The physician writes an order for 250 mg of a medication for a patient weighing 168 pounds the label on the vial states 100 mg per ml. one teaspoon is approximately equal to five milliliters.

The number of teaspoons that should be administered is about 0.4 teaspoons.
250 milligrams / 100 milligrams = 2.5 milliliters
5 milliliters / 2.5 milliliters = 2 milliliters
2 milliliters = 0.405768 teaspoons