> mean distribution and elimination half-lives (reported as
> mean +/- SD) of about 0.20 +/- 0.04 hours and 1.57 +/- 0.08 hours,
> respectively."  Going by 5 half-lives, it seems that 10 hrs. at the most
> ought to be okay for elimination, but what does "two-compartment" mean?
>
> "Gadoteridol is eliminated in the urine with 94.4 +/- 4.8% (mean +/- SD) of
> the dose excreted within 24 hours post-injection."  This seemed to conflict
> with the half-lives listed in the previous paragraph--why are we now
> talking about 24 hours?
>
I think another reading of the distribution and elimination half-lives
times will clear this up. The times are listed in tenths of an hour with
one-tenth of an hour equaling six minutes. Thus, rewritten in minutes
these times would be 6 minutes +/- 1.44 minutes and 63.42 minutes +/-
4.8 minutes. Ten hours is plenty generous - more like five hours
according to these numbers (63 min * 5 half-lives = 317.1 minutes / 60
minutes = 5.285 hours) to reach 5 half-lives for excretion. Thus, the
next statement that 94% of the dose is excreted in urine by 24 hours is
in line with the preceeding information. Advising 24 hours simply gives
an extremely safe time-frame for excretion (providing the liver and
kidneys are functioning normally. These numbers should be adjusted
accordingly (using their own labwork for guidance) for patients with
altered liver and/or kidney function.)

Any package insert is generated by the manufacturer, and since studies
regarding breastfeeding probably have *not* been done (too expensive,
low numbers of patients, etc), the pharmaceuticals will simply take the
stance of "don't do it until nearly fully excreted". This is where a
careful consideration of the pharmacokinetics of the drug in question
and the nature of lactation, including milk production, and the
*current* breastfeeding situation (1 week old vs 1 year old) is demanded
in order to arrive at an opinion about what's going on. Many HCPs will
welcome our careful advice, in my experience.

Katharine West, BSN, MPH
Sherman Oaks, CA