Antibiotic Use

A clinical diagnosis most often helps us to predict causative pathogens fitting in to a clinical syndrome which would tailor the correct antibiotic rather than blindly relying on fever, procalcitonin levels, WBC counts, cultures or radiology to make a diagnosis of infection. Our thought process here should be

Diagnosis of infection

• Is it an infection?
• A risk assessment of how likely is it that the patient has an infection?
• What are the possible non-infectious mimics?
• Have we taken the appropriate cultures to confirm the final diagnosis?

to genuine seriously ill patients. Generally, empiric antibiotic therapy is ONLY recommended for a select group of patients as described below after taking appropriate cultures

• Febrile neutropenia
• Severe sepsis and septic shock
• Community acquired pneumonia
• Ventilator associated pneumonia
• Necrotizing fasciitis

Hence, it is important to start smart and then focus, i.e., evaluate if empiric therapy can be justified or de-escalated and then make a plan with regard to the duration of therapy.

Approach includes

• Identify the clinical syndrome
• Elucidate possible sources of infection
• Predict possible microbial pathogens
• Predict the local resistance pattern based on institutional antibiogram

• Based on the spectrum of the antibiotic taking into account possible resistant patterns
• Use the correct dose, route and duration
• Ensure chosen antibiotic has adequate tissue penetration at the site of infection
• Optimize PK-PD parameters according to co-morbidities

• Modify empiric broad spectrum antibiotics depending on culture and antimicrobial susceptibility reports and patient status
• Stop polymyxins and glycopeptides if no carbapenem resistant organisms (CRO) or methicillin resistant Staphylococcus aureus (MRSA) identified on cultures
• Avoid double or redundant gram negative or anaerobic coverage
• Discontinue antibiotics if a non-infectious mimic identified
• De-escalate combination therapy to a single agent
• Change a broad spectrum antibiotic to a narrow spectrum one
• Change IV to oral antibiotics

De-escalation is safe in all patients including febrile neutropenia and septic shock and reduces mortality and length of hospital stay.

1. Respiratory tract syndromes
   • Viral pharyngitis
   • Viral rhinosinusitis
   • Viral bronchitis
   • Non-infectious cardio-pulmonary syndromes misdiagnosed as pneumonia
2. Skin and Soft Tissue Infections
   • Subcutaneous abscesses
   • Lower extremity stasis dermatitis
3. Asymptomatic bacteriuria and pyuria including in catheterized patients
4. Microbial colonization and culture contamination
5. Low grade fever

Practice guidelines and recommendations for optimum duration of therapy for various infectious disease syndromes suggest the following durations:
Community acquired pneumonia: 5 days
Hospital acquired pneumonia: 8 days
Skin and Soft tissue infections: 5 days
Urinary tract infections

• Cystitis: 3-5 days
• Pyelonephritis: 5-14 days
• Catheter associated: 7 days
• Staphylococcal aureus bacteraemia
  • low risk of complications = 2 weeks
  • high risk of complications = 4-6 weeks
• Intra-abdominal infection: 4-7 days
• Surgical antibiotic prophylaxis: 1 dose

A stop date should be planned and recorded in advance to ensure antibiotic is not given beyond the recommended duration.

Optimizing Pk-PD parameters include loading doses when needed, therapeutic drug monitoring for toxicity and efficacy and optimization of drug infusion or administration. For e.g.,

• Loading dose of Colistin 9 million units stat and then followed by 3 million units Q8H or 4.5 million units Q12H [to target Colistin Average Steady State Plasma Concentration (C_ss,avg = 2-2.5 mg/L)
• Inj vancomycin 1g IV Q12H and dose to be adjusted to maintain a trough level between 15-20 µg/ml [however there are increasing recent data that suggests that AUC/MIC may be a better indicator of clinical efficacy than a trough level]
• Extended infusion of β lactams

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