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.
