Thyforon Flavoured 800 Microgram Tablets for Dogs
Active ingredient: L Thyroxine Sodium
Form
Tablet
Species
Manufacturer
Eurovet Animal Health B.V.
VMD MA No.
16849/4037
What it's used for
For the long term treatment of thyroid insufficiency in dogs.
Full indications, dosage and side effects ↓The prescription itself has a price. See what practices near you charge for a consultation and the written prescription fee.
Paying less for L Thyroxine Sodium
-
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.
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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.
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Prescription required
Your vet must provide a written prescription on request. You can then purchase from any licensed online retailer.
Thyforon Flavoured 800 Microgram Tablets for Dogs — SPC Details
Source: VMD Summary of Product Characteristics (SPC). Last updated 27 Mar 2026.
orally every 12 hour. Because of variability in absorption and metabolism, the
dosage may require alterations before a complete clinical response is observed. The
initial dosage and frequency of administration are merely a starting point. Therapy
has to be highly individualised and tailored to the requirements of the individual dog.
When initiating dosing of dogs weighing less than 5 kg bodyweight, a quarter of one
200 μg
carefully. In the dog, absorption of levothyroxine sodium may be affected by the
presence of food. The timing of treatment and its relation to feeding should therefore
be kept consistent from day to day. To adequately monitor therapy, trough values
AN: 03132/2024 and 03133/2024
(just prior to treatment) and peak values (about three hours after dosing) of plasma
T4 can be measured. In adequately dosed dogs peak plasma concentration of T4
should be in the high-normal range (approximately 30 to 47 nmol/l) and trough
values should be above approximately 19 nmol/l. If T4 levels are outside this range
the levothyroxine dose can be adjusted in 50 to 200 µg increments using the
appropriate strength(s) of tablets until the patient is clinically euthyroid and serum T4
is within the reference range. Plasma T4 levels can be retested two weeks after
change of dosage, but clinical improvement is an equally important factor in
determining individual dosage and this will take four to eight weeks. When the
optimum replacement dose has been attained, clinical and biochemical monitoring
may be performed every 6 - 12 months.
To break a tablet accurately and easily, place the tablet score
side up and apply pressure with your thumb.
To break the tablet in two parts; hold one half of the tablet down and press down the
other half.
Do not use in cases of hypersensitivity to the active substance or to any of the
excipients.
Very rare
(<1 animal / 10 000 animals
treated, including isolated
reports):
Weight loss
a,b
, Polydipsia
a
, Polyphagia
a
Hyperactivity
a
, Excitation
a
Panting
a
Tachycardia
a
Polyuria
a
Hypersensitivity reaction (Pruritus)
a
Adverse reactions of thyroid hormones are generally associated with excessive
dosage and correspond to the symptoms of hyperthyroidism, see also section 3.10.
b
Without loss of appetite.
Restoration of physical activity may unmask or intensify other health-related
problems, such as osteoarthrosis.
AN: 03132/2024 and 03133/2024
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.
AN: 03132/2024 and 03133/2024
Special precautions for safe use in the target species:
The tablets are flavoured. In order to avoid any accidental ingestion, store tablets out
of reach of animals. A sudden increase in demand for oxygen delivery to peripheral
tissues, plus the chronotropic effects of levothyroxine sodium, may place undue
stress on a poorly functioning heart, causing decompensation and signs of
congestive heart failure. Hypothyroid dogs suffering from hypoadrenocorticism have
a decreased ability to metabolise levothyroxine sodium and therefore an increased
risk of thyrotoxicosis. Dogs with concurrent hypoadrenocorticism and hypothyroidism
should be stabilised with glucocorticoid and mineralocorticoid treatment prior to
treatment with levothyroxine sodium to avoid precipitating a hypoadrenocortical
crisis. After this, thyroid tests should be repeated, then gradual introduction of
levothyroxine therapy, starting with 25% of the normal dose, increasing by 25%
increments every fortnight until optimal stabilisation is achieved is recommended.
Gradual introduction of therapy is also recommended for dogs with other concurrent
illnesses; particularly in dogs with cardiac disease, diabetes mellitus and renal or
hepatic dysfunction.
Special precautions to be taken by the person administering the veterinary medicinal
product to animals
Any unused tablet portion(s) should be returned to the open blister for use at the
next administration.
Wash hands after administering the tablets. Pregnant women should handle the
veterinary medicinal product with caution. In case of accidental ingestion, seek
medical advice immediately and show the package leaflet or the label to the
physician.
To the physician: This veterinary medicinal product contains a high concentration of
L-thyroxine sodium and may present a risk to humans, in particular children, if
ingested.
Special precautions for the protection of the environment:
Not applicable.
alter thyroid hormone metabolism (e.g. barbiturates, antacids, anabolic steroids,
diazepam, furosemide, mitotane, phenylbutazone, phenytoin, propranolol, large
doses of salicylates, and sulphonamides). When treating dogs that are receiving
concurrent medication the properties of these drugs should be taken into
consideration.
Oestrogens may increase thyroid requirements.
Ketamine may cause tachycardia and hypertension when used in patients receiving
thyroid hormones. The effect of catecholamines and sympathomimetics is increased
by levothyroxine.
An increase in the dosage of digitalis may be necessary in a patient that had
previously compensated congestive heart failure and that is placed on thyroid
hormone supplementation. Following treatment of hypothyroidism in dogs with
concurrent diabetes, careful monitoring of diabetic control is recommended.
Most dogs on chronic high-dose, daily glucocorticoid therapy will have very low or
undetectable serum T4 concentrations, as well as subnormal T3 values.
Return any divided tablet to the opened blister and use within 4 days.
4.
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.
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Other Products Containing L Thyroxine Sodium
These products share the same active ingredient and may be suitable alternatives. Always consult your vet.
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Leventa 1 mg/ml Oral Solution for Dogs
POM-VIntervet International B.V.
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Soloxine 0.2 mg Tablet
POM-VVirbac
Soloxine 0.3 mg Tablet
POM-VVirbac
Soloxine 0.5 mg Tablet
POM-VVirbac
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