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Absorption and clearance

An IV drip enters a vein through a small catheter and skips absorption in the gut. Each ingredient is then cleared by the kidneys, the liver or blood enzymes at its own rate.

Drip types

By ingredient

How the body takes up and clears each drip

1. The vein and catheter

Peripheral IV catheter insertion is the most common invasive hospital procedure, and 35% to 50% of these catheters fail. In a survey of IV vitamin C use, 6 of 9,328 patients had vein irritation or phlebitis.[1][2]

2. Vitamin C: gut limit and kidney clearance

By mouth, absorption is complete at 200 mg and falls at single doses of 500 mg and above, and blood levels saturate at 1000 mg a day. By vein, 50 g is predicted to reach 13,400 micromol/L against 220 micromol/L for the largest tolerated oral dose. After 1000 mg IV the half-life was 7.4 hours; above the kidney threshold most is excreted in urine, and part is converted to oxalate.[1][2][3]

3. Glutathione: broken down in the gut

A single 3 g oral dose did not raise blood glutathione in 7 healthy volunteers, because enzymes in the gut and liver break it down. This low oral uptake is the reason given for IV glutathione, which has no FDA-approved product in the US.[1][2][3]

4. NAD+: removed from blood

In the first human study of an IV NAD+ infusion (6 hours at 3 micromol/min), blood levels of NAD+ and its breakdown products did not change for the first 2 hours. Urine showed NAD+ and methylnicotinamide by 6 hours.[1]

5. Fluid: blood volume and thirst

IV saline restored plasma volume faster than drinking. It bypasses the mouth and throat, which drive thirst and the release of antidiuretic hormone; thirst was lower after drinking than after IV fluid.[1][2]

6. Vitamin B12: oral versus injection

In 3 trials with 153 people, oral B12 at 1000 mcg a day gave blood levels similar to intramuscular B12, and one trial at 2000 mcg a day found higher levels by mouth.[1]