Parenteral administration refers to any route of drug administration that bypasses the gastrointestinal (GI) tract. Unlike oral medications that undergo digestion and first-pass metabolism, parenteral routes deliver drugs directly into the body tissues or bloodstream, ensuring rapid and predictable absorption.
This method is particularly useful for medications that are poorly absorbed orally, degraded in the GI tract, or required in emergencies.
This article provides a comprehensive guide to parenteral administration, including intradermal, subcutaneous, intramuscular, and intravenous routes, with details on uses, needle sizes, angles, sites, and safety considerations.
Why Choose Parenteral Administration?
- Rapid action: Ideal for emergencies (e.g., IV adrenaline in anaphylaxis).
- Avoids GI tract: Useful for patients with nausea, vomiting, or GI disorders.
- Precision: Allows accurate dosing and bioavailability.
- Suitable for irritant drugs: Some medications cause GI irritation if taken orally.
1. Intradermal (ID) Administration
Definition: Medication is injected just below the epidermis, into the dermal layer of the skin.
Uses:
- Tuberculosis (TB) testing (Mantoux test)
- Allergy testing
Clinical Note:
- Should form a “bleb” or small bubble under the skin if administered correctly.
- Only small volumes (0.1 mL) are administered intradermally.
2. Subcutaneous (Subcut or Sublet) Administration
Definition: Medication is injected into the fatty tissue beneath the skin but above the muscle.
Uses:
- Non-irritating, water-soluble medications
- Insulin injections
- Heparin administration
Needle Length: 3/8–5/8 inch (1.0–1.6 cm)
Angle of Insertion:
- 90° angle for normal to overweight clients
- 45° angle for thin clients
Clinical Note:
- Rotate injection sites to prevent lipodystrophy (fat tissue damage).
- Absorption is slower than IM but faster than oral medications.
3. Intramuscular (IM) Administration
Definition: Medication is injected deep into the muscle tissue, which is highly vascular, allowing for faster absorption.
Uses:
- Irritating drugs (e.g., some antibiotics, vaccines)
- Solutions in oils or aqueous suspensions
Angle of Insertion: 90°
Usual Sites:
- Deltoid (upper arm) – maximum 2 mL
- Vastus lateralis (thigh) – preferred in infants and small children
- Ventrogluteal (hip) – safest and least painful site for adults
Special Considerations:
- Do not inject more than 3 mL per site (2 mL for deltoid).
- For larger volumes, divide into two syringes and use different sites.
- Z-track method recommended for irritating medications to prevent leakage into subcutaneous tissue.
4. Intravenous (IV) Administration
Definition: Medication is injected directly into the vein, allowing immediate entry into circulation.
Uses:
- Administering fluids
- Blood transfusions
- Emergency drugs
- Continuous infusions (antibiotics, chemotherapy, pain medications)
Needle Size:
- 16-gauge: for trauma patients (rapid fluid replacement)
- 18-gauge: for surgery and blood administration
- 22–24 gauge: for children, older adults, and patients with fragile veins
Clinical Note:
- IV route offers 100% bioavailability.
- Risk of complications such as infection, infiltration, phlebitis, or air embolism if not performed correctly.
Comparison of Parenteral Routes
| Route | Depth | Angle | Needle Size | Volume Limit | Common Uses |
|---|---|---|---|---|---|
| Intradermal (ID) | Just below epidermis | 10–15° | 25–27 G | 0.1 mL | TB test, allergy test |
| Subcutaneous (Subcut) | Fatty tissue | 45–90° | 25–27 G | 0.5–1.5 mL | Insulin, heparin |
| Intramuscular (IM) | Muscle tissue | 90° | 18–25 G | ≤3 mL (≤2 mL deltoid) | Vaccines, antibiotics |
| Intravenous (IV) | Direct into vein | 25° | 16–24 G | Unlimited (depends on therapy) | Fluids, blood, emergency meds |
Safety Considerations in Parenteral Administration
- Aseptic Technique: Prevents infection at the injection site.
- Correct Needle and Site Selection: Ensures proper absorption and minimizes tissue damage.
- Patient-Specific Adjustments: Consider age, weight, muscle mass, and health condition.
- Rotation of Sites: Prevents tissue damage, especially with repeated Subcut or IM injections.
- Monitoring for Reactions: Observe patients for pain, swelling, allergic reactions, or systemic side effects.
Frequently Asked Questions (FAQs)
Q1. Why is intradermal injection used for TB testing?
Because it allows localized immune response observation, forming a bleb that can be measured after 48–72 hours.
Q2. Why rotate insulin injection sites?
To prevent lipodystrophy (fat tissue thickening or thinning), which can affect insulin absorption.
Q3. What is the Z-track method in IM injections?
A technique where skin is pulled laterally before injection, preventing medication leakage and reducing irritation.
Q4. Which IV needle size is used for blood transfusion?
An 18-gauge needle is commonly used for blood administration.
Q5. What is the safest IM injection site in adults?
The ventrogluteal site is preferred as it avoids major nerves and blood vessels.
