Usage
Selenium dioxide is not typically used as a medicine. It’s an industrial chemical used in various applications like:
- Oxidizing agent in organic synthesis.
- Colorant in glass manufacturing.
- Toner in photographic development.
Selenium itself, as selenious acid, is used in total parenteral nutrition (TPN) to prevent selenium deficiency. It’s an essential trace mineral important for various bodily functions like thyroid hormone metabolism, antioxidant defense, and immune function. It is often prescribed to treat selenium deficiency. Selenium is classified as a trace mineral or dietary supplement.
The mechanism of action of selenium involves its incorporation into selenoproteins, which exert various biological effects.
Alternate Names
- Selenium(IV) oxide
- Selenious anhydride
- Dioxyde de Sélénium
How It Works
Pharmacodynamics: Selenium exerts its effects primarily through its incorporation into selenoproteins. These proteins have diverse roles in the body, including:
- Antioxidant activity: Glutathione peroxidases and thioredoxin reductases containing selenium act as antioxidants, protecting cells from oxidative stress.
- Thyroid hormone metabolism: Iodothyronine deiodinases, selenoproteins, are essential for converting thyroxine (T4) to the active thyroid hormone, triiodothyronine (T3).
- Immune function: Selenium influences immune responses by affecting the activity of various immune cells.
Pharmacokinetics:
- Absorption: Selenium is absorbed in the gastrointestinal tract, with organic forms like selenomethionine being more bioavailable than inorganic forms like selenite.
- Metabolism: Selenium undergoes various metabolic transformations, including methylation and incorporation into selenoproteins.
- Elimination: Selenium is primarily excreted in the urine, with smaller amounts eliminated in feces and breath.
Mode of action: At the cellular level, selenium functions as a component of the amino acid selenocysteine, which is incorporated into selenoproteins. Selenocysteine resembles cysteine, but it contains selenium in place of sulfur. This unique amino acid is essential for the catalytic activity of many selenoproteins.
Receptor binding, enzyme inhibition, or neurotransmitter modulation: Selenium’s mode of action is primarily related to its role as a catalytic center in selenoproteins rather than through direct receptor binding, enzyme inhibition, or neurotransmitter modulation.
Elimination pathways: Selenium is primarily excreted in the urine as various metabolites. Some selenium is also eliminated in feces and expired air.
Dosage
The recommended daily allowance (RDA) of selenium varies depending on age, gender, and life stage. The dosage should be individualized.
Standard Dosage
Adults: The RDA for adults is 55 mcg/day. Supplementation can range between 100-200 mcg/day. The upper tolerable intake level is 400 mcg/day.
Children: Selenium requirements for children vary with age. Consult pediatric guidelines for specific recommendations.
Special Cases: Dosage should be adjusted for specific populations:
- Elderly Patients: The RDA for elderly individuals is the same as for adults (55 mcg/day).
- Patients with Renal Impairment: Dose adjustments may be necessary based on renal function.
- Patients with Hepatic Dysfunction: Dose modifications should be considered in patients with liver disease.
- Patients with Comorbid Conditions: Certain comorbid conditions may require individualized dosing.
The following section applies to Selenium as selenious acid for use in TPN, not selenium dioxide:
Clinical Use Cases Selenium is primarily given through TPN in clinical settings where oral or enteral nutrition isn’t feasible, like:
- Intubation
- Surgical Procedures
- Mechanical Ventilation
- Intensive Care Unit (ICU) Use
For TPN, the standard dose in adults is 20-40 mcg/day.
Dosage Adjustments
- Renal/hepatic dysfunction: Dose adjustments may be necessary in patients with impaired renal or hepatic function.
Side Effects
Common Side Effects
Selenium toxicity can cause:
- Nausea
- Vomiting
- Fatigue
- Hair loss
- Nail changes
Rare but Serious Side Effects
- Severe gastrointestinal symptoms
- Neurological abnormalities (e.g., numbness, tremors)
- Respiratory distress
Long-Term Effects
Chronic selenium toxicity, known as selenosis, can lead to:
- Garlic breath odor
- Hair and nail loss
- Brittle nails
- Gastrointestinal disturbances
- Skin rashes
- Nervous system effects
Adverse Drug Reactions (ADR)
Severe selenium toxicity can result in renal failure, cardiac dysfunction, and even death.
Contraindications
- Hypersensitivity to selenium
Drug Interactions
- Medications that decrease the immune system (Immunosuppressants)
- Chemotherapeutic agents
Pregnancy and Breastfeeding
The RDA for selenium during pregnancy is 60 mcg/day, and 70 mcg/day during breastfeeding. Higher doses should be avoided.
Drug Profile Summary
- Mechanism of Action: Antioxidant, thyroid hormone metabolism support, immune function modulation.
- Side Effects: Nausea, vomiting, fatigue, hair loss, nail changes; serious effects are rare.
- Contraindications: Hypersensitivity.
- Drug Interactions: Immunosuppressants.
- Pregnancy & Breastfeeding: RDA is increased; avoid high doses.
- Dosage: RDA: Adults - 55 mcg/day; children - varies with age. TPN: 20-40 mcg/day in adults.
- Monitoring Parameters: Plasma selenium levels.
Popular Combinations
Not applicable to selenium dioxide.
Precautions
- General Precautions: Monitor plasma selenium levels.
- Specific Populations: Pregnant/breastfeeding women: Adhere to RDA.
- Lifestyle Considerations: Encourage a balanced diet with selenium-rich foods.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for selenium supplementation?
A: The RDA for adults is 55 mcg/day. Supplementation can range between 100-200 mcg/day, not exceeding 400 mcg/day.
Q2: What are the signs and symptoms of selenium toxicity?
A: Symptoms can include gastrointestinal issues (nausea, vomiting, diarrhea), garlic breath odor, hair loss, nail changes, fatigue, and neurological symptoms. Severe toxicity can lead to organ damage.
Q3: Can selenium be used during pregnancy and breastfeeding?
A: Yes, but it’s important to adhere to the RDA (60 mcg/day during pregnancy and 70 mcg/day while breastfeeding) and avoid excessive intake.
Q4: What foods are good sources of selenium?
A: Brazil nuts, seafood, meat, poultry, and grains are good dietary sources of selenium.
Q5: What is the role of selenium in the body?
A: Selenium is crucial for thyroid hormone metabolism, antioxidant defense, immune function, and DNA synthesis.
Q6: How is selenium deficiency diagnosed?
A: Selenium deficiency is typically diagnosed by measuring plasma or serum selenium levels.
Q7: Are there any drug interactions with selenium?
A: Selenium can interact with immunosuppressants and some chemotherapeutic agents.
Q8: What is the difference between selenium and selenium dioxide?
A: Selenium is an essential trace element, while selenium dioxide is an industrial chemical. Selenious acid, a form of selenium, is used medicinally. Selenium dioxide is not used medicinally.
Q9: Is there any link between selenium and cancer?
A: Some studies suggest that adequate selenium intake may have a protective effect against certain cancers, while excessive intake may increase the risk of others. More research is needed.
