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July/August 2014 Today's Veterinary Practice 41 FOCUS ON PHARMACOLOGY | MeTHiMAzOLe: MANAGeMeNT OF FeLiNe HYPeRTHYROidiSM tvpjournal.com MONITORING Follow-Up At each monitoring visit, clinical signs and quality of life should be evaluated, with special attention to possible development of azotemia, hypertension, and iatrogenic hypothyroidism. When starting treatment, the pet is re-evaluated at 2-week intervals with assessment of clinical signs, renal function tests, and a TT4. When euthyroidism has been achieved, monitoring visits are recommended after 1 month, 3 months, and twice yearly thereafter via laboratory testing as outlined below (Laboratory Analysis). Laboratory Analysis Laboratory monitoring should include a complete blood count, serum biochemistry profile, TT4 concentration, and urinalysis. With regard to TT4 concentration: • The biochemical therapeutic endpoint is a TT4 con- centration within the lower half of the laboratory ref- erence range. • Values below the reference range indicate hypothy- roidism, which has been linked to progression of renal disease and increased mortality. • Values in the upper 50% of the reference range may result in fT4 concentrations above the reference range, causing persistent signs of hyperthyroidism. • Timing of blood draw with relationship to time of dosing with methimazole is not a factor when assess- ing response to treatment. 9 IN sUMMARY Methimazole (oral and transdermal) is a safe and effec- tive medication for the treatment of feline hyperthyroid- ism when dosed and monitored appropriately. n fT4 = free thyroxine; PLO = pluronic lecithin organogel; T4 = thyroxine; TSH = thyroid stimulating hormone; TT4 = total thyroxine References 1. trepanier la. Pharmacologic management of feline hyperthyroidism. Vet Clin North Am Small Anim Prac 2007; 37(4):775-788. 2. longhofer sl, Martín-Jiménez t, soni-Gupta J. serum concentrations of methimazole in cats after a single oral dose of controlled-release carbimazole or sugar-coated methimazole (thiamazole). Vet Ther 2010; 11(3):e1-e7. 3. hill Ke, Gieseg Ma, bridges J, Chambers JP. the pharmacokinetics of methimazole in a novel lipophilic formulation administered transdermally to healthy cats. N Z Vet J 2014; 62(4):208-213. 4. daminet s, Kooistra hs, Fracassi F, et al. best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs. J Small Anim Pract 2014; 55(1):4-13. 5. Caney sM. an online survey to determine owner experiences and opinions on the management of their hyperthyroid cats using oral anti-thyroid medications. J Feline Med Surg 2013; 15(6):494-502. 6. boretti Fs, sieber-ruckstuhl ns, schäfer s, et al. transdermal application of methimazole in hyperthyroid cats: a long-term follow-up study. J Feline Med Surg 2013; 16(6):453-459. 7. snead e, Kerr M, Macdonald v. Cutaneous lymphoid hyperplasia mimicking cutaneous lymphoma in a hyperthyroid cat. Can Vet J 2013; 54(10):974- 978. 8. bell et, Mansfield Cs, James Fe. immune-mediated myasthenia gravis in a methimazole-treated cat. J Small Anim Pract 2012; 53(11):661-663. 9. rutland be, nachreiner rF, Kruger JM. optimal testing for thyroid hormone concentration after treatment with methimazole in healthy and hyperthyroid cats. J Vet Intern Med 2009; 23(5):1025-1030. 10. Felimazole-Coated tablets. Product insert, available at dechra-us.com/ files/dechraUsa/downloads/Product%20inserts/Felimazole.pdf. David Bruyette, DVM, Diplomate ACVIM, is the medical director at West Los Ange- les Animal Hospital and a clinical professor in the Department of Radiation Oncology at University of California—Los Angeles. Prior to his current positions, he was an assistant professor and head of internal medicine at Kansas State University and director of its Analytical Chemis- try Laboratory. Dr. Bruyette received his DVM from University of Missouri and completed an internship at Purdue University and residency in internal medicine at University of California— Davis. He then became a staff internist at West Los Angeles Veterinary Medical Group and member of the Department of Comparative Medicine at Stanford University. OWNER EDUCATION: 10 Key Points Owners should be familiar with the following key points about methimazole. Drug Facts 1. The veterinary approved formulations are not approved for use in humans. 2. Methimazole may cause vomiting, gastric distress, headache, fever, arthralgia, pruritus, and pancytopenia in humans. safe Use 3. The medication should be kept out of reach of children. 4. Tablets should not be broken or crushed. 5. Protective gloves should be worn to prevent direct contact with litter, feces, urine, or vomit of treat- ed cats, and with broken or moistened tablets. 6. Owners should wash hands with soap and water after administration of the drug to avoid exposure. 7. Owners should also wash hands after han- dling the litter of treated cats. Pregnancy & Lactation 8. Methimazole is a human teratogen and crosses the placenta, concentrating in the fetal thyroid gland. There is also a high rate of transfer into breast milk. 9. Pregnant women, women who may become pregnant, and nursing mothers should wear gloves when handling tablets, litter, or bodily fluids of treated cats. Ingestion or Overdose 10. in the event of accidental ingestion/overdose, seek medical advice immediately, and show the product label to the physician. 10