IV Vitamin C Infusion Rate and Dosing
For adults with normal renal function receiving IV vitamin C, infuse doses of 1-3 grams diluted in 50-250 mL normal saline or dextrose solution over 30-60 minutes, with higher doses (>3 grams) requiring slower infusion over 1-2 hours to minimize adverse reactions. 1
Standard Infusion Protocols by Clinical Indication
Critical Illness and Acute Inflammation
- Administer 2-3 g/day IV during the acute inflammatory phase (Grade B recommendation, 84% consensus) 2, 1
- This higher repletion dose is necessary because plasma vitamin C concentrations decline rapidly when C-reactive protein exceeds 10 mg/L 2, 1
- IV administration is essential in critically ill patients due to unpredictable enteral absorption from impaired gut function and limited intestinal transporter capacity 1
Continuous Renal Replacement Therapy (CRRT)
- Use 2-3 g/day IV for patients on CRRT 2, 1
- Higher doses compensate for increased clearance through dialysis circuits
Perioperative Cardiac Surgery
- Administer 1-2 g/day IV for 5-7 days perioperatively 2, 1
- This dosing supports wound healing and reduces oxidative stress from surgical trauma
Severe Sepsis Protocols
- Some protocols use 200 mg/kg/day for 4 days in severe sepsis and acute respiratory failure 1
- For a 70 kg adult, this equals approximately 14 g/day divided into multiple doses
Infusion Rate Guidelines
Preparation and Dilution
- Dilute vitamin C with normal saline or glucose solution before IV administration to minimize adverse reactions 1
- For doses of 1-3 grams: dilute in 50-100 mL and infuse over 30-60 minutes
- For doses >3 grams: dilute in 250 mL and infuse over 1-2 hours 3
Rate Considerations
- Slower infusion rates reduce the risk of dose-related adverse effects including hypotension and osmotic effects 3
- Rapid bolus administration should be avoided; controlled infusion allows for monitoring and early detection of adverse reactions
Pharmacokinetic Rationale
Why IV Administration Achieves Therapeutic Levels
- Oral vitamin C produces tightly controlled plasma concentrations that never exceed 220 μmol/L even with maximum tolerated oral doses of 3 g every 4 hours 4, 5
- IV administration bypasses intestinal absorption limits and can achieve pharmacologic concentrations of 25-30 mmol/L (25,000-30,000 μmol/L) 5
- A 50-g IV dose produces predicted peak plasma concentrations of 13,400 μmol/L compared to only 220 μmol/L from maximum oral dosing 4
Duration of Elevated Levels
- Pharmacologic ascorbate concentrations are maintained until excess is eliminated by glomerular filtration and renal excretion 5
- The biological half-life at high plasma levels is approximately 30 minutes, requiring sustained or repeated dosing 6
Monitoring and Safety
When NOT to Measure Plasma Levels
- Do not measure plasma vitamin C during critical illness or severe inflammation (Grade GPP, 92% consensus) 2, 1
- Blood levels become undetectable when CRP >40 mg/L, making interpretation impossible 2, 1
- Plasma levels decline as soon as CRP >10 mg/L 2, 1
When Measurement May Be Useful
- Consider measuring plasma vitamin C only in patients with suspected scurvy or chronic low intake in the absence of acute inflammation 2, 1
Clinical Monitoring
- Monitor blood pressure during infusion, as rapid administration can cause transient hypotension 3
- Observe for signs of fluid overload in patients with cardiac or renal compromise 3
- Clinical response (wound healing, resolution of symptoms) is more practical than laboratory monitoring during inflammatory states 7
Absolute Contraindications and Dose Limits
Maximum Safe Dosing
- Do not exceed 2-3 g/day in patients with renal impairment, history of kidney stones, or on CRRT due to risk of fatal nephrotoxicity 2
- The tolerable upper level is 2 g/day based on gastrointestinal upset; higher doses may cause severe diarrhea and increase oxalate absorption 2
Specific Contraindications
- Avoid in patients with hemochromatosis or iron overload as vitamin C enhances iron absorption 7
- Avoid in G6PD deficiency when using vitamin C as treatment for methemoglobinemia, though this is a specific therapeutic context 3
- Use caution in pregnant women due to theoretical teratogenicity concerns 3
Duration of Therapy
Acute Phase Treatment
- Continue IV vitamin C for 4-7 days during the acute phase of critical illness 2
- For wound healing after major surgery or amputation, continue throughout the acute healing phase (approximately 2-4 weeks) or until adequate healing is achieved 7
Transition to Maintenance
- Sustained therapy is needed to prevent recurrence of hypovitaminosis 1, 7
- Once enteral function is restored, transition to oral supplementation at 200-500 mg/day for maintenance 2, 7
Common Pitfalls to Avoid
Inadequate Dosing in Inflammation
- Do not use standard RDA doses (75-90 mg/day) during critical illness—these are insufficient to restore plasma concentrations in inflammatory states 2, 8
- Shocked surgical, trauma, and septic patients require 3 g/day to restore normal plasma ascorbate concentrations, far exceeding the recommended PN dose of 100 mg/day 8
Route of Administration Errors
- Do not rely on oral dosing to achieve therapeutic levels in critical illness—intestinal absorption is saturated and unpredictable 1, 4
- Oral vitamin C at 1.25 g produces peak plasma concentrations of only 135 μmol/L versus 885 μmol/L for the same IV dose 4
Infusion Rate Mistakes
- Avoid rapid bolus injection of doses >100 mg to minimize arthralgias, myalgias, and hypotension 3
- Do not infuse >125 mg of certain formulations (e.g., iron gluconate preparations) as a bolus 3
Patient-Specific Factors Affecting Response
- Cancer patients with high tumor burden or inflammation achieve lower post-infusion plasma levels despite identical dosing 9
- Patients deficient in vitamin C prior to therapy tend to achieve lower plasma levels post-infusion 9
- Metastatic disease lowers peak plasma ascorbate concentrations compared to localized tumors 9