1. First-Line Anti-Pseudomonal Beta-Lactams

Broad-spectrum beta-lactams covering Pseudomonas aeruginosa are the cornerstone of initial empiric therapy in high-risk febrile neutropenia. Agent selection and dosing must account for pharmacokinetic/pharmacodynamic (PK/PD) targets and renal function.

2. Indications for Gram-Positive Coverage

Routine empiric addition of vancomycin is discouraged due to risks of nephrotoxicity and resistance. Gram-positive agents should only be added when specific risk factors or infection sources are present.

A. Vancomycin

• Dosing: Initiate with a loading dose of 20-25 mg/kg, followed by 15–20 mg/kg IV q8–12h. Adjust dose to achieve target troughs of 15–20 mg/L for severe infections (e.g., MRSA pneumonia, bacteremia) or 10–15 mg/L for less severe infections. AUC/MIC-guided dosing is preferred if available.
• Toxicity: Nephrotoxicity risk is increased with concomitant nephrotoxins (e.g., piperacillin-tazobactam, aminoglycosides). Monitor for infusion-related reactions.

B. Linezolid and Daptomycin

• Linezolid: 600 mg IV/PO q12h. Offers excellent lung penetration and oral bioavailability. Monitor complete blood count (CBC) for thrombocytopenia, especially with therapy >14 days. Use with caution in patients on serotonergic agents.
• Daptomycin: 6-10 mg/kg IV q24h (adjust dose and interval in renal impairment). Inactivated by pulmonary surfactant, making it ineffective for pneumonia. Monitor creatine phosphokinase (CPK) weekly.

3. Adjunctive and Second-Line Agents

Aminoglycosides and fluoroquinolones are reserved for targeted scenarios. Novel beta-lactam/beta-lactamase inhibitor combinations are crucial for addressing multidrug-resistant (MDR) gram-negative pathogens.

A. Aminoglycosides

• Dosing: Use extended-interval dosing (e.g., gentamicin/tobramycin 5–7 mg/kg IV q24h). Target peak concentrations of 5–10 mg/L and trough concentrations <2 mg/L to minimize toxicity.
• Role: Primarily used for synergy in combination with a beta-lactam for suspected or documented resistant Pseudomonas infections. Routine double coverage is not recommended.

B. Fluoroquinolones

• Role: Reserved for outpatient management of low-risk febrile neutropenia (MASCC score ≥21), typically as ciprofloxacin 750 mg PO BID plus amoxicillin-clavulanate 875/125 mg PO BID.
• Risks: Widespread use for prophylaxis has driven resistance. Associated with C. difficile infection, QT prolongation, and tendinopathy.

C. Novel Agents for Resistant Pathogens

Agents like ceftazidime–avibactam and ceftolozane–tazobactam should be reserved as salvage therapy for documented MDR Pseudomonas, carbapenem-resistant Enterobacterales (CRE), or ESBL-producing organisms not responding to standard therapy.

4. PK/PD and Organ Dysfunction Adjustments

Critical illness alters drug volume of distribution and clearance. Dosing must be adapted, particularly in patients with renal impairment, those on renal replacement therapy (RRT), and in cases of hepatic dysfunction. Extended or continuous infusion strategies are key to optimizing beta-lactam exposure.

A. Volume of Distribution (Vd)

Sepsis and systemic inflammation can lead to capillary leak and an increased Vd for hydrophilic drugs like beta-lactams. In such cases, consider using higher loading doses (e.g., meropenem 2 g IV) to rapidly achieve therapeutic concentrations.

B. Renal Replacement Therapy (RRT)

Continuous renal replacement therapy (CRRT) can significantly enhance drug clearance. Standard intermittent dosing is often inadequate. Typical dosing strategies during CRRT include:

• Cefepime: 2 g IV q8h
• Vancomycin: 15–20 mg/kg IV q48h (monitor troughs closely)

C. Hepatic Dysfunction

Most beta-lactams require minimal to no dose adjustment. However, agents with significant hepatic metabolism or toxicity risk, like linezolid, may require dose reduction in severe liver failure.

D. Extended vs. Continuous Infusion

Administering beta-lactams over an extended period (3–4 hours) or as a continuous infusion (after a loading dose) is the most effective way to maximize the %fT>MIC, a key predictor of clinical success. For example, piperacillin-tazobactam can be given as a 4.5 g IV loading dose, followed by a continuous infusion of 13.5 g over 24 hours. Always verify stability data for continuous infusions with institutional pharmacy resources.

5. Antifungal and Antiviral Strategies

Empiric antifungal therapy is indicated for persistent fever in high-risk patients. Antivirals are used for prophylaxis and treatment of specific viral pathogens like Herpes Simplex Virus (HSV) and Cytomegalovirus (CMV).

A. Empiric Antifungal Therapy

• Indication: Persistent or recurrent fever after 72–96 hours of broad-spectrum antibiotics in patients with expected neutropenia >7 days.
• First-line: An echinocandin, such as caspofungin (70 mg IV loading dose, then 50 mg IV daily) or micafungin (100 mg IV daily).
• Alternatives: Liposomal amphotericin B (3–5 mg/kg IV daily) for broad coverage, or voriconazole (6 mg/kg IV BID for 2 doses, then 4 mg/kg IV BID) if mold coverage is a primary concern.
• Monitoring: Renal function and electrolytes (amphotericin B), liver function tests (all agents), and therapeutic drug levels (azoles).

B. Antiviral Therapy

• Prophylaxis: Acyclovir 400 mg PO BID is often used for HSV prophylaxis in seropositive patients undergoing intensive chemotherapy or stem cell transplant.
• Treatment: For active HSV/VZV infection, use acyclovir 5 mg/kg IV q8h (adjusted for renal function). For CMV disease, use ganciclovir 5 mg/kg IV q12h (monitor CBC for myelosuppression).

6. Route Selection and Delivery Devices

Central venous access is required for irritant/vesicant agents and for prolonged courses of therapy. Clear clinical criteria must be met to guide a safe transition from intravenous (IV) to oral (PO) antibiotics.

A. Vascular Access Choice

• Central Lines: Essential for the administration of vesicants/irritants (e.g., vancomycin, amphotericin B) and for patients requiring prolonged (>5 days) antibiotic courses.
• Peripheral IVs: May be used for short courses of non-irritating drugs. The site must be inspected frequently (e.g., every 4 hours) for signs of phlebitis or infiltration.

B. IV-to-Oral Conversion

Transitioning from IV to PO therapy can reduce length of stay and healthcare costs. The patient must meet all of the following criteria:

• Clinically stable and afebrile for ≥48–72 hours.
• Evidence of hematopoietic recovery (ANC >500/µL and rising).
• Intact and functioning gastrointestinal tract, without severe mucositis or graft-versus-host disease (GVHD).

Common oral regimens include a fluoroquinolone, with or without amoxicillin-clavulanate or clindamycin (for penicillin-allergic patients).

7. Monitoring and Stewardship

Therapeutic drug monitoring (TDM) and frequent clinical reassessment are vital to ensure efficacy and safety. Antimicrobial stewardship practices are essential for reducing costs, minimizing toxicity, and mitigating the development of resistance.

A. Therapeutic Drug Monitoring (TDM)

• Vancomycin: Target trough 15–20 mg/L for severe infections; AUC/MIC monitoring is the preferred standard.
• Aminoglycosides: Monitor peak and trough levels according to institutional protocols.
• Beta-lactams: TDM is not yet standard practice but may be beneficial for critically ill patients, those on RRT, or when treating pathogens with high MICs.

B. Markers of Efficacy

• Clinical: Defervescence, hemodynamic stability, and resolution of infection-specific signs.
• Laboratory: Rising ANC, negative follow-up blood cultures.
• Biomarkers: Procalcitonin is under investigation as a tool to guide de-escalation, but its role is not yet fully established in this population.

C. Pharmacoeconomics and Stewardship

Initial monotherapy with cefepime or piperacillin-tazobactam is more cost-effective than combination regimens. Novel, expensive agents should be restricted to cases with confirmed MDR infections. Promoting timely IV-to-oral conversions is a key strategy for reducing direct healthcare costs.