12 Overdose Flashcards
Drug Overdose
- The ingestion or application of a drug or other substance in quantities greater than are recommended or generally practiced;
- Accidentally: e.g. children – e.g. paracetamol;
- Deliberately: e.g. suicide, or drug abuse (next lecture)
- The drugs most frequently used for intentional self-poisoning are benzodiazepines, analgesics and antidepressants, often taken with alcohol;
Risks of drug overdose - Drug with Risk
- narrow therapeutic window (digoxin, teophylline)
- steep dose-response curve (warfarin, sulhonylurea der.)
- enzyme inhibitors (ketoconazole, erythromycin)
- enzyme inducers (rifampicin, carbamazepine)
- high toxic potential (aminoglycosides)
Risks of drug overdose - Patient with Risk
- polymorbidity
- polypharmacy
- treatment lasting long time
- chronic diseases e.g. disorders of elimination functions
- abusus
- non-compliance • self-treatment
- simultaneous ordination of more drugs by different physicians
Therapeutic Index =
Therapeutic Index =
Dose causing toxicity/ Dose providing efficacy
Drugs with Narrow Therapeutic Window
Aminoglycoside antibiotics - gentamicin, tobramycin
Anticoagulants - warfarin, heparins, high protein bound
Aspirin (salicylate derivatives),
high protein bound
Carbamazepine
enzyme inducer
Conjugated / Esterified estrogens
OC pills, enzyme inducers
Cyclosporine
immunosupressant
Digoxin
cardiac stimulant/tonic
Hypoglycemic agents
Levothyroxine
Lithium
Phenytoin
nonlinear pharmacokinetics
Procainamide - heart arrhythmia
Quinidine - heart arrhythmia
Theophylline (aminophylline)
Tricyclic antidepressants
Valproic acid
Principles of treating overdose
- Overdose
- Immediate measures Evaluation,
Remove contact, ABC, history, evidence - Supportive measures
Cardiac/respiratory arrest Hypotension, Arrhythmia Convulsions, Renal or Hepatic failure, temperature - Prevent Absorption
(Emesis), Activated charcoal, Gastric Aspiration/lavage - Elimination
Alkaline diuresis (sodium bicarb.)
Acid diuresis (ammonium chloride)
Haemodialysis - Antidotes
- Psychiatric assessment
Supportive care
- ABC (airway, breathing, circulation)
- Protect airway
- Vital signs, mental status, and pupil size
- Pulse oximetry, cardiac monitoring, ECG
- Intravenousaccess
- cervical immobilization if suspect trauma
- Rule out hypoglycaemia
Preventing absorption
Gastric lavage
- Flexible tube is inserted through the nose into the stomach
- Stomach contents are then suctioned via the tube
- A solution of saline is injected into the tube
- Not in unconscious patient unless intubated (risk aspiration)
Preventing absorption
Induced Vomiting
• Not routinely recommended, due to risk of aspiration
Preventing absorption Activated charcoal
- Adsorbs toxic substances or irritants, inhibiting GI absorption
- Oral: 25-100 g as a single dose
- repetitive doses useful to enhance the elimination of certain drugs (eg, theophylline, phenobarbital, carbamazepine, aspirin)
- However, charcoal does not absorb petroleum distillates, inorganic acid and alkali, alcohol, metal ions, cyanide, lithium.
Elimination of poisons
Renal elimination
• Medication to stimulate urination or defecation may be given to try to flush the excess drug out of the body faster.
Elimination of poisons
Forced alkaline diuresis
- Infusion of large amount of NS+NAHCO3
- Used to eliminate acidic drug that mainly excreted by the kidney eg salicylates
- Serious fluid and electrolytes disturbance may occur
Elimination of poisons
Hemodialysis or haemoperfusion
- Reserved for severe poisoning
- Drug should be dialyzable i.e. protein bound with low volume of distribution
- may also be used temporarily or as long term if the kidneys are damaged due to the overdose.
Antidotes
Agents with a specific action against the activity or effect of drugs involved in poisoning cases.
Antidotes mechanisms and
examples
Pharmacological antagonists
Naloxone (opiate poisoning) Ethanol (methanol poisoning)
Enhance physiological function to compensate
Physostigmine (belladona alkaloid poisoning)
Restore active site of drug target
Pralidoxime (poisoning by organophosphates, e.g. pesticides, war gas)
Bypass block
Glucagon (beta-blocker poisoning)
Sequester poison
Digibind (digoxin poisoning
Speed up excretion
Chloride is used as an antidote for bromide / iodide overdoes.