Thiopental (Pentothal)¶

Overview¶

Field	Detail
Drug class	Ultra-short-acting barbiturate / Hypnotic agent
Stock vial	500 mg powder for injection
Reconstituted conc.	25 mg/mL (add 20 mL WFI)
Storage	Room temp before reconstitution; 2–8°C after

Preparation¶

Reconstitution

Thiopental follows a specific 25 mg/mL reconstitution for testing. Ensure the 20 mL of Water for Injections (WFI) is added slowly and the solution is clear before use.

Equipment needed¶

1 × Thiopental 500 mg powder vial
Water for Injections (WFI) or Normal saline (NS) — for reconstitution
Normal saline (NS) — for IDT dilutions
10 mL and 20 mL syringes
1 mL syringes × 4 (for test doses/dilutions)
25 G needles

Step 1 — Reconstitute the stock (25 mg/mL)¶

Add 20 mL of WFI to the 500 mg powder vial.
Shake gently until completely dissolved. (This is 25 mg/mL).
Draw up 0.5–1 mL into a 1 mL syringe.
Label: "Thiopental SPT 25 mg/mL".

Step 2 — Prepare IDT dilutions¶

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

IDT 2.5 mg/mL (1:10):
- Draw 0.1 mL of stock (25 mg/mL) into a 1 mL syringe. Add 0.9 mL NS. Mix. (This is 2.5 mg/mL — 1:10).
- Label: "Thiopental IDT 2.5 mg/mL".
IDT 0.25 mg/mL (1:100):
- Draw 0.1 mL of the 2.5 mg/mL syringe into a new 1 mL syringe. Add 0.9 mL NS. Mix. (This is 0.25 mg/mL — 1:100).
- Label: "Thiopental IDT 0.25 mg/mL".
IDT 0.025 mg/mL (1:1,000):
- Draw 0.1 mL of the 0.25 mg/mL syringe into a new 1 mL syringe. Add 0.9 mL NS. Mix. (This is 0.025 mg/mL — 1:1,000).
- Label: "Thiopental IDT 0.025 mg/mL".

Skin prick test (SPT)¶

Reagent	Concentration
Test solution	Neat (25 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	1:1,000	0.025 mg/mL	0.1 mL of 0.25 mg/mL + 0.9 mL NS
2	1:100	0.25 mg/mL	0.1 mL of 2.5 mg/mL + 0.9 mL NS
3	1:10	2.5 mg/mL	0.1 mL neat + 0.9 mL NS

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