Thyroxanil 200 Microgram Tablets for Dogs and Cats

Oral use.
The recommended starting dose for dogs and cats is 20 µg levothyroxine sodium per
kg body weight per day given as a single daily dose or in two equally divided doses.
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 animal especially for
cats and small dogs. See also section 4.5 ‘Special precautions for use in animals’ for
use in animals <2.5 kg. The dose should be adjusted based on clinical response and
plasma thyroxine levels. In the dog and cat, 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 (just prior to treatment) and peak values (about four hours
after dosing) of plasma T4 can be measured. In adequately dosed animals 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 sodium dose can be adjusted in appropriate
increments until the patient is clinically euthyroid and serum T4 is within the reference
range. The 200 µg tablets enable adjustment of the levothyroxine dose by 50 µg
increments per animal and 600 µg tablets enable adjustment of the levothyroxine
dose by 150 µg increments per animal. Plasma T4 levels can be retested two weeks
after change of dosage, but clinical improvement is an equally important factor in

Revised: February 2021
AN: 00902/2020Page 4 of 7
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.
The following table is intended as a guide to dispensing the product at approximately
the standard
day.
Administration once
daily
Administration twice
dailyBody weight
Thyroxanil
200 µg
Thyroxanil
600 µg
Actual
dose
per kg
(μg)
Thyroxanil
200 µg
Thyroxanil
600 µg
>2.5 kg – 5
kg
20 - 10->5 kg – 7.5
kg
20 - 13.3>7.5 kg – 10
kg or
20 - 15>10 kg – 12.5
kg
20 - 16>12.5 kg – 15
kg or
24 - 20
or
>15 kg – 17.5
kg
23.3 - 20>17.5 kg – 20
kg
22.9 - 20>20 kg – 22.5
kg or
22.5 - 20>22.5 kg – 25
kg
22.2 - 20>25 kg – 30
kg or
24 - 20
or
>30 kg – 40
kg and
26.7 - 20
>40 kg – 50
kg
and
25 - 20>50 kg – 60
kg
24 - 20
= ¼ Tablet = ½ Tablet = ¾ Tablet = 1 Tablet
Tablets can be divided into halves or quarters to ensure accurate dosing. Place the
tablet on a flat surface, with its scored side facing up and the convex (rounded) side
facing the surface.

Revised: February 2021
AN: 00902/2020Page 5 of 7
Halves: press down with your thumbs on both sides of the tablet.
Quarters: press down with your thumb in the middle of the tablet.