Parenteral injections deliver drugs into tissue layers that differ in depth, blood supply, and absorption speed.

Factors affecting absorption: blood flow to the site (increased by heat, exercise, massage; reduced by shock, cold, and poor perfusion), drug solubility and viscosity (oily or depot preparations absorb slowly), and the site chosen. In shock or hypoperfusion, IM and SC absorption is unreliable — the IV route is used.

• Allergies, indication, and relevant labs (e.g., platelet count for heparin and enoxaparin; glucose for insulin)
• Site condition: avoid areas with bruising, scars, lesions, edema, inflammation, lipohypertrophy, tattoos, or impaired circulation
• Muscle mass and subcutaneous fat — choose needle length by body size, not a single standard
• Coagulation status — IM injections in clients with thrombocytopenia or on anticoagulants increase hematoma risk
• Client's age, mobility, and ability to relax the muscle; fear of needles

Tuberculin skin test (Mantoux)

• 0.1 mL of purified protein derivative (5 tuberculin units) intradermally on the inner (volar) surface of the forearm, bevel up, at 5–15 degrees, producing a pale wheal of about 6–10 mm
• Do not massage or cover with a bandage
• Read in 48–72 hours: measure induration (hardness), not redness, in millimeters across the forearm
• Positive thresholds: 5 mm or more (HIV, recent contact with active TB, fibrotic chest X-ray, immunosuppression), 10 mm or more (recent arrivals from high-prevalence countries, health care workers, injection drug use, other risk groups, children under 4), 15 mm or more (no known risk factors)
• Prior BCG vaccination can cause a false-positive result; interferon-gamma release assays (blood tests) are unaffected by BCG

Allergy skin testing — very small volumes intradermally (commonly about 0.02–0.05 mL) with emergency equipment ready.

Equipment and technique by route (adults)

IM sites

The rectus abdominis and periumbilical abdomen are not IM sites.

SC sites: abdomen (at least 5 cm (2 inches) from the umbilicus), outer back of the upper arm, anterior thigh, upper buttock or upper back. Insulin absorption is fastest from the abdomen, then the arms, then the thighs and buttocks.

Z-track technique — for irritating or staining drugs (e.g., iron dextran, some depot antipsychotics); many nurses use it for all IM injections.

1. Pull the skin and subcutaneous tissue about 2.5–3.5 cm (1–1.5 inches) laterally and hold
2. Insert the needle at 90 degrees, inject slowly
3. Wait about 10 seconds, withdraw the needle, then release the skin — this seals the track and prevents leakage into subcutaneous tissue
4. Do not massage

The older "air-lock" technique (a small air bubble behind the drug) is not needed with modern calibrated syringes and is not routinely recommended.

Listed in priority order.

1. Safety first: correct client, drug, dose, route, and site; allergies; emergency equipment available for drugs with anaphylaxis risk (e.g., iron dextran requires a test dose per labeling, and clients are observed for hypotension and anaphylaxis)
2. Needlestick prevention: use safety-engineered devices; never recap used needles; activate the safety feature and discard immediately into a sharps container
3. Asepsis: hand hygiene; clean the vial top; clean the skin (commonly alcohol, allowed to dry completely — wet alcohol stings and can inactivate some products and interfere with TB test reading); gloves when contact with blood is likely
4. Preparing drugs: from an ampule, use a filter needle to draw up and change to a regular needle before injecting; from a vial, inject an equal volume of air first. Remove air bubbles by holding the syringe needle-up and gently pushing the plunger. Mix insulins by drawing clear (short-acting) before cloudy (NPH); do not mix other insulins unless labeling allows
5. Reducing pain: position to relax the muscle (e.g., side-lying with the upper hip and knee flexed for ventrogluteal; prone with toes pointed in for dorsogluteal), dart the needle in quickly, inject slowly (about 10 seconds per mL for IM), withdraw at the same angle, apply light pressure with dry gauze. Distraction, cold, or topical anesthetic for children
6. Heparin SC: abdomen, no aspiration, no massage (hematoma); apply gentle pressure. Monitor for bleeding and platelets (heparin-induced thrombocytopenia — a drop of about 50% or new thrombosis 5–10 days after starting). Protamine sulfate reverses heparin
7. Enoxaparin (low-molecular-weight heparin): client lying down; do not expel the air bubble in the prefilled syringe; pinch a skin fold on the anterolateral or posterolateral abdomen, insert the full length of the needle at 90 degrees, hold the fold throughout the injection; do not rub; alternate sides. Monitor platelets, bleeding, hemoglobin, and kidney function (dose reduced when creatinine clearance is below 30 mL/min). Contraindicated with immune-mediated heparin-induced thrombocytopenia within the past 100 days or circulating HIT antibodies; risk of spinal/epidural hematoma with neuraxial anesthesia. Protamine only partially reverses enoxaparin
8. Insulin SC: rotate sites within one body region to prevent lipohypertrophy (which causes erratic absorption) and lipoatrophy; do not massage after injection (speeds absorption, risk of hypoglycemia). With pen devices, hold the needle in place about 10 seconds. Check glucose before; ensure food is available
9. Intradermal: stretch skin taut, bevel up, insert just under the epidermis until the bevel is covered, inject slowly to form a bleb; do not massage; mark the site if required
10. After any injection: observe for immediate reactions; for vaccines, observe for about 15 minutes (syncope, anaphylaxis); document drug, dose, route, site, time, and response

• Self-injection of insulin or enoxaparin: hand hygiene, site selection and rotation, technique, sharps disposal at home
• Report pain, redness, swelling, or a hard lump at injection sites; unusual bruising or bleeding with anticoagulants; signs of hypoglycemia with insulin
• After a TB skin test: do not scratch or cover; return in 48–72 hours for reading
• Vaccine side effects: sore arm, low-grade fever; seek care for difficulty breathing, facial swelling, or high fever

• Angles: ID 5–15°, SC 45–90°, IM 90°
• Volumes: ID ≤0.1 mL, SC ≤ about 1 mL, deltoid ≤1 mL, ventrogluteal and vastus lateralis up to about 3 mL
• IM needle: 22–25 G, 1–1.5 inch in most adults; SC 25–31 G, 1/2–5/8 inch; ID 25–27 G
• Ventrogluteal is the safest adult IM site; vastus lateralis for infants; avoid dorsogluteal (sciatic nerve)
• TB skin test: 0.1 mL ID, inner forearm, wheal; read 48–72 hours; measure induration
• Z-track: pull skin 1–1.5 inches, inject, wait 10 seconds, release; no massage — for iron dextran and other irritants
• Heparin/enoxaparin SC: abdomen at least 5 cm from the umbilicus, no aspiration, no massage; monitor platelets
• Enoxaparin: keep the air bubble, pinch a skin fold, 90°
• Insulin: abdomen absorbs fastest; rotate sites to prevent lipohypertrophy; no massage
• No aspiration for vaccines; never recap needles