How do you dilute permethrin for lice? - briefly
Combine the 1 % permethrin concentrate with an equal volume of distilled water to obtain a 0.5 % solution for topical use. Apply the diluted mixture to dry hair, leave for 10 minutes, then rinse thoroughly.
How do you dilute permethrin for lice? - in detail
To prepare a usable permethrin solution for head‑lice treatment, follow these precise steps.
First, confirm the concentration of the stock product. Commercial permethrin preparations commonly contain 1 % (10 mg mL⁻¹) or 5 % (50 mg mL⁻¹) active ingredient. The target concentration for scalp application is typically 0.5 % (5 mg mL⁻¹). Use the formula:
[ \text{Desired volume (mL)} \times \text{Target concentration (mg/mL)} = \text{Required amount of permethrin (mg)}. ]
Then calculate the volume of stock needed:
[ \text{Volume of stock (mL)} = \frac{\text{Required amount (mg)}}{\text{Stock concentration (mg/mL)}}. ]
Example for a 100‑mL final solution using a 1 % stock:
- Target amount = 100 mL × 5 mg/mL = 500 mg.
- Stock concentration = 10 mg/mL.
- Stock volume = 500 mg ÷ 10 mg/mL = 50 mL.
- Add 50 mL of distilled water to reach 100 mL total.
If the stock is 5 %, the calculation changes:
- Required amount remains 500 mg.
- Stock concentration = 50 mg/mL.
- Stock volume = 500 mg ÷ 50 mg/mL = 10 mL.
- Add 90 mL of distilled water.
Key procedural points:
- Equipment – Use a calibrated measuring cylinder or syringe, a clean glass beaker, and a stir rod or magnetic stirrer.
- Mixing – Add the measured permethrin stock to the water gradually while stirring continuously to ensure uniform distribution.
- Temperature – Perform the dilution at room temperature (20‑25 °C); excessive heat can degrade the active ingredient.
- Container – Transfer the solution to an amber glass bottle with a tight‑closing cap to protect from light.
- Labeling – Mark the bottle with concentration, preparation date, and expiration (generally 30 days when stored properly).
- Safety – Wear nitrile gloves, eye protection, and work in a well‑ventilated area. Avoid skin contact with the concentrated stock.
Before application, verify the solution’s clarity; any precipitation indicates improper mixing and the batch should be discarded. Store the diluted product away from direct sunlight and keep it out of reach of children.
By adhering to these calculations and handling guidelines, the resulting permethrin preparation will achieve the intended therapeutic concentration for effective lice eradication.