All of the following are techniques of extracorporeal elimination of toxins EXCEPT:
Answer: A: Once a drug or toxin has been absorbed and has the potential to exert significant toxicity, a number of methods can be considered to enhance elimination of the drug from the body. These can be nonextracorporeal or extracorporeal methods. Non-extracorporeal methods of enhanced toxin elimination are:
Extracorporeal methods of enhanced elimination are:
Methods such as CVVH and CAVH may cause less haemodynamic instability than HD and HP, but the toxin clearance rates achieved can be slower. The most commonly used extracorporeal elimination method is HD. However, the most effective method to remove a toxin from the body is maintenance of optimal renal, liver, lung and cardiovascular functions through good supportive care. Therefore HD and HP should be considered in specific toxicities where aggressive resuscitation and supportive care alone are less likely to be lifesaving.
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Haemodialysis is LEAST likely to be useful in which ONE of the following toxicities?
Answer: D: The specific toxic substances that are likely to be removed by HD and HP are described in the following mnemonic.
COP, I’VE STUMBLED
Methanol and ethylene glycol, sodium valproate, salicylates and lithium are the most commonly encountered severe toxicities that are amenable to removal by HD. HP provides a higher rate of clearance for theophylline than HD; however, both can be considered.
In metformin toxicity severe life-threatening lactic acidosis can develop:
HD is very useful in severe metformin toxicity because it rapidly clears lactic acidosis and removes metformin thereby reducing the lactate production. HD is not indicated in systemic iron toxicity. Desferrioxamine chelation therapy is the treatment of choice in that situation.
MDAC is indicated for which ONE of the following overdoses?
Answer: D: MDAC can be considered for enhanced elimination of specific drugs or substances from the body after its absorption. Current available evidence suggests that MDAC can accelerate drug clearance and is able to achieve clearance rates as good as that can be achieved from haemodialysis for specific drugs. There are two proposed mechanisms of action:
The most common indication for the use of MDAC is life-threatening carbamazepine overdose. For carbamazepine toxicity, because of high protein binding, MDAC in combination with HP is favoured for enhanced elimination.
MDAC increases clearance in the following toxicities and therefore may be useful:
After the initial dose of activated charcoal, further reduced doses are given every 2 hours for a maximum duration of 6 hours. Airway protection is generally indicated prior to commencement of MDAC. Activated charcoal is not indicated for lithium and iron overdoses, as these metals are poorly bound to activated charcoal.
All of the following are complications of urinary alkalinisation EXCEPT:
Answer: C: Few drugs that are excreted through the kidneys and that are weak acids with small volumes of distribution can be eliminated more rapidly by manipulation of urine pH to alkalinity. In alkaline urine these weak acids are more ionized and therefore prevents their renal absorption, promoting more rapid elimination from the body.
Urine alkalinization increases urinary elimination of the following agents:
Urine alkalinization should be considered as first-line treatment for patients with moderate to severe salicylate poisoning who do not meet the criteria for haemodialysis.
Administration of bicarbonate to alkalinize the urine results in alkalaemia. Hypokalaemia is the most common complication but can be corrected by giving intravenous potassium supplements. Alkalotic tetany can occur occasionally, but hypocalcaemia is rare. Volume overload can occur in urinary alkalization due to bicarbonate therapy. Dehydration is not a typical complication. Hyponatraemia is not a complication of urinary alkalization. Forced diuresis can cause hyponatraemia. The term urine alkalinization emphasises urine pH manipulation rather than a diuresis as the prime objective of treatment.
Sodium bicarbonate is used for immediate correction of profound life-threatening metabolic acidosis in all of the following EXCEPT:
Answer: A: Sodium bicarbonate is used for immediate correction of life-threatening acidosis in cyanide poisoning, isoniazid overdose and toxic alcohol poisoning. Sodium bicarbonate prevents cardiotoxicity secondary to fast sodium channel blockade in TCA, propranolol, flecainide and quinidine toxicities etc. and it prevents redistribution of drugs to the central nervous system (CNS) in severe salicylate toxicity. It also increases urinary solubility of drugs (in methotrexate toxicity) and enhances urinary drug elimination (in salicylate and phenobarbitone toxicities).
In carbamazepine toxicity, sodium bicarbonate is used to treat the rare event of ventricular dysrhythmias and it is not used for life-threatening acidosis.
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