Table 1.

Typical pharmacokinetic properties of an orally administered pharmaceutical drug vs. those of vitamin C obtained from food sources or supplements (modified from Refs. [3]).

Pharmacokinetic property	Typical orally administered low molecular weight drug	Vitamin C from food sources or supplements
Absorption	1st order absorption kinetics within the therapeutic range. Absorption through passive transport resulting in plasma concentrations in the nano- to micromolar range.	Nonlinear absorption kinetics due to a mixture of saturable active transport through SVCT1 and facilitated diffusion through GLUT transporters resulting in micromolar plasma concentrations and millimolar tissue concentrations.
Distribution	Primarily distributed through passive diffusion. Immediate distribution primarily determined by blood flow and tissue perfusion. Homeostasis largely based on physical-chemical properties of the drugs including lipofilicity, pKa and protein binding.	Primarily distributed through active transport. Immediate distribution based on tissue priority governed by SVCT2 transporter expression and saturation kinetics. Homeostasis depends on adequacy of dose and vitamin C status of bodily compartments.
Metabolism	Catabolized unspecifically by phase I & II enzymes potentially generating a range of metabolites and/or conjugates with increased water solubility.	Specifically and unspecifically oxidized through electron donor and antioxidant properties, respectively, but efficiently regenerated intracellularly to its reduced form by numerous cell types.
Excretion	Most often 1st order elimination kinetics though passive glomerular filtration and passive reabsorption depending on pKa. Overall relatively rapid excretion of parent compound and metabolites through urine and bile.	Nonlinear concentration-dependent elimination kinetics resulting in anything from 0 to 100% active renal reabsorption depending on vitamin C availability and saturation of bodily compartments.
Modelling	Kinetics can usually be modelled well by simple compartment and non-compartment models.	Does not comply with the basic assumption of terminal 1st order kinetics used in both compartmental and non-compartmental analysis.