Choloxin: Uses, Dosage, Side Effects & Interactions

1. Introduction to Choloxin

Choloxin, also known as dextrothyroxine, is a synthetic thyroid hormone that was used as a lipid-lowering drug in the 1960s and 1970s. It is an isomer of levothyroxine ( Synthroid), the most commonly prescribed form of thyroid hormone replacement therapy. Choloxin was developed with the goal of reducing cholesterol levels and managing thyroid hypofunction.

2. Chemical Properties of Choloxin

The molecular formula of choloxin is C15H10I4NNaO4, and its molecular weight is 798.85 g/mol. It is chemically known as dextrothyroxine sodium or D-thyroxine sodium salt. Other synonyms include Detyroxin and Dynothel. The compound belongs to the class of synthetic organic thyroid hormones.

3. Mechanism of Action

Choloxin works by mimicking the effects of thyroid hormones in the body. It interacts with thyroid hormone receptors, leading to an increase in metabolic rate and a reduction in LDL cholesterol levels. However, the exact mechanism of action for its lipid-lowering properties is not fully understood. Studies suggest that choloxin may also have an impact on hepatic function and lipid metabolism [1].

4. Medical Uses and Indications

Choloxin was primarily used as a lipid-lowering agent to reduce high cholesterol levels. It was considered as a potential therapeutic option for patients with hypercholesterolemia and thyroid disorders. However, its effectiveness in managing lipid profiles was found to be limited compared to other lipid-lowering drugs available at the time, such as norethandrolone (Nilevar) [2].

5. Research and Clinical Trials

Several clinical trials were conducted to evaluate the lipid-lowering effects of choloxin. A controlled study published in 1967 compared the efficacy of choloxin with the anabolic steroid norethandrolone in reducing cholesterol and triglyceride levels. The results showed that while both drugs reduced lipid levels, norethandrolone had a more significant impact on triglycerides [2].

6. Side Effects and Risks

Choloxin was associated with various side effects, ranging from mild to severe. Common side effects included headache, fatigue, nervousness, and gastrointestinal disturbances. More severe side effects, particularly cardiac complications, led to its eventual withdrawal from the market. Long-term use of choloxin was linked to an increased risk of cardiovascular events and arrhythmias.

7. Regulatory and Market History

Choloxin was approved by the FDA in 1967 for the treatment of hypercholesterolemia and thyroid disorders. It was marketed by pharmaceutical companies such as Knoll Pharma Inc. and Baxter in various countries, including the United States and the United Kingdom. However, due to concerns over its cardiac side effects and limited efficacy, choloxin was discontinued and withdrawn from the market.

8. Pharmacokinetics and Metabolism

After oral administration, choloxin is absorbed from the gastrointestinal tract and undergoes hepatic metabolism. It has a half-life of approximately 7 days in the plasma. The drug is primarily excreted through the kidneys, with a small amount eliminated in the feces. The pharmacokinetic profile of choloxin is similar to that of levothyroxine, but with some differences in bioavailability and metabolism.

9. Comparison with Other Thyroid Drugs

Choloxin differs from levothyroxine ( Synthroid) in its chemical structure and pharmacological properties. While both drugs are synthetic forms of thyroid hormone, choloxin is the dextrorotary isomer of thyroxine. Levothyroxine is the levorotary isomer and is the preferred treatment for hypothyroidism. Choloxin was primarily used for its lipid-lowering effects, while levothyroxine is used for thyroid hormone replacement therapy.

10. Dosage Forms and Administration

Choloxin was available in tablet form, with a typical dosage of 4 mg per tablet. The recommended dosage varied depending on the individual patient’s condition and response to treatment. It was administered orally, usually once daily. Dose adjustments were made based on the patient’s lipid profile and thyroid function tests. Careful monitoring by healthcare providers was necessary to assess the drug’s effectiveness and manage potential side effects.

In conclusion, choloxin (dextrothyroxine) was a synthetic thyroid hormone used in the past as a lipid-lowering agent. Despite its initial promise, the drug was discontinued due to its cardiac side effects and limited efficacy compared to other available treatments. Today, levothyroxine remains the primary choice for thyroid hormone replacement therapy, while newer and safer lipid-lowering drugs have replaced the use of choloxin in managing hypercholesterolemia.