Which abbreviation denotes "once every hour"?

The abbreviation that denotes "once every hour" is indeed Q1H. This abbreviation is derived from the Latin term "quaque hora," which translates to "every hour." In medical practice, it communicates to health care providers that a certain action, such as medication administration, should occur hourly. Understanding such abbreviations is crucial for accurate medication management and ensuring the safety of patient care.

The other options correspond to different meanings—Q12H indicates a frequency of every twelve hours, HQ and H are not standard abbreviations that signify a specific time interval like Q1H does. Therefore, Q1H is the correct choice for indicating medication or treatment to be administered once every hour.