Pharmacy Guide
Patient leaflets and SmPCs, drug interaction checker, official dosages and NHS pharmacy opening hours — all in one place.
Pharmacy Guide
Patient leaflets and SmPCs, drug interaction checker, official dosages and NHS pharmacy opening hours — all in one place.
ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe
⚠ This medicine appears to have been discontinued
The electronic medicines compendium (emc) no longer publishes a Summary of Product Characteristics for this product, which usually means it is no longer marketed in the UK. The patient leaflet below is kept for reference, but the product may not be available.
If you were prescribed this medicine, other products containing Clesrovimab may still be available. Do not stop your treatment — ask your pharmacist or GP what to use instead.
What it is and what it is used for
for
ENFLONSIA contains the active substance clesrovimab. This is an antibody (a protein that the body uses to fight harmful germs) that helps prevent lung disease caused by respiratory syncytial virus (RSV) disease. It is given to newborns and babies up to 12 months of age who are born during or entering their first RSV season. RSV season is the time of year when RSV infections are most common, usually occurring autumn through spring of the next year. RSV is a common respiratory virus that usually causes symptoms similar to the common cold but can also affect the lungs. Signs of RSV infection may include a runny nose, trouble feeding, difficulty breathing, coughing, sneezing, wheezing (whistling sound during breathing) or fever. Anyone can become infected by RSV. Almost all children get an RSV infection by the time they are 2 years old. While most recover quickly, RSV can cause severe illness including inflammation of the small airways in the lung (bronchiolitis) and infection of the lungs (pneumonia) that may lead to hospitalisation and even death. Children at greatest risk include newborns and babies up to 12 months of age, especially those 6 months and younger, or with medical vulnerabilities, for example being born too soon or with heart or lung problems.
2.
What you need to know before your child is given ENFLONSIA
Do not give ENFLONSIA Your child must not be given ENFLONSIA if they are allergic to clesrovimab or any of the other ingredients of this medicine (listed in section 6).
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Tell your child's doctor, pharmacist or nurse about any medical conditions or allergies your child has or had.
Warnings and precautions Serious allergic reactions may happen with ENFLONSIA. Tell your child's doctor or seek medical care right away if your child has any of the following signs and symptoms of a serious allergic reaction, which may include:
• • •
swelling of the face, mouth, or tongue
•
blue tint to the colour of skin, lips or under fingernails
• •
muscle weakness
difficulty swallowing or breathing unresponsiveness
severe rash, hives or itching
Talk to your child's healthcare professional before your child is given ENFLONSIA if they have any bleeding problems, bruises easily, or are taking medicines to prevent blood clots.
Children and adolescents Do not give this medicine to children between the age of 1 and 18 years of age. This is because it has not yet been studied in this group. Other medicines and ENFLONSIA
Tell your child's doctor or pharmacist if your child is taking, has recently taken or might take any other medicines. ENFLONSIA may be given at the same time as vaccines that are part of the national immunisation programme.
ENFLONSIA contains polysorbate 80 This medicine contains 0.14 mg of polysorbate 80 per dose. Polysorbates may cause allergic reactions. Tell your doctor if your child has any known allergies.
3.
How to take it
ENFLONSIA is given by a healthcare professional as an injection in the muscle. It is usually given in the thigh. The recommended dose is 105 mg given as a single injection. This is given before the start of or during the RSV season.
Your child's healthcare professional can tell you when the RSV season starts in your area. If your child is scheduled to have surgery for certain types of heart disease, your child's healthcare professional may need to give your child an additional injection of ENFLONSIA after surgery.
Your child may still get RSV disease after receiving this medicine. Talk to your child's healthcare professional about what signs to look for.
If you have any further questions on the use of this medicine, ask your child's doctor, pharmacist or nurse.
4.
Possible side effects
Like all medicines, this medicine can cause side effects, although not everybody gets them. Tell your child's doctor, pharmacist or nurse if your child has any of the following side effects: 2
Common (may affect up to 1 in 10 children)
• •
pain, redness (erythema), or swelling where your child got the injection rash
Uncommon (may affect up to 1 in 100 children)
•
red, itchy swollen bumps on the skin; also called hives
Reporting of side effects
If your child gets any side effects, talk to your child's doctor, pharmacist or nurse. This includes any
Possible side effects
not listed in this leaflet. You can also report side effects directly via the Yellow Card Scheme at www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store. By reporting side effects, you can help provide more information on the safety of this medicine.
5.
How to store it
ENFLONSIA
Your child's doctor, pharmacist or nurse is responsible for storing this medicine and disposing of any unused product correctly. The following information is intended for healthcare professionals. Keep this medicine out of reach of children. Do not use this medicine after the expiry date which is stated on the carton after EXP. The expiry date refers to the last day of that month. Store in a refrigerator (2 °C – 8 °C). Do not freeze. After removal from the refrigerator, the medicine must be used within 48 hours or discarded. Keep the pre-filled syringe in the outer carton in order to protect from light. Do not shake. Any unused medicine or waste material should be disposed of in accordance with local requirements.
6.
Contents of the pack and other information
What ENFLONSIA contains The active substance is clesrovimab. One pre-filled syringe of 0.7 mL contains 105 mg of clesrovimab. The other ingredients are histidine, histidine hydrochloride monohydrate, arginine hydrochloride, sucrose, polysorbate 80 (E433) (see section 2 "ENFLONSIA contains polysorbate 80") and water for injections. What ENFLONSIA looks like and contents of the pack ENFLONSIA is a clear to slightly opalescent, colourless to slightly yellow solution for injection. ENFLONSIA is available in the following pack sizes:
• • • • • • •
1 pre-filled syringe 1 pre-filled syringe + 1 needle 1 pre-filled syringe + 2 needles 10 pre-filled syringes 10 pre-filled syringes + 10 needles 10 pre-filled syringes + 20 needles Multipacks comprising 5 cartons, each containing 10 pre-filled syringes.
3
Not all pack sizes may be marketed.
Marketing Authorisation Holder and Manufacturer Marketing Authorisation Holder: Merck Sharp & Dohme (UK) Limited, 120 Moorgate, London, EC2M 6UR, United Kingdom Manufacturer: Merck Sharp & Dohme B.V., Waarderweg 39, 2031 BN Haarlem, The Netherlands For any information about this medicine, please contact: Merck Sharp & Dohme (UK) Limited Tel: +44 (0) 208 154 8000 [email protected]
This leaflet was last revised in March 2026 © 2026 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved. New MAA ————————————————————————————————————————
The following information is intended for healthcare professionals only:
•
Before injection, remove the carton from the refrigerator and allow the pre-filled syringe to come to room temperature for approximately 15 minutes.
•
Visually inspect the medicinal product for particulate matter and discolouration. The medicinal product is a clear to slightly opalescent, colourless to slightly yellow solution. It should not be used if particulate matter or discolouration is found.
•
Do not use ENFLONSIA if the pre-filled syringe has been dropped or damaged, the security seal on the carton has been broken, or the expiry date has passed.
•
Hold the syringe barrel in one hand to unscrew the tip cap by twisting it counter-clockwise with the other hand. Do not remove the Luer lock adaptor or the finger flange extender.
•
Attach a sterile Luer lock needle by twisting in a clockwise direction until the needle fits securely on the pre-filled syringe. If not provided, due to the viscosity of the medicinal product, use a 25 gauge or larger needle. Inject the entire contents of the pre-filled syringe intramuscularly in the anterolateral aspect of the
•
thigh. The medicinal product should not be injected in the gluteal area or areas where there may be a major nerve trunk and/or blood vessel. Any unused medicine or waste material should be disposed of in accordance with local requirements. In order to improve the traceability of biological medicinal products, the name and the batch number of the administered product should be clearly recorded. © 2026 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved. New MAA
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Frequently asked questions about ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe
How do I take ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe?
ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe comes as injection containing 105mg / 0.7ml. Always follow the dose your doctor or pharmacist has given you, and read the leaflet that comes with the medicine.
What is the active substance in ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe?
The active substance in ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe is clesrovimab.
Where does this information come from?
This leaflet reproduces the patient information leaflet approved for ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe, as published on the electronic medicines compendium (emc). The version printed inside your medicine’s packaging is the one that applies to you.
Can I get ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe without a prescription?
Whether a medicine is available over the counter or on prescription only depends on its licence. Check the leaflet, or ask your pharmacist — they can tell you straight away.
About this leaflet
The text above reproduces the patient information leaflet approved for this medicine, restructured for easier reading.
- Source: electronic medicines compendium (emc), Datapharm
- Active substance: clesrovimab
- Official document: view the original leaflet on emc →
⚕For healthcare professionals — Summary of Product Characteristics (SmPC)Full SmPC: dosage, interactions, contraindications, warnings+
4.1. Therapeutic indications
ENFLONSIA is indicated for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants during their first RSV season.
ENFLONSIA should be used in accordance with official recommendations.
4.2. Posology and method of administration
Posology
Neonates and infants: first RSV season
The recommended dose is 105 mg administered as a single 0.7 mL intramuscular (IM) injection.
For neonates and infants born during the RSV season, ENFLONSIA should be administered starting from birth. For infants born outside the RSV season, it should be administered once prior to the start of their first RSV season (see section 5.1).
Dosing in infants with a body weight between 0.5 kg and 1.1 kg is based on extrapolation; no clinical data are available. Exposure in infants < 1.1 kg is anticipated to yield higher exposures than in those weighing more. The benefits and risks of clesrovimab in infants < 1.1 kg should be carefully considered.
There are limited clinical data available in extremely preterm infants (gestational age (GA) < 29 weeks) who are of chronological age less than 8 weeks. No clinical data are available in infants with a postmenstrual age (GA plus chronological age) of less than 32 weeks (see section 5.1).
Infants undergoing cardiac surgery with cardiopulmonary bypass
For infants undergoing cardiac surgery with cardiopulmonary bypass during the RSV season, an additional 105 mg dose is recommended as soon as the infant is stable after surgery to ensure adequate clesrovimab serum levels.
Children from 1 to 18 years of age
The safety and efficacy of clesrovimab in children aged 1 to 18 years have not yet been established. No data are available.
Method of administration
ENFLONSIA is for intramuscular use only.
The medicinal product should be administered intramuscularly by a healthcare professional, in the anterolateral aspect of the thigh. It should not be injected in the gluteal area or areas where there may be a major nerve trunk and/or blood vessel.
For instructions on handling of the medicinal product before administration, see section 6.6.
4.3. Contraindications
Hypersensitivity to the active substance or to any of the excipients listed in section 6.1.
4.4. Special warnings and precautions for use
Traceability
In order to improve the traceability of biological medicinal products, the name and the batch number of the administered product should be clearly recorded.
Hypersensitivity including anaphylaxis
If signs and symptoms of a clinically significant hypersensitivity reaction or anaphylaxis occur, appropriate treatment and/or supportive therapy should be initiated.
Individuals with thrombocytopenia and coagulation disorders
As with any other intramuscular injections, clesrovimab should be given with caution to infants with thrombocytopenia or any coagulation disorder, because bleeding or bruising may occur following an intramuscular administration in these individuals.
Excipients with known effect
This medicinal product contains 0.14 mg of polysorbate 80 per dose. Polysorbates may cause allergic reactions.
4.5. Interaction with other medicinal products and other forms of interaction
No interaction studies have been performed. Monoclonal antibodies do not typically have significant interaction potential, as they do not directly affect cytochrome P450 enzymes and are not substrates of hepatic or renal transporters. Indirect effects on cytochrome P450 enzymes are unlikely as the target of clesrovimab is an exogenous virus.
Clesrovimab does not interfere with reverse transcriptase polymerase chain reaction (RT-PCR) or rapid antigen detection RSV diagnostic assays that employ commercially available antibodies targeting antigenic site 0, I, II, III, or V on the RSV fusion (F) protein. For rapid antigen detection RSV diagnostic assay results which are negative when clinical observations are consistent with RSV infection, it is recommended to confirm using an RT-PCR-based assay.
Concomitant administration with childhood vaccines
Since clesrovimab is a monoclonal antibody, a passive immunisation specific for RSV, it is not expected to interfere with the active immune response to co-administered vaccines.
There is limited experience of co-administration with vaccines. In clinical studies, when clesrovimab was given concomitantly with routine childhood vaccines, the safety profile of the co‑administered regimen was similar to the safety profile when clesrovimab and childhood vaccines were administered alone. Clesrovimab can be given concomitantly with childhood vaccines.
When clesrovimab is administered concomitantly with injectable vaccines, it should be given using a separate syringe and at a different injection‑site. It should not be mixed with any vaccines or medications in the same syringe or vial (see section 6.2).
There are no data regarding substitution of clesrovimab for palivizumab once prophylaxis treatment is initiated with palivizumab for the RSV season.
4.6. Fertility, pregnancy and lactation
Not relevant.
4.7. Effects on ability to drive and use machines
Not relevant.
4.8. Undesirable effects
Summary of the safety profile
The most frequent adverse reactions were injection-site pain (6.5%), injection‑site erythema (4.4%), injection‑site swelling (3.2%) and rash (2.3%). Most (> 96%) of the adverse reactions were mild or moderate.
Tabulated list of adverse reactions
Safety was evaluated in 2 854 infants who received clesrovimab in phase 2b/3 and phase 3 clinical studies (Study 004 and Study 007, respectively) (see section 5.1).
Table 1 presents the adverse reactions reported in 2 409 preterm and full‑term infants (GA ≥ 29 weeks) who received clesrovimab.
Adverse reactions reported with clesrovimab are listed by MedDRA system organ class and in decreasing order of frequency. Frequencies are defined as very common (≥ 1/10), common (≥ 1/100 to < 1/10), uncommon (≥ 1/1 000 to < 1/100), rare (≥ 1/10 000 to < 1/1 000), and very rare (< 1/10 000) and not known (cannot be estimated from available data).
Table 1: Adverse reactions
System organ class
Adverse reaction
Frequency
Skin and subcutaneous tissue disorders
Rash*
Common
Urticaria
Uncommon
General disorders and administration site conditions
Injection-site pain†
Common
Injection-site erythema†
Common
Injection‑site swelling†
Common
*Rash was defined by the following grouped preferred terms occurring within 14 days post‑dose: rash, rash erythematous, rash papular, rash maculo‑papular, rash vesicular, dermatitis allergic, and drug eruption
†Solicited on Day 1 through Day 5 post‑dose
The safety profile of clesrovimab in 445 infants at increased risk of severe RSV disease entering their first season (Study 007, see section 5.1) was similar to palivizumab (450 infants) and consistent with the safety profile of clesrovimab in infants in Study 004.
Serious adverse events reported in early preterm infants GA < 29 weeks were similar in number and pattern between recipients of clesrovimab (21/97 participants) and palivizumab (31/108 participants).
Subgroup analyses by age groups at randomisation (< 3 months; ≥ 3 to ≤ 6 months and > 6 months) in Study 004 and Study 007 showed similar safety results in the clesrovimab and control arms (see section 5.1) across the age-groups in each study.
Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.
4.9. Overdose
There is no specific treatment for an overdose with clesrovimab. In the event of an overdose, the individual should be monitored for the occurrence of adverse reactions and provided with symptomatic treatment as appropriate.
🇷🇴 Known in Romania as
Medicines sold in Romania with the same active substance: Cunoscut în România ca
- ENFLONSIA 105 mg prescriptionCLESROVIMABUM · injection / infusion
Same active substance. The strength, the form and whether you need a prescription can differ. Always ask a pharmacist before you switch. Romanian medicines in the UK →
🇵🇱 Known in Poland as
Medicines sold in Poland with the same active substance: W Polsce znany jako
- EnflonsiaClesrovimab · injection / infusion
Same active substance. The strength, the form and whether you need a prescription can differ. Always ask a pharmacist before you switch. Polish medicines in the UK →
💬 Ask about this leaflet
Ask anything about ENFLONSIA 105 mg/0.7 ml Solution for injection in pre-filled syringe. The assistant answers only from this leaflet — if the leaflet does not cover it, it will say so. It does not give medical advice.
Answers come from the patient leaflet published on the electronic medicines compendium (emc). They are not medical advice. Ask a pharmacist or your GP if you are unsure. For urgent help call NHS 111, or 999 in an emergency.