Question 9

Describe the pharmacology of 4% albumin

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College Answer

This question required the candidate to consider 4% albumin from a pharmacological perspective. The examiners were therefore after a description that included presentation, pharmaceutics (including correct content description and osmolality), indications, pharmacodynamics, pharmacokinetics, adverse effects, special precautions and dosing.


Name 4% Albumin
Class Colloid fluid
Chemistry Human plasma protein; presented as 4% solution (40g/L) in slightly hypotonic saline (usually 140 mmol/L sodium and 128 mmol/L chloride) - but can also be presented with isotonic saline (NaCl 0.9%, with a sodium concentration closer to 154 mmol/L)
Routes of administration IV only
Absorption Zero oral bioavailability; degraded into component peptides by digestive enzymes
Solubility pKa 6.75; good water solubility
Distribution VOD = 0.07L/kg (effectively confined to the circulating volume); minimally protein bound
Target receptor Various molecules in the bloodstream bind and form complexes
Metabolism Metabolised mainly by the reticuloendothelial system
Elimination Minimal renal excretion, except in cases of protein-losing nephropathy. Most of it is degraded by macrophages; 10% is eliminated though the gut
Time course of action Albumin molecules have a half life of around 27 days; the volume effect lasts perhaps 6-12 hours, depending on the leakiness of capillaries
Mechanism of action Expands the extracellular fluid volume and changes the biochemistry of the body fluids
Clinical effects Multiple roles, including oncotic, immunomodulatory and transport roles. Acts as a binding substrate for xenobiotics.
Volume expansion:
- Isoosmolar and isooncotic: infused volume should theoretically remain in the circulation for some hours
- This 500mml (10%) change may trigger circulatory reflxes, resulting in baroreceptor-mediated decrease in heart rate and some peripheral vasodilation
Change in osmolality:
- minimal; unnoticed by osmoreceptors (100ml of hypotonic saline carrier fluid is too small a volume)
Change in biochemistry:
- similar to the effects of infusion 500ml of isotonic saline (as this is the carrier fluid)
Single best reference for further information Griffel and Kaufman (1992)


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