What is the usual dose of marbofloxacin and what concentration does it reach in prostate tissue?

Marbofloxacin Dosing and Prostatic Tissue Penetration

Marbofloxacin is a veterinary fluoroquinolone antibiotic dosed at 1.25-2.5 mg/lb (2.75-5.5 mg/kg) orally once daily in dogs, achieving prostatic tissue concentrations of 5.6 μg/g at 2 hours and 1.1-2.0 μg/g at 24 hours after a single dose, which represents excellent tissue penetration well above MIC values for most prostatic pathogens. 1

Standard Dosing Regimens

For dogs:

• Recommended dose: 1.25-2.5 mg/lb (2.75-5.5 mg/kg) orally once daily 1
• Bioavailability: 94% after oral administration 1
• Time to peak concentration (Tmax): 1.5-1.8 hours 1
• Peak plasma concentration (Cmax): 2.0 μg/mL at 1.25 mg/lb dose; 4.2 μg/mL at 2.5 mg/lb dose 1
• Elimination half-life: 10.7-10.9 hours 1

For cats:

• Recommended dose: 2.5 mg/lb (5.5 mg/kg) orally once daily 1
• Time to peak concentration: 1.2 hours 1
• Peak plasma concentration: 4.8 μg/mL 1
• Elimination half-life: 12.7 hours 1

Prostatic Tissue Concentrations in Dogs

After 1.25 mg/lb dose:

• 2 hours post-dose: 5.6 ± 1.4 μg/g 1
• 18 hours post-dose: 1.8 ± 0.6 μg/g 1
• 24 hours post-dose: 1.1 ± 0.4 μg/g 1

After 2.5 mg/lb dose:

• 2 hours post-dose: 11 ± 3 μg/g 1
• 18 hours post-dose: 2.7 ± 1.0 μg/g 1
• 24 hours post-dose: 2.0 ± 0.5 μg/g 1

Clinical Significance of Tissue Penetration

Marbofloxacin demonstrates superior prostatic tissue penetration compared to plasma concentrations:

• Prostatic tissue concentrations remain well above MIC90 values for common pathogens including Staphylococcus intermedius (MIC90 = 0.25 μg/mL), Escherichia coli (MIC90 = 0.06 μg/mL), and Proteus mirabilis (MIC90 = 0.125 μg/mL) throughout the 24-hour dosing interval 1
• The tissue concentrations at 24 hours (1.1-2.0 μg/g) exceed the MIC90 for these pathogens by 4-32 fold, supporting once-daily dosing 1

Steady-State Considerations

Accumulation with repeated dosing:

• Steady-state is reached after the third dose 1
• Steady-state concentrations are approximately 25% higher in dogs than single-dose levels 1
• In cats, steady-state concentrations are approximately 35% higher than single-dose levels 1

Tissue Distribution Beyond Prostate

Marbofloxacin achieves high concentrations in multiple tissues relevant to urogenital infections:

• Kidney: 7.1-12.7 μg/g at 2 hours (dose-dependent) 1
• Bladder: 4.8-12 μg/g at 2 hours 1
• Lymph nodes: 5.5-8.3 μg/g at 2 hours 1
• Muscle: 4.1-7.5 μg/g at 2 hours 1

Comparison to Human Fluoroquinolones in Prostate

While marbofloxacin data is veterinary-specific, context from human fluoroquinolone studies demonstrates that newer fluoroquinolones achieve better prostatic penetration than older agents. Moxifloxacin achieves prostatic tissue concentrations approximately twice plasma levels (tissue/serum ratio of 1.7-2.0) in humans 2, and demonstrates 59% higher tissue distribution than levofloxacin 3. This pattern of enhanced tissue penetration with newer fluoroquinolones suggests marbofloxacin's excellent prostatic concentrations are consistent with the pharmacokinetic profile expected from this drug class.

Key Clinical Pearls

Important considerations for marbofloxacin use:

• Approximately 40% of the oral dose is excreted unchanged in urine in dogs, making it suitable for both prostatic and urinary tract infections 1
• Plasma protein binding is low (9.1% in dogs, 7.3% in cats), allowing high free drug concentrations for tissue penetration 1
• The long elimination half-life (10.7-12.7 hours) supports once-daily dosing 1
• Absorption increases proportionally over the 1.25-2.5 mg/lb dose range, allowing dose adjustment based on infection severity 1