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Therapy: Hyperthroidism in cats - Coggle Diagram
Therapy: Hyperthroidism in cats
Oral anti-thyroid drugs
control the disease
Methimazole (Tapazole)
drug of choice
Primarily renal excreted
Uses
Therapeutic trial in suspect cats or concerns for pre-existing renal disease
Pre-surgical stabilization
Long-term management
Advantages (compared to surgery or I131)
Inexpensive on a daily basis, readily available
No special training, facilities, hospitalization
Administered by owners
Transdermal route an option (variable efficacy)
Relatively safe
Does not cause permanent hypothyroidism
adverse effects reverse if drug is stopped
Drug protocol
Conservative, slow increase to minimize side effects
2.5 mg BID for two weeks
recheck CBC and platelets (not T4-yet)
if OK > to 2.5 mg TID for two weeks
Recheck CBC, platelets, T4, BUN, Cr at 4wks
If normal or near normal continue at 2.5 mg TID for 2-6 weeks and recheck again
If T4 still elevated, increase total daily dosage by 2.5 mg every two weeks until normal range
Always check CBC/chem panel every 2 to 4 weeks for first 8-12 weeks
Side effects (~15% of cats)
Worsening of renal disease
Anorexia, vomiting, lethargy
Blood dyscrasia
Facial pruritus, excoriations
Hepatic disease – often reversible
rare after 3mo therapy
What to expect
appropriate dosages should be WNL within 7-14 days
Effective dosages range from 5 to 15 mg/day
Clinical response is from 2 to 6 weeks
AFTER the T4 normalizes
Long-term evaluations
After initial 3 month period
monitor at 3-6 month intervals
CBC/Chem
T4
PE
renal
may need adjustments over time
Disadvantages
BID to TID dosing for life
cost adds up
Side effects (early)
Hypothyroidism-common
decrease dosage by 25-50%
recheck T4
Drugs are NOT cytotoxic
disease returns as soon as the drugs are stopped (same for diet).
block thyroid hormone synthesis
Radioactive iodine I131(“curative”)
Thyroid cells take up both normal and radioactive iodine.
Atrophied normal thyroid tissue does not become irradiated
Only functioning tissue is affected
Monitoring
Recheck T4 and renal panel 2-4 weeks after.
If T4 low, Thyroxine supplementation to prevent kidney injury
Advantages
minimal risk to the cat
95% cure
Disadvantages
Cost
Availability
Radiation exposure (10-14 days of isolation)
Hypothyroidism (rare)
Re-treatment occasionally (2-5%)
Surgical removal (“curative”)
rarely done anymore
anesthesia is the main concern
Renal Concerns
If mild to moderate renal disease prior to therapy
initially treat with methimazole
monitor renal parameters (creatinine)
Renal Failure Cats
If T4 declines to normal and renal parameters are stable
continue with methimazole
consider surgical excision
consider I131 therapy
Diet Therapy
Hill’s low iodine food Y/D (low iodine)
Y/D = ~0.3ppm Iodine No independent studies yet
dietary iodine needs of cats is not really known
Debate within specialists as to the
utility
when to use
Must have perfect compliance
potential alternative