I get my important Vitamin C in my diet ... approx 600+ mg day ... importantly, throughout the day.
The promising high Vitamin C therapy for Covid-19 was IV Vitamin C ... where high plasma concentrations can occur for a few hours... until the next IV addition.
From the Linus Pauling Institute.....
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One hundred percent absorption efficiency is observed when ingesting vitamin C at doses up to 200 mg at a time. Higher doses (>500 mg) result in fractionally less vitamin C being absorbed as the dose increases. Once plasma vitamin C concentrations reach saturation, additional vitamin C is largely excreted in the urine. Notably, intravenous administration of vitamin C bypasses absorptive control in the intestine such that very high concentrations of vitamin C can be achieved in the plasma; within a few hours, renal excretion restores vitamin C to baseline plasma concentrations (see Cancer Treatment) (25). ******