4.3 Bronchiolitis, RSV Prevention (Nirsevimab, Clesrovimab, Palivizumab) & Viral Lower Respiratory Infections

Board Certified Pediatric Pharmacy Specialist BCPPS

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1 Chapter 1: Pediatric Patient Characteristics — Growth, Anthropometrics & Perinatal Exposure

1.1 Normal Growth, Development & Growth-Chart Interpretation 1.2 Anthropometrics: Body Surface Area, Dosing Weights & Maximum-Dose Caps 1.3 Medication Use in Pregnancy and Lactation

2 Chapter 2: Developmental Pharmacokinetics & Neonatal Principles

2.1 Developmental PK: Absorption, Distribution & Body Water Dynamics 2.2 Hepatic Metabolism & CYP/UGT Isoenzyme Maturation 2.3 Renal Function Maturation & Glomerular Filtration Development

3 Chapter 3: Neonatal Critical Care & Prematurity Complications

3.1 Neonatal Sepsis & Meningitis (Early-Onset vs Late-Onset Sepsis) 3.2 Respiratory Distress Syndrome, Surfactant & Bronchopulmonary Dysplasia 3.3 Patent Ductus Arteriosus, Apnea of Prematurity & Necrotizing Enterocolitis

4 Chapter 4: Pediatric Infectious Diseases — Respiratory & ENT Infections

4.1 Acute Otitis Media, Sinusitis & Pharyngitis 4.2 Pediatric Community-Acquired Pneumonia & Parapneumonic Effusion 4.3 Bronchiolitis, RSV Prevention (Nirsevimab, Clesrovimab, Palivizumab) & Viral Lower Respiratory Infections

5 Chapter 5: Pediatric Infectious Diseases — Systemic, Bone & CNS Infections

5.1 Pediatric Meningitis, Encephalitis & Brain Abscess 5.2 Skin, Soft Tissue, Osteomyelitis & Septic Arthritis 5.3 Pediatric Sepsis, Febrile Neutropenia & Central Line-Associated Bloodstream Infections

6 Chapter 6: Pediatric Pulmonary Medicine — Asthma & Status Asthmaticus

6.1 Chronic Pediatric Asthma Assessment & Stepwise Outpatient Pharmacotherapy 6.2 Status Asthmaticus & Acute Exacerbation Pharmacotherapy in ED/PICU 6.3 Aerosol Drug Delivery, Spacers & Specialized Inhalation Devices

7 Chapter 7: Cystic Fibrosis & Chronic Pediatric Respiratory Disorders

7.1 Pathophysiology, Diagnosis & Airway Clearance in Cystic Fibrosis 7.2 CFTR Modulator Therapies & Monitoring 7.3 CF Pulmonary Exacerbations, Chronic Infection Management & Comorbidities

8 Chapter 8: Pediatric Cardiology & Hemodynamics

8.1 Congenital Heart Defects & Ductal-Dependent Lesions 8.2 Pediatric Heart Failure & Cardiomyopathies 8.3 Pediatric Arrhythmias & Syncope Management

9 Chapter 9: Pediatric Resuscitation, Shock & Critical Care Support

9.1 PALS Resuscitation Algorithms & Cardiac Arrest Pharmacotherapy 9.2 Pediatric Shock States & Vasoactive / Inotropic Selection 9.3 Extracorporeal Membrane Oxygenation (ECMO) & Critical Care PK

10 Chapter 10: Pediatric Neurology & Psychiatric Disorders

10.1 Neonatal Seizures & Pediatric Status Epilepticus 10.2 Pediatric Epilepsy Syndromes & Maintenance Anticonvulsants 10.3 Attention-Deficit/Hyperactivity Disorder (ADHD) & Pediatric Mood Disorders

11 Chapter 11: Pediatric Endocrinology & Metabolic Disorders

11.1 Pediatric Type 1 Diabetes Mellitus Management & Insulin Technologies 11.2 Diabetic Ketoacidosis (DKA) Protocols & Cerebral Edema Prevention 11.3 Growth Hormone, Pubertal Disorders & Congenital Adrenal Hyperplasia

12 Chapter 12: Pediatric Hematology, Oncology & Supportive Care

12.1 Sickle Cell Disease: Vaso-occlusive Crises & Disease-Modifying Therapies 12.2 Pediatric Acute Lymphoblastic Leukemia (ALL) & Chemotherapy Toxicities 12.3 Oncologic Emergencies: Tumor Lysis Syndrome & Supportive Care

13 Chapter 13: Pediatric Medication Safety & Error Prevention

13.1 High-Alert Pediatric Medications & Ten-Fold Dosing Calculation Traps 13.2 Smart Infusion Pumps & Dose Error Reduction Systems (DERS) 13.3 Medication Reconciliation & Pediatric Care Transitions

14 Chapter 14: Pediatric Compounding & Formulation Technology

14.1 Non-Sterile Compounding (USP <795>) & Liquid Formulations 14.2 Sterile Compounding (USP <797>) & Micro-Dosing Considerations 14.3 Hazardous Drug Handling (USP <800>) & Excipient Toxicities

15 Chapter 15: Fluids, Electrolytes & Clinical Nutrition Support

15.1 Fluid Requirements, Dehydration Assessment & Maintenance Therapy 15.2 Electrolyte Disturbances: Sodium, Potassium & Calcium Management 15.3 Pediatric & Neonatal Parenteral Nutrition (PN) Formulation

16 Chapter 16: Pediatric Pain Management, Sedation & Delirium

16.1 Age-Specific Pain Assessment Tools & Analgesic Selection 16.2 Procedural Sedation & Rapid Sequence Intubation in Children 16.3 PICU Delirium, Iatrogenic Withdrawal & Weaning Strategies

17 Chapter 17: Biostatistics & Study Design in Pediatric Research

17.1 Observational vs Experimental Pediatric Study Designs 17.2 Biostatistical Testing, Power & Sample Size in Small Pediatric Cohorts 17.3 Diagnostic Testing, Sensitivity, Specificity & Predictive Values

18 Chapter 18: Pediatric Evidence Appraisal, Regulatory Framework & Ethics

18.1 Pediatric Drug Legislation: BPCA, PREA & Labeling Nuances 18.2 Institutional Review Boards (IRB), Assent & Informed Consent in Minors 18.3 Evaluating Clinical Practice Guidelines & Formulating Off-Label Recommendations

19 Chapter 19: Pediatric Education, Health Literacy & Communication

19.1 Caregiver Health Literacy & Pediatric Medication Adherence 19.2 Interprofessional Education & Clinical Teaching Strategies 19.3 Developing Age-Appropriate Patient Educational Materials

20 Chapter 20: Pediatric Immunizations & Public Health Advocacy

20.1 ACIP Pediatric Immunization Schedule: Routine Childhood Vaccines 20.2 Adolescent Immunizations, Vaccine Hesitancy & Catch-Up Schedules 20.3 Pediatric Public Health Disparities & Special Population Advocacy

21 Chapter 21: Pediatric Practice Management — Laboratory Stewardship, Pharmacoeconomics & Informatics

21.1 Pediatric Laboratory Practices: Blood Conservation, Sampling Timing & Age-Specific Reference Intervals 21.2 Pharmacoeconomics, Formulary Management & Cost-Containment in Pediatrics 21.3 Clinical Informatics, CPOE Decision Support & Drug Shortage Management

4.3 Bronchiolitis, RSV Prevention (Nirsevimab, Clesrovimab, Palivizumab) & Viral Lower Respiratory Infections

Key Takeaways Explain This Topic AI

AAP bronchiolitis guidelines recommend strictly supportive care (oxygen only if persistent SpO2 <90%, gentle suctioning, hydration); routine use of bronchodilators, systemic corticosteroids, hypertonic saline in the ED, and antibiotics is explicitly not recommended.

Nirsevimab is a long-acting monoclonal antibody targeting the prefusion F protein with an engineered YTE Fc region (half-life 69-100 days), dosed as a single IM injection (50 mg for <5 kg; 100 mg for >=5 kg) providing at least 5 months of universal protection for infants <8 months.

Clesrovimab (Enflonsia), FDA-approved June 9, 2025 and ACIP-recommended June 25, 2025, is an alternative to nirsevimab for infants under 8 months entering their first RSV season, given as a single 105 mg IM dose that is identical regardless of body weight; it is not recommended at or after 8 months, so second-season high-risk children must receive nirsevimab.

Maternal RSV vaccination with bivalent RSVpreF (Abrysvo) at 32-36 weeks gestation provides passive transplacental infant protection through 6 months; infant nirsevimab is not needed unless birth occurs <14 days post-vaccination or maternal response is impaired.

Pediatric influenza pharmacotherapy with oseltamivir requires tiered dosing (3 mg/kg BID for infants 0-8 months; 3.5 mg/kg BID for 9-11 months; weight-tiered 30 to 75 mg BID for >=1 year) for 5 days, initiated as early as possible within 48 hours.

Last updated: September 2026

4.3 Bronchiolitis, RSV Prevention & Viral Respiratory Infections

Quick Answer: Pediatric bronchiolitis is managed with supportive care alone : oxygen if SpO 2 < 90 % \text{SpO}_2 < 90\% SpO 2 ​ < 90% , gentle suctioning, and hydration. The AAP guideline explicitly advises against routine bronchodilators, systemic corticosteroids, and hypertonic saline in the emergency department. For RSV immunoprophylaxis, nirsevimab (Beyfortus) has superseded palivizumab as the standard of care for all infants <8 months entering their first RSV season (dosed 50 mg IM for <5 kg, 100 mg IM for ≥5 kg ), providing ≥5 months of protection via an engineered YTE Fc domain. If the mother received Abrysvo (RSVpreF) at 32–36 weeks gestation ≥14 days prior to delivery , infant nirsevimab is not needed. Pediatric influenza is treated with weight-tiered oseltamivir for 5 days .

1. Acute Viral Bronchiolitis: Pathophysiology & Clinical Course

Bronchiolitis is the leading cause of hospitalization in infants younger than 12 months in the United States, peaking between December and March.

Etiology & Pathogenesis

Respiratory Syncytial Virus (RSV) accounts for 50% to 80% of cases.

Other viral agents: Human rhinovirus, human metapneumovirus (hMPV), parainfluenza virus types 1–3, influenza, adenovirus, and coronavirus.

Pathophysiology : Direct viral infection and destruction of ciliated respiratory epithelial cells in the bronchioles triggers lymphocytic infiltration, submucosal edema, epithelial necrosis, and excessive mucus production. The accumulation of cellular debris and viscous mucus causes ball-valve luminal obstruction , leading to hyperinflation, patchy atelectasis, dynamic airway narrowing, and severe ventilation-perfusion ( V / Q V/Q V / Q ) mismatch.

Clinical Presentation

Infants typically experience a 2- to 3-day viral upper respiratory prodrome (rhinorrhea, low-grade fever, sneezing), progressing on days 3 to 5 to lower respiratory tract involvement: tachypnea (respiratory rate >50–70 breaths/min), persistent wheezing, diffuse fine rales/crackles, intercostal and subcostal retractions, nasal flaring, grunting, and feeding intolerance.

2. American Academy of Pediatrics (AAP) Guidelines: The "Do Not Do" Core

The 2014 AAP clinical practice guideline (reaffirmed 2019/2023) transformed bronchiolitis management by explicitly designating most historical pharmacotherapies as non-beneficial or harmful. +-----------------------------------------------------------------------------------------+

• | AAP Bronchiolitis Guideline Recommendations |
• +-----------------------------------------------------------------------------------------+
• | Intervention | AAP Recommendation | Clinical Rationale |
• |----------------------------|---------------------------------|--------------------------|
• | Diagnostic Viral / X-ray | DO NOT routinely order viral | Clinical diagnosis. Does |
• | Testing | panels or chest radiographs | not alter management. |
• | Inhaled Bronchodilators | DO NOT routinely administer | No reduction in admission|
• | (Albuterol, Epinephrine) | (albuterol or epinephrine) | or length of stay (LOS). |
• | Systemic Corticosteroids | DO NOT administer corticosteroids| Ineffective; does not |
• | (Dexamethasone, Prednisone)| in any formulation | alter airway pathology. |
• | Nebulized Hypertonic Saline| DO NOT administer in emergency | Does not reduce admission|
• | (3% NaCl) | department setting | rates from ED. |
• | Antibacterials | DO NOT administer unless proven | Secondary bacterial rate |
• | | concurrent bacterial infection | is extremely low (<1-2%).|
• | Supplemental Oxygen | Administer ONLY if SpO2 < 90% | Avoid over-monitoring and|
• | | continuously | delayed discharge. |
• +-----------------------------------------------------------------------------------------+
• Why Bronchodilators and Corticosteroids Fail in Bronchiolitis

Inhaled Bronchodilators : Unlike asthma, in which airway obstruction is caused by smooth muscle bronchospasm, bronchiolitis obstruction is mechanical—driven by sloughed necrotic epithelium, mucosal edema, and mucus plugging. Infant bronchiolar smooth muscle is poorly developed and lacks adequate beta-2 receptor coupling. Meta-analyses demonstrate albuterol does not reduce hospitalization rates or hospital length of stay, while inducing tachycardia, tremor, and paradoxical hypoxemia via worsening V / Q V/Q V / Q mismatch.

Systemic Corticosteroids : The inflammatory cascade in viral bronchiolitis is predominantly neutrophilic and monocytic epithelial destruction rather than eosinophilic allergic inflammation. Multiple large multicenter trials (e.g., Corneli et al.) demonstrated that oral dexamethasone or prednisolone produces no clinical improvement, does not reduce admissions, and may prolong viral shedding.

Supportive Care Fundamentals

Oxygen Therapy : Indicated only if SpO 2 \text{SpO}_2 SpO 2 ​ persistently falls below 90% during quiet, awake states. Continuous pulse oximetry should be avoided in clinically stable infants weaning oxygen, as it artificially prolongs hospitalization.

Hydration & Nutrition : Assess hydration status. If respiratory rate exceeds 60 to 70 breaths/min, oral feeding carries an aspiration risk. Provide isotonic IV fluids (e.g., D 5 D_5 D 5 ​ 0.9% NaCl) or nasogastric enteral feeds.

Airway Clearance : Gentle superficial nasal suctioning with saline drops before feeding and sleep. Deep nasopharyngeal suctioning causes traumatic mucosal edema and should be avoided.

3. RSV Immunoprophylaxis: Nirsevimab, Clesrovimab & Palivizumab

The introduction of nirsevimab-alip (Beyfortus) marked a paradigm shift from selective high-risk prophylaxis to universal infant passive immunization, and a second long-acting monoclonal antibody, clesrovimab-cfor (Enflonsia) , joined it in 2025.

Important

ACIP recommends that every infant be protected by one of three routes: (1) maternal RSV vaccination during pregnancy, (2) infant nirsevimab , or (3) infant clesrovimab . Nirsevimab and clesrovimab are alternatives to each other — never give both. +-----------------------------------------------------------------------------------------+

• | Nirsevimab vs Palivizumab Pharmacologic Comparison |
• +-----------------------------------------------------------------------------------------+
• | Characteristic | Nirsevimab (Beyfortus) | Palivizumab (Synagis) |
• |----------------------------|---------------------------------|--------------------------|
• | Molecular Structure | Recombinant human IgG1kappa | Humanized mouse-human |
• | Target Antigen | Prefusion F protein (Site 0) | F protein (Sites A/II) |
• | Fc Modification | YTE mutation (M252Y/S254T/T256E)| Wild-type Fc domain |
• | Elimination Half-Life (t1/2)| 69 to 100 days | 18 to 20 days |
• | Duration of Protection | >= 5 months (entire RSV season) | ~30 days per injection |
• | Dosing Regimen | Single IM injection once | Monthly IM x up to 5 doses
• | Target Population | ALL infants <8 months entering | Restricted high-risk only|
• | | Season 1; select high-risk S2 | (prematurity, CLD, CHD) |
• +-----------------------------------------------------------------------------------------+
• Clesrovimab (Enflonsia): The Weight-Independent Alternative

The FDA approved clesrovimab on June 9, 2025 , and ACIP recommended it on June 25, 2025 as an alternative to nirsevimab for infants aged <8 months born during or entering their first RSV season who are not protected by maternal vaccination (MMWR 2025;74:No. 32).

Dose: A single 105 mg IM injection (0.7 mL prefilled syringe) — the same dose for every infant regardless of body weight , which removes the <5 kg / ≥5 kg weight-tier calculation step that drives nirsevimab dosing errors.

Target: Binds a distinct site on the RSV fusion (F) protein; unlike nirsevimab it does not use an Fc half-life-extension mutation, relying instead on high potency and slow clearance.

Trials: Phase 2b/3 CLEVER and Phase 3 SMART demonstrated reductions in RSV-associated medically attended lower respiratory infection and in RSV hospitalization.

Hard Age Limit: Clesrovimab is not recommended at or after 8 months of age . Children aged 8 through 19 months who remain at increased risk and are entering their second RSV season must receive nirsevimab , not clesrovimab — a frequent distractor.

The YTE Technology Explained

Nirsevimab incorporates a triple amino-acid substitution ( M252Y / S254T / T256E , designated YTE ) into the constant ( C H 2 C_H2 C H ​ 2 ) region of its Fc domain. This mutation dramatically increases the antibody's binding affinity to the neonatal Fc receptor (FcRn) at an acidic pH (6.0) inside endosomes, while preserving dissociation at neutral physiological pH (7.4) in extracellular fluid. As a result, endocytosed nirsevimab is efficiently diverted away from lysosomal degradation and recycled back into the systemic circulation, prolonging its terminal elimination half-life to 69–100 days .

Nirsevimab Dosing & ACIP Indications

Season 1 (Universal) : All infants <8 months of age born during or entering their first RSV season whose mothers did not receive the maternal RSV vaccine:

Body weight < 5 kg : 50 mg IM as a single dose.

Body weight ≥ 5 kg : 100 mg IM as a single dose.

Season 2 (High-Risk Only) : Children aged 8 through 19 months entering their second RSV season who remain at increased risk of severe RSV disease (chronic lung disease of prematurity requiring medical support, severe immunocompromise, cystic fibrosis with severe pulmonary involvement or weight-for-length <10th percentile, American Indian and Alaska Native children):

Dose : 200 mg IM administered as two 100 mg injections at separate anatomical sites.

Palivizumab Restricted Modern Indications

Palivizumab (15 mg/kg IM monthly for up to 5 doses) is now reserved exclusively for clinical situations where nirsevimab is unavailable or contraindicated. Under traditional AAP guidance, qualifying criteria included:

Infants born at <29 weeks, 0 days gestation who are <12 months old at season start.

Infants with chronic lung disease of prematurity (CLD) (<32 weeks GA requiring >21% oxygen for ≥28 days after birth) who require medical support within 6 months.

Infants with hemodynamically significant congenital heart disease (CHD) (cyanotic lesions, congestive heart failure requiring inotropes/diuretics, moderate-to-severe pulmonary hypertension).

4. Maternal RSV Immunization: Abrysvo (RSVpreF)

In 2023, the FDA approved and CDC/ACIP recommended the unadjuvanted bivalent RSV prefusion F protein vaccine (Abrysvo) for pregnant individuals. +-----------------------------------------------------------------------------------------+

• | Maternal Vaccine vs Infant Monoclonal Algorithm |
• +-----------------------------------------------------------------------------------------+
• | Clinical Scenario | Infant Recommendation |
• |-------------------------------------------------------|---------------------------------|
• | Mother received Abrysvo at 32-36 weeks GA | NO nirsevimab needed. |
• | >=14 days prior to delivery | Infant protected by maternal IgG|
• | Mother received Abrysvo <14 days prior to delivery | Give nirsevimab OR clesrovimab |
• | | (Inadequate transplacental IgG) |
• | Mother immunocompromised (e.g., solid organ transplant)| Administer nirsevimab to infant |
• | Mother did NOT receive Abrysvo during pregnancy | Give nirsevimab OR clesrovimab |
• | Infant undergoes cardiopulmonary bypass or ECMO | Re-dose nirsevimab (loss in CPB)|
• +-----------------------------------------------------------------------------------------+
• Maternal Timing Rationale

Abrysvo is administered strictly between 32 weeks, 0 days and 36 weeks, 6 days of gestation using seasonal administration (September through January in most of the continental US). This window maximizes transplacental IgG transport via FcRn receptors into the fetal circulation while eliminating the theoretical risk of preterm birth observed when given earlier in gestation.

5. Pediatric Influenza Pharmacotherapy

Antiviral treatment is recommended as early as possible for any child hospitalized with suspected or confirmed influenza, children with severe, complicated, or progressive illness, or children at high risk of influenza complications (e.g., age <2 years, chronic pulmonary disorders including asthma, congenital heart disease, neurodevelopmental conditions, immunosuppression, sickle cell disease, chronic kidney disease). +-----------------------------------------------------------------------------------------+

• | Pediatric Influenza Antiviral Pharmacotherapy |
• +-----------------------------------------------------------------------------------------+
• | Drug | Mechanism & Spectrum | Approved Age & Dosing |
• |----------------------------|---------------------------------|--------------------------|
• | Oseltamivir (Tamiflu) | Neuraminidase inhibitor | Treatment: Any age |
• | (Oral suspension/capsule) | Influenza A and B | (including preterm/term) |
• | | | Dosing tiered by weight/age
• | Baloxavir marboxil | Cap-dependent endonuclease | Treatment & Prophylaxis: |
• | (Xofluza) (Oral tablet) | inhibitor (Influenza A & B) | Age >= 5 years |
• | | | Single oral dose |
• | Zanamivir (Relenza) | Neuraminidase inhibitor | Treatment: >= 7 years |
• | (Oral dry powder inhaler) | Influenza A and B | Prophylaxis: >= 5 years |
• | | | CONTRAINDICATED in asthma|
• | Peramivir (Rapivab) | Neuraminidase inhibitor | Treatment: >= 6 months |
• | (Intravenous infusion) | Influenza A and B | Single IV dose: 12 mg/kg |
• +-----------------------------------------------------------------------------------------+
• Oseltamivir Pediatric Dosing Protocol (Treatment Duration: 5 Days)

Preterm Infants (Postmenstrual age <38 weeks): 1 mg/kg/dose orally BID.

Preterm Infants (Postmenstrual age 38 to 40 weeks): 1.5 mg/kg/dose orally BID.

Term Infants 0 to 8 Months : 3 mg/kg/dose orally BID.

Term Infants 9 to 11 Months : 3.5 mg/kg/dose orally BID.

Children ≥1 Year (Weight-Tiered Dosing) :

≤15 kg : 30 mg orally BID.

>15 to 23 kg : 45 mg orally BID.

>23 to 40 kg : 60 mg orally BID.

>40 kg : 75 mg orally BID (standard adult dose).

Prophylaxis : Administer the same weight-tiered doses once daily for 7 to 10 days.

Baloxavir Marboxil (Xofluza) Clinical Nuances

Approved for treatment and post-exposure prophylaxis in children ≥5 years of age .

Weight-based single dose: 2 mg/kg for children <20 kg; 40 mg for 20 to <80 kg; 80 mg for ≥80 kg.

Drug Interaction Warning : Co-administration with polyvalent metal cations (calcium, iron, magnesium, aluminum, zinc, dairy products, antacids, sucralfate) causes severe chelation, drastically reducing baloxavir bioavailability and leading to treatment failure.

Zanamivir Inhalation Warning

Zanamivir is delivered via an oral dry-powder diskhaler. It is strictly contraindicated in children with asthma, reactive airway disease, or chronic obstructive lung conditions due to documented cases of severe, fatal bronchospasm.