Dilution of Medications: Effects on Stability and Compatibility
Both D5W and normal saline are acceptable diluents for most emergency medications including epinephrine and ketamine, while Lactated Ringer's should be avoided for ketamine due to documented incompatibility.
Epinephrine Infusions
Recommended Diluents
Epinephrine infusions can be safely prepared with either D5W or normal saline 1. The guidelines specifically describe two standard preparations:
- D5W preparation: 1 mg (1 mL) of 1:1000 epinephrine diluted in 250 mL D5W yields 4.0 μg/mL 1
- Normal saline preparation: 1 mg (1 mL) epinephrine in 100 mL saline yields a 1:100,000 solution 1
Stability Considerations
Epinephrine maintains excellent stability in both diluents. Epinephrine solutions in 5% dextrose remain stable for up to 30 days at both room temperature (25°C) and refrigeration (4°C), maintaining >95% of initial concentration 2. This applies to standard concentrations of 25,50, and 100 μg/mL, with no changes in pH, color, or precipitation observed.
Lactated Ringer's Concerns
Avoid Lactated Ringer's for fluid resuscitation when using epinephrine infusions 1. The guidelines explicitly state that "Lactated Ringer's solution might potentially contribute to metabolic acidosis, and dextrose is rapidly extravasated from the intravascular circulation to the interstitial tissues" 1. While this refers to volume resuscitation rather than drug dilution specifically, normal saline is the preferred crystalloid for IV access and fluid replacement in anaphylaxis management.
Ketamine Dilution
FDA-Approved Diluents
The FDA label explicitly approves three diluents for ketamine: Sterile Water for Injection, 0.9% Sodium Chloride (Normal Saline), or 5% Dextrose in Water 3. These are the only solutions with documented safety and efficacy data.
Specific Preparation Guidelines
For induction dosing:
- Dilute the 100 mg/mL concentration with an equal volume of approved diluent 3
- Use immediately after dilution 3
For maintenance infusions:
- Transfer 10 mL from 50 mg/mL vial OR 5 mL from 100 mg/mL vial to 500 mL of either 5% Dextrose or Normal Saline to achieve 1 mg/mL 3
- For fluid restriction: add to 250 mL to achieve 2 mg/mL concentration 3
Critical Incompatibility Warning
Ketamine is physically incompatible with Lactated Ringer's solution 4. A compatibility study testing 94 IV drugs found that ketamine was one of only 8 drugs incompatible with LR during simulated Y-site administration. This incompatibility was confirmed through visual evaluation and particle counting tests 4.
General Principles for Medication Dilution
D5W vs Normal Saline: Clinical Considerations
D5W characteristics:
- Dextrose rapidly extravasates from intravascular to interstitial space 1
- Less effective for volume resuscitation
- Preferred for certain vasopressor infusions (dopamine: 400 mg in 500 mL D5W) 1
Normal Saline characteristics:
- Remains intravascular longer, better for volume expansion 1
- May cause hyperchloremic metabolic acidosis with large volumes 5, 6
- Preferred for fluid resuscitation in shock states
Lactated Ringer's: When to Avoid
Do not use Lactated Ringer's for:
- Ketamine dilution (documented incompatibility) 4
- Situations requiring rapid intravascular volume expansion in anaphylaxis 1
- Potential contribution to metabolic acidosis in specific clinical contexts 1
Lactated Ringer's may be acceptable for:
- General fluid resuscitation in sepsis (some evidence suggests improved outcomes vs NS) 5
- Maintenance fluids in children (though isotonic saline preferred) 7
Common Pitfalls to Avoid
Never use the 100 mg/mL ketamine concentration IV without dilution - this can cause severe adverse effects 3
Do not assume all crystalloids are interchangeable - ketamine-LR incompatibility is a documented safety issue 4
Avoid mixing epinephrine with Lactated Ringer's during resuscitation - use normal saline for IV access and volume replacement 1
Use diluted solutions immediately - while epinephrine has 30-day stability, the FDA label for ketamine specifies immediate use after dilution 3
Monitor for hyperchloremia with large-volume normal saline - particularly relevant in prolonged resuscitations 5, 6
Practical Algorithm for Diluent Selection
For epinephrine infusions:
- First choice: D5W (standard guideline preparation) 1
- Alternative: Normal saline (equally acceptable) 1
- Avoid: Lactated Ringer's
For ketamine:
- Approved options: Normal saline OR D5W OR Sterile Water 3
- Never use: Lactated Ringer's 4
- Default to normal saline for simplicity in emergency settings
For IV access/volume resuscitation: