Where Does Subcutaneous Injection of a GBCA Go?

This would be true of all subcutaneous injections and some drugs are deliberately injected subcutaneously, including some of the chelating agents. Reasons for deliberate subcutaneous injection include primarily that there is slow access to the vascular system and therefore prolonged effect of the agent injected. So this would also be true of a subcutaneous injection of a GBCA. In some ways this may emulate the conditions that are created with por renal function, GBCA injection, and development of NSF. The combined factors of a GBCA injection (almost always linear with NSF) and prolonged retention in the body secondary to renal failure, represent the fertile grounds for developing NSF.

So my estimates, if we use the example of 10 ml of GBCA injected subcutaneously, probably for the first 24 hours much of it stays locally in the subcutaneous tissues, from then progressively much of the agent will be removed, probably 40% by lymphatics, 40% by capillary - venous system, and 20 % stays locally, bound in some fashion. To reach this equilibrium probably takes 2 weeks.

There may be animal studies performed on subcutaneous injections that evaluate the pathways of distribution of various substances, possibly even radionuclide studies in humans. If I come across these I will compare to my estimates and update if necessary. My impression also is that the incidence of GDD is greater with subcutaneous injection compared to intravascular. This may not be surprising, again because this is a circumstances where there is prolonged intracorporeal retention of the GBCA, not only because it will take probably 2 weeks before the bulk of it has travelled into the vascular system by either lymphatic or capillary access, but also because the local repository of Gd will still be substantial for a very extended period of time.