Describe the pharmacology of 4% albumin
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.
|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.
- 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)|
Schultze, Heremans "Nature and metabolism of extracellular proteins" Elsevier, 1966
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Chien, Shih-Chieh, et al. "Critical appraisal of the role of serum albumin in cardiovascular disease." Biomarker research 5.1 (2017): 1-9.
Taverna, Myriam, et al. "Specific antioxidant properties of human serum albumin." Annals of intensive care 3.1 (2013): 1-7.