If a drug is ordered to be taken every six hours and the first dose is at 2200 hours, when is the next dose due?

When a drug is scheduled to be taken every six hours, you simply add six hours to the time of the first dose to determine when the next dose is due.

Starting at 2200 hours (10 PM), you add six hours:

• 2200 (10 PM) + 0600 (6 hours) = 0400 (4 AM).

Thus, the next dose is due at 0400 hours. This calculation is straightforward, as adding six hours directly follows the standard method of timekeeping in a 24-hour format.

Therefore, the correct answer is 0400.