Question 3(p.2)

Describe the mechanism of actions and duration of effect of drugs used to lower potassium in hyperkalaemia.

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College Answer

A good answer to this question required the collation of knowledge from broad range of areas, ie drug activity. Marks were divided between each of the following: 8.4%NaHCO3-,insulin/glucose, K+ exchange resin,  frusemide/loop diuretics, Beta2 agonists and K+ free fluid rehydration/dilution. Candidates often overlooked the fact that only loop diuretics and K+ exchange resins lower total body K+ content, whilst the others induce an intracellular K+ shift which is not sustained and do not directly result in body elimination of K+. Intravenous
fluid rehydration lowers total body K+ if there is a resulting diuresis. Most candidates just passed this question. Common omissions included NaHCO3, loop diuretics and beta 2 agonists. No candidate mentioned rehydration/dilution. Calcium does not lower serum potassium.

Discussion

Drugs used to treat hyperkalemia:

  • Rehydration (i.e. IV fluids)
    • Dosing: 1000-2000ml
    • Mechanism: dilution; support of diuresis
    • Time to onset: minutes
    • Duration of action: hours
  • Intracellular movement (temporary)
    • Bicarbonate (esp. isotonic bicarbonate)
      • Dosing: 100-200mmol
      • Mechanism: H+/K+ exchange, using the Na+/K+ ATPase.
      • Time to onset: minutes
      • Duration of action: 1-2hours
    • β-agonists
      • Mechanism: increase the activity Na+/K+ ATPase pumps
      • Dosing: 5mg nebulised salbutamol
      • Time to onset: minutes
      • Duration of action: hours
    • Insulin
      • Dosing: 10-50 units, administered with dextrose
      • Mechanism: the insertion of extra Na+/K+ ATPase pumps into cell membranes, thus increased cellular potassium uptake
      • Time to onset: seconds/minutes
      • Duration of action: hours
  • Removal via the urine
    • Furosemide, other diuretics
    • Mechanism: increased sodium delivery to the distal nephron; exchange of sodium for potassium, and thus kaliuresis
    • Dosing: 40-80mg
    • Time to onset: 20-40 minutes
    • Duration of action: hours
  • Removal via the bowel
    • Cation exchange resin
    • Mechanism: binding of potassium into the resin in exchange for another cation (eg. calcium or sodium)
    • Dosing: 10-50g
    • Time to onset: hours
    • Duration of action: hours

References

Rastegar, Asghar. "Serum potassium." Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition (1990).

Palmer, Biff F. "Regulation of potassium homeostasis." Clinical Journal of the American Society of Nephrology 10.6 (2015): 1050-1060.

Gumz, Michelle L., Lawrence Rabinowitz, and Charles S. Wingo. "An integrated view of potassium homeostasis." New England Journal of Medicine 373.1 (2015): 60-72.

Greenlee, Megan, et al. "Narrative review: evolving concepts in potassium homeostasis and hypokalemia." Annals of internal medicine 150.9 (2009): 619-625.

Stone, Michael S., Lisa Martyn, and Connie M. Weaver. "Potassium intake, bioavailability, hypertension, and glucose control." Nutrients 8.7 (2016): 444.