Q8hr Medication Examples
Common medications prescribed every 8 hours (q8hr) include antibiotics like cefazolin, meropenem, metronidazole, clindamycin, and cefotaxime, which are frequently dosed at this interval for serious infections.
Antibiotics Commonly Dosed Q8hr
The most prevalent q8hr medications are antimicrobials used for severe infections, particularly skin and soft tissue infections and necrotizing infections:
Beta-Lactams and Carbapenems
- Cefazolin: 1 g IV every 8 hours for staphylococcal infections 1
- Meropenem: 1 g IV every 8 hours for mixed necrotizing infections 1
- Imipenem-cilastatin: 1 g IV every 6-8 hours 1
- Piperacillin-tazobactam: 3.37 g IV every 6-8 hours (can be dosed q8hr) 1
- Cefotaxime: 2 g IV every 6 hours (often extended to q8hr) 1
Anaerobic Coverage
- Metronidazole: 500 mg IV every 8 hours for anaerobic infections 1
- Important caveat: Recent evidence suggests q12hr dosing may be equally effective for most anaerobic infections, though q8hr remains standard in guidelines 2. The q8hr interval is still recommended for CNS infections, C. difficile, and amebiasis where q12hr data is lacking.
- Clindamycin: 600-900 mg IV every 8 hours for streptococcal and clostridial infections 1
Other Antimicrobials
- Ampicillin-sulbactam: 1.5-3.0 g IV every 6-8 hours for bite wounds 1
- Cefoxitin: 1 g IV every 6-8 hours 1
Clinical Context
These q8hr medications are predominantly used for:
- Necrotizing soft tissue infections requiring broad-spectrum coverage
- Surgical site infections with systemic involvement
- Animal/human bite wounds
- Severe cellulitis requiring hospitalization
The q8hr interval is pharmacokinetically driven—these drugs have elimination half-lives of approximately 1-2 hours, requiring frequent dosing to maintain therapeutic levels above the minimum inhibitory concentration throughout the dosing interval 1.
Common Pitfall
Prescribing "three times daily" (TID) instead of "every 8 hours" leads to subtherapeutic overnight gaps. Studies show TID dosing creates a mean 12.2-hour gap overnight versus only 5.7-6.1 hours between daytime doses, potentially reducing trough levels by 64% 3. Always specify "q8hr" or provide exact times (e.g., 0600-1400-2200) rather than "TID" for time-dependent antibiotics.