In administering phenytoin 200 mg PO, how many mL should be given if the elixir is 125 mg/5 mL?

To determine how many mL of the elixir containing phenytoin should be administered, you need to first establish the concentration of the medication and then calculate the required volume based on the desired dose.

The concentration of the phenytoin elixir is 125 mg per 5 mL. To find out how many mL are equivalent to 200 mg of phenytoin, follow these steps:

1. Calculate the amount of mg present in 1 mL of the elixir. This can be found by dividing the total mg by the total mL:

• 125 mg / 5 mL = 25 mg/mL.

2. Next, determine how many mL will provide the required 200 mg. This can be calculated by dividing the desired dose by the concentration:

• 200 mg ÷ 25 mg/mL = 8 mL.

Thus, administering 8 mL of the elixir will deliver the correct dose of 200 mg of phenytoin. This calculation aligns with the drug's concentration and meets the dosing requirement, confirming that the correct answer is indeed 8 mL.