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Cefazolin

Overview

Field Detail
Drug class Cephalosporin (1st generation)
Route IV
Stock vial 1 g powder for injection
Reconstituted concentration 100 mg/mL (add 10 mL water for injection)
Diluent Water for Injection (WFI)
Storage Use within 24 hours at 2–8°C

Preparation

Before you start

Check the expiry date and vial integrity before opening. Label every syringe immediately after drawing up — never leave unlabelled syringes on the tray.

Equipment needed

  • 1 × Cefazolin 1 g powder vial
  • 1 × 10 mL syringe (for reconstitution)
  • Water for Injection (WFI) — 10 mL
  • Normal saline (0.9% sodium chloride) — at least 20 mL (for dilutions and IV challenge)
  • 1 mL syringes × 3 (one for SPT, two for IDT dilutions)
  • 21 G needle (for vial entry)
  • 25 G needles (for drawing up)
  • Labels or marker pen

Step 1 — Reconstitute the stock vial

  1. Draw up 10 mL of Water for Injection (WFI) into a 10 mL syringe.
  2. Inject into the Cefazolin 1 g vial using aseptic technique.
  3. Gently swirl until fully dissolved. Do not shake.
  4. The resulting stock solution is Cefazolin 100 mg/mL. It should appear clear to pale yellow. Discard if cloudy, discoloured or if particles are visible.
  5. Write the date, time and your initials on the vial.

Step 2 — Prepare the SPT solution (100 mg/mL — neat)

  1. Draw up 0.5–1 mL of the 100 mg/mL stock directly into a 1 mL syringe.
  2. This is used neat for the skin prick test.
  3. Label: "Cefazolin SPT — 100 mg/mL".

Step 3 — Prepare IDT dilutions

Prepare in this order, using a fresh syringe for each step.

  1. IDT 10 mg/mL (1:10): Draw 0.1 mL of neat (100 mg/mL) into a 1 mL syringe. Add 0.9 mL NS. Mix. Label: "Cefazolin IDT 10 mg/mL".
  2. IDT 1 mg/mL (1:100): Draw 0.1 mL of the 10 mg/mL syringe into a new 1 mL syringe. Add 0.9 mL NS. Mix. Label: "Cefazolin IDT 1 mg/mL".

Skin prick test (SPT)

Reagent Concentration
Test solution Neat (100 mg/mL)
Positive control Histamine 10 mg/mL
Negative control Normal saline

Interpretation: Wheal ≥3 mm vs negative control = positive.

Intradermal test (IDT)

Dilution series

Step Dilution Concentration Preparation
1 1:100 1 mg/mL 0.1 mL of 10 mg/mL + 0.9 mL NS
2 1:10 10 mg/mL 0.1 mL neat + 0.9 mL NS

Inject: 0.05 mL intradermal. Read at 15–20 minutes.

Challenge (IV)

IV graded dose protocol

Step Dose Interval
1 100 mg 15 min
2 200 mg 15 min
3 300 mg 15 min
4 400 mg 60 min observation

(Administered as slow IV push or infusion)

Notes

  • Cefazolin is the preferred pre-operative prophylactic antibiotic and the most commonly tested cephalosporin in this department.
  • Often tested as part of a GA workup alongside muscle relaxants.
  • Cross-reactivity with penicillins is low but possible — refer to AMO if result is positive.