POM-V Prescription Required

Myorelax 100 mg/ml Solution for Infusion for Horses

Active ingredient: Guaifenesin

Form

Solution

Species

Horses

Manufacturer

Eurovet Animal Health B.V.

VMD MA No.

16849/3010

What it's used for

Depending on the procedure, guaifenesin can be used in combination with different anaesthetics: - in combination with a sedative, and local anaesthetics fo...

Full indications, dosage and side effects ↓

View official SPC (PDF)

The prescription itself has a price. See what practices near you charge for a consultation and the written prescription fee.

Paying less for Guaifenesin

1

Ask your vet for a written prescription

They must provide one on request. Under the CMA Order the fee is capped at £21 from 2027.
2

Fill it at a registered online retailer

The CMA found online pharmacies 50–60% cheaper than practice dispensing on common medicines — typically £200–£300 a year.

Your prescription rights → VMD register of retailers →

Prescription required

Your vet must provide a written prescription on request. You can then purchase from any licensed online retailer.

Clinical information

Myorelax 100 mg/ml Solution for Infusion for Horses — SPC Details

Source: VMD Summary of Product Characteristics (SPC). Last updated 27 Mar 2026.

Depending on the procedure, guaifenesin can be used in combination with different
anaesthetics:
- in combination with a sedative, and local anaesthetics for short procedures
- in combination with appropriate general anaesthetics, for induction and/or
maintenance of muscle relaxation during anaesthesia.

Revised June 2024

Dose: 100 mg guaifenesin per kg body weight per infusion, equivalent to 100 ml solution
per 100 kg body weight.
Guaifenesin can be used in combination with different anaesthetics, as follows:
Local anaesthetics for short procedures:
Once the horse is properly sedated, guaifenesin is administered by rapid infusion until
the animal lies down. A local anaesthetic should be used for painful procedures.
Additional guaifenesin can be infused when the horse is recumbent, if needed.
General anaesthetics:
•
Pre-medication with an α-2
acepromazine. If guaifenesin is to be administered with ketamine, pre-medication with
one of the α-2 receptor agonists is recommended.
Guaifenesin is administered by rapid infusion until the animal begins to sway on its feet.
At this stage either ketamine, thiopental or propofol is administered at a bolus dose.
The duration of action of these combinations is variable depending on the animal and
the other drugs administered. Surgical anaesthesia will be approximately 10-20 minutes
duration and recumbency will be approximately 30-40 minutes duration.

Revised June 2024
•
Guaifenesin, administered by continuous IV infusion (50-100 mg/kg) at an infusion rate
of approximately 1 ml/kg/h, can be used as part of total intravenous anaesthesia (TIVA)
in combination with other injectable anaesthetics for procedures lasting up to 1 hour.
•
Guaifenesin can be used as an adjunct to balanced anaesthesia using volatile
anaesthetics for longer procedures.
Guidance on anaesthetic protocols and doses of individual veterinary medicinal
products can be found in veterinary textbooks and scientific literature.
For safe use with other pharmaceuticals, reference must be made to the relevant
product literature.

None.

Horse (ponies and equines, not intended for human consumption):
Undetermined frequency (cannot
be estimated from the available
data):
Hypotension, Thrombophlebitis
a
, Injection site
reaction
b
a
due to irritative properties. To reduce the incidence of thrombophlebitis, the catheter
can be flushed with heparinised saline.

Revised June 2024
b
extravascular reactions have been reported; the use of an intravenous catheter and
careful technique will help prevent such occurrences.
Reporting adverse events is important. It allows continuous safety monitoring of a
veterinary medicinal product. Reports should be sent, preferably via a veterinarian, to
either the marketing authorisation holder or its local representative or the national
competent authority via the national reporting system. See the package leaflet for
respective contact details.

Guaifenesin should not be used alone. Animals must be properly sedated before
immobilisation with the veterinary medicinal product. Adequate analgesia should always
be provided for surgical and/or painful procedures.
Animals should undergo a thorough pre-anaesthetic examination before administration
of the product. Except in the case of an acute emergency, feed should be withheld for
12 hours prior to anaesthesia. Water should be freely available until a short time before
anaesthesia.

Special precautions for safe use in the target species:
Due to the irritative effects of the solution, it should be administered strictly
intravenously using a catheter. See also section

The action of anaesthetic agents is potentiated by guaifenesin.

This veterinary medicinal product does not require any special storage conditions.

Not authorised for use in horses intended for human consumption.

This information is sourced from the official Summary of Product Characteristics (SPC) published by the Veterinary Medicines Directorate (VMD). It is provided for informational purposes only and does not replace professional veterinary advice. Always consult your vet before administering any medication.