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SERYNOX 50%/50% MEDICINAL COMPRESSED GAS

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About the medicine

How to use SERYNOX 50%/50% MEDICINAL COMPRESSED GAS

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This page provides general information and does not replace a doctor’s consultation. Always consult a doctor before taking any medication. Seek urgent medical care if symptoms are severe.

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Introduction

Package Leaflet: Information for the User

Serynox 50% / 50% Compressed Medical Gas

Nitrous oxide/oxygen

Read all of this leaflet carefully before you start using this medicine because it contains important information for you.

  • Keep this leaflet, you may need to read it again.
  • If you have any further questions, ask your doctor, pharmacist, or nurse.
  • If you experience any side effects, talk to your doctor, pharmacist, or nurse, even if they are not listed in this leaflet. See section 4.

Contents of the Package Leaflet

  1. What is Serynox and what is it used for
  2. What you need to know before you start using Serynox
  3. How to use Serynox
  4. Possible side effects
    1. Storage of Serynox
  1. Contents of the pack and further information

1. What is Serynox and what is it used for

Serynox contains a mixture of two medicinal gases:

  • Nitrous oxide at 50% (‘laughing gas’ medicinal),
  • Oxygen at 50% (medical oxygen).

It is used by inhaling the gas mixture. At this concentration, Serynox does not have a narcotic (anesthetic) effect.

Serynox belongs to the group of nitrous oxide combinations.

Serynox can be used in adults, adolescents, and children over 1 month of age.

Serynox works by reducing the sensation of pain and increasing patient relaxation during:

  • short-term analgesia for procedures or situations with mild to moderate pain intensity and sedation during dental surgery, when rapid onset and offset of analgesia are required.
Doctor consultation

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2. What you need to know before you start using Serynox

Do not use Serynox

  • if you have had a gas injected into your eye during eye surgery, inform your doctor so that they can ensure that administration does not cause serious postoperative complications due to increased intraocular pressure;
  • if your condition requires the administration of 100% oxygen;
  • in case of excessive pressure in the head (intracranial hypertension);
  • in case of altered consciousness (consciousness is not completely normal);
  • in case of known, untreated vitamin B12 or folic acid deficiency;
  • in case of neurological disorders of unknown cause that have occurred recently;
  • in patients with heart failure or cardiac dysfunction (e.g., after cardiac surgery).

When inhaling Serynox, gas bubbles and air-filled cavities can expand in the body and cause serious damage. Therefore, Serynox should not be used in case of:

  • head trauma
  • facial or jaw trauma
  • air accumulation between the lungs and the chest cavity (pneumothorax)
  • severe lung disease that causes breathing problems (severe emphysema)
  • formation of air bubbles in the bloodstream (gas embolism)
  • deep diving with risk of decompression syndrome
  • brain radiography
  • surgery on the middle or inner ear or paranasal sinuses
  • presence of air in the abdomen that causes severe abdominal discomfort
  • having received spinal anesthesia to eliminate pain from the hips down (epidural anesthesia) during which air was injected

Warnings and precautions

Talk to your doctor before you start using Serynox.

Serynox should be administered by trained personnel. However, self-administration under medical supervision is preferred to assess the patient's level of consciousness. NEVER manipulate the Serynox cylinder.

Areas where Serynox is used should be well-ventilated and/or equipped with extraction equipment to keep the concentration of nitrous oxide in the ambient air as low as possible.

You should breathe normally when inhaling Serynox.

Use in neonates is not recommended.

Monitor for possible adverse effects in newborns, especially respiratory depression, when Serynox is administered to the mother during labor.

Prolonged or repeated administration of Serynox can lead to abuse and dependence.

With repeated or prolonged administration of Serynox, vitamin B12 may lose its effectiveness in the body. Your doctor may need to prescribe vitamin B12 for you.

Talk to your doctor in the following situations, as there is a risk of vitamin B12 deficiency:

  • if you have anemia, a specific type of stomach inflammation (atrophic gastritis), or a brain disease;
  • if you are a vegetarian;
  • if you are an alcoholic.

If you or your children have an acute ear infection, inform your doctor.

Using Serynox with other medicines

Tell your doctor or pharmacist if you are using, have recently used, or might use any other medicines.

Inform your doctor if:

  • you have received a gas injection into your eye during eye surgery, as there is a risk of postoperative complications if the pressure inside the eye increases too much;
  • you are taking medicines that act on the central nervous system (such as morphine derivatives, benzodiazepines, and other psychotropic medicines), as they may increase the hypnotic effects;
  • you are taking vitamin B12/folic acid, as vitamin B12 may lose its effectiveness due to Serynox.

Serynox may enhance the toxicity of methotrexate by interfering with folate metabolism.

Pulmonary toxicity associated with active ingredients such as bleomycin, amiodarone, nitrofurantoin, and similar antibiotics may be exacerbated by inhalation of high concentrations of oxygen.

Pregnancy, breastfeeding, and fertility

If you are pregnant or breastfeeding, think you may be pregnant, or plan to become pregnant, consult your doctor or pharmacist before using this medicine.

Serynox can be used during pregnancy when clinically indicated.

If used near the time of delivery, monitor for possible adverse reactions in the baby.

After short-term use of Serynox, it is not necessary to interrupt breastfeeding.

Driving and using machines

Serynox affects perception and behavior related to movement (cognitive and psychomotor functions).

After administration of Serynox, you will be monitored until all effects have disappeared and you have regained the same level of alertness as before administration. After administration of nitrous oxide, it is not recommended to drive or use machines or perform other activities that require psychomotor functions for a reasonable period after exposure.

3. How to use Serynox

Dosage

Serynox should only be administered by personnel familiar with this type of medicine. Your doctor will explain how to use Serynox, how it works, and what effects its use produces. For certain procedures, you will be asked to hold the gas administration equipment. This will allow you to dose the gas yourself.

During the entire time you use Serynox, you and the administration of the medicine will be monitored to confirm that it is administered safely.

Administration of Serynox should be stopped if verbal contact is interrupted.

The maximum analgesic effect is achieved after at least 3 minutes.

Method of administration

Serynox is administered by inhalation.

Serynox is a mixture of two medicinal gases that you will inhale and will be administered through a mask placed on your face by means of a suitable device.

During inhalation of Serynox, you should breathe normally.

When you stop using Serynox, the mask will be removed, and you should rest and recover until you feel you have mentally recovered.

Duration of use

The use of Serynox depends on the duration of the procedure and should not normally exceed 60 minutes of inhalation per day. Repeated administration of Serynox should not exceed 15 days.

If you use more Serynox than you should

It is very unlikely that you will receive too much gas, as you can control the amount of gas you inhale through the mask and are closely monitored.

If you breathe more rapidly than normal and therefore receive more nitrous oxide than you would normally receive by breathing normally, you may feel noticeably tired and somewhat disconnected from your surroundings.

In such circumstances, you should immediately inform the medical staff and interrupt administration.

If your skin turns blue (cyanosis) during the use of Serynox, the medical staff will immediately interrupt treatment. If the cyanosis does not decrease rapidly, you will be ventilated with air using a manual ventilation balloon or with oxygen.

In case of overdose or accidental ingestion, consult your doctor or pharmacist immediately or call the Toxicology Information Service, phone: 91 562 04 20, indicating the medicine and the amount ingested.

If you stop using Serynox

The analgesic effect disappears immediately after the end of Serynox administration without irreversible effects.

If you have any further questions about the use of this medicine, ask your doctor or pharmacist.

Medicine questions

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Discuss your symptoms and treatment with a doctor online.

4. Possible side effects

Like all medicines, this medicine can cause side effects, although not everybody gets them.

The following side effects may occur during treatment and usually disappear a few minutes after the end of inhalation of the mixture:

Common: may affect up to 1 in 10 people

  • dizziness
  • drowsiness
  • nausea
  • vomiting

Uncommon: may affect up to 1 in 100 people

  • tingling (paresthesia)
  • deep sedation (somnolence)
  • hallucinations
  • anxiety
  • agitation
  • euphoria
  • dreams

Frequency not known: cannot be estimated from the available data

  • headache
  • seizure
  • increased intracranial pressure (see section 2, Do not use Serynox)
  • ear pain
  • psychosis
  • confusion
  • disorientation
  • respiratory depression (in newborns during labor)
  • severe visual impairment (caused by the expansion of intraocular gas, see section 2, Do not use Serynox)

After prolonged and repeated use of Serynox

Frequency not known: cannot be estimated from the available data

After increased breathing during inhalation (hyperventilation), abnormal movements may occur.

Neurological disorders such as spinal cord diseases (myeloneuropathies).

Decrease in the number of red blood cells, accompanied by a decrease in the number of white blood cells (megaloblastic anemia with leukopenia).

Abuse and dependence.

Vitamin B12 deficiency (see section 2, Do not use Serynox, Warnings and precautions, and Using Serynox with other medicines).

Reporting of side effects

If you experience any side effects, talk to your doctor, pharmacist, or nurse, even if they are not listed in this leaflet. You can also report side effects directly through the Spanish Medicines Monitoring System: www.notificaRAM.es. By reporting side effects, you can help provide more information on the safety of this medicine.

5. Storage of Serynox

Keep this medicine out of the sight and reach of children.

Do not use this medicine after the expiry date which is stated on the gas cylinder after CAD.

Storage of gas cylinders

Store gas cylinders as follows:

Gas cylinders must be stored securely in an UPRIGHT POSITION (full cylinders in the gas storage area, full cylinders in use, full cylinders for transport within healthcare facilities and vehicles, storage of empty cylinders).

This medicine does not require any special storage conditions at a certain temperature.

Different types of medicinal gases must be stored separately. Full and empty gas cylinders must be stored separately.

Storage of full cylinders in a gas cylinder storage area

Full cylinders must be stored in an UPRIGHT POSITION in a clean, well-ventilated area where there is no combustible material and which is protected from the weather. This room must be reserved for the storage of medicinal gases and locked.

Full and empty cylinders must be stored separately.

Full cylinders must be protected from impacts and falls and kept away from heat sources and ignition sources and flammable substances. They must also be protected from the weather and, in particular, from cold. Once delivered by the manufacturer, the cylinders must have an intact safety seal.

Transport of full cylinders

In healthcare facilities, full cylinders must be securely stored in an UPRIGHT POSITION using suitable means (trolleys with chains, hoops, or bars) for transport to protect them from impacts and falls. During transport in vehicles, full cylinders must be securely stored in an UPRIGHT POSITION. Emergency services must be warned that the cylinders must be protected from cold both in vehicles and during use outdoors. In the case of cylinders with residual pressure valves, special attention must be paid to the connection of the pressure regulator to avoid accidental damage.

Storage of empty cylinders

Empty cylinders must be stored securely in an UPRIGHT POSITION.

The valves must be closed.

6. Container Content and Additional Information

Composition of Serynox

  • The active ingredients are:

Nitrous oxide at 50% and oxygen at 50%

  • Serynox does not contain any other component.

Appearance of the Product and Container Content

Serynox is a colorless compressed medical gas.

Aluminum and/or steel gas cylinders of 2 liters, 5 liters, 10 liters, 15 liters, and 20 liters (identified with a blue and white tip and a white body) filled to a pressure of 170 bar, equipped with a residual pressure valve and/or valves with an integrated pressure regulator with a specific outlet connection in both cases.

Water capacity of the container [l]

Quantity of nitrous oxide/oxygen gas mixture equivalent in m³ at 1 bar and 15 °C

2

0.59

5

1.49

10

2.97

15

4.46

20

5.95

Only some container sizes may be marketed.

Marketing Authorization Holder and Manufacturer

Marketing authorization holder

Messer Ibérica de Gases S.A.U.

Autovía Tarragona-Salou, km. 3.8

E-43480, Vilaseca (Tarragona)

Spain

Manufacturer:

MESSER FRANCE

ZI Lafayette, 35 rue de l'Europe

38790 Saint-Georges-d'Espéranche

France

This medicinal product is authorized in the Member States of the European Economic Area under the following names:

Austria, Germany:Serynox 50% / 50% Gas zur medizinischen Anwendung, druckverdichtet

Belgium:Placynox 50% / 50% v/v medicinaal gas, samengeperst / gaz médicinal comprimé

Croatia:Serynox 50%/50% V/V medicinski plin, stlacen

Czech Republic:Serynox

Estonia, Latvia, Lithuania:Serynox

France:Placynox 50% / 50% gaz médicinal comprimé

Poland:Serynox

Romania:Serynox 50% / 50% Gaz medicinal comprimat

Slovenia:Serynox 50 %/50 % V/V medicinski plin, stisnjeni

Slovakia:Serynox 50% / 50% stlacený medicinálny plyn

Spain:Serynox 50% / 50% gas comprimido medicinal

Date of the last revision of this leaflet:November 2020

Detailed and updated information on this medicinal product is available on the website of the Spanish Agency for Medicines and Health Products (AEMPS) http://www.aemps.gob.es/

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This information is intended only for healthcare professionals

Serynox cylinders should only be used for medical purposes.

Prepare the filled cylinders 48 hours before use

The mixture is unstable below -5 °C; if it is cooled below this temperature, the liquefaction of part of the nitrous oxide may occur, so that an unequal mixture of gases containing too much oxygen (mixture with reduced analgesic activity) is administered at the beginning of treatment and too much nitrous oxide (hypoxic mixture) at the end of treatment. For this reason, the filled gas cylinders must be placed for at least 48 hours in a HORIZONTAL POSITION at a temperature above +10 °C, in a transition area of the pharmacy or maintenance department before their first use. The cylinders must be in a place where they are protected from shocks, heat sources or ignition, and flammable materials. The valves of the gas cylinders must be closed.

Place the gas cylinders in a VERTICAL POSITION before their first use.

The rooms where Serynox is frequently used must be equipped with a system for extracting residual gases or satisfactory ventilation.

Different types of medical gases must be separated from each other. Filled and empty gas cylinders must be stored separately.

Never use oil or grease, even if the cylinder valve is stiff or difficult to connect the regulator. Handle the valves and accompanying equipment with clean, grease-free hands (hand cream, etc.).

Turn off the equipment in case of fire or if it is not in use. If there is a risk of fire, transfer the gas cylinder to a safe place.

Use only conventional equipment indicated for the 50% N2O and 50% O2 gas mixture.

Check that the gas cylinders are sealed before their first use.

Smoking and open flames are strictly prohibited in the rooms where treatment with Serynox takes place.

When using the cylinder, it must be secured in a suitable support.

After use, the cylinder valve must be closed tightly by hand. Eliminate the pressure from the regulator or connection.

The gas cylinder must not be discarded when empty. The supplier will collect the empty gas cylinders.

Online doctors for SERYNOX 50%/50% MEDICINAL COMPRESSED GAS

Discuss questions about SERYNOX 50%/50% MEDICINAL COMPRESSED GAS, including use, safety considerations and prescription review, subject to medical assessment and local regulations.

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Taisiia Proida

Psychiatry 7 years exp.

Dr. Taisiia Proida is a psychiatrist and cognitive behavioural therapist (CBT), and a member of the European Psychiatric Association. She offers online consultations for adults aged 18 and over, combining evidence-based medicine with an individualised approach to mental health care.

She specialises in consultations and ongoing support for a wide range of mental health concerns, including:

  • Mood disorders: depression, bipolar disorder, postpartum depression.
  • Anxiety disorders: generalised anxiety, OCD, panic attacks, phobias.
  • Post-traumatic stress disorder (PTSD) and complex PTSD.
  • Attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Assessment is provided only after an initial psychiatric evaluation and during a follow-up appointment.
  • Personality disorders and emotional instability.
  • Cyclothymia and mood fluctuations.
  • Schizophrenia spectrum and related conditions.

Dr. Proida combines clinical expertise with an empathetic approach, offering structured support based on evidence-based practices. Her work integrates CBT techniques with medical management, with a focus on anxiety and depressive disorders.

She works with clients from different countries and cultural backgrounds, adapting her communication style and recommendations to individual needs. With experience in international clinical trials (Pfizer, Merck), she values clarity, trust, and collaborative partnership in patient care.

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Alexander Nazarchuk

Allergology 7 years exp.

Dr. Alexander Nazarchuk is a physician specialising in allergology and internal medicine. He provides online consultations for adults, following the principles of evidence-based medicine — no outdated treatments or unnecessary tests, with clear explanations and a personalised approach. He helps patients with a wide range of allergic and therapeutic conditions, from common day-to-day complaints to complex cases involving allergies, gastrointestinal issues, cardiovascular concerns, respiratory symptoms, and more.

You can consult Dr. Nazarchuk for:

  • Test interpretation and guidance on diagnostic plans.
  • Allergic rhinitis, hay fever, bronchial asthma (including severe cases).
  • Food and drug allergies, skin rashes, angioedema.
  • Atopic dermatitis, urticaria, contact allergies.
  • Allergen-specific immunotherapy (AIT) – initiation and ongoing management.
  • Abdominal pain, bloating, changes in bowel habits, nausea, heartburn.
  • High blood pressure and adjustment of baseline antihypertensive therapy.
  • Hyperlipidaemia and elevated cholesterol.
  • Cough, nasal congestion, fever, sore throat.
  • Anaemia, including iron deficiency and related conditions.
  • Other issues related to allergology and internal medicine.

During consultations, Dr. Nazarchuk takes a thorough, structured approach — analysing symptoms, identifying potential causes, and helping patients make informed decisions. Whether treatment, further investigation, or monitoring is needed, he explains each step clearly so you understand your health and how best to manage it.

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Frequently Asked Questions

Is a prescription required for SERYNOX 50%/50% MEDICINAL COMPRESSED GAS?
SERYNOX 50%/50% MEDICINAL COMPRESSED GAS requires a prescription in Spain. You can check with a doctor online whether this medicine may be appropriate for your situation.
What is the active substance in SERYNOX 50%/50% MEDICINAL COMPRESSED GAS?
The active ingredient in SERYNOX 50%/50% MEDICINAL COMPRESSED GAS is nitrous oxide, combinations. This information helps identify medicines with the same composition but different brand names.
Who manufactures SERYNOX 50%/50% MEDICINAL COMPRESSED GAS?
SERYNOX 50%/50% MEDICINAL COMPRESSED GAS is manufactured by Messer Iberica De Gases, S.A.U.. Pharmacy brands and packaging may differ depending on the distributor.
Which doctors can assess the use of SERYNOX 50%/50% MEDICINAL COMPRESSED GAS online?
Doctors such as Family doctors, Psychiatrists, Dermatologists, Cardiologists, Endocrinologists, Gastroenterologists, Pulmonologists, Nephrologists, Rheumatologists, Hematologists, Infectious disease physicians, Allergists, Geriatricians, Paediatricians, Oncologists may assess whether SERYNOX 50%/50% MEDICINAL COMPRESSED GAS is appropriate, depending on your situation and local regulations. You can book an online consultation to discuss your symptoms and possible next steps.
What are the alternatives to SERYNOX 50%/50% MEDICINAL COMPRESSED GAS?
Other medicines with the same active substance (nitrous oxide, combinations) include ACTYNOX 50%/50% MEDICINAL COMPRESSED GAS, DONOPA 50%/50% MEDICINAL COMPRESSED GAS, ENTONOX 50%/50% MEDICINAL GAS COMPRESSED. These may have different brand names or formulations but contain the same therapeutic ingredient. Always consult a doctor before switching or starting a new medicine.
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