Elimination Flashcards
(34 cards)
What are the three conditions that must be satisfied for forced diuresis to be appropriate?
1) A substantial proportion of the drug is excreted unchanged.
2) The drug is distributed mainly in extracellular fluid.
3) The drug is minimally protein-bound.
Which drugs are examples where forced alkaline diuresis is most useful?
Phenobarbitone, lithium, and salicylates.
Why is forced acid diuresis no longer recommended?
It is ineffective and poses unnecessary risks; no drug or poison (e.g., amphetamines, quinine) currently warrants its use.
What are the three key factors that make a substance suitable for haemodialysis?
1) Easily diffuses through a dialysis membrane.
2) Present in plasma water or rapidly equilibrates with it.
3) Pharmacological effect correlates with blood concentration.
What are the “best indications” for initiating haemodialysis regardless of clinical condition?
After heavy metal chelation in renal failure, or significant ethylene glycol/methanol ingestion.
Name four complications of haemodialysis.
Infection (e.g., hepatitis B, AIDS), thrombosis, hypotension, air embolism.
How does haemoperfusion differ from haemodialysis in toxin removal?
Haemoperfusion removes toxins that are poorly dialysable (e.g., protein-bound or lipid-soluble) using adsorption.
What is a major complication of haemoperfusion due to heparin use?
Bleeding disorders.
What is the primary advantage of haemofiltration over haemodialysis?
It removes larger molecules (up to 40,000 Da), such as aminoglycosides or metal chelates.
Which poisoning cases is plasmapheresis effective for, despite its risks?
Theophylline, carbamazepine, amanita, mercury, or hemlock overdoses.
Why is peritoneal dialysis rarely recommended for detoxification?
It is only 10–25% as effective as haemodialysis and requires 24 hours for completion.
What are two key complications of plasmapheresis?
Bleeding disorders (e.g., DIC) and citrate toxicity (e.g., tetany, arrhythmias).
What type of poisoning might cardiopulmonary bypass be used for experimentally?
Overdoses involving cardiac depressants like verapamil or lidocaine.
What is the main principle behind forced diuresis for drug elimination?
Altering urine pH to ionize drugs, trapping them in urine for excretion.
What is a critical limitation of haemodiafiltration?
Limited evidence on its advantages, as it is rarely used and poorly studied.
Which technique combines plasmapheresis and haemoperfusion?
Plasma perfusion (rarely used in poisoning).
What is a major risk of peritoneal dialysis during catheter insertion?
Perforation of viscus or vascular laceration.
What makes a drug’s pKa value relevant to elimination strategies?
It determines ionization at physiological pH, influencing excretion via urine alkalinization/acidification.
Name two agents where haemodialysis is considered “very good” for severe intoxication.
Lithium and theophylline.
What is a key disadvantage of plasmapheresis?
It sacrifices the patient’s plasma proteins, increasing risks of complications like anaphylaxis or fluid overload.
What historical milestones are associated with haemodialysis?
First used experimentally in 1913; clinically applied in 1950 for salicylate overdose.
What specific blood flow rates are targeted during acute haemodialysis?
Begins at 50–100 ml/min, increasing to 250–300 ml/min for maximal clearance.
Which drugs fall under “fairly good indications” for haemodialysis?
Alcohols, amphetamines, anilines (if patient deteriorates despite supportive care).
What complication of haemoperfusion involves low calcium levels?
Hypocalcaemia (due to citrate in anticoagulants binding calcium).
