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-threatening thyrotoxicosis. 2 Among the various treatment modalities for FHT, methimazole administration, 2 – 4 radioactive iodine, 2 – 4 iodine-restricted diets, 5 and thyroidectomy 6 – 9 have been commonly applied. In general, radioactive iodine is selected as part of
Various methods for treating cats with hyperthyroidism have been described, 1,2 with the most common medical treatments involving administration of methimazole or radioactive iodine. Although several reports on the effects of treatment of
Abstract
Objective—To determine whether once daily administration of methimazole was as effective and safe as twice daily administration in cats with hyperthyroidism.
Design—Randomized, nonblinded, clinical trial.
Animals—40 cats with newly diagnosed hyperthyroidism.
Procedure—Cats were randomly assigned to receive 5 mg of methimazole, PO, once daily (n = 25) or 2.5 mg of methimazole, PO, twice daily (15). A complete physical examination, including measurement of body weight; CBC; serum biochemical analyses, including measurement of serum thyroxine concentration; and urinalysis were performed, and blood pressure was measured before and 2 and 4 weeks after initiation of treatment.
Results—Serum thyroxine concentration was significantly higher in cats given methimazole once daily, compared with cats given methimazole twice daily, 2 weeks (3.7 vs 2.0 μg/dL) and 4 weeks (3.2 vs 1.7 μg/dL) after initiation of treatment. In addition, the proportion of cats that were euthyroid after 2 weeks of treatment was lower for cats receiving methimazole once daily (54%) than for cats receiving methimazole twice daily (87%). Percentages of cats with adverse effects (primarily gastrointestinal tract upset and facial pruritus) were not significantly different between groups.
Conclusions and Clinical Relevance—Results suggest that once daily administration of methimazole was not as effective as twice daily administration in cats with hyperthyroidism and cannot be recommended for routine use. (J Am Vet Med Assoc 2003; 222:954–958)
Summary
A bolus dose of methimazole (mmi) was administered iv over 1 minute to 5 healthy adult dogs at a dosage (40 mg/kg of body weight) known to impart protection against cisplatin-induced renal disease. Blood and urine samples for pharmacokinetic analysis were collected over a 24-hour period. Physical examination, CBC, determination of serum thyroid hormone concentrations, and serum biochemistry analysis were performed over a 10-day period to evaluate short-term toxicoses. At this dosage, mmi appears to be safe and well tolerated in dogs; only 1 of the 5 dogs had mild and transient increases in serum activity of hepatic enzymes. In addition, mmi did not alter serum thyroid hormone concentrations. Half-life of 8.82 hours and mean residence time of 12.18 hours were determined for mmi. Renal clearance of native mmi, along with sulfate and glucuronide conjugates, represented only 20 % of total systemic clearance. Results of this study provide further information concerning clinical use of mmi in dogs and may contribute to better understanding of the mechanism of mmi protection against chemically induced nephrotoxicosis.
Objective
To determine whether increases in BUN and serum creatinine (SCr) concentrations, which have been reported to develop after surgical bilateral thyroidectomy in hyperthyroid cats, also develop after treatment of hyperthyroidism with radioactive iodine and methimazole.
Design
Prospective, clinical trial.
Animals
58 hyperthyroid cats.
Procedure
Urine specific gravity, SCr, BUN, and serum thyroxine (T4) concentrations were determined before and 30 and 90 days after treatment of hyperthyroidism with radioactive iodine, methimazole, or surgical bilateral thyroidectomy.
Results
Mean SCr and BUN concentrations determined 30 and 90 days after treatment were significantly higher than those measured before treatment. Mean SCr, BUN, and T4 concentrations were not different among groups before treatment or 30 and 90 days after treatment.
Clinical Implications
Reduction of serum T4 concentrations after treatment of hyperthyroidism may result in azotemia in older cats with chronic renal disease. Treating azotemic hyperthyroid cats with methimazole until it can be determined whether correction of the hyperthyroid state will exacerbate the azotemia may be prudent. (J Am Vet Med Assoc 1996;208:875–878)
Objective—
To evaluate the efficacy and safety of ipodate in the treatment of hyperthyroidism in cats.
Design—
Prospective case series.
Animals—
12 cats with hyperthyroidism treated at The Animal Medical Center between November 1994 and March 1996.
Procedure—
Each cat initially received 100 mg of ipodate/d, PO, The drug's effects on clinical signs, body weight, heart rate, and serum triiodothyronine (T3) and thyroxine concentrations were evaluated 2, 4, 6, 10, and 14 weeks after initiation of treatment. A CBC and serum biochemical analyses were performed at each evaluation to monitor potential adverse effects of the drug. Dosage of ipodate was increased to 150 mg/d and then to 200 mg/d at 2-week intervals if a good clinical response was not observed.
Results—
8 cats responded to treatment and 4 did not. Among cats that responded, mean body weight increased and mean heart rate and serum T3 concentration decreased during the study period. Among cats that did not respond, mean body weight decreased and mean heart rate and serum T3 concentration were not significantly changed. Serum thyroxine concentration remained high in all cats. Adverse clinical signs or hematologic abnormalities attributable to ipodate treatment were not reported in any of the cats.
Clinical Implications—
Ipodate may be a feasible alternative to methimazole for medical treatment of hyperthyroidism in cats, particularly those that cannot tolerate methimazole and are not candidates for surgery or radiotherapy. Cats with severe hyperthyroidism are less likely to respond to ipodate than are cats with mild or moderate disease, and cats in which serum T3 concentration does not return to the reference range are unlikely to have an adequate improvement in clinical signs. (J Am Vet Med Assoc 1997; 211:63–67)
Abstract
Objective—To determine the efficacy and safety of percutaneous ethanol injection (PEI) for the treatment of hyperthyroidism caused by bilateral hyperplastic thyroid nodules in cats.
Design—Prospective study.
Animals—7 cats.
Procedure—Hyperthyroidism was diagnosed on the basis of clinical signs and increased serum total thyroxine (TT4) concentrations. The presence of 2 cervical thyroid nodules was confirmed by use of ultrasonography and technetium Tc 99m albumin thyroid scans. After the death of 1 cat that received PEI in both thyroid nodules at the same time, the protocol was changed to injecting ethanol into 1 nodule at a time, with at least 1 month between injections. Clinical signs, serum TT4 concentrations, serum ionized calcium concentrations, laryngeal function, findings on ultrasonographic examinations of the ventral cervical region, and results of thyroid scans were monitored.
Results—Serum TT4 concentrations transiently decreased in all 6 cats (into the reference range in 5 of 6 cats) within 4 days of the first staged ethanol injection. Each subsequent injection resulted in a transient decrease in serum TT4 concentration. The longest period of euthyroidism was 27 weeks. Adverse effects included Horner's syndrome, dysphonia, and laryngeal paralysis. One cat died of unrelated causes. One cat underwent bilateral thyroidectomy, 2 cats were treated with methimazole, and 2 cats that had increased serum TT4 concentrations were not treated further, because they remained clinically normal.
Conclusions and Clinical Relevance—Percutaneous ethanol ablation of bilateral thyroid nodules as a treatment for cats with hyperthyroidism is not recommended. This treatment is not as efficacious as the medical and surgical treatments presently used. (J Am Vet Med Assoc 2001;218:1293–1297)
Summary
Administration of triiodothyronine (liothyronine, 15 μg, q 8 h, for 6 treatments) caused marked decrease in serum concentration of thyroxine (T4) and estimates of free T4 (fT4) concentration in clinically normal cats. A prospective clinical study was done to evaluate the use of this suppression test for diagnosis of hyperthyroidism in cats with clinical signs suggestive of the disease, but lacking high serum concentration of iodothyronines.
Twenty-three cats were confirmed as hyperthyroid on the basis of histologic changes in the thyroid gland or clinical improvement in response to administration of methimazole. Mean ± sd serum concentration of T4 (34.3 ± 12.7 to 31.3 ± 11.5 nmol/L) and estimate of fT4 concentration (26.6 ± 6.4 to 25.6 ± 6.9 pmol/L) did not change after administration of liothyronine to these cats. Twenty-three cats were classified as nonhyperthyroid by histologic confirmation of other disease, abnormal results of other diagnostic tests that strongly supported primary disease other than hyperthyroidism, or spontaneous remission of weight loss without treatment. Mean ± sd serum concentration of T4 (27.9 ± 10.3 to 11.7 ± 6.4 nmol/L) and estimate of fT4 concentration (21.7 ± 5.4 to 10.4 ± 4.4 pmol/L) decreased significantly (P < 0.001) in response to administration of liothyronine.
Discriminant analysis was used to identify variables from iodothyronine assays (eg, absolute concentration of T4 or absolute estimate of fT4 concentration, or changes of T4 or fT4 concentration) that provided the best diagnostic sensitivity and specificity. The endocrine end points that best differentiated hyperthyroid vs nonhyperthyroid cats were the concentration of T4 or estimate of fT4 concentration in serum obtained after liothyronine administration and predictive values ues calculated from postliothyronine serum concentration of T4 or fT4 and percentage decrease of T4 concentration. Difference in diagnostic sensitivity among endocrine end points compared was not apparent. Use of postliothyronine estimate of fT4 concentration alone or as part of a predictive value improved diagnostic specificity for differentiation of hyperthyroid vs non-hyperthyroid cats (P ≤ 0.081).
Results of this study further confirm existence of hyperthyroidism in cats that do not have high serum concentration of iodothyronines. We concluded that the triiodothyronine suppression test is a safe and accurate test for diagnosis of hyperthyroidism in cats with suggestive clinical signs of the disease, but lacking high serum concentration of iodothyronines.
been diagnosed in the cat. At that time, the cat was treated with methimazole, atenolol, and amlodipine and it had gained and maintained weight. Ten months earlier, the hyperthyroidism was no longer adequately regulated with methimazole as evident by
influence the prudent use of antimicrobials. Survival times for cats with hyperthyroidism 559 Little information is available comparing survival times for cats treated with methimazole versus iodine 131. Review of the medical records of 167 cats with
