Oral Levofloxacin Has Excellent Bioavailability
Oral levofloxacin has approximately 99% bioavailability, making it essentially equivalent to intravenous administration and allowing seamless interchangeability between routes without dose adjustment. 1
Pharmacokinetic Evidence
The FDA drug label definitively establishes that oral levofloxacin achieves complete absorption:
- Absolute bioavailability is 99% ± 0.08 from a 500 mg tablet and 99% ± 0.06 from a 750 mg tablet 1
- Peak plasma concentrations occur within 1-2 hours after oral dosing 1
- Total drug exposure (AUC) is equivalent between intravenous and oral formulations at the same milligram-per-kilogram dose 2
The plasma concentration-time profiles are virtually superimposable between oral and IV routes, confirming that oral administration delivers the same systemic drug exposure as intravenous infusion 1. This means a patient receiving 500 mg orally achieves the same therapeutic effect as 500 mg given intravenously.
Clinical Implications for Practice
Seamless Route Switching
The oral and IV routes can be considered completely interchangeable without dose modification 1. This has major practical advantages:
- Patients can transition from IV to oral therapy once clinically stable without concern for reduced drug exposure 3
- Even patients with bacteremia can be effectively treated with oral levofloxacin 3
- The high bioavailability allows certain patients with moderately severe illness to be treated entirely with oral therapy as outpatients 3
Food Effects Are Minimal
Food prolongs time to peak concentration by approximately 1 hour and decreases peak concentration by only 14% with tablets 1. This minor effect is clinically insignificant, and levofloxacin tablets can be administered without regard to food 1.
Critical Absorption Pitfall
The one major exception to excellent bioavailability occurs with concurrent administration of antacids or medications containing divalent cations (aluminum, magnesium, calcium, iron), which markedly decrease levofloxacin absorption 2. These agents must not be administered within 2 hours of levofloxacin 4, 2. This is the single most important drug interaction affecting bioavailability.
Supporting Clinical Data
Multiple clinical trials confirm the therapeutic equivalence of oral and IV formulations:
- Oral levofloxacin achieved 87-96% clinical success rates in community-acquired pneumonia, comparable to IV comparators 5
- The bioequivalence between oral and IV routes has been validated across multiple infection types including respiratory, urinary, and skin infections 6, 7
- Pharmacokinetic studies demonstrate oral absorption is very rapid and complete, with little difference in serum concentration-time profiles between 500 mg oral versus IV doses 8
The excellent oral bioavailability of levofloxacin represents a significant clinical advantage, allowing flexible dosing strategies and early hospital discharge with oral therapy 3, 9.