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CLINICAL TOXICOLOGY Lecture 1 & 2 Introduction Dr. Tavga A. Baban Introduction Clinical toxicology:- is concerned with diseases and illnesses associated with short term or long term exposure to toxic chemicals. Who is more prone to toxicity? Children less than 5 years old. Why? 1. 2. 3. The environment: includes the area around the home. Children are curious and investigative. Many household products are marked in attractive packages. 4. The natural tendency of children to place everything into their mouth. 5. Taking medication in the presence of children “If I see it, I can do it,” 6. Dosing errors 7. Poisons are often left in easy view and accessible. Poisoning also occur because many products are used in unvented areas. Another factor that increase toxicity is the absence of information about the constituents of many products. Common Causes of Death in the Acutely Poisoned Patient Comatose patient: – Loss of protective reflexes – Airway obstruction by flaccid tongue – Aspiration of gastric contents into tracheobronchial tree – Loss of respiratory drive – Respiratory arrest Hypotension – due to depression of cardiac contractility Common Causes of Death in the Acutely Poisoned Patient Shock – due to hemorrhage or internal bleeding Hypovolemia – due to vomiting, diarrhea or vascular collapse Hypothermia – worsened by i.v. fluids administered rapidly at room temperature Cellular hypoxia – in spite of adequate ventilation and O2 admin. – due to CN, CO or H2S poisoning Common Causes of Death in the Acutely Poisoned Patient Seizures – may result in pulmonary aspiration; asphyxia Muscular hyperactivity resulting in hyperthermia, muscle breakdown, myoglobinemia, renal failure, lactic acidosis and hyperkalemia Behavioral effects –traumatic injury from fights, accidents, fall from high places. Suicides, etc Common Causes of Death in the Acutely Poisoned Patient Massive system: damage to a specific organ – Liver (acetaminophen; amanita phylloides [poison mushroom] – Lungs (paraquat) – Brain (demoic acid) – Kidney (ethylene glycol) – Heart (cobalt salts) Note: death may occur in 48 – 72 hrs APPROACH TO THE POISONED PATIENT Table 3.1 page 42 History; Oral statements concerning details Call Poison Control Center Initial physical examination Assessment of vital signs Eye examination (miosis or mydriasis, nystagmus, and vision disturbance) CNS and mental status examination APPROACH TO THE POISONED PATIENT Examination of the skin Mouth examination Lab (clinical chemistry and x-ray procedures Renal function tests ECG Other screening tests TREATMENT OF ACUTE POISONING Treat the patient, not the poison", promptly Supportive therapy essential Maintain respiration and circulation – primary Judge progress of intoxication by: Measuring and charting vital signs and reflexes TREATMENT OF ACUTE POISONING - 1st Goal - keep concentration of poison as low as possible by preventing absorption and increasing elimination - 2nd Goal - counteract toxicological effects at effector site, if possible PREVENTION OF ABSORPTION OF POISON Decontamination from skin surface Emesis: indicated after oral ingestion of most chemicals; – must consider time since chemical ingested Contraindications: ingestion of corrosives such as strong acid or alkali; if patient is comatose or delirious; if patient has ingested a CNS stimulant or is convulsing; if patient has ingested a petroleum distillate if patient has ingested sharp object if patient less than 6 months PREVENTION OF ABSORPTION OF POISON Induce emesis in the following ways: mechanically by stroking posterior pharynx; use of syrup of ipecac, 15ml for children and 30ml for adults followed by one glass of water; use of apomorphine parenterally PREVENTION OF ABSORPTION OF POISON Gastric lavage: insert tube into stomach and wash stomach with water or normal saline to remove unabsorbed poison Contraindications are the same as for emesis except that the procedure should not be attempted with young children PREVENTION OF ABSORPTION OF POISON Chemical Adsorption activated charcoal will adsorb many poisons thus preventing their absorption adsorbent in intestines may interrupt enterohepatic circulation PREVENTION OF ABSORPTION OF POISON Purgation Used for ingestion of enteric coated tablets when time after ingestion is longer than one hour Use saline cathartics such as sodium or magnesium sulfate Chemical Inactivation Not generally done, particularly for acids or bases or inhalation exposure For ocular and dermal exposure as well as burns on skin; treat with copious water Metabolism of some compounds produces highly reactive electrophilic intermediates; if nucleophiles present, toxicity is minimal; if nucleophiles depleted, toxicity results Increase Elimination Of Toxic Agents Increasing urinary excretion by acidification or alkalinization Decreasing passive resorption from nephron lumen Diuresis Cathartics Peritoneal dialysis Hemodialysis Hemoperfusion Forced diuresis and pH alteration It is useful when compounds or active metabolites are eliminated by the kidney and diuresis enhances their excretion. Mannitol and furosemide are generally used. This method is no longer indicated because it increase the excretion of chemical only two fold. Alkaline diuresis is achieved by administration of sodium bicarbonate, 1-2 mEq/kg every 3-4 hr. The potential uses of urine alkalinization have been with weak acid such as salicylates and phenobarbital. Acid diuresis is possible by using ammonium chloride, 75mg/kg/24hr. Acid diuresis increase the elimination of weak bases, such as amphetamine, phencyclidine, and quinidine. This procedure is no longer recommended. Dialysis and hemoperfusion Peritoneal Dialysis The procedure is undertaken by inserting a tube through a small incision made in the abdominal area into the peritoneum. The peritoneal membrane serves as the semipermeable (dialyzing) membrane. The dialyzable chemical diffuses from blood across the peritoneal membrane into the dialyzing fluid (from higher concentration to lower concentration). Peritoneal Dialysis 1. 2. 1. 2. 3. Advantages:Easy. Lowest risk for complications. Disadvantages:The least effective method for removing most poisons. It is 5-10 time less efficient than hemodialysis. Not suitable when rapid removal of a toxic substance is needed. Complications include:- abdominal pain, intraperitoneal bleeding, intestinal, bladder, liver, or spleen perforation; peritonitis; water and electrolyte imbalance; and protein loss. Procedure for peritoneal dialysis Hemodialysis Two catheters are inserted into the patient’s femoral vein. Blood is pumped from one catheter through the dialysis unit, across the semipermeable membrane, and back through the other catheter. The procedure is continued for 6-8 hr. the solubilized chemical diffuses across the semipermeable membrane into the dialysis solution. Clearance of the toxic agent is based on differences in osmotic and concentration gradients. Procedure for hemodialysis Procedure for hemodialysis Disadvantages 1. 2. 3. 4. The chemical that removed by this way must have a low molecular size. Less effective for drug that are highly protein-bound. Useless for chemicals that are extensively taken by the tissues. Complications include clotting, and seepage of blood from around connections, hypotension, convulsions, arrhythmias, infection, and hematologic defects. Hemoperfusion 1. 2. 3. The passage of blood through columns of adsorptive material, such as activated charcoal, to remove toxic substances from the blood. It is more effective than peritoneal dialysis and hemodialysis for removing compound that are: lipid soluble. protein bound. Poorly dialyzable. Complications include:- trapping of white blood cells and platelets and microembolization. Newer systems solved this problem. Procedure for hemoperfusion Antagonism of the absorbed poison A. B. Chemical antagonism e.g. protamine sulfate + heparin, chelators of metal ions Functional or physiological antagonism e.g. glucagon + Bblockers C. Pharmacological or receptor antagonism e.g. naloxone + opioid D. Dispositional antagonism (pharmacokinetic interaction) Strategies for Treatment of the Poisoned Patient Evaluate and stabilize vital signs Give supportive therapy, if needed Determine the type and specifics of the poison Time of exposure Determine the presumed current location of the poison Determine Volume of Distribution for the poison Strategies for Treatment of the Poisoned Patient Determine the immediate (real time) risk or hazard for absorption Initiate body burden reduction procedures or specific antidotes based on the above information Strategies for Treatment of the Poisoned Patient If volume of distribution is very large; do not waste time on any type of dialysis X-ray for location of enteric coated pills and use cathartics if in the stomach Use hypocholesteremics for poisons trapped in enterohepatic biliary system SPECIFIC ANTIDOTES Poison Acetaminophen Acetylcholinesterases, OP’s, physostigmine Iron salts Methanol, Ethylene glycol Mercury, lead Narcotic drugs Anti/muscarinicscholinergics OP anticholinergics Antidote Acetylcysteine Atropine Deferoxime Ethanol Metal Chelators Naloxone Physostigmine Praladoxime (2-PAM) Poison Warfarin Digoxin INH BZD Chloroquin Heparin Snake bite B-blockers TCA Antidote Vit. K Fab AB Vit. B6 Flumazenil Diazepam Protamine sulphate Antivenom Glucagon Physostigmine, NaHCO3
