The good week

[schoonder]

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Jackie07 mentioned that frequent dividing cells can play a role in the chemo's performance.
An other consideration is the time drug remains active in the system after the infusion. If drug's half-life is about 10 days, then the final 11 days, time prior to the next treatment, a slowly decaying drug (smaller in quantity) will be easier to tolerate. By the time next injection is scheduled, system will pretty much have cleared residuals.
Surely there are more reasons to select a 3 weekly treatment cycle, like if there isn't a significant improvement in a weekly doding regimen, it's much easier on patient to make that doctor's visit once every three weeks.