What is the appropriate dosage and treatment duration of Ceftriaxone for an adult patient with a bacterial infection, assuming no allergy to cephalosporins and normal renal function?

Ceftriaxone Dosing for Adult Bacterial Infections

For most adult bacterial infections with normal renal function, administer ceftriaxone 1-2 grams IV/IM once daily, with dosing frequency and duration determined by infection severity and site. 1, 2

Standard Dosing by Infection Severity

Mild to Moderate Infections

• Uncomplicated infections: 1 gram IV/IM once daily 1, 2
• Skin and soft tissue infections: 1 gram every 12-24 hours depending on severity 1, 3
• Urinary tract infections: Single 1 gram dose initially, then transition to oral therapy 1
• Community-acquired pneumonia: 1-2 grams once daily 4

Severe Infections Requiring Higher Dosing

• Bacterial meningitis: 2 grams IV every 12 hours (total 4 grams daily) for 10-14 days 5, 1, 6
• Meningococcal meningitis/sepsis: 2 grams IV every 12 hours for 5 days 5, 1, 6
• Pneumococcal meningitis: 2 grams IV every 12 hours for 10-14 days, extending if delayed response 5, 1, 6
• Haemophilus influenzae meningitis: 2 grams IV every 12 hours for 10 days 5, 1, 6
• Enterobacteriaceae CNS infections: 2 grams IV every 12 hours for 21 days 5, 1, 6

Critical Dosing Considerations

CNS Infections Require Twice-Daily Dosing

Never use once-daily dosing for meningitis or CNS infections - twice-daily administration of 2 grams is essential for the first 24 hours to achieve rapid CSF sterilization and maintain adequate concentrations throughout the dosing interval 1, 6. Once-daily dosing is inadequate for CSF penetration in these life-threatening infections 6.

Resistant Organisms

• Penicillin-resistant pneumococci: Add vancomycin 15-20 mg/kg IV every 12 hours (targeting trough 15-20 mg/L) to ceftriaxone 2 grams every 12 hours 5, 1, 6
• Ceftriaxone-resistant strains or elevated MICs: Use twice-daily dosing of 2 grams to achieve free plasma concentrations of 2-3 mg/L at 24 hours 1, 6
• Pharyngeal gonorrhea with elevated MICs: Higher doses are required due to treatment failures documented with standard 250-500 mg doses 1

Special Clinical Scenarios

Gonococcal infections:

• Uncomplicated cervical/urethral/rectal: 250 mg IM single dose (must add antichlamydial coverage if chlamydia not ruled out) 1, 2
• Disseminated gonococcal infection: 1 gram IM/IV every 24 hours initially, continue 24-48 hours after improvement, then switch to oral therapy to complete 7 days 1
• Gonococcal meningitis: 1-2 grams IV every 12 hours for 10-14 days 1
• Gonococcal endocarditis: 1-2 grams IV every 12 hours for at least 4 weeks 1

Endocarditis:

• HACEK organisms: 2 grams IV/IM once daily for 4 weeks (6 weeks for prosthetic valve) 1
• Highly penicillin-susceptible viridans streptococci (MIC ≤0.12 μg/mL): 2 grams IV/IM once daily for 4 weeks as monotherapy 1

Surgical prophylaxis: 1 gram IV single dose 30 minutes to 2 hours before surgery 2, 7

Administration Guidelines

Route and Timing

• IV administration: Infuse over 30 minutes for adults 2
• IM administration: Inject deep into large muscle mass; IM injections are painful and patients should be counseled 1, 2
• Concentrations: IV concentrations between 10-40 mg/mL are recommended 2

Critical Safety Warnings

Never use calcium-containing diluents or co-administer with calcium-containing IV solutions - precipitation of ceftriaxone-calcium can occur, which is potentially fatal 2. Flush lines thoroughly between infusions if sequential administration is necessary in non-neonates 2.

Treatment Duration by Infection Type

• Meningococcal disease: 5 days if clinically recovered 5, 1
• Pneumococcal meningitis: 10 days if stable, up to 14 days if delayed response 5, 1
• Culture-negative meningitis: 10 days if clinically recovered 1
• Enterobacteriaceae CNS infections: 21 days (not the 10-14 days used for other meningitis) 5, 6
• Brain abscess: 6-8 weeks IV (4 weeks if completely excised) 8
• Most other serious infections: Continue at least 2 days after signs/symptoms resolve, usual duration 4-14 days 2
• Streptococcus pyogenes infections: Minimum 10 days 2

Common Pitfalls to Avoid

1. Underdosing CNS infections: Using 1 gram once daily for meningitis is inadequate and dangerous 6
2. Forgetting vancomycin for resistant pneumococci: Always add vancomycin to ceftriaxone for penicillin-resistant pneumococcal meningitis 5, 6
3. Wrong duration for Enterobacteriaceae: These require 21 days, not 10-14 days 5, 6
4. Omitting antichlamydial coverage: Must add for gonococcal infections if chlamydia not excluded 1, 2
5. Inadequate dosing for resistant gonorrhea: Standard 250-500 mg doses fail for pharyngeal infections with elevated MICs 1

Monitoring and Adverse Effects

Common adverse effects include rash, fever, diarrhea, neutropenia, liver function abnormalities, and gallbladder "sludging" 1, 8. No dosage adjustment is necessary for isolated renal or hepatic impairment, though caution is warranted with combined dysfunction 2. The maximum daily dose should not exceed 4 grams 2.