Usage
- Dextrothyroxine is prescribed to lower high cholesterol levels in the blood (hyperlipidemia), specifically type II hyperlipoproteinemia, in patients who haven’t responded adequately to diet and other treatments. It is no longer commonly used due to its cardiac side effects.
- Pharmacological Classification: Antihyperlipidemic agent, thyroid hormone analog.
- Mechanism of Action: Dextrothyroxine increases the breakdown (catabolism) of low-density lipoproteins (LDL), leading to increased excretion of cholesterol and bile acids through the biliary route. It also stimulates hepatic lipase activity, improving triglyceride utilization and lowering lipoprotein(a).
Alternate Names
- Dextrothyroxine sodium
- D-Thyroxine
- Brand Name: Choloxin (discontinued)
How It Works
- Pharmacodynamics: Dextrothyroxine primarily affects lipid metabolism, promoting the breakdown and excretion of cholesterol. It also has some metabolic effects similar to other thyroid hormones, but less pronounced.
- Pharmacokinetics:
- Absorption: Absorbed orally.
- Metabolism: Metabolized in the liver, but specifics are not fully elucidated.
- Elimination: Excreted primarily via the biliary route into the feces, with some renal excretion. The elimination half-life is not precisely defined.
- Mode of Action: The exact mechanism isn’t fully understood. It acts on the liver to increase LDL formation, though the greater effect is increased LDL catabolism. It also increases hepatic lipase activity. Information on receptor binding, enzyme inhibition, or neurotransmitter modulation is not widely documented.
Dosage
It’s important to note that due to its cardiac side effect profile and the availability of better tolerated alternatives, Dextrothyroxine is rarely used clinically today and the following dosage information is primarily for informational purposes based on its previous use.
Standard Dosage
Adults:
- Initial: 1-2 mg orally per day.
- Increase by 1-2 mg at monthly intervals as needed based on cholesterol response.
- Usual Maintenance Dose: 4-8 mg per day.
- Maximum: 8 mg/day.
Children:
- Not generally recommended due to limited safety and efficacy data.
Special Cases:
- Elderly Patients: Start with lower doses (1 mg/day) and titrate cautiously due to an increased risk of cardiovascular adverse effects.
- Patients with Renal Impairment: Caution is advised, dosage adjustments may be necessary. Close monitoring for side effects is crucial.
- Patients with Hepatic Dysfunction: Caution is advised, dosage adjustments may be necessary. Close monitoring is essential.
- Patients with Comorbid Conditions: Contraindicated in patients with known heart disease (angina pectoris, myocardial infarction history, cardiac arrhythmias), hypertension (other than mild), or thyrotoxicosis. Use with caution in patients with diabetes mellitus, as it may worsen glycemic control.
Clinical Use Cases
Dextrothyroxine is not indicated for intubation, surgical procedures, mechanical ventilation, intensive care unit (ICU) use, or emergency situations.
Dosage Adjustments
- Renal or hepatic dysfunction: Monitor closely and adjust dosage as needed.
- Diabetes mellitus: Monitor blood glucose closely and adjust antidiabetic medications if necessary.
Side Effects
Common Side Effects:
- Insomnia
- Nervousness
- Tremor
- Weight loss
- Diarrhea
- Hair loss
- Headache
- Skin rash
Rare but Serious Side Effects:
- Allergic reaction
- Myocardial infarction (heart attack)
- Angina pectoris
- Cardiac arrhythmias
- Excessive sweating
Long-Term Effects:
The long-term effects of Dextrothyroxine are not well-studied due to the discontinuation of its widespread use.
Adverse Drug Reactions (ADR):
- Allergic reactions
- Cardiovascular events (e.g., myocardial infarction, angina, arrhythmias).
Contraindications
- Hypersensitivity to dextrothyroxine
- Thyrotoxicosis
- Known heart disease
- Moderate to severe hypertension
- Adrenal insufficiency (requires careful monitoring)
Drug Interactions
- Warfarin: Dextrothyroxine potentiates warfarin’s anticoagulant effect; reduce warfarin dosage.
- Digitalis glycosides: May increase sensitivity to digitalis; careful monitoring recommended.
- Oral hypoglycemics/insulin: May worsen glucose control; monitor glucose closely.
- Catecholamines: May increase cardiovascular effects; careful monitoring recommended.
Pregnancy and Breastfeeding
- Pregnancy: Historically categorized as Pregnancy Category X (contraindicated) due to potential risks to the developing fetus. Safer alternatives should be used.
- Breastfeeding: Avoid use as it may pass into breastmilk and affect the infant’s thyroid function.
Drug Profile Summary
- Mechanism of Action: Increases LDL catabolism and excretion of cholesterol.
- Side Effects: Insomnia, nervousness, tremor, weight loss, cardiovascular effects.
- Contraindications: Heart disease, hypertension, thyrotoxicosis.
- Drug Interactions: Warfarin, digitalis, oral hypoglycemics, catecholamines.
- Pregnancy & Breastfeeding: Contraindicated in pregnancy; avoid during breastfeeding.
- Dosage: 1-8 mg/day orally (adults).
- Monitoring Parameters: Cholesterol levels, thyroid function tests, ECG in patients with cardiac risk factors.
Popular Combinations
Dextrothyroxine is generally not used in combination therapies due to its adverse effects and discontinuation.
Precautions
- Monitor for cardiovascular side effects, especially in elderly patients.
- Closely monitor thyroid function tests.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dextrothyroxine?
A: While rarely used now, previous guidelines suggest 1-2 mg orally per day initially for adults, increasing by 1-2 mg monthly to a maximum of 8 mg/day, based on cholesterol response. Not recommended for children.
Q2: What are the main side effects of Dextrothyroxine?
A: Common side effects include insomnia, nervousness, tremor, weight loss, diarrhea, and cardiovascular events (rare but serious).
Q3: Who should not take Dextrothyroxine?
A: Individuals with heart disease, uncontrolled hypertension, or thyrotoxicosis should not take dextrothyroxine.
Q4: Does Dextrothyroxine interact with other medications?
A: Yes, it can interact with warfarin, digitalis glycosides, oral hypoglycemics, and catecholamines.
Q5: Can Dextrothyroxine be taken during pregnancy or while breastfeeding?
A: No, it is contraindicated in pregnancy and should be avoided while breastfeeding.
Q6: How does Dextrothyroxine lower cholesterol?
A: It promotes the breakdown and excretion of LDL cholesterol, leading to lower blood cholesterol levels.
Q7: Is Dextrothyroxine still commonly prescribed?
A: No, safer and more effective alternatives are available. Dextrothyroxine is rarely used now due to its cardiovascular risks.
Q8: What should patients do if they experience chest pain while taking Dextrothyroxine?
A: They should stop the medication immediately and seek medical attention as chest pain can be a sign of a serious side effect.
Q9: What is the mechanism of action of Dextrothyroxine?
A: Though not completely understood, its main effect seems to be increased LDL cholesterol breakdown.
Q10: Are there any dietary considerations while taking Dextrothyroxine?
A: A cholesterol-lowering diet should be continued. Patients should follow the prescribed dosage instructions and maintain regular check-ups with their doctors.
