What is the initial choice of antibiotic for bacterial infections?

Initial Antibiotic Selection for Bacterial Infections

For empiric treatment of bacterial infections, amoxicillin or amoxicillin-clavulanic acid are recommended as first-choice antibiotics from the WHO Access group, which have good clinical activity against commonly susceptible bacteria with lower resistance potential. 1

First-Choice Antibiotics (Access Group)

• Amoxicillin or amoxicillin-clavulanic acid are recommended as first-choice options for most common bacterial infections due to their favorable risk-benefit ratios and lower resistance potential 1, 2
• These antibiotics are widely available, affordable, and of assured quality, making them suitable for empiric first-line therapy 1
• Amoxicillin can be taken with or without food, making it convenient for patient use 3
• For lower urinary tract infections, first-choice options include amoxicillin-clavulanic acid, nitrofurantoin, and sulfamethoxazole-trimethoprim 2

Second-Choice Antibiotics (Watch Group)

• When first-choice antibiotics are ineffective or contraindicated, second-choice options from the Watch group may be considered 1
• Watch group antibiotics include fluoroquinolones, carbapenems, and third-generation cephalosporins, which have greater concerns regarding toxicity and potential for developing antimicrobial resistance 1
• These antibiotics should be targets of antimicrobial stewardship programs and used judiciously 1
• For example, cefalexin and doxycycline are recommended as second-choice options for certain respiratory infections 2

Site-Specific Recommendations

Respiratory Tract Infections

• For exacerbations of COPD, amoxicillin or amoxicillin-clavulanic acid are recommended as first-choice antibiotics 2
• Antibiotics should only be used if there is purulent sputum or clinical/radiographic evidence of pneumonia 2

Intra-abdominal Infections

• For community-acquired intra-abdominal infections, recommended regimens include:
  • Cephalosporin-based regimens: ceftriaxone, cefotaxime, or cefepime, each in combination with metronidazole 2
  • Quinolone-based regimens: ciprofloxacin plus metronidazole 2
• Aminoglycoside-based regimens are not recommended for routine use in community-acquired intra-abdominal infections due to toxicity concerns 2

Biliary Infections

• For mild episodes of bacterial cholangitis, an aminopenicillin/beta-lactamase inhibitor (like amoxicillin-clavulanic acid) is recommended as first-line therapy 2
• For more severe cases, intravenous antibiotics with piperacillin/tazobactam or third-generation cephalosporins with anaerobic coverage are recommended 2
• Fluoroquinolones should be saved for specific cases due to high resistance rates and unfavorable side effect profiles 2

Special Considerations

Antibiotic Resistance

• Local resistance patterns should be considered when selecting empiric antibiotics 2
• The WHO recommends that local resistance rates for empirically selected antibiotics should be <10% for pyelonephritis and <20% for treatment of lower urinary tract infection 2
• Monitoring of serum drug concentrations is helpful for predicting therapeutic success and toxicity with certain antibiotics, such as aminoglycosides 2

Duration of Therapy

• For established infections, antimicrobial therapy should be continued until resolution of clinical signs of infection, including normalization of temperature and WBC count, and return of gastrointestinal function 2
• For patients with persistent or recurrent clinical evidence of infection after 5-7 days of therapy, appropriate diagnostic investigation should be undertaken 2

Adverse Effects and Precautions

• Patients should be counseled that antibiotics should only be used to treat bacterial infections, not viral infections 3, 4
• Patients should be advised to take the full course of antibiotics as prescribed to prevent resistance development 3, 4
• Fluoroquinolones have been associated with disabling and potentially permanent side effects affecting tendons, muscles, joints, peripheral neuropathy, and central nervous system 2

Monitoring and Follow-up

• The inhibitory quotient (IQ), which is the ratio of achievable antibiotic concentration at the infection site to the minimum inhibitory concentration for the infecting organism, is a strong predictor of therapeutic outcome 5
• IQ values <4 predict failure, while values ≥6 predict cure 5
• For patients with persistent clinical symptoms after appropriate antibiotic therapy, further investigation for source control is warranted 2