Drugs for treating hormone disorders Flashcards
Describe Levothyroxine.
● Synthetic form of thyroxine (T4)
● Treatment of canine hypothyroidism
● Life long T4 PO supplementation
● Bioavailability 10-50%, Lower when administered with food. (So high doses needed!)
● q12/24h (q12h lower peak concentrations and less fluctuation in circulating T4)
● Individual variation of the effect of a given dose of T4 - dosage and frequency based on monitoring.
Goal of levothyroxine treatment.
Monitoring?
Goal: no clinical signs of disease
Improvement can take weeks to months.
Monitoring: clinical response + peak circulating TT4 concentration.
Doubling the T4 dose increases TT4 concentrations 50-60%. But more often, available tablet size has more bearing.
Gradual introduction (25-50% of starting dose) when concurrent illnesses
(cardiac, hypoadrenocorticism, DM) present. E.g. increase over 2-4 months.
Levothyroxine overdose in animals.
Overdose:
● Dogs are resistant to thyrotoxic effects of excessive T4 supplementation.
● Some dogs require up to 20 times the standard dosage to induce euthyroidism.
Clinical thyrotoxicosis (>90 nmol/l) signs: PU/PD/PP, panting, weight loss, hyperactivity, tachycardia, hyperthermia.
Most signs resolve within a few days of withdrawing therapy.
Describe Anti-thyroid drugs
● Treatment of feline hyperthyroidism.
● Methimazole most commonly used.
● Transdermal available as well.
● Decrease production of thyroid hormone, deplete follicular cellular stores of pre-made hormone, decrease circulating concentrations of thyroid hormone, reverse
thyrotoxicosis.
● q12h
● Dose must be titrated to individual needs
● Euthyroidism within 2 to 3 weeks.
● Doses should be adjusted to achieve a basal serum tT4 concentration that is at or
below the MIDDLE of the reference range for tT4.
Adverse effects of anti-thyroid drugs:
Within the first 3 months typically.
Life threatening adverse effects: agranulocytosis, thrombocytopenia, severe hepatopathy, non-thrombocytopenia associated bleeding - stop treatment with anti-thyroid drug.
Common and mild adverse effects: GI signs (nausea, vomiting, lethargy, diarrhea), leukopenia, eosinophilia, lymphocytosis - usually resolve despite continuing treatment.
● Facial excoriation - stop treatment
● Is a life long therapy
The disease tends to advance despite treatment with anti-thyroid drugs, and
this commonly necessitates increases in the drug dosage over time in order to
maintain euthyroidism.
Describe exogenous insulin.
Regulates glucose metabolism: increases glucose uptake in peripheral tissues, increases glucose storage in the liver, inhibits gluconeogenesis.
Treatment of diabetes mellitus.
The goal of treating with exogenous insulin:
Goal: control BG below the renal threshold for as much of a 24 h period as possible, improve clinical signs of DM, avoid clinically significant hypoglycemia.
Describe Various types of available exogenous insulin:
Various types of insulin, intermediate/long acting, initial recommendations:
● Fe: glargine insulin (long acting) 0.5 U/kg q12h if BG >20 mmol/l and 0.25 U/kg q12h if BG <20 mmol/l, do not exceed 2 U per cat q12h.
● Ca: porcine insulin zinc (intermediate acting) 0.25 U/kg q12h rounded to the nearest whole U.
Dosages should be based on the patient’s estimated ideal body weight (don’t medicate fat).
Dosages should not be increased more than q1-2w.
Pharmacokinetics vary depending on insulin type, product formulation, and the individual patient’s response.
Freezing/heating inactivates insulin. Store in the refrigerator up to 3-6 months.
How accurate do you need to be with giving insulin at the same time every day?
12 +/- 2 h window on each side of the dosing interval and occasional missed doses are considered acceptable.
Describe trilostane.
● Treatment of choice for canine pituitary
dependent hyperadrenocorticism (Cushing’s). Tradename Vetoryl.
● Inhibit synthesis of adrenocortical hormones cortisol and aldosterone.
Goal: control of cortisol secretion
Administer with food to enhance absorption, q12h.
Frequent monitoring:
● Clinical signs
● ACTH stim
Trilostane Adverse effects
Well tolerated but,
● Lethargy
● Mild electrolyte abnormalities
● GI signs: vomiting, diarrhea, inappetence
are possible.
Flowchart for the monitoring of trilostane dosages.
Glucocorticoids for the treatment of what hormonal deficiency?
Treatment of canine hypoadrenocorticism/Addison’s.
Glucocorticoid + mineralocorticoid deficiency. Atypical Addison’s has only glucocorticoid deficiency.
Acute treatment: dexamethasone IV (does not interfere with endocrine testing but other glucocorticoids do!)
Chronic treatment: prednisolone PO (lifelong supplementation)
● Initially higher dose, then taper to physiologic needs.
● Increase dose if hypoadrenocorticism signs (lethargy, anorexia, vomiting, diarrhea) persist and decrease if signs of glucocorticoid excess/iatrogenic Cushing’s (PP/PU/PD, weight gain) are present.
● 2-3 times the normal dose during times of stress! Preemptively a higher dose and continue for 2 days after the stress.
Mineralocorticoids for the treatment of what hormonal deficiency?
Treatment of typical hypoadrenocorticism/ Addison’s in addition to glucocorticoids given. (Atypical Addison’s has only glucocorticoid deficiency.)
Drug Deoxycorticosterone pivalate inj.(DOCP)/fludrocortisone tabl.
DOCP
Drug Deoxycorticosterone pivalate inj.
Addison’s treatment
Example protocol:
● SC/IM q25d
● Serum electrolyte monitoring (days 14 and 25 after treatment) and adjust dose.
● HyperK/hypoNa on day 14 - increase next dose 5-10%
● Electrolytes normal on day 14 but abnormal at day 25 - shorten dosing interval by 48 h.
● Electrolytes normal on day 14 and 25 - increase dosing interval by several days.
● HypoK/hyperNa on day 14 - decrease next dose 10%
● After dose and dosing interval are determined, clients can be taught to give DOCP at home.
Describe mineralcorticoid fludrocortisone.
Addison’s treatment
● Tablet PO q12h
● Dose adjusted by assessing serum Na and K concentration q5d, increased until Na:K is >28.
● Prednisolone should be given with fludrocortisone initially but may be tapered and eventually stopped after normalization of electrolytes.
Treatment of choice for canine adrenal dependent hyperadrenocorticism
surgery of adrenal neoplasia
trilostane
mitotane (old school)
ketoconazole
