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.
| 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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