the dose of drug in which 50% of individuals will result in morbidity o Dose that would predict death in 50% of population o Monitored if response expected is death o Experimented in lab animals (mice) Therapeutic Index - ratio of the TD50 to the ED50 Used to relate period/duration and frequency of exposure to observed toxic effects Acute Toxicity o Associated with single short-term exposure but with sufficient dose that can cause immediate toxic effect o Manifestations are immediate, abrupt, or sudden o Examples: suicide attempts, accidental exposures Chronic Toxicity o Associated with repeated frequent exposure for extended periods o The dose of toxic substance is insufficient to cause immediate toxic effects o Gradual/chronic manifestation of toxic effect o Example: occupational exposure ROUTES OF EXPOSURE & DOSE-RESPONSE RELATIONSHIP • • Toxins can enter the body via several routes, with ingestion, inhalation, and transdermal absorption being the most common ones. Absorption of toxins from the gastrointestinal tract occurs via several mechanisms. Some are taken up by processes intended for dietary nutrients. However, most are absorbed by passive diffusion. This process requires that the substance cross the cellular barriers. Hydrophobic substances have the ability to diffuse across cell membranes and, therefore, can be absorbed anywhere along the gastrointestinal tract. DOSE–RESPONSE RELATIONSHIP • • Toxicity Rating System Toxicity Rating Lethal Oral Dose in Average Adult Super toxic <5 mg/kg Extremely toxic 5-50 mg/kg Very toxic 50-500 mg/kg Moderately toxic 0.5-5 g/kg Slightly toxic 5-15 g/kg Practically nontoxic >15 g/kg Paracelsus (1493 to 1591) pioneered the use of chemicals in medicine and coined the term “the dose makes the poison.” Understanding this dose–response relationship is fundamental and relevant to modern toxicology. There is a need to establish an index of the relative toxicity of substances to allow assessment of their potential to cause pathologic effects. • • • • • Dose–response relationship. Comparison of responses of a therapeutic drug over a range of doses. The ED50 is the dose of drug in which 50% of treated individuals will experience benefit. The TD50 is the dose of drug in which 50% of individuals will experience toxic adverse effects. The LD50 is the dose of drug in which 50% of individuals will result in mortality. BARBITURATES • TOXICOLOGY OF SPECIFIC AGENTS • • • • • • • • Toxicology is the study of toxic drugs or poisons. A toxicant (poison) is any substance that, when taken in sufficient quantity, causes sickness or death. Toxicity is a relative term used to compare one substance with another; a toxic substance is one with a toxicity defined as “extremely” or “super” toxic. Specific drugs considered to be toxicants are composed of several categories. Some of these drugs are also considered to be therapeutic in nature. Acute toxicity – single, short-term exposure to a substance Chronic toxicity – repeated exposure for extended period of time. TD 50 (Threshold dose / median Toxic dose) o Dose that would be predicted to produce a toxic response in 50% of the population. LD 50 (Lethal dose) o Dose that would predict death in 50% of the population ED 50 (Effective dose) o Dose that would be predicted to be effective or have a therapeutic benefit in 50% of the population Classification of Toxins o Analgesics o Barbiturates o Narcotics o Pesticides o Carbon monoxide o Metal poisoning • Are anti-inflammatory agents and painkillers. These drugs are also considered to be therapeutic. Salicylate (aspirin) is considered toxic at a serum level of >90 mg/dL 6 hours following ingestion. The time since ingestion must be known to determine severity of toxicity. o Salicylate intoxication results in the following: stimulation of the respiratory system with initial respiratory alkalosis, conversion of pyruvate to lactate, inhibition of oxidative phosphorylation, and breakdown of fatty acids to produce ketoacids. Eventually, metabolic acidosis occurs. o Renal clearance of salicylate can be increased by forced alkaline diuresis. Are short-acting (pento-, secobarbital); intermediate-acting (amo-, β-, butabarbital); and long-acting (phenobarbital) sedatives that exert a tranquilizing effect through their depressant effect on the CNS. The barbiturates can be considered as substances of abuse or as analgesics. o Barbiturate intoxication results in cardiac arrest and respiratory depression through its effect on the CNS. o There are no real antidotes for barbiturate overdose except the establishment of an open airway, aiding respiration, and maintaining cardiac output. NARCOTICS (OPIOIDS) • • Compounds include heroin, morphine, codeine, & methadone. Most of these drugs are habit forming and can be considered drugs of abuse. o Intoxication. The toxic effects of overdose include depression of respiration caused by a decreased sensitivity to carbon dioxide and coma. Heroin is metabolized by the liver to form morphine and is excreted by the kidney as morphine glucuronide. o Antidote. The effective antidote for narcotic overdose is naloxone, a narcotic antagonist. PESTICIDES • • ANALGESICS • Acetaminophen, if present in serum at 300 mcg/mL 2 hours after ingestion, induces hepatic toxicity. Time since ingestion is critical in determining acetaminophen intoxication. o Intoxication results in hepatocystic necrosis 3 to 4 days after overdose because of the inability of the liver to adequately conjugate the metabolite of acetaminophen (i.e.,acetamidoquinone) to glutathione. High levels of acetamidoquinone in the liver induce hepatocyte death. o Antidote. The effective antidote for acetaminophen overdose is Nacetylcysteine, which is thought to act as a glutathione substitute and binds to metabolite. Exist as organic complexes, organophosphates (largest single group of pesticides), and carbamates. These compounds inhibit AChE, which results in specific effects on the heart and respiratory centers, muscle cramps, and certain CNS effects. o Intoxication. The method used for the determination of pesticide poisoning is the examination of PChE (an isoenzyme of AChE found in serum). o Antidote. The effective antidote for pesticide poisoning is atropine sulfate. CARBON MONOXIDE • • • Is a tasteless gas with 200-fold greater affinity for hemoglobin than oxygen. Intoxication. During carbon monoxide poisoning, hemoglobin cannot adequately exchange carbon dioxide for oxygen because of the increased amount of carboxyhemoglobin present. Suffocation and death follow. Antidote. The effective antidote for carbon monoxide poisoning is removal of the source of carbon monoxide or removal of the victim from the source. o METAL POISONING • • • • Includes intoxication by heavy metals lead, arsenic, & mercury. Lead poisoning is most typically caused by lead paint ingestion or continuous exposure to lead in the soil. o Intoxication. Lead is found primarily in RBCs in intoxicated victims but produces wide spread effects, such as gastrointestinal irritation, weight loss, kidney damage, convulsions, and in children, altered cognition and encephalopathy. Death occurs because of peripheral vascular collapse or brain involvement. o Antidote. Administration of ethylenediaminetetraacetic acid (EDTA), penicillamine,and other lead chelates that bind the lead and allow it to be excreted by the kidney. o Examination of urinary ALA levels and RBC protoporphyrins can determine the occurrence of lead poisoning after serum and urine lead levels have returned to normal. Mercury (mercury salts) is found in antibacterial agents, photographic reagents, pesticides, and batteries. Poisoning by these agents is typically the result of overexposure or ingestion. o Intoxication. Effects of mercury poisoning include gastrointestinal irritation, severe kidney damage, or neurologic symptoms. o Antidote. As with lead poisoning, chelates, such as EDTA, penicillamine, or dimercaprol [also referred to as British antilewisite (BAL)] bind the mercury and render it able to be excreted. Arsenic is found in pesticides, weed killer, & some paints. o Intoxication. Arsenic induces purging gastroenteritis, shredding of the stomach lining, and causes Mees’ lines in fingernails because of keratin binding. Death typically occurs because of hemorrhagic gastroenteritis o Because arsenic is cleared rapidly from the blood, urine is the specimen of choice for analysis. o Antidote. Chelation therapy with penicillamine or BAL is effective. • • • • DRUG & TOXIN TESTS • SUBSTANCES OF ABUSE • • • Include a variety of compounds that, when found in high levels in the urine or serum, can incriminate an individual. It is mandatory in substance-of-abuse analysis to obtain a satisfactory specimen and to process the specimen in a secure part of the laboratory. Ethanol is the most common toxicant and substance of abuse seen in patients in emergency departments in the United States. o It acts by depressing the CNS and increasing the heart rate and blood pressure. Ethanol metabolism occurs in the liver by alcohol dehydrogenase, which converts alcohol to acetaldehyde, which is then excreted to acetate. A blood level of 0.1 g/dL is defined as intoxicating. Methanol is widely used in paints, solvents, antifreeze, and solid canned fuels. Poisoning with methanol is typically caused by ingestion. o Intoxication by methanol is considered more dangerous than ethanol poisoning because of the formation in humans of formaldehyde and formic acid as metabolites. Formic acid formation results in metabolic acidosis, pancreatic necrosis, and visual system impairment. Antidotes for methanol poisoning include the administration of sodium bicarbonate to treat the acidosis and ethanol to bind alcohol dehydrogenase and block the formation of the metabolites. Amphetamines are CNS stimulants that block dopamine receptors in the brain. Amphetamine metabolism occurs in the liver and produces benzoic acid. o Intoxication by amphetamines can produce severe depression, respiratory difficulties, and episodes of paranoia. o Antidote. The antidote for amphetamine overdose is forced acid diuresis. Cocaine - is a CNS stimulant that is metabolized by cholinesterase to form benzoylecgonine, which is excreted by the kidney. o Intoxication. Cocaine overdose produces hypertension, myocardial infarction, or seizure. Cardiotoxicity can occur and result in sudden death following cocaine use. o Antidote. There is no antidote for cocaine overdose except the passage of time and urinary excretion. Cannabinoid compounds [tetrahydrocannabinol (THC), marijuana] o Produce psychologic effects and are stored in fat cells. o THC is excreted in the urine for an extended period of time depending on use. Overdose of this drug is rare and is not severe enough to be life-threatening. Phencyclidine (PCP, angel dust) is an abused anesthetic that is illegally used as a hallucinogen. o Intoxication. This drug can produce violence, seizures, respiratory depression, or death. o Antidote. Treatment for PCP overdose is diazepam. PCP is unmetabolized and excreted in the urine as phencyclidine. • The drug screen rapidly identifies a drug or drugs present in the blood, urine, or gastric contents of a patient suffering from toxicity. Neutral and basic drugs as well as drug metabolites are best detected in urine, whereas acidic drugs are best found in detectable concentrations in blood and serum. Following a positive drug screen, confirmatory methods must be used to quantitatively analyze drug levels in a patient. o Handheld immunoassays are the most common type of drug screen. They detect a wide variety of drugs but cannot separate closely related compounds. Blood and urine can both be analyzed with this method. o Gas-liquid chromatography allows for greater sensitivity in the identification of drugs. It can be used as a confirmatory technique for drugs detected by drug screen. Confirmatory drug tests are required to confirm and quantify those drugs found in a patient’s serum or urine using drug-screening methods. o Gas chromatography/mass spectrometry is a sensitive technique used to confirm drugs detected by screening techniques. Typically, urine samples are initially analyzed by gas chromatography to determine the presence of compounds, then reanalyzed by mass spectrometry to examine fragments of these compounds for relative abundance in the sample. o o o Immunoassay techniques use antibodies to detect drugs. These methods are usually automated and in the form of enzyme immunoassays. Ethanol testing is typically performed using gas chromatography. However, an enzyme assay using alcohol dehydrogenase and measuring the increase in NADH formation following the reaction is widely used and can be automated. Heavy metal testing is most often performed by atomic absorption spectrophotometry.