The other thing to be aware of, is if you are dealing with patients with GI cancer, they have significant bleeding and their plasma compartment may indeed be larger. The Volume of distribution term is necessary to put a volume term on both sides of the equation. That reason could be the MAb still in the vessel and not mixed in the circulation well. In a simplified sense, if the Ke is estimated in an increasing phase, then equation 2 would predict an decreased Vd. I have clinical case that may throw a wrench in all of this.
Patient is in respiratory failure.
Blood and urine cultures are positive for Gram Positive Staph Coagulase positive. Staph aureus sepsis suspected. Vancomycin levels ordered, pharmacy consult. Based on prior experience I would anticipate the levels to be low. WBC 16.8, left shift and significant bandemia.