Thyroid Desiccated

Introduction Overview

Generic Name

thyroid desiccated

Brand Name

NP Thyroid

Dosage Form

Oral tablets

Drug Class

Thyroid drugs

Pharmacokinetics

Absorption:
Thyroid desiccated hormones, primarily thyroxine (T4) and triiodothyronine (T3), are absorbed in the gastrointestinal tract, mainly in the small intestine. Absorption kinetics can vary with gastric pH, presence of food, and concomitant medications. Peak serum concentrations typically occur within 2 to 4 hours post-administration. Factors such as malabsorption syndromes, celiac disease, or concurrent use of antacids or bile acid sequestrants can reduce bioavailability. Clinical monitoring involves serum TSH and thyroid hormone levels to ensure effective absorption and dosing.

Distribution:
After absorption, thyroid hormones are extensively bound to plasma proteins such as thyroxine-binding globulin (TBG), transthyretin, and albumin, with less than 1% circulating as free, active hormone. The volume of distribution approximates 10-12 liters. Desiccated thyroid provides both T3 and T4, allowing direct tissue uptake. Distribution affects onset and duration of action, with peripheral conversion of T4 to T3 in target tissues contributing to physiological effects.

Metabolism:
Metabolism primarily involves deiodination of T4 to T3 or reverse T3 (inactive) in peripheral tissues including liver, kidney, and muscle. These processes regulate hormone activity and are influenced by factors such as illness, certain medications (e.g., steroids, amiodarone), and nutritional status. Thyroid hormones also undergo conjugation to glucuronides and sulfates facilitating biliary excretion. The presence of exogenous T3 in desiccated thyroid leads to a faster onset but requires careful titration.

Elimination:
Thyroid hormones are eliminated predominantly via hepatic metabolism and biliary excretion into the feces, with some renal clearance of hormone metabolites. The half-life of T4 is about 6-7 days, while T3 has a shorter half-life around 1 day. Desiccated thyroid administration affects hormone levels similarly but with more variable hormone profiles due to natural hormone ratios. Clearance rates can be altered in liver disease, pregnancy, or with concomitant drugs influencing hepatic enzyme activity.

Dosage Forms

Available Dosage Forms:
NP Thyroid is available as oral tablets containing thyroid desiccated hormone derived from porcine thyroid glands. The tablets provide both thyroxine (T4) and triiodothyronine (T3) in natural ratios. Specific available strengths include:
- 15 mg
- 30 mg
- 60 mg
- 90 mg
- 120 mg
- 180 mg

Dosages for Adults and Adolescents:
Initial dosing depends on the severity of hypothyroidism, age, weight, cardiac status, and prior thyroid hormone replacement. General adult initial dosing may start at 30 mg daily, titrated every 2-3 weeks by clinical response and serum TSH measurement. Maintenance doses typically range from 60 mg to 120 mg daily. Elderly or patients with cardiac disease require cautious dosing to avoid precipitating ischemic events. Pediatric dosing should be individualized, often starting lower and carefully titrated.

Specific Patient Populations:
- Pregnancy: Dosage adjustments are commonly necessary due to increased thyroid hormone requirements during gestation; close monitoring is essential.
- Elderly and cardiac patients: Initiate at lower doses with gradual titration to prevent cardiac adverse effects.
- Patients with adrenal insufficiency: Adrenal function should be assessed and optimized prior to thyroid hormone therapy to prevent adrenal crisis.
- Malabsorption syndromes: May require dosage adjustment or alternative formulations.
- Patients undergoing surgery: Temporary cessation may be needed and perioperative management planned to maintain euthyroidism.

Mechanism Of Action

Thyroid desiccated acts by supplying exogenous thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), which are identical to endogenous hormones produced by the thyroid gland. Upon administration, these hormones bind intracellular thyroid hormone receptors, regulating gene expression and modulating cellular metabolism.

At the molecular level, T3, the active form, binds nuclear thyroid hormone receptors alpha and beta, influencing transcription of genes involved in energy metabolism, protein synthesis, and development. The resultant metabolic effects include increased basal metabolic rate, oxygen consumption, and thermogenesis. T4 serves as a prohormone which is peripherally converted into T3 by deiodinase enzymes, ensuring sustained biologic activity.

Cellular signaling pathways modified include upregulation of mitochondrial oxidative phosphorylation and modulation of adrenergic receptors, leading to enhanced cardiac output, heat production, and metabolic rate. These actions restore euthyroid state in hypothyroid patients by compensating for endogenous hormone deficiency.

Compared to levothyroxine (synthetic T4), desiccated thyroid provides both T4 and T3 in a fixed natural ratio, potentially offering more immediate effects due to T3 content but with greater variability in hormone content and pharmacokinetics. Clinical studies have debated the efficacy and safety of desiccated thyroid versus synthetic thyroid hormone preparations; however, it remains a viable option particularly for patients desiring 'natural' hormone therapy, with careful dose titration to minimize adverse effects.

Pharmacological Actions

Replacement of deficient thyroid hormones T3 and T4 in hypothyroid states
Normalization of basal metabolic rate and energy metabolism through genomic effects
Enhancement of mitochondrial oxygen consumption and ATP production
Regulation of protein synthesis, carbohydrate and lipid metabolism
Increase in cardiac output and enhancement of sympathetic nervous system sensitivity
Promotion of normal growth and development, particularly in pediatric patients
Modulation of thermogenesis and regulation of body temperature
Restoration of normal mental function and mood stability by correcting thyroid hormone deficiency
Stimulation of erythropoiesis by enhancing erythropoietin activity
Regulation of cholesterol levels by increasing LDL receptor expression and lipid metabolism
Increase in gastrointestinal motility and function by normalizing metabolic activity
Maintenance of normal reproductive function and menstrual regularity
Support of normal skeletal development and bone turnover
Influence on renal function by modulating renal blood flow and glomerular filtration rate
Correction of bradycardia and other cardiovascular symptoms associated with hypothyroidism

Therapeutic Or Clinical Uses

Treatment of hypothyroidism due to thyroid gland failure or surgical removal
Prevention or treatment of goiter (thyroid gland enlargement)
Replacement therapy following thyroidectomy or radioactive iodine treatment
Management of chronic lymphocytic thyroiditis (Hashimoto's thyroiditis)
Suppression therapy in some thyroid cancer maintenance regimens
Adjunctive treatment in diagnostic evaluation of thyroid disorders
Correction of hypothyroid states associated with pituitary or hypothalamic dysfunction
Support in myxedema coma as part of combination thyroid hormone therapy
Treatment of congenital hypothyroidism to promote normal growth and neurodevelopment
Management of subclinical hypothyroidism in select populations
Therapy for simple or multinodular goiters to reduce gland size
Improvement of symptoms like fatigue, weight gain, cold intolerance attributable to hypothyroidism
Treatment in iodine deficiency-related hypothyroid conditions
Use in patients intolerant or unresponsive to levothyroxine alone
Palliative therapy in metastatic thyroid carcinoma where suppression of endogenous TSH is desired

Side Or Adverse Effects

Signs of thyroid hormone overdose such as palpitations, tachycardia, and chest pain
Nervousness, anxiety, and irritability possibly indicating overtreatment
Excessive sweating and heat intolerance
Weight loss despite normal or increased appetite
Diarrhea or increased bowel movements secondary to hypermetabolism
Menstrual irregularities including amenorrhea
Temporary hair loss, especially in pediatric patients during initial therapy
Insomnia or sleep disturbances
Increased risk of osteoporosis with prolonged excessive dosing
Muscle weakness or tremors related to excessive hormone levels
Possible allergic reactions including rash, urticaria, or angioedema
Chest discomfort or exacerbation of angina pectoris in patients with coronary artery disease
Headache and occasional fever
Rare cases of thyroid storm if dosing is inappropriate or in preexisting thyrotoxicosis
Increased risk of arrhythmias particularly atrial fibrillation in elderly or cardiac patients

Precautions

Use cautiously in patients with underlying cardiovascular disease, including angina and arrhythmias
Monitor thyroid function tests regularly to avoid over- or undertreatment
Carefully adjust doses in elderly patients to minimize cardiac side effects
Assess adrenal function before initiating therapy in patients with suspected adrenal insufficiency
Inform healthcare providers of use prior to surgical procedures due to possible effects on anesthetic management
Adjust dosage during pregnancy as thyroid hormone requirements increase
Avoid use in patients with untreated thyrotoxicosis or thyroid storm
Consider potential interactions with other medications affecting thyroid hormone metabolism
Monitor blood glucose levels in diabetic patients as thyroid hormones can alter glucose metabolism
Use caution during lactation; minimal hormone passes into breast milk but monitor infants
Avoid abrupt discontinuation to prevent hypothyroid symptoms
Maintain consistent administration schedule with regard to food and other medications to optimize absorption
Screen for osteoporosis in patients on long-term therapy especially if overtreated
Advise patients to report symptoms of overdose or allergic reactions promptly
Evaluate for changes in mental status or mood disturbances during therapy

Warnings

Do not use NP Thyroid if patient has thyrotoxicosis or uncontrolled adrenal gland problems
Risk of thyroid hormone toxicity manifesting as chest pain, palpitations, nervousness, or excessive sweating
May precipitate or exacerbate angina or cardiac arrhythmias, especially in elderly patients
Overreplacement can lead to osteoporosis and increased fracture risk
Hypersensitivity reactions to porcine proteins can occur; discontinue if signs of allergy develop
Not indicated for weight loss or obesity treatment; misuse can result in serious adverse effects
Use during pregnancy requires dose adjustment and close monitoring to protect fetal development
Patients undergoing surgery should inform surgeons about thyroid hormone therapy
Abrupt withdrawal may result in hypothyroid crisis; tapering advised if discontinuing
Concomitant use with certain drugs may necessitate dose modification and monitoring
Avoid use in heart failure patients without adequate control and monitoring
Monitor for signs of overtreatment regularly to prevent thyroid toxicity
Emergency medical attention required for overdose due to risk of thyrotoxic crisis
Use with caution in psychiatric patients as fluctuations may affect mood
Not a substitute for other thyroid hormone replacement therapies without medical supervision

Contraindication

Known hypersensitivity to thyroid desiccated products or porcine proteins
Diagnosis of thyrotoxicosis or hyperthyroidism
Uncontrolled adrenal insufficiency without appropriate steroid replacement
Untreated or uncontrolled cardiac ischemia or arrhythmias
Acute myocardial infarction during convalescence due to risk of increased cardiac workload
Severe hyperthyroid states such as thyroid storm
Use as a weight loss agent or for obesity management
Concurrent use with agents that may cause severe interaction without monitoring
Known intolerance to excipients in the formulation
Pregnancy where benefits do not outweigh risks (only under physician supervision)
Pediatric use without specialist guidance due to dosing complexity
Patients with uncorrected pituitary or hypothalamic dysfunction without combined therapy
Severe systemic illness where thyroid replacement may worsen clinical status
Patients with active thyroid cancer unless used for TSH suppression under oncologist care
Any condition where increased metabolism would exacerbate patient status

Drug Interactions

Cholestyramine and colestipol reduce absorption when taken within 4 hours of NP Thyroid
Antacids may impair thyroid hormone absorption if administered concurrently within 4 hours
Warfarin and other anticoagulants: thyroid hormones may enhance anticoagulant effects increasing bleeding risk
Insulin and oral hypoglycemic agents: thyroid hormones can alter glucose metabolism requiring dose adjustments
Iodine-containing medications (e.g., I-131) may interfere with thyroid function and hormone efficacy
Salicylates (aspirin and derivatives) can displace thyroid hormones from binding proteins increasing free hormone levels
Corticosteroids such as prednisone may decrease conversion of T4 to T3 affecting hormone levels
Estrogen-containing contraceptives or hormone replacement therapy increase thyroxine binding globulin thereby altering free hormone availability
Amiodarone can cause thyroid dysfunction and alter thyroid hormone metabolism
Cholesterol-lowering agents like colestipol sequester thyroid hormones thus reduce their absorption
Certain antidepressants and antiepileptics may alter thyroid hormone metabolism and clearance
Drugs that affect liver enzyme activity can modify thyroid hormone metabolism and requirements
Phenytoin and carbamazepine can increase clearance of thyroid hormones requiring dosage adjustments
Concomitant use with sympathomimetic agents may amplify cardiovascular adverse effects
Herbal supplements such as St. John's Wort may induce hepatic enzymes and alter hormone levels

Preparations Of The Drug

NP Thyroid oral tablets standardized to contain desiccated porcine thyroid hormone
Available strengths: 15 mg, 30 mg, 60 mg, 90 mg, 120 mg, and 180 mg tablets facilitating dose titration
Each tablet contains a natural ratio of thyroxine (T4) and triiodothyronine (T3) hormone
Manufactured under strict quality controls to ensure consistent hormone content
Packaged for oral administration ensuring stability at room temperature
Supplied in blister packs or bottles with moisture-resistant packaging
Available as prescription-only medication requiring physician supervision
Formulated without common allergens such as gluten or lactose to minimize adverse reactions
Labeling includes detailed dosage instructions and warnings
Intended to be stored away from excessive heat and moisture to preserve potency
Not intended for intravenous or other non-oral administration forms
Contains inactive ingredients compatible with thyroid hormone stability
Non-hormonal excipients included to facilitate tablet formulation and patient compliance
Prescription labeling advised for patient education regarding lifelong therapy necessity
Regular batch testing performed to ensure purity and absence of contaminants