ENFLONSIA CLESROVIMAB 150 mg/mL Injection, Solution, 10 syringes
🆔 Identity & classification
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🏷️ RxNorm drug class
This medicine belongs to the Antiviral monoclonal antibodies class.
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🏭 Manufacturer & labeler
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🩺 Clinical
Clesrovimab-cfor is used to prevent lung disease caused by Respiratory Syncytial Virus (RSV) infection in neonates or infants in their first RSV season (usually November through April in most parts of the United States). Clesrovimab-cfor is in a class of medications called monoclonal antibodies. It works by preventing RSV from infecting cells and causing disease.
Read the full MedlinePlus article ↗Patient education
Supplement & herbal interactions
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🧪 Inactive Ingredients / Excipients
Inactive ingredients, also called excipients, are components of the drug product other than the active ingredient. They may include fillers, dyes, coatings, preservatives, flavors, or other formulation ingredients.
💡 Tap an ingredient (hover on desktop) to see what it is and why it’s used.
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UNII F7LTH1E20Y
Arginine hydrochloride is an amino acid salt used as a buffer and pH adjuster in medicines. It helps maintain the correct acidity level to keep the drug stable and effective.
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UNII 4QD397987E
An amino acid used as a buffer and stabilizer in medications. It helps maintain the pH balance and protects the active drug from breaking down during storage and use.
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UNII X573657P6P
Histidine monohydrochloride monohydrate is an amino acid salt used as a buffer in medicines. It helps maintain the proper acidity level of liquid formulations to keep the drug stable and effective.
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UNII 6OZP39ZG8H
Polysorbate 80 is a synthetic emulsifier derived from sorbitol and oleic acid. It helps mix oil and water-based ingredients together in medications and improves how the product disperses in the body.
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UNII C151H8M554
A natural sugar derived from sugar cane or sugar beets. It's used as a sweetener, filler, and binder to improve taste, add bulk, and help hold tablet or capsule ingredients together.
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UNII 059QF0KO0R
Water is a liquid solvent that dissolves and mixes ingredients together in liquid medicines, syrups, and injections. It helps distribute the active drug evenly throughout the product.
6 inactive ingredients listed in the exact product block matched to this NDC.
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ingredient classCode="IACT" elements from the exact product block matched by this NDC. Label-section narrative from DailyMed / the openFDA label index is shown separately when available.Inactive ingredient FAQ
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💲 Pricing
A drug doesn't have one price. Each row is a different public payment system, and none is what you'd pay at the counter — that depends on your insurance. The ⓘ on each row explains what it measures.
| Price system | Per mL | Per package |
|---|---|---|
| Retail pharmacies payNADAC · weekly | Not in the retail survey — common for institutional, discontinued, or low-volume packs. | |
| Medicaid paysCMS SDUD · 12 mo | $10.00 | $70.03 / 7 ml |
| Medicare drug plans payPart D · quarterly | No Part D plan price is available for this NDC in our data. | |
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🔁 Therapeutic equivalents
| Product | Labeler | Pack | NADAC/unit | TE | Status | Price vs. this |
|---|---|---|---|---|---|---|
| Enflonsia 150 mg/mLthis 00006-5073-02 | Merck | 10 syringes | — | — | FDA listed | — |
Where does this data come from?
⏳ Availability & biosimilar status
Biologics have no small-molecule generics; biosimilar competition is tracked in the FDA Purple Book.
Why the date isn’t exact: Biosimilar timing can change because patents may be challenged, settled, licensed, added or removed, and litigation can move the real date earlier or later.
🛈 What do these terms mean?
- Biologic patent
- A patent the reference product’s maker has publicly listed. A biosimilar generally can’t launch until these expire — unless they’re invalidated or resolved in a settlement.
- Reference-product exclusivity
- A flat 12 years of FDA market protection from the biologic’s first licensure (the BPCIA). No biosimilar can be licensed before it ends, regardless of patents.
- Interchangeable exclusivity
- The first interchangeable biosimilar can earn a period as the only interchangeable version (pharmacists can substitute it without the prescriber).
- Earliest biosimilar (LOE)
- The latest of all the dates above — the soonest a biosimilar can realistically reach the market. Litigation and settlements can move it earlier.
Biologics have no small-molecule “generics” — competition comes from FDA-licensed biosimilars, tracked in the FDA Purple Book.
| Code | What it grants | Expires |
|---|---|---|
| RefProduct | Reference-product exclusivity (12-year, BPCIA) — no biosimilar can be licensed before this date | Jun 9, 2037 |
Is there a biosimilar for ENFLONSIA 105 MG/0.7 ML SYRNG?
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🗺️ Medicaid utilization & spend
💊 Medicaid utilization by pack size
🔬 Reported adverse events (FAERS)
Top reported reactions
Age at onset
Reporter sex
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📦 Packaging — all sizes for this product
| Package NDC | Description | Marketing start | Status |
|---|---|---|---|
| 00006-5073-01 | 1 SYRINGE, GLASS in 1 CARTON (0006-5073-01) / .7 mL in 1 SYRINGE, GLASS (0006-5073-99) | 2025-06-09 | Active |
| 00006-5073-02 You're viewing this | 10 SYRINGE, GLASS in 1 CARTON (0006-5073-02) / .7 mL in 1 SYRINGE, GLASS (0006-5073-99) | 2025-06-09 | Active |
In Medicaid, this is the most-dispensed pack of this product — about 82% of fills over the last four reported quarters. See all packs ↓
Pack size FAQ
What quantity is in NDC 00006-5073-02?
What is the difference between NDC 00006-5073-02 and NDC 00006-5073-01?
What NDC number is used to bill for this package of ENFLONSIA CLESROVIMAB 150 mg/mL Injection, Solution?
🧭 About this NDC listing & data coverage
What data is (and isn’t) available for this NDC — tap to expand
| NDC identity (package / product / labeler codes) | ✓ Available |
| Labeler | ✓ Available |
| Product & package description | ✓ Available |
| Marketing category & status | ✓ Available |
| Active ingredient / dosage form / route | ✓ Available |
| FDA label (SPL via DailyMed) | ✓ Available |
| Package photos | ✓ Available |
| Inactive ingredients (structured) | ✓ Available |
| NADAC pharmacy acquisition price (CMS) | — Not published for this NDC CMS publishes NADAC only for NDCs reported in its retail-pharmacy survey. |
| Orange Book / therapeutic-equivalence data | ✓ Available |
| HCPCS J-code billing crosswalk | — Not published for this NDC Most self-administered / retail products have no J-code — that is normal. |
| Medicaid utilization (CMS SDUD) | ✓ Available |
Questions about this listing
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📄 Full prescribing information FDA SPL
🎯 Indications and Usage ▾
1 INDICATIONS AND USAGE ENFLONSIA is indicated for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants who are born during or entering their first RSV season. ENFLONSIA is a respiratory syncytial virus (RSV) F protein-directed fusion inhibitor indicated for the prevention of RSV lower respiratory tract disease in neonates and infants who are born during or entering their first RSV season. ( 1 )
⏱️ Dosage and Administration ▾
2 DOSAGE AND ADMINISTRATION Recommended dosage: 105 mg administered as a single intramuscular (IM) injection. ( 2.1 )
2.1Recommended Dosage The recommended dose for neonates and infants born during or entering their first RSV season is 105 mg administered as a single intramuscular (IM) injection. For neonates and infants born during the RSV season, administer ENFLONSIA once starting from birth. For infants born outside the RSV season, administer ENFLONSIA once prior to the start of their first RSV season considering the duration of protection provided by ENFLONSIA [see Clinical Pharmacology (12.2) ].
Infants Undergoing Cardiac Surgery with Cardiopulmonary Bypass For infants undergoing cardiac surgery with cardiopulmonary bypass during or entering their first RSV season, an additional 105 mg dose administered as an IM injection is recommended as soon as the infant is stable after surgery to ensure adequate clesrovimab-cfor serum levels.
2.2Administration Instructions ENFLONSIA must be administered by a healthcare provider. Before injection, remove ENFLONSIA from the refrigerator and allow the prefilled syringe to come to room temperature for approximately 15 minutes. Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.
ENFLONSIA is a clear to slightly opalescent, colorless to slightly yellow solution. This product should not be used if particulate matter or discoloration is found. Do not use if the prefilled syringe has been dropped or damaged, the security seal on the carton has been broken, or the expiration date has passed.
Refer to Figure 1 for prefilled syringe components. Figure 1: Prefilled Syringe Components Step 1: Hold the syringe barrel in one hand and unscrew the tip cap by twisting it counter-clockwise with the other hand. Do not remove the Luer Lock adaptor and the finger flange extender.
Step 2: Attach a sterile Luer Lock needle by twisting in a clockwise direction until the needle fits securely on the syringe. Due to the viscosity of the product, use a 22- to 25-gauge needle. Step 3: Inject the entire contents of the ENFLONSIA prefilled syringe intramuscularly in the anterolateral aspect of the thigh.
ENFLONSIA should not be injected in the gluteal area or areas where there may be a major nerve trunk and/or blood vessel. Step 4: Discard syringe into a sharps container. Co-administration with Childhood Vaccines and Immunoglobulin Products ENFLONSIA can be given concomitantly with childhood vaccines [see Clinical Pharmacology (12.3) ] .
When ENFLONSIA is administered concomitantly with injectable vaccines, it should be given using a separate syringe and at a different injection site. Do not mix ENFLONSIA with any vaccines or medications in the same syringe or vial. There is no information regarding co-administration of ENFLONSIA with other immunoglobulin products.
There are no data regarding substitution of ENFLONSIA for palivizumab once prophylaxis treatment is initiated with palivizumab for the RSV season. Prefilled Syringe
💊 Dosage Forms and Strengths ▾
3 DOSAGE FORMS AND STRENGTHS Injection: 105 mg/0.7 mL clear to slightly opalescent, colorless to slightly yellow solution in a single-dose prefilled syringe. Injection: 105 mg/0.7 mL in a single-dose prefilled syringe. ( 3 )
⛔ Contraindications ▾
4 CONTRAINDICATIONS ENFLONSIA is contraindicated in infants with a history of serious hypersensitivity reactions, including anaphylaxis, to any component of ENFLONSIA [see Warnings and Precautions (5.1) and Description (11) ]. ENFLONSIA is contraindicated in infants with a history of serious hypersensitivity reactions, including anaphylaxis, to any component of ENFLONSIA. ( 4 )
⚠️ Warnings and Cautions ▾
5 WARNINGS AND PRECAUTIONS Hypersensitivity Including Anaphylaxis: Serious hypersensitivity reactions, including anaphylaxis, have been observed with other human immunoglobulin G1 (IgG1) monoclonal antibodies. Initiate appropriate medications and/or supportive care if such reactions occur. ( 5.1 )
5.1Hypersensitivity Including Anaphylaxis Serious hypersensitivity reactions, including anaphylaxis, have been observed with other human immunoglobulin G1 (IgG1) monoclonal antibodies. If signs or symptoms of a clinically significant hypersensitivity reaction or anaphylaxis occur, initiate appropriate medications and/or supportive therapy.
5.2RSV Diagnostic Test Interference Clesrovimab-cfor may interfere with some immunologically-based RSV diagnostic assays (i.e., rapid antigen tests) as observed in laboratory studies. Confirmation using a reverse transcriptase polymerase chain reaction (RT-PCR) assay is recommended when rapid antigen assay results are negative and clinical observations are consistent with RSV infection [see Drug Interactions (7.1) ].
🤒 Adverse Reactions ▾
6 ADVERSE REACTIONS Most common adverse reactions were injection-site erythema (3.8%), injection-site swelling (2.7%) and rash (2.3%). ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Merck Sharp & Dohme LLC at 1-877-888-4231 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch .
6.1Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The safety of ENFLONSIA was evaluated in 2,858 infants who received ENFLONSIA in Phase 2b/3 and Phase 3 clinical trials (Trial 004 and Trial 007). Neonates and Infants Entering Their First RSV Season (Trial 004) Trial 004 was a Phase 2b/3, randomized, double-blind placebo-controlled, multisite trial conducted in early and moderate preterm infants (≥29 to <35 weeks gestational age (GA)) and late preterm and full-term infants (≥35 weeks GA).
Participants were randomized 2:1 and received a single 105 mg dose of ENFLONSIA (N=2,412, including 422 early and moderate preterm infants) or saline placebo (N=1,202, including 209 early and moderate preterm infants) by IM injection. Participants were monitored for 30 minutes post-dose. Safety was assessed using an electronic diary device from Days 1 through 42 post-dose.
Participants were monitored for serious adverse events (SAEs) through the duration of their participation for up to 365 days post-dose. A subset of participants was monitored for SAEs for up to 515 days post-dose. Table 1 summarizes the adverse reactions in participants who received ENFLONSIA.
Most (≥97%) of the adverse reactions were toxicity grade 1 (mild) or grade 2 (moderate). Table 1: Adverse Reactions Reported at an Incidence Higher Than Placebo (Trial 004) Adverse Reaction ENFLONSIA N=2,412 Sample size reflects the number of participants included in the safety analysis population. % Placebo N=1,202 % Injection-site erythema Solicited on Day 1 through Day 5 post-dose using an electronic diary device. (occurring within 5 days post-dose) 3.8
3.3Injection-site swelling (occurring within 5 days post-dose) 2.7
2.6Rash Defined by the following grouped preferred terms: rash, rash erythematous, rash macular, rash papular, rash maculo-papular, rash vesicular, rash exfoliative, dermatitis allergic, drug eruption and toxic skin eruption. (occurring within 14 days post-dose) 2.3
1.9Infants Born at ≤35 Weeks Gestational Age and Infants with Chronic Lung Disease (CLD) of Prematurity or Hemodynamically Significant Congenital Heart Disease (CHD) Entering Their First RSV Season (Trial 007) Trial 007 was a Phase 3, randomized, partially-blind, palivizumab-controlled, multisite trial conducted in infants at increased risk of severe RSV disease. Participants were randomized and received a single 105 mg dose of ENFLONSIA (N=446) followed by a dose of placebo one month later or 3 to 5 monthly doses of 15 mg/kg palivizumab (N=450) by IM injection.
Of the 446 participants who received ENFLONSIA, 176 had CLD of prematurity or CHD and 270 were early or moderate preterm infants (≤35 weeks GA) without CLD of prematurity or CHD. Participants were monitored for 30 minutes post-dose. Safety was assessed using an electronic diary device from Day 1 (dose 1) through 14 days post-dose 2, and 14 days after each subsequent dose.
Participants were monitored for serious adverse events in the first RSV season for up to 365 days. The safety profile of ENFLONSIA in infants at increased risk of severe RSV disease entering their first season was similar to palivizumab and consistent with the safety profile of ENFLONSIA in infants in Trial 004.
🔄 Drug Interactions ▾
7 DRUG INTERACTIONS
7.1Interference with Rapid Antigen Detection RSV Diagnostic Assays Clesrovimab-cfor may interfere with some immunologically-based RSV diagnostic assays (i.e., rapid antigen tests) as observed in laboratory studies. Confirmation using an RT-PCR assay is recommended when rapid antigen RSV diagnostic assay results are negative and clinical observations are consistent with RSV infection. Clesrovimab-cfor does not interfere with RT-PCR diagnostic assays [see Warnings and Precautions (5.2) ] .
👥 Use in Specific Populations ▾
8 USE IN SPECIFIC POPULATIONS The safety and effectiveness of ENFLONSIA have not been established in children older than 12 months of age. ( 8.4 )
8.1Pregnancy ENFLONSIA is not indicated for use in females of reproductive potential.
8.2Lactation ENFLONSIA is not indicated for use in females of reproductive potential.
8.4Pediatric Use The safety and effectiveness of ENFLONSIA have been established for the prevention of RSV lower respiratory tract disease in neonates and infants born during or entering their first RSV season and the information on this use is discussed throughout the labeling. The safety and effectiveness of ENFLONSIA have not been established in children older than 12 months of age.
🤰 Pregnancy ▾
8.1Pregnancy ENFLONSIA is not indicated for use in females of reproductive potential.
🧒 Pediatric Use ▾
8.4Pediatric Use The safety and effectiveness of ENFLONSIA have been established for the prevention of RSV lower respiratory tract disease in neonates and infants born during or entering their first RSV season and the information on this use is discussed throughout the labeling. The safety and effectiveness of ENFLONSIA have not been established in children older than 12 months of age.
🆘 Overdosage ▾
10 OVERDOSAGE There is limited experience of overdose with ENFLONSIA. There is no specific treatment for an overdose with ENFLONSIA. In the event of an overdose, the infant should be monitored for the occurrence of adverse reactions and provided with symptomatic treatment as appropriate.
🧬 Clinical Pharmacology ▾
12 CLINICAL PHARMACOLOGY
12.1Mechanism of Action ENFLONSIA is a monoclonal antibody with anti-RSV activity [see Microbiology (12.4) ].
12.2Pharmacodynamics RSV serum neutralizing antibody titer correlates with clesrovimab-cfor serum concentration. Following IM administration of clesrovimab-cfor in infants, the RSV neutralizing antibody titers in serum were estimated to be approximately 7 times higher than baseline at 4 hours after clesrovimab-cfor dosing and maximum titers were reached by day 7, for a typical infant weighing 5 kg. Exposure-Response Relationship In the Phase 2b/3 trial evaluating the recommended dose of clesrovimab-cfor (a single dose of 105 mg) in healthy preterm and full-term infants (Trial 004), no significant relationship was observed between AUC (from day 1 to day 150) and clinical outcomes (e.g., RSV-associated Medically Attended Lower Respiratory Infection (MALRI)).
Duration of Protection Based on clinical trial data, the duration of protection demonstrated by a single dose of ENFLONSIA extends through 5 months [see Clinical Studies (14.2) ].
12.3Pharmacokinetics The PK of clesrovimab-cfor is approximately dose-proportional following a single IM administration of doses ranging from 20 mg to 210 mg in infants. Following IM administration of the 105 mg recommended dose, the geometric mean (% geometric CV) area under the time concentration curve from day 1 to day 150 (AUC 0-150 ) is 6,470 mcg×d/mL (22.6%), peak concentration (C max ) is 120 mcg/mL (25.4%), and the concentration at day 150 (C 150 ) is 10.3 mcg/mL (36.6%). In the first RSV season, the clesrovimab-cfor serum exposures were similar in neonates and infants in Trial 004, in preterm neonates and infants born at less than or equal to 35 weeks GA (including less than 29 weeks GA) in Trial 007, and in neonates and infants with CLD or CHD in Trial 007.
Absorption The median time to maximum concentration is 6.5 days (5.9, 7.4 which are the 2.5 and 97.5 percentiles, respectively). Distribution The estimated apparent volume of distribution for clesrovimab-cfor is 830 mL, for a typical infant weighing 5 kg. Elimination The clesrovimab-cfor terminal half-life is approximately 44.0 days and the estimated apparent clearance is 19.7 mL/day for a typical infant weighing 5 kg.
Metabolism Clesrovimab-cfor is degraded into small peptides by catabolic pathways. Specific Populations No clinically significant differences in the pharmacokinetics of clesrovimab-cfor were observed based on race or vulnerability to severe RSV disease (i.e., CLD, CHD, or GA <29 weeks). An effect of renal or hepatic impairment on clesrovimab-cfor pharmacokinetics is not expected.
Drug Interaction Studies Since clesrovimab-cfor is eliminated by catabolism, no metabolic drug-drug interactions are expected. However, no formal drug interaction studies have been performed with ENFLONSIA. Clinical Studies Vaccines : In clinical trials, when ENFLONSIA was given concomitantly with routine childhood vaccines, the safety profile of the co-administered regimen was generally comparable to the safety profile when ENFLONSIA and childhood vaccines were administered alone.
12.4Microbiology Mechanism of Action Clesrovimab-cfor is a recombinant human immunoglobulin G1 kappa (IgG1κ) neutralizing monoclonal antibody with a YTE triple amino acid substitution (M252Y/S254T/T256E) in the Fc region which increases binding to the neonatal Fc receptor leading to an extended serum half-life. Passive immunity is provided by clesrovimab-cfor, which targets the extracellular domain of the RSV fusion (F) protein to prevent fusion of the viral and cellular membranes and viral entry. Clesrovimab-cfor binds to a conserved epitope on antigenic site IV on the F protein and binds to RSV A pre-fusion F glycoprotein and post-fusion F glycoprotein with equilibrium dissociation constant values (K D ) of 71 pM and 480 pM, respectively.
Antiviral Activity A neutralization assay in Hep-2 cells was used to determine clesrovimab-c…
🧬 Mechanism of Action ▾
12.1Mechanism of Action ENFLONSIA is a monoclonal antibody with anti-RSV activity [see Microbiology (12.4) ].
📦 How Supplied / Storage and Handling ▾
16 HOW SUPPLIED/STORAGE AND HANDLING How Supplied ENFLONSIA injection is a sterile, preservative-free, clear to slightly opalescent, colorless to slightly yellow solution supplied as follows: Carton containing one or ten single-dose prefilled type I glass syringe(s) with Luer Lock and plunger stopper. The prefilled syringe is not made with natural rubber latex. Prefilled syringe Pack Size NDC 105 mg/0.7 mL single-dose Carton of 1 0006-5073-01 105 mg/0.7 mL single-dose Carton of 10 0006-5073-02 Storage and Handling Store prefilled syringes under refrigeration at 36°F to 46°F (2°C to 8°C).
Keep the prefilled syringe in the original carton to protect from light until time of use. ENFLONSIA may be kept at room temperature between 68°F to 77°F (20°C to 25°C) for a maximum of 48 hours. After removal from the refrigerator, ENFLONSIA must be used within 48 hours or discarded.
Do not freeze. Do not shake.
📦 Storage and Handling ▾
Storage and Handling Store prefilled syringes under refrigeration at 36°F to 46°F (2°C to 8°C). Keep the prefilled syringe in the original carton to protect from light until time of use. ENFLONSIA may be kept at room temperature between 68°F to 77°F (20°C to 25°C) for a maximum of 48 hours. After removal from the refrigerator, ENFLONSIA must be used within 48 hours or discarded. Do not freeze. Do not shake.
📋 Description ▾
11 DESCRIPTION Clesrovimab-cfor is a respiratory syncytial virus F protein-directed fusion inhibitor. Clesrovimab-cfor is a fully human immunoglobulin G1 kappa (IgG1κ) monoclonal antibody produced in recombinant Chinese hamster ovary (CHO) cells. The molecular weight is approximately 149 kDa.
ENFLONSIA (clesrovimab-cfor) injection is a sterile, preservative-free, clear to slightly opalescent, colorless to slightly yellow solution for intramuscular injection. Each 0.7 mL contains 105 mg of clesrovimab-cfor, arginine hydrochloride (10.33 mg), histidine (0.55 mg), L-histidine monohydrochloride monohydrate (0.74 mg), polysorbate 80 (0.14 mg), sucrose (35 mg) and water for injection (USP). The pH is 6.0.
💬 Information for Patients ▾
17 PATIENT COUNSELING INFORMATION Advise the child’s caregiver to read the FDA-approved patient labeling ( Patient Information ). Hypersensitivity Reactions Including Anaphylaxis Inform the patient’s caregiver of the signs and symptoms of potential hypersensitivity reactions, and advise the caregiver to seek medical attention immediately if the infant experiences a hypersensitivity reaction to ENFLONSIA [see Warnings and Precautions (5.1) ]. Dosage and Administration Advise the caregiver that the infant will receive ENFLONSIA by IM injection by a healthcare provider [see Dosage and Administration (2.1) ].