What are the indications and typical doses for intravenous (IV) amino acids in adult patients with impaired oral or enteral nutrition?

Intravenous Amino Acids: Indications and Dosing

Primary Indications

IV amino acids are indicated when patients cannot meet nutritional requirements through oral or enteral routes, with specific dosing ranging from 0.8-1.5 g/kg/day depending on clinical context. 1

Core Indications for IV Amino Acid Administration

• Intestinal failure requiring parenteral nutrition when enteral absorption is inadequate to sustain life 1
• Critical illness in ICU patients who cannot be adequately nourished enterally within 5-7 days 1, 2
• Acute liver failure or decompensated cirrhosis when oral/enteral nutrition is ineffective or not feasible 1
• Acute renal failure in critically ill patients, particularly those on continuous renal replacement therapy 1
• Malnutrition in patients unable to achieve adequate oral intake despite counseling and oral nutritional supplements 1

Standard Dosing Protocols

General Adult Populations

For metabolically stable adults on home parenteral nutrition: 0.8-1.0 g amino acids/kg/day 1

For critically ill ICU patients: 0.8-1.5 g/kg/day, with optimal protein-sparing effects achieved at 1.3-1.5 g/kg/day in trauma and sepsis 1, 2

Total energy provision: 20-35 kcal/kg/day, with non-protein energy at 100-150 kcal per gram of nitrogen 1

Disease-Specific Dosing

Liver Disease

• Compensated cirrhosis: Standard amino acid solutions at 0.8-1.0 g/kg/day 1
• Hepatic encephalopathy: BCAA-enriched solutions (35-45% BCAA content) with reduced aromatic and sulfur-containing amino acids 1, 3
• Acute hepatic injury: Up to 120 grams of BCAA-enriched amino acids tolerated with improvement in encephalopathy in 75-87% of patients 3

Renal Failure

• Acute renal failure with continuous renal replacement therapy: 0.4 g nitrogen/kg/day (approximately 2.5 g amino acids/kg/day) to achieve positive nitrogen balance 1
• Chronic renal failure (conservatively treated): 0.55-0.60 g/kg/day of high biological value protein 1
• Hypocaloric feeding states: Increase nitrogen requirements by 25-30% 1

Pediatric Populations

• Full-term infants and children up to 5 years: 100 mcg zinc/kg/day as adjunct; amino acids at 1.0-1.5 g/kg/day 4
• Premature infants (<1500g): 300 mcg zinc/kg/day as adjunct 4

Critical Supplementation Requirements

Glutamine Supplementation in Critical Illness

When PN is indicated in ICU patients, amino acid solutions MUST contain 0.2-0.4 g/kg/day of L-glutamine (equivalent to 0.3-0.6 g/kg/day alanyl-glutamine dipeptide). 1

• Glutamine depletion occurs in critical illness with plasma levels falling below normal 1
• Low plasma glutamine levels are associated with worse outcomes 1
• No study has shown harmful effects with doses of 10-30 g glutamine/24 hours 1
• Glutamine supplementation is now considered standard of care in critically ill patients receiving PN 1

Micronutrient Requirements

Thiamine must be administered BEFORE initiating carbohydrate-containing nutrition in at-risk patients: 100-300 mg IV daily, with 300 mg given before starting nutrition therapy in refeeding syndrome 5

Zinc supplementation for adults on PN: 2.5-4 mg/day, with an additional 2 mg/day in acute catabolic states 4

Administration Guidelines

Route and Formulation

• Central venous access (tunneled catheters or implanted ports) required for long-term PN; PICC lines not recommended for home PN 1
• 3-in-1 formulations (total nutrient admixtures containing amino acids, dextrose, and lipids) are safe and represent standard of care in adults 6
• Cyclic administration is recommended over continuous infusion 1
• Infusion pumps should be used for controlled delivery 1

Energy Distribution

• Carbohydrates: Approximately 60% of non-protein energy, avoiding glucose administration exceeding 7 mg/kg/min 1, 2
• Lipids: Approximately 40% of non-protein energy, not exceeding 1 g/kg/day for long-term PN (>6 months) 1, 2
• Fat/glucose ratio: Should not exceed 40:60 to prevent PN-associated liver disease 1

Critical Pitfalls to Avoid

Never administer IV amino acids without adequate energy substrate - this leads to amino acid oxidation for energy rather than protein synthesis 1, 2

Avoid overfeeding - hyperalimentation at acute disease stages increases complications and mortality; energy supply should be adapted to disease stage 1, 2

Do not use BCAA-enriched solutions as monotherapy for hepatic encephalopathy - they are adjunctive to standard treatments like lactulose 7

Never give glucose before thiamine in malnourished or at-risk patients - this precipitates Wernicke-Korsakoff syndrome 5

Monitor for refeeding syndrome - start with low calories (5-15 kcal/kg/day) in starvation states and increase gradually over 5-10 days 8

Prevent line infections - cirrhotic patients are particularly prone to sepsis from IV line infections 1

Monitoring Requirements

• Biochemistry and anthropometry at all visits for home PN patients 1
• Trace elements and vitamins every 6 months 1
• Plasma electrolytes to avoid hypokalaemia/hypophosphataemia after initiating nutrition (refeeding syndrome) 1
• Zinc blood levels when exceeding usual maintenance dosing 4
• Liver function tests regularly, as PN-associated liver disease relates to composition and underlying disease 1