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I'm trying to determine the best sampling points for a Phase III trial
of drugs in pregnant women which includes a nested population PK study
with sparse sampling. One arm of the trial is sulfadoxine-pyrimethamine
(the apparent elimination half-life ranges from 150 to 200 hours for
sulfadoxine and from 80 to 95 hours for pyrimethamine) in a single dose,
the other is mefloquine (half-life of elimination was 385 hours in
healthy volunteers and 493 in malaria patients) also single dose, and
the third arm is SP as above (single dose) + azithromycin (terminal
half-life 68 hours) once a day for 3 days.
I've seen some posts here saying that sampling should go out to 3-5
times the half-life (in rich PK studies). What's the thinking on this
for pop PK? Currently we are taking a pre-dose sample, one between 6 and
42 hours post-dose (at a specified time) and another between 48 and 144
hours post-dose. My concerns are:
1) for the SP/Az arm, since Az is given over 3 days, when should
post-dose sampling begin? i.e., after first or third dose?
2) is 144 hours long enough for the drugs we're using here, or should we
get some later samples?
3) proposed sample size is 77 per treatment arm -- does this seem
reasonable (without doing precise power/sample size calcs)?
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