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Year 4 - Toxicology > 2 - General Methods for Overdose > Flashcards

2 - General Methods for Overdose Flashcards

1
Q

How can you prevent absorption?

A
  • Gastric emptying (emesis, gastric lavage)
  • Adsorption (activated charcoal)
  • Catharsis
  • Dilution
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2
Q

When is emesis used?

A
  • Rarely used

- Only recommended if a recent ingestion or no other option (can cause aspiration)

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3
Q

When is gastric lavage recommended?

A

When you know the agent is still in the stomach

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4
Q

Contraindications to emesis

A
  • Drowsiness
  • Coma
  • Convulsions
  • No gag reflex (ex: children)
  • Corrosive/ caustic agents in the stomach
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5
Q

Complications of emesis

A
  • Aspiration pneumonitis
  • Bleedings
  • GI rupture
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6
Q

What is used to induce emesis?

A

Syrup of ipecac

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7
Q

Contraindications to gastric lavage

A
  • Corrosive/ caustic agents

- Petroleum distillate

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8
Q

Complications of gastric lavage

A
  • Cardiac arrhythmias
  • Low pO2
  • Laryngospasm
  • Pharyngeal injury
  • Esophageal or gastric perforation
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9
Q

What method of absorption prevention can be combined w/ gastric lavage?

A

Activated charcoal

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10
Q

Can gastric lavage cause aspiration?

A

Less risk than emesis, but still possible so must protect the airways

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11
Q

How does activated charcoal work?

A
  • 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
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12
Q

Which poisonings can not be treated w/ activated charcoal?

A
  • Corrosive agents (acids, alkalis)
  • Methanol, ethanol
  • Ethylene glycol
  • Heavy metals
  • Tobramycin
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13
Q

Contraindications to activated charcoal

A
  • Ingestion of caustic substances

- Presence of ileus or bowel obstruction

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14
Q

Complications of activated charcoal

A
  • Vomiting
  • Aspiration pneumonitis
  • Constipation (more likely w/ larger amounts)
  • GI obstruction
  • Charcoal empyema (charcoal goes into abdominal cavity)
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15
Q

How is activated charcoal administered?

A
  • 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)
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16
Q

Benefit of MDAC (multiple dose activated charcoal)

A
  • 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.)
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17
Q

Problems w/ MDAC

A

Same as single-dose regimens (vomiting, constipation, GI obstruction)

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18
Q

Adult dose of MDAC

A

25 g over 2 h or 50 g over 4-6 h

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19
Q

Whole-bowel irrigation indications

A
  • Ingestion of iron or zinc salts
  • Ingestion of SR medications
  • Ingestion of drug packets – “body packers”
  • Ingestion of “crack” vials – “body stuffers”
20
Q

Whole-bowel irrigation contraindications

A
  • Uncooperative px
  • Presence of ileus or GI obstruction
  • GI bleeding or perforation
21
Q

Whole-bowel irrigation complications

A
  • Abdominal cramping
  • Vomiting
  • Profuse diarrhea
  • Hyperchloremia – essential to monitor electrolytes
22
Q

Whole-bowel irrigation technique

A
  • 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)
23
Q

What is the purpose of cathartics? Contraindications and complications? Examples?

A
  • 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
24
Q

Describe the process of dilution. Indication and contraindications

A
  • Fluid administration (water or milk) first few minutes after ingestion
  • Value in some ingestions of corrosive agents
  • Contraindicated in coma or convulsions
25
Q

What methods can be used to enhance elimination?

A
  • *MDAC, hemodialysis, hemoperfusion
  • Diuresis
  • Peritoneal dialysis
  • Hemofiltration
  • Plasmapheresis and exchange transfusion
26
Q

What are indications for enhancement of elimination?

A
  • 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
27
Q

What is diuresis? What is the objective?

A
  • Manipulation of pH
  • Increase renal clearance (works only if poison or active metabolites are excreted in urine; based on concept of “ion-trapping”)
28
Q

What is the difference between acid and alkaline diuresis?

A
  • 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)
29
Q

What is forced diuresis? What are the risks?

A
  • Volume expansion w/ sodium-containing solutions (valid if glomerular filtration is important determinant of excretion)
  • Risks – volume overload manifested by pulmonary and cerebral edema
30
Q

What must be monitored when you give a diuretic?

A
  • Electrolytes, fluid balance, acid-base balance, and response to diuretic
  • Risk of metabolic alkalosis and hypokalemia
31
Q

When can peritoneal dialysis be used?

A
  • 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
32
Q

What is the formula for MDAC?

A

dC/dt = [DAK (C1-C2)] / h

33
Q

Which overdoses is MDAC effective in?

A
  • Phenobarbital
  • Theophylline
  • Valproic acid
34
Q

What is required when hemodialysis is done?

A

Anticoagulation with heparin

35
Q

Indications for hemodialysis

A
  • 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)
36
Q

Hemodialysis complications

A
  • Clotting and leaking of blood from around connections (thrombosis, bleeding)
  • Embolus (rare)
  • Hypotension, arrhythmias
  • Convulsions
  • Infections
37
Q

Describe charcoal hemoperfusion

A
  • 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)
38
Q

Which drugs is charcoal hemoperfusion used for?

A
  • Carbamazepine
  • Phenobarbital
  • Phenytoin
  • Theophylline
39
Q

Complications of charcoal hemoperfusion

A

Similar to hemodialysis

40
Q

Describe hemofiltration

A
  • 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
41
Q

Advantages of hemofiltration

A
  • 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
42
Q

Disadvantages of hemofiltration

A
  • 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
43
Q

Describe plasmapheresis and exchange transfusion. Indication?

A
  • 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
44
Q

Disadvantages of plasmapheresis and exchange transfusion

A
  • Risk of infections and allergic reactions (replacement of plasma)
  • Expensive
45
Q

When is lipids rescue used?

A
  • Local anesthetics (lidocaine, bupivacaine)
  • TCAs
  • CCBs
46
Q

Formula for clearance

A

Cl = Q * ER

ER = [(Cin - Cout)/ Cin] * 100

Year 4 - Toxicology (22 decks)

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