Q4h

Q4H is a medical abbreviation that stands for a dosing interval of every four hours. It is commonly used in prescriptions, patient charts, and nursing notes to indicate how frequently a drug or intravenous fluid should be administered. The notation can appear as Q4H, q4h, or Q4h and is understood in many healthcare settings, though its exact interpretation can vary by institution or country.

In practice, Q4H instructs a dose to be given at four-hour intervals, typically around the clock, which can result in six doses over a 24-hour period. The phrase is used for a wide range of medications, including analgesics, antibiotics, and fluids, but the appropriateness of a four-hour schedule depends on the medication’s pharmacokinetics, the patient’s condition, and clinical judgment. When a medication is to be given “as needed,” orders may read Q4H PRN, indicating a four-hour interval only if symptoms require treatment.

Variants and considerations include different interval notations such as Q6H or Q8H, which reflect six- or eight-hour intervals, respectively. In some settings, there is a move toward writing out the interval more explicitly or using electronic systems that standardize the instruction to reduce misinterpretation. Many healthcare organizations discourage the use of ambiguous abbreviations in favor of clear, explicit language to minimize medication errors.

See also: dosage intervals, QID, Q6H, t.i.d.; pharmacokinetics and dosing schedules; hospital and pharmacy practice standards.