Selenium

Usage

• Selenium is primarily used as a nutritional supplement to prevent or treat selenium deficiency. It plays a crucial role in various physiological processes. Selenium is indicated for Keshan disease, a type of cardiomyopathy, and is being researched for potential benefits in other health conditions.

• Pharmacological Classification: Nutritional supplement, antioxidant.

• Mechanism of Action: Selenium is incorporated into selenoproteins, which exert antioxidant, anti-inflammatory, and thyroid hormone-modulating effects.

Alternate Names

• No alternate generic names. The term “selenium” refers to the element itself.

• Brand Names: Selepen (and various other brand names for selenium-containing supplements).

How It Works

• Pharmacodynamics: Selenium is an essential component of selenoproteins, including glutathione peroxidases and thioredoxin reductases, which protect cells from oxidative damage. It is involved in thyroid hormone metabolism, immune function, and DNA synthesis.

• Pharmacokinetics: Selenium is absorbed in the gastrointestinal tract, with selenomethionine having higher bioavailability than selenite. It is distributed throughout the body, with higher concentrations in the liver, kidneys, and skeletal muscle. Selenium is excreted primarily in urine.

• Mode of Action: Selenium acts as an antioxidant by catalyzing the reduction of hydrogen peroxide and other reactive oxygen species, preventing cellular damage. It also modulates the activity of deiodinases, enzymes involved in thyroid hormone activation and deactivation.

• Receptor binding, enzyme inhibition, or neurotransmitter modulation: Selenium’s primary mechanism is integration into selenoproteins, which act as enzymes (e.g., glutathione peroxidases). It does not directly bind to receptors or modulate neurotransmitters.

• Elimination Pathways: Primarily renal excretion, with some elimination through the lungs and feces at higher doses. Metabolism occurs via methylation and other pathways.

Dosage

Standard Dosage

Adults:

• Recommended Dietary Allowance (RDA): 55 mcg/day.
• Therapeutic doses: 100-200 mcg/day, up to 400 mcg/day.
• Administration: Oral, preferably with meals.

Children:

• RDA varies by age (see sources). Pediatric dosing should be determined based on age and nutritional needs.

Special Cases:

• Elderly Patients: Standard adult dose. Monitor for toxicity.
• Patients with Renal Impairment: Dose adjustments may be necessary.
• Patients with Hepatic Dysfunction: Dose adjustments may be necessary.
• Patients with Comorbid Conditions: Consider underlying conditions and potential drug interactions.

Clinical Use Cases

The use of selenium for specific clinical conditions, such as those listed below, is still being researched. Dosage varies based on the trial.

• Intubation: Specific guidelines not established.
• Surgical Procedures: Specific guidelines not established.
• Mechanical Ventilation: Specific guidelines not established.
• Intensive Care Unit (ICU) Use: Some research suggests that selenium supplementation may be beneficial, but optimal dosing and method of administration are not standardized.
• Emergency Situations: No specific emergency uses are established.

Dosage Adjustments: Individualized dosing based on patient factors like renal/hepatic function, selenium status, and coexisting medical conditions is necessary.

Side Effects

Common Side Effects:

• Nausea
• Vomiting
• Diarrhea
• Hair Loss
• Fatigue
• Garlic-like breath odor

Rare but Serious Side Effects:

• Selenosis (selenium toxicity): Symptoms can include gastrointestinal distress, neurological symptoms, and, in severe cases, organ failure.

Long-Term Effects:

• Increased risk of type 2 diabetes with prolonged high-dose supplementation.

Adverse Drug Reactions (ADR):

• Severe selenosis, allergic reactions.

Contraindications

• Hypersensitivity to selenium.
• History of skin cancer (long-term use may increase the risk of recurrence).

Drug Interactions

• Eltrombopag

Pregnancy and Breastfeeding

• Pregnancy Safety Category: A (when taken in recommended amounts). Doses above the RDA might be harmful.
• Adequate selenium intake is important for fetal development and maternal health during pregnancy. Higher doses should be avoided.
• Selenium is excreted in breast milk. Lactating individuals can take recommended daily amounts of selenium.

Drug Profile Summary

• Mechanism of Action: Antioxidant, incorporated into selenoproteins.
• Side Effects: Nausea, vomiting, diarrhea, hair loss, fatigue, garlic-like breath odor. Selenosis at high doses.
• Contraindications: Selenium hypersensitivity, history of skin cancer.
• Drug Interactions: Eltrombopag.
• Pregnancy & Breastfeeding: Safe at RDA levels. Higher doses should be avoided.
• Dosage: RDA: 55 mcg/day for adults. Therapeutic doses: 100-200 mcg/day, up to 400 mcg/day. Pediatric dosing varies by age.
• Monitoring Parameters: Selenium blood levels.

Popular Combinations:

• Selenium is often included in multivitamin/mineral supplements.

Precautions

• General Precautions: Avoid exceeding the tolerable upper intake level (400 mcg/day for adults).
• Specific Populations: Monitor pregnant and breastfeeding individuals for selenium status.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Selenium?

A: The RDA for adults is 55 mcg/day. Therapeutic doses range from 100-200 mcg/day, up to a maximum of 400 mcg/day.

Q2: What are the signs and symptoms of selenium deficiency?

A: Muscle weakness, cardiomyopathy (Keshan disease), impaired thyroid function, weakened immune system.

Q3: Can selenium be given intravenously?

A: Yes, intravenous selenium is used in certain clinical settings, particularly for critically ill patients. The dosage and administration method vary.

Q4: What is the role of selenium in thyroid function?

A: Selenium is essential for the function of deiodinase enzymes, which are involved in thyroid hormone metabolism.

Q5: How is selenium toxicity (selenosis) treated?

A: There is no specific antidote for selenosis. Treatment focuses on supportive care and managing symptoms.

Q6: Does selenium interact with any other medications?

A: Yes, selenium can interact with eltrombopag.

Q7: Can selenium be used to treat cancer?

A: The relationship between selenium and cancer is complex and still under investigation. While some studies suggest potential benefits, there is no conclusive evidence supporting its use as a cancer treatment.

Q8: What is the best way to ensure adequate selenium intake?

A: Consuming a balanced diet that includes selenium-rich foods like seafood, meat, poultry, and grains is usually sufficient. Supplementation can be considered for individuals at risk of deficiency.

Q9: Is it safe to take selenium during pregnancy?

A: Selenium is essential during pregnancy, and the RDA is 60 mcg/day. However, high doses above the recommended intake should be avoided.

Q10: What are the clinical applications of selenium in critical care?

A: Research suggests potential benefits of selenium supplementation in critically ill patients, but optimal dosing and clinical use remain a subject of ongoing investigation.