Ampicillin¶
Overview¶
| Field | Detail |
|---|---|
| Drug class | Beta-lactam / aminopenicillin |
| Route | IV |
| Stock vial | 500 mg powder for injection |
| Reconstituted concentration | 50 mg/mL (add 10 mL water for injection) |
| Diluent | Water for Injection (WFI) |
| Storage | Use within 1 hour of reconstitution at room temperature |
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 × Ampicillin 500 mg powder vial
- 1 × 10 mL syringe (for reconstitution)
- Water for Injection (WFI) — 10 mL
- Normal saline (0.9% sodium chloride) — at least 10 mL (for dilutions)
- 1 mL syringes × 3 (one for SPT, two for IDT dilutions)
- 21 G needle (for vial entry)
- 25 G needles (for drawing up dilutions)
- Labels or marker pen
Step 1 — Reconstitute the stock vial¶
- Draw up 10 mL of Water for Injection (WFI) into a 10 mL syringe.
- Inject into the Ampicillin 500 mg vial using aseptic technique.
- Gently swirl until the powder is completely dissolved. Do not shake.
- The resulting stock solution is Ampicillin 50 mg/mL. It should appear clear to pale yellow. Discard if cloudy, discoloured or if particles are visible.
- Write the date, time and your initials on the vial.
Step 2 — Prepare the SPT solution (50 mg/mL — neat)¶
- Draw up 0.5–1 mL of the 50 mg/mL stock directly into a 1 mL syringe.
- This is used neat for the skin prick test.
- Label: "Ampicillin SPT — 50 mg/mL".
Step 3 — Prepare IDT dilutions¶
Prepare in this order, using a fresh syringe for each step.
- 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: "Ampicillin IDT 10 mg/mL".
- 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: "Ampicillin 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.
Notes¶
- Cross-reactivity with amoxicillin is high — if positive, both are likely affected.
- Often tested alongside other beta-lactams.