2 - General Methods for Overdose Flashcards
How can you prevent absorption?
- Gastric emptying (emesis, gastric lavage)
- Adsorption (activated charcoal)
- Catharsis
- Dilution
When is emesis used?
- Rarely used
- Only recommended if a recent ingestion or no other option (can cause aspiration)
When is gastric lavage recommended?
When you know the agent is still in the stomach
Contraindications to emesis
- Drowsiness
- Coma
- Convulsions
- No gag reflex (ex: children)
- Corrosive/ caustic agents in the stomach
Complications of emesis
- Aspiration pneumonitis
- Bleedings
- GI rupture
What is used to induce emesis?
Syrup of ipecac
Contraindications to gastric lavage
- Corrosive/ caustic agents
- Petroleum distillate
Complications of gastric lavage
- Cardiac arrhythmias
- Low pO2
- Laryngospasm
- Pharyngeal injury
- Esophageal or gastric perforation
What method of absorption prevention can be combined w/ gastric lavage?
Activated charcoal
Can gastric lavage cause aspiration?
Less risk than emesis, but still possible so must protect the airways
How does activated charcoal work?
- Pyrolysis (oxidizing agents)
- Hydrogen bonding, dipole, and Van der Waals’ forces
- Large surface (generally administered in large amounts)
- Decreases systemic absorption of poisons
- Binds poisons that have left the stomach
Which poisonings can not be treated w/ activated charcoal?
- Corrosive agents (acids, alkalis)
- Methanol, ethanol
- Ethylene glycol
- Heavy metals
- Tobramycin
Contraindications to activated charcoal
- Ingestion of caustic substances
- Presence of ileus or bowel obstruction
Complications of activated charcoal
- Vomiting
- Aspiration pneumonitis
- Constipation (more likely w/ larger amounts)
- GI obstruction
- Charcoal empyema (charcoal goes into abdominal cavity)
How is activated charcoal administered?
- PO or by gastric tube
- Adult dose = 30-100 g as a slurry in water
- Child dose based on weight (1-2 g/kg in < 10 y/o; 15-20 g in 10-12 y/o)
Benefit of MDAC (multiple dose activated charcoal)
- May help prevent reabsorption of drug in the GI tract
- Increases clearance of drugs excreted w/ the feces
- Ensures that there is a marked serum to GI lumen concentration gradient (which increases elimination of the drug)
- Helpful if route of administration of poison is other than oral
- Effective for a number of agents (ex: analgesics, sedatives, beta-blockers, anticonvulsants, etc.)
Problems w/ MDAC
Same as single-dose regimens (vomiting, constipation, GI obstruction)
Adult dose of MDAC
25 g over 2 h or 50 g over 4-6 h
Whole-bowel irrigation indications
- Ingestion of iron or zinc salts
- Ingestion of SR medications
- Ingestion of drug packets – “body packers”
- Ingestion of “crack” vials – “body stuffers”
Whole-bowel irrigation contraindications
- Uncooperative px
- Presence of ileus or GI obstruction
- GI bleeding or perforation
Whole-bowel irrigation complications
- Abdominal cramping
- Vomiting
- Profuse diarrhea
- Hyperchloremia – essential to monitor electrolytes
Whole-bowel irrigation technique
- Administer large volumes of isotonic, non-absorbable polyethylene glycol/ electrolyte solution over 40 minutes to several hours
- Note: wait for a rectal discharge that looks like the fluid administered (can take 6-12 h to appear)
What is the purpose of cathartics? Contraindications and complications? Examples?
- Used to move the poison or poison/ charcoal complex through GI tract
- Can help remove poison and/ or decrease absorption
- Can help prevent formation of concretions of drug or drug/ charcoal complex
- Same contraindications and complications as w/ whole-bowel irrigation
- Ex: sorbitol (typically added to activated charcoal mixtures), magnesium citrate, magnesium/ sodium sulfate
Describe the process of dilution. Indication and contraindications
- Fluid administration (water or milk) first few minutes after ingestion
- Value in some ingestions of corrosive agents
- Contraindicated in coma or convulsions
What methods can be used to enhance elimination?
- *MDAC, hemodialysis, hemoperfusion
- Diuresis
- Peritoneal dialysis
- Hemofiltration
- Plasmapheresis and exchange transfusion
What are indications for enhancement of elimination?
- Failure to respond adequately to full supportive care (intractable hypotension, HF, seizures, metabolic acidosis, or dysrhythmias)
- Px in whom the normal route of elimination of the toxin is impaired (renal or hepatic dysfunction, pre-existent or caused by the overdose)
- Remember it takes a while to set up dialysis and takes time for it to start working; not an immediate fix
- Px in whom amount of toxin absorbed or the plasma concentration indicate high risk of morbidity or mortality
- Px who have concurrent disease or are in age group at particular risk (elderly, infants)
- Px overdosed w/ a drug that is known to be successfully removed by such methods
What is diuresis? What is the objective?
- Manipulation of pH
- Increase renal clearance (works only if poison or active metabolites are excreted in urine; based on concept of “ion-trapping”)
What is the difference between acid and alkaline diuresis?
- Alkaline diuresis – give NaHCO3 IV to increase urinary pH to 7-8 (increases renal excretion of salicylate, isoniazid, phenobarbital)
- Acid diuresis – give NH4Cl IV to reduce urinary pH to 4.5-5.5 (claimed to work w/ weak bases; ex: amphetamines and phencyclidine; however, no evidence of efficacy)
What is forced diuresis? What are the risks?
- Volume expansion w/ sodium-containing solutions (valid if glomerular filtration is important determinant of excretion)
- Risks – volume overload manifested by pulmonary and cerebral edema
What must be monitored when you give a diuretic?
- Electrolytes, fluid balance, acid-base balance, and response to diuretic
- Risk of metabolic alkalosis and hypokalemia
When can peritoneal dialysis be used?
- Theoretically can be performed to enhance elimination of water soluble, low MW, poorly protein bound compounds w/ a low Vd (ex: alcohols, lithium, salicylates, theophylline)
- High clearance can be obtained for molecules w/ MW < 500 Daltons
- Relatively simple method, but too slow; rarely used
What is the formula for MDAC?
dC/dt = [DAK (C1-C2)] / h
Which overdoses is MDAC effective in?
- Phenobarbital
- Theophylline
- Valproic acid
What is required when hemodialysis is done?
Anticoagulation with heparin
Indications for hemodialysis
- Poison is dialysable
- Pt deteriorating despite care
- Severe electrolyte problems
- Potentially lethal blood levels are present
- Risk from prolonged coma, or risk of renal failure
- Specific poisonings (methanol, ethylene glycol, salicylate, theophylline, ethanol)
Hemodialysis complications
- Clotting and leaking of blood from around connections (thrombosis, bleeding)
- Embolus (rare)
- Hypotension, arrhythmias
- Convulsions
- Infections
Describe charcoal hemoperfusion
- Compounds adsorbed by activated charcoal
- Cartridge containing a sorbent w/ very large surface area (no direct contact)
- Usually performed for 4-6 hours; cartridge changed as often as every 2-4 hours
- Not limited by plasma protein binding (hemodialysis is)
Which drugs is charcoal hemoperfusion used for?
- Carbamazepine
- Phenobarbital
- Phenytoin
- Theophylline
Complications of charcoal hemoperfusion
Similar to hemodialysis
Describe hemofiltration
- Movement of plasma across a semipermeable membrane in response to hydrostatic pressure gradient
- No dialysate solution on the other side of the membrane
- Smaller solutes transported across the membrane following the water (bulk flow) while larger solutes, depending on permeability characteristics of membrane, are excluded
Advantages of hemofiltration
- Continue therapy for 24 h
- Remove drugs like lithium and procainamide that distribute slowly from tissue binding sites and from intracellular compartment
- Ultrafiltrate flows of 100-600 mL/min can be achieved
Disadvantages of hemofiltration
- Rate of removal of drugs may not be sufficient to benefit the critically ill px
- Complexity, experienced ICU staff required for monitoring (4-6 h)
- Clearances achieved are significantly lower than those achieved w/ hemodialysis
Describe plasmapheresis and exchange transfusion. Indication?
- Used to eliminate molecules w/ large MW (MW > 15,000 Daltons; ex: immunoglobulins)
- Both techniques remove plasma proteins (benefit of removing protein-bound molecules, digoxin-digoxin antibody complexes, thyroxine)
- Exchange transfusion appropriate in management of small infants or neonates
Disadvantages of plasmapheresis and exchange transfusion
- Risk of infections and allergic reactions (replacement of plasma)
- Expensive
When is lipids rescue used?
- Local anesthetics (lidocaine, bupivacaine)
- TCAs
- CCBs
Formula for clearance
Cl = Q * ER
ER = [(Cin - Cout)/ Cin] * 100
