Amoxicillin Dosing in Adults with Normal Renal Function
For adults with normal renal function, the recommended dosing for amoxicillin is 500 mg every 12 hours or 250 mg every 8 hours for mild to moderate infections, and 875 mg every 12 hours or 500 mg every 8 hours for severe infections. 1
Standard Dosing Regimens
- For mild to moderate ear, nose, throat, skin, and genitourinary tract infections: 500 mg every 12 hours or 250 mg every 8 hours 1
- For severe ear, nose, throat, skin, and genitourinary tract infections: 875 mg every 12 hours or 500 mg every 8 hours 1
- For lower respiratory tract infections (both mild/moderate and severe): 875 mg every 12 hours or 500 mg every 8 hours 1
Special Clinical Scenarios
- For H. pylori eradication in adults: 1
- Triple therapy: 1 gram amoxicillin twice daily (every 12 hours) for 14 days, combined with 500 mg clarithromycin and 30 mg lansoprazole twice daily
- Dual therapy: 1 gram amoxicillin three times daily (every 8 hours) for 14 days, combined with 30 mg lansoprazole three times daily
Administration Considerations
- To minimize gastrointestinal intolerance, amoxicillin should be taken at the start of a meal 1
- Treatment should generally be continued for a minimum of 48 to 72 hours beyond the time that the patient becomes asymptomatic 1
- For Streptococcus pyogenes infections, a minimum of 10 days of treatment is recommended to prevent acute rheumatic fever 1
Dosing Adjustments for Renal Impairment
- For patients with severe renal impairment (GFR 10-30 mL/min): 500 mg or 250 mg every 12 hours, depending on infection severity 1
- For patients with very severe renal impairment (GFR <10 mL/min): 500 mg or 250 mg every 24 hours, depending on infection severity 1
- Patients on hemodialysis: 500 mg or 250 mg every 24 hours with an additional dose both during and at the end of dialysis 1
- The 875 mg dose should NOT be used in patients with GFR <30 mL/min 1
Pharmacodynamic Considerations
- The pharmacodynamic efficacy target of amoxicillin is 40% time above the minimal inhibition concentration (40%T > MIC) 2
- Studies have shown that the standard dosing regimen may not achieve this target in all patients, particularly for organisms with higher MICs 2
- For severe infections with suspected resistant organisms, higher or more frequent dosing may be necessary to maintain adequate plasma concentrations 2
Common Pitfalls and Caveats
- Underdosing is common in patients with severe infections, particularly when targeting organisms with higher MICs 2
- Once-daily dosing of amoxicillin has been studied for streptococcal pharyngitis and found to be non-inferior to multiple daily dosing regimens, which may improve compliance in outpatient settings 3
- For complicated intra-abdominal infections, amoxicillin is not typically used as monotherapy but may be part of combination regimens 4
- The pharmacokinetically enhanced formulation of amoxicillin/clavulanate (2000/125 mg) has been developed to maintain therapeutic plasma concentrations for longer periods, which may be beneficial for resistant pathogens 5