How should I write a prescription for amoxicillin 1 g orally three times daily for 5–7 days in a patient without penicillin allergy and with normal renal function?

How to Write a Prescription for Amoxicillin 1 g Orally Three Times Daily for 5–7 Days

For a patient without penicillin allergy and normal renal function, prescribe amoxicillin 1000 mg (1 g) orally three times daily for 5–7 days, ensuring the total daily dose does not exceed 3000 mg. 1

Prescription Format

Write the prescription as follows:

Rx: Amoxicillin 500 mg capsules

• Sig: Take 2 capsules (1000 mg total) by mouth three times daily
• Disp: 30–42 capsules (for 5–7 days)
• Refills: None

Alternatively, if using 1000 mg tablets:

Rx: Amoxicillin 1000 mg tablets

• Sig: Take 1 tablet by mouth three times daily
• Disp: 15–21 tablets (for 5–7 days)
• Refills: None

Clinical Context and Indications

This high-dose regimen (3000 mg/day total) is appropriate for specific severe infections requiring aggressive therapy. 1 The 1 g three times daily dosing exceeds the standard 500 mg three times daily regimen typically used for common infections like cellulitis, which has a 96% success rate. 1

For severe infections requiring this dose level:

• Community-acquired pneumonia in hospitalized patients may warrant 1 g every 6–8 hours (up to 4 g/day). 2
• Intra-abdominal infections in non-critically ill patients use amoxicillin-clavulanate 1.2–2.2 g every 6 hours. 2
• Infective endocarditis requires IV dosing of 100–200 mg/kg/day divided into 4–6 doses. 1

Duration Selection: 5 vs. 7 Days

Choose 5 days for:

• Uncomplicated cellulitis, where 5-day courses are as effective as longer durations. 1
• Acute bacterial rhinosinusitis, where 5–7 days is equivalent to 10 days. 3

Choose 7 days for:

• Community-acquired pneumonia, where 7–10 days is standard. 2, 3
• Respiratory tract infections when clinical response is slower. 2

Critical Prescribing Considerations

Verify normal renal function before prescribing: This dose requires creatinine clearance >30 mL/min. 1 For CrCl 10–30 mL/min, reduce frequency to every 12 hours or decrease dose by 50%. 3 For CrCl <10 mL/min, reduce to every 24 hours or decrease dose by 75%. 3

Confirm no penicillin allergy: Patients with documented penicillin allergy require alternative antibiotics such as clindamycin 300 mg three times daily or azithromycin 500 mg daily for 5 days. 2

Counsel on adherence: Instruct patients to complete the full course even if symptoms improve, particularly for streptococcal infections to prevent complications like acute rheumatic fever. 4 Allow 3–5 days to assess clinical response before considering therapy changes. 4

Common Pitfalls to Avoid

Do not use amoxicillin monotherapy for:

• Cellulitis with MRSA risk factors (recent hospitalization, IV drug use, known MRSA colonization), which require MRSA-active antibiotics. 1
• Infections in areas with >10% penicillin-resistant Streptococcus pneumoniae, which may require high-dose amoxicillin-clavulanate (2000 mg/125 mg twice daily). 3

Do not extend treatment beyond indicated duration based solely on residual erythema, as inflammation can persist after bacterial eradication. 1

Do not substitute formulations incorrectly: When using amoxicillin-clavulanate, never substitute two 250 mg tablets for one 500 mg tablet, as this results in excessive clavulanate dosing and increased gastrointestinal side effects. 4

Monitoring and Follow-Up

Assess clinical response at 48–72 hours after initiating therapy to determine need for alternative management. 3 Expect improvement in fever and symptoms within this timeframe for most infections. 2

Educate patients on adverse effects: Gastrointestinal symptoms (nausea, diarrhea) occur in 15–40% of patients but rarely require discontinuation. 3 Instruct patients to report severe diarrhea, which may indicate Clostridioides difficile infection requiring evaluation. 5