Question 19.1

College Answer

The relevant physical features include

• Haemodialysis 
• Small molecule < 500 Da
• Water Soluble
• Non-protein bound
• Low volume of distribution

Haemoperfusion 

• Larger non-protein-bound molecules 1000 to 1500 KDa

Examples

Haemodialysis :  Lithium, metformin
Haemoperfusion: Phenobarbitone, theophylline

Discussion

A more detailed discussion  is available regarding the use of haemoperfusion and haemodialysis in toxicology There's also a revision page about haemoperfusion in a broader context.  Interestingly, the college question asked for the properties of filters which make them suitable for use, rather than the properties of the drugs (which is what the college answer consists of).

If were to actually answer the question, it would look something like this:

Haemodialysis filters:

• Large surface area of the membrane increases the rate of molecule transport
• Porosity of the membrane affects the maximum molecular weight of the transported molecules
• Ultrafiltration rate, as a function of porosity (among other factors) affects the rate of removal for larger molecules
• Dialysate flow rate affects the rate of clearance for drugs with smaller molecules
• Features which favour drug clearance are small molecule size, small volume of distribution, and large protein-unbound fraction
• One example is lithium

Hemoperfusion filters:

• Large surface area of resin or charcoal filter enhances adsorption by presenting a larger contact surface for the filtered blood
• Features which favour drug clearance include high affinity for activated charcoal, or the presence of specific antibody-coated resin on the filter
• One example is theophylline

Nenov, Vesselin D., et al. "Current applications of plasmapheresis in clinical toxicology." Nephrology dialysis transplantation 18.suppl 5 (2003): v56-v58.

Holubek, William J., et al. "Use of hemodialysis and hemoperfusion in poisoned patients." Kidney international 74.10 (2008): 1327-1334.

Ghannoum, Marc, et al. "Hemoperfusion for the treatment of poisoning: technology, determinants of poison clearance, and application in clinical practice." Seminars in dialysis. Vol. 27. No. 4. 2014.

Ghannoum, Marc, et al. "Blood purification in toxicology: nephrology’s ugly duckling." Advances in chronic kidney disease 18.3 (2011): 160-166.

Takki, S., et al. "Pharmacokinetic evaluation of hemodialysis in acute drug overdose." Journal of pharmacokinetics and biopharmaceutics 6.5 (1978): 427-442.