What is the appropriate dosage of amoxicillin-clavulanic acid for a 75-year-old male patient with a serum creatinine of 0.9 mg/dL and weighing 71 kg?

Amoxicillin-Clavulanic Acid Dosing in Elderly Patient with Mild Renal Impairment

For a 75-year-old male patient weighing 71 kg with serum creatinine of 0.9 mg/dL, the standard adult dose of amoxicillin-clavulanic acid (875 mg/125 mg twice daily) is appropriate as the patient's estimated creatinine clearance is approximately 60-65 mL/min, which does not require dose adjustment.

Patient Assessment

First, let's calculate the estimated creatinine clearance using the Cockcroft-Gault equation:

CrCl = [(140 - age) × weight (kg)] / [72 × serum creatinine (mg/dL)] × 0.85 (if female)

CrCl = [(140 - 75) × 71] / [72 × 0.9] ≈ 65 mL/min

This indicates mild renal impairment (CrCl 50-80 mL/min).

Dosing Recommendations

Standard Dosing

• Amoxicillin-clavulanic acid 875 mg/125 mg twice daily
• Alternative: 500 mg/125 mg three times daily

Rationale for Dosing

• The patient's renal function is mildly impaired but does not require dose adjustment
• Dose adjustment is only needed when CrCl falls below 30 mL/min 1
• The pharmacokinetics of amoxicillin and clavulanic acid are differentially affected by renal impairment 2:
  • Amoxicillin clearance decreases more significantly than clavulanic acid with declining renal function
  • At CrCl >50 mL/min, standard dosing remains appropriate

Monitoring Recommendations

• Assess clinical response within 48-72 hours of initiating therapy
• Monitor renal function if treatment extends beyond 7-10 days
• Watch for signs of adverse effects:
  • Gastrointestinal symptoms (diarrhea, nausea)
  • Hypersensitivity reactions
  • Liver function abnormalities (rare)

Important Considerations

Potential Drug Interactions

• No significant interactions with commonly used medications in elderly patients
• Avoid concurrent use with probenecid (increases amoxicillin levels)

Elderly-Specific Concerns

• Elderly patients may have decreased renal function despite "normal" serum creatinine
• The calculated CrCl is more reliable than serum creatinine alone for dosing decisions
• Dehydration can worsen renal function and increase risk of adverse effects

When to Adjust Dosing

If the patient's renal function deteriorates (CrCl <30 mL/min), dose adjustment would be necessary:

• For CrCl 10-30 mL/min: 500 mg/125 mg twice daily
• For CrCl <10 mL/min: 500 mg/125 mg once daily

Common Pitfalls to Avoid

1. Relying solely on serum creatinine rather than calculated CrCl for dosing decisions in elderly patients
2. Underdosing due to age alone without considering actual renal function
3. Failing to reassess renal function if the patient becomes dehydrated or acutely ill
4. Not considering the differential effect of renal impairment on amoxicillin versus clavulanic acid clearance

The standard adult dose is appropriate for this patient as his estimated creatinine clearance indicates only mild renal impairment that does not warrant dose adjustment.