What is the difference in bioavailability of Augmentin (amoxicillin-clavulanate) when administered intravenously (IV) versus orally?

Bioavailability of Augmentin: IV vs Oral

Intravenous Augmentin has 100% bioavailability by definition, while oral Augmentin has approximately 50-70% bioavailability for amoxicillin and lower bioavailability for clavulanic acid, making IV administration superior for severe infections requiring maximal drug exposure.

Key Pharmacokinetic Differences

Oral Formulation Characteristics

• Amoxicillin component: Well absorbed orally with good bioavailability, chosen specifically for co-administration with clavulanic acid due to its favorable oral absorption profile 1
• Clavulanic acid component: Lower and more variable oral bioavailability compared to amoxicillin 2
• Peak concentrations: Oral dosing of 25 mg/kg in pediatric patients achieved mean peak plasma concentrations of 7.2 mg/L for amoxicillin and 2.0 mg/L for clavulanic acid at 60-90 minutes post-dose 2

Intravenous Formulation Advantages

• Complete bioavailability: IV administration bypasses first-pass metabolism and gastrointestinal absorption variability, ensuring 100% of the dose reaches systemic circulation 3
• Rapid therapeutic levels: Immediate achievement of therapeutic concentrations without absorption delay 3, 4
• Predictable pharmacokinetics: Eliminates variability from gastrointestinal factors (food, pH, motility) 5

Clinical Application Algorithm

When to Use IV Augmentin

• Severe infections: Bacteremia, severe invasive polymicrobial sepsis, or life-threatening infections requiring immediate maximal drug exposure 4
• Hospitalized patients: Those unable to tolerate oral medications or requiring guaranteed drug delivery 3, 5
• Initial therapy: First 3 days of treatment for serious bacterial infections, particularly respiratory tract infections 3

When to Transition to Oral

• Clinical improvement: After initial IV therapy (typically 3 days) when patient shows clinical response 3
• Adequate oral intake: Patient can tolerate oral medications and has functioning gastrointestinal absorption 3
• Same dosage: Transition maintains the same dosage (1 g amoxicillin plus 200 mg clavulanic acid every 8 hours in adults) 3

Critical Dosing Considerations

Pediatric Dosing

• Oral syrup: 25 mg/kg (20 mg/kg amoxicillin + 5 mg/kg clavulanate) three times daily provides adequate therapy for childhood bacterial infections 2
• IV dosing: 100-200 mg/kg/day administered in 3-4 divided doses by short IV infusion for severe infections 5

Adult Dosing

• IV regimen: 1 g amoxicillin plus 200 mg clavulanic acid every 8 hours for severe infections 3
• Oral conversion: Same dosage maintained when transitioning from IV to oral route 3

Common Pitfalls to Avoid

• Premature oral conversion: Do not switch to oral route before adequate clinical response is demonstrated, particularly in bacteremia or severe infections where suboptimal bioavailability could lead to treatment failure 4
• Underdosing severe infections: The lower bioavailability of oral formulations means they may be inadequate for life-threatening infections requiring maximal drug exposure 3, 4
• Ignoring gastrointestinal function: Oral bioavailability assumes normal GI absorption; critically ill patients with ileus, vomiting, or malabsorption require IV therapy 3
• Food interactions: While oral Augmentin is generally well-tolerated, absorption can be affected by gastric pH and food intake, unlike IV administration 2

Clinical Efficacy Evidence

The clinical cure rate with IV Augmentin in severe infections is 88.4%, with successful treatment of bacteremia in multiple cases 3. Pediatric studies showed complete clinical cure or distinct improvement in all assessable cases with 92% bacteriological success using IV formulations 5. This superior efficacy in severe infections reflects the guaranteed drug delivery and complete bioavailability of the IV route 4, 5.