Lecture 2: Increasing Poison Elimination

Question 1

4 main methods for increasing poison elimination

Answer 1

• Multiple-dose activated charcoal
• Urine alkalisation
• Haemodialysis
• Haemoperfusion

Question 2

How is AC given and how many doses given

Answer 2

• Normally orally administered - patient conscious
• Nasogastric tube - patient unconscious
• Normally 4 doses given

Question 3

Advantages of MDAC

Answer 3

• simple, inexpensive and safe
• avoids need for haemodialysis and haemoperfusion
• reduces elimination half-life
• increases drug clearance

Question 4

Disadvantages of MDAC

Answer 4

• Nasogastric tube often required
• Drug-induced vomiting may stop use
• Complications include bowel obstruction and pulmonary asphyxiation

Question 5

When should MDAC be used?

Answer 5

after ingestion of slow-release preparations or drugs that decrease gastric motility

Question 6

How does MDAC affect enterohepatic recirculation of drugs

Answer 6

• Charcoal absorbs drugs secreted in bile, preventing reabsorption
• drug eliminated bound to charcoal in gut
• repeated doses needed to interrupt enterohepatic recirculation

Question 7

How does MDAC affect entero-enteric recirculation

Answer 7

• after absorption drug can re-enter gut by passive diffusion as long as conc. lower in gut than in blood
• Charcoal absorbs drug that diffuses from circulation into gut, interrupting entero-enteric recirculation

Question 8

What are the kinetic characteristics that favour elimination by MDAC

Answer 8

• prolonged half-life following OD
• small Vd

Question 9

What drugs does MDAC increase elimination of (5)

Answer 9

• Phenobarbital
• Carbamazepine
• Theophylline
• Quinine
• Dapsone

Question 10

How to maximise efficiency of MDAC

Answer 10

given at rate which:
- keeps small intestines filled
- avoids saturation of charcoal by exogenous compounds

Question 11

What pH urine does urine alkalinisation create?

Answer 11

pH > 7.5

Question 12

what compounds does urine alkalinisation increase the elimination of

Answer 12

• salicylate
• phenobarbital
• 2,4-D

Question 13

Haemodialysis method

Answer 13

blood circulated through filter to remove poisons, then blood returned to body

Question 14

Conditions for using haemodialysis

Answer 14

• poison should diffuse through membrane
• significant portion of poison should be present in plasma water
• small Vd

Question 15

Haemoperfusion method

Answer 15

passing blood through AC or resin cartridge so it will reabsorb drug passing through it