Azithromycin¶
Overview¶
| Field | Detail |
|---|---|
| Drug class | Macrolide antibiotic |
| Route | IV |
| Stock formulation | 500 mg powder for injection |
| Reconstituted conc. | 100 mg/mL (add 4.8 mL WFI) |
| Diluent | Water for injection |
| Storage | Room temperature before reconstitution; use immediately after reconstitution |
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 × Azithromycin 500 mg vial
- Water for injection (WFI) — for reconstitution
- Normal saline (NS) — for IDT dilutions
- 1 mL syringes × 3
- 25 G needles
Step 1 — Prepare the SPT solution (100 mg/mL — neat)¶
- Reconstitute the 500 mg vial with 4.8 mL WFI to yield 100 mg/mL.
- Draw up 0.5–1 mL of the reconstituted solution (100 mg/mL) into a 1 mL syringe.
- Label: "Azithromycin SPT 100 mg/mL".
Step 2 — Prepare IDT dilutions¶
Prepare in this order, using a fresh syringe for each step.
-
IDT 0.01 mg/mL (1:10,000):
- Draw 0.1 mL of stock (100 mg/mL) into a 1 mL syringe. Add 0.9 mL NS. Mix. (This is 10 mg/mL — 1:10).
- Draw 0.1 mL of this 10 mg/mL into a new 1 mL syringe. Add 0.9 mL NS. Mix. (This is 1 mg/mL — 1:100).
- Draw 0.1 mL of this 1 mg/mL into a new 1 mL syringe. Add 0.9 mL NS. Mix. (This is 0.1 mg/mL — 1:1,000).
- Draw 0.1 mL of this 0.1 mg/mL into a new 1 mL syringe. Add 0.9 mL NS. Mix. (This is 0.01 mg/mL — 1:10,000).
- Label: "Azithromycin IDT 0.01 mg/mL".
-
IDT 0.1 mg/mL (1:1,000):
- Draw 0.1 mL of the 1 mg/mL solution prepared above into a new 1 mL syringe. Add 0.9 mL NS. Mix. (This is 0.1 mg/mL — 1:1,000).
- Label: "Azithromycin IDT 0.1 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 | 1:10,000 | 0.01 mg/mL | 0.1 mL of 1 mg/mL + 0.9 mL NS |
| 2 | 1:1,000 | 0.1 mg/mL | 0.1 mL of 10 mg/mL + 0.9 mL NS |
Inject: 0.05 mL intradermal. Read at 15–20 minutes.