Medications that are vesicants or have extreme pH or osmolarity should not be administered through a midline catheter. Midline catheters are a type of peripheral catheter designed for intermediate-term intravenous therapy, but they terminate in a large peripheral vein, typically in the upper arm, and not in a central vein. This makes them unsuitable for infusions that require rapid hemodilution or could cause significant damage to the peripheral vasculature.
Why Certain Medications Are Unsuitable for Midlines
The primary concern with administering specific medications through a midline is the potential for local vein irritation, phlebitis (inflammation of the vein), thrombosis (blood clot formation), and extravasation (leakage of fluid into surrounding tissue). Unlike central lines, which empty into large central veins (like the superior vena cava) where blood flow is high, midlines are in smaller, peripheral veins. This means there's less blood volume to dilute irritating solutions quickly, increasing the risk of adverse reactions.
Categories of Medications to Avoid via Midline
Understanding the characteristics that make certain drugs unsuitable for midline administration is crucial for patient safety.
1. Vesicants
Definition: Vesicants are medications that can cause severe tissue damage, blistering, and necrosis (tissue death) if they extravasate (leak out of the vein into the surrounding tissue).
Risks: When administered through a peripheral device like a midline, the risk of extravasation and subsequent severe local injury is significantly higher compared to a central line where the catheter tip is in a large vein with high blood flow, allowing for rapid dilution.
Examples of Vesicant Medications:
- Chemotherapeutic Agents: Many chemotherapy drugs are potent vesicants, including:
- Doxorubicin (Learn more about doxorubicin extravasation)
- Vincristine
- Vinblastine
- Paclitaxel
- Vasopressors: Used to raise blood pressure, these can cause vasoconstriction and tissue ischemia if extravasated:
- Norepinephrine (Levophed)
- Dopamine
- Epinephrine
- Other Medications:
- High-concentration potassium chloride (KCL > 0.1 mEq/mL)
- Promethazine (Phenergan)
- Calcium chloride
- Nafcillin
2. Medications with Extreme pH
Definition: Medications with a pH that is significantly outside the physiological range of blood (which is approximately 7.35-7.45) can cause chemical irritation to the vein wall. Solutions that are highly acidic (low pH) or highly alkaline (high pH) are particularly irritating.
Risks: Administering solutions with extreme pH through a midline can lead to chemical phlebitis, pain, and vein damage due to the direct irritating effect on the endothelial lining of the blood vessel.
Examples of Medications with Extreme pH:
- Highly Acidic (<5.0):
- Vancomycin
- Doxycycline
- Aminophylline
- Phenytoin (despite its alkaline pH in solution, it can precipitate in acidic environments and its extravasation is highly damaging)
- Highly Alkaline (>9.0):
- Sodium Bicarbonate
- IV Acyclovir
- Phenytoin (some formulations)
3. Medications with Extreme Osmolarity
Definition: Osmolarity refers to the concentration of solutes in a solution. Solutions with very high or very low osmolarity (compared to blood plasma, which is approximately 280-295 mOsm/L) can cause osmotic shifts across cell membranes, leading to damage to red blood cells and vein walls.
Risks: Infusing hypertonic solutions (high osmolarity) through a peripheral vein can draw water out of endothelial cells, causing them to shrink and damage the vein lining. Hypotonic solutions (low osmolarity) can cause cells to swell and burst. Both can lead to phlebitis and thrombosis.
Examples of Medications with Extreme Osmolarity:
- High Osmolarity (>600 mOsm/L):
- Total Parenteral Nutrition (TPN) (Read about TPN and osmolarity)
- Dextrose concentrations greater than 10% (e.g., D20W, D50W)
- Mannitol
- Concentrated electrolyte solutions (e.g., high-concentration sodium chloride, calcium gluconate)
Summary Table
| Medication Category | Characteristics | Primary Risks via Midline |
|---|---|---|
| Vesicants | Cause severe tissue damage upon extravasation | Tissue necrosis, blistering, pain, nerve damage |
| Extreme pH | Highly acidic (<5.0) or highly alkaline (>9.0) | Chemical phlebitis, vein irritation, thrombosis, pain |
| Extreme Osmolarity | Solutions with very high (>600 mOsm/L) or very low osmolarity | Venous irritation, phlebitis, thrombosis, hemolysis, pain |
Important Considerations:
- Always consult a pharmacist, drug monographs, or institutional policies for specific guidance on medication administration routes.
- While midlines are useful for extended courses of antibiotics, pain management, or hydration with non-irritating solutions, they are not a substitute for central venous access when indicated.
