Pyridoxamine dihydrochloride

Usage

Pyridoxamine dihydrochloride, a form of vitamin B6, is primarily used for preventing and treating vitamin B6 deficiency. It may also be used in specific B6-dependent seizures. Although other forms of vitamin B6 are used for other conditions (such as nausea during pregnancy, sideroblastic anemia), pyridoxamine dihydrochloride’s primary use is for B6 deficiency.

• Pharmacological Classification: Vitamin, water-soluble.

• Mechanism of Action: Pyridoxamine dihydrochloride is converted in the body to pyridoxal 5’-phosphate (PLP), the active form of vitamin B6. PLP is a crucial coenzyme in numerous metabolic reactions, including amino acid metabolism, neurotransmitter synthesis, and glycogenolysis.

Alternate Names

• Pyridoxamine
• Vitamin B6

How It Works

• Pharmacodynamics: Pyridoxamine dihydrochloride acts as a coenzyme in various enzymatic reactions, including transamination, decarboxylation, and racemization of amino acids. It also plays a role in heme synthesis and neurotransmitter function.

• Pharmacokinetics:

  • Absorption: Well-absorbed orally.
  • Metabolism: Converted to the active coenzyme PLP in the liver.
  • Elimination: Primarily renal excretion as 4-pyridoxic acid.

• Mode of Action: Acts as a coenzyme by binding to enzymes and facilitating metabolic reactions.

• Receptor Binding, Enzyme Inhibition, or Neurotransmitter Modulation: Primarily functions as a coenzyme, facilitating enzymatic activity rather than directly affecting receptors or neurotransmitters.

Dosage

Standard Dosage

Adults:

• For vitamin B6 deficiency: Oral dosages typically range from 50 mg to 150 mg daily, often divided into multiple doses. Up to 600 mg daily has been used in some cases of B6 dependency syndromes.

Children:

• Pediatric dosing is based on age and the specific condition. For dietary deficiency, doses range from 0.1mg/day (infants up to 6 months) up to 1.3mg/day (adolescents 14-18 years old). For isoniazid-induced neuropathy prophylaxis in children, 5 mg (under 5kg) or 10 mg (over 5kg) is typically used. For pyridoxine-dependent seizures, doses range from 10 mg to 100 mg intravenously/intramuscularly. Consult pediatric dosage guidelines for specific recommendations.

Special Cases:

• Elderly Patients: Similar dosing to adults, but dose adjustments may be needed based on renal function.
• Patients with Renal Impairment: Dose adjustment may be required.
• Patients with Hepatic Dysfunction: Caution is advised, as the liver is involved in the metabolism of vitamin B6.
• Patients with Comorbid Conditions: Consider individual needs and adjust accordingly.

Clinical Use Cases

Pyridoxamine dihydrochloride is not typically used for intubation, surgical procedures, mechanical ventilation, ICU use, or in emergency situations like status epilepticus or cardiac arrest.

Dosage Adjustments

Adjustments may be needed in renal impairment.

Side Effects

Common Side Effects:

• Nausea
• Headache
• Drowsiness
• Mild numbness or tingling in the extremities

Rare but Serious Side Effects:

• Severe sensory neuropathy (with prolonged high-dose use)

Long-Term Effects:

• Sensory neuropathy (with prolonged high-dose use)

Adverse Drug Reactions (ADR):

• Allergic reactions (rare)

Contraindications

• Hypersensitivity to pyridoxine hydrochloride

Drug Interactions

• Levodopa: Pyridoxine can decrease the effectiveness of levodopa.
• Anticonvulsants (e.g., phenytoin, phenobarbital): Pyridoxine can reduce the blood levels and efficacy of these medications.
• Isoniazid, cycloserine, penicillamine: These drugs can increase the body’s need for pyridoxine.
• Oral contraceptives: May increase vitamin B6 requirements.

Pregnancy and Breastfeeding

• Pregnancy Safety Category: A (when used in recommended doses). However, excessive doses should be avoided.
• Fetal Risks: No known adverse effects at recommended doses.
• Breastfeeding: Pyridoxine is excreted in breast milk. While generally considered safe at recommended dosages, very high doses might affect lactation.

Drug Profile Summary

• Mechanism of Action: Converted to PLP, a coenzyme for various metabolic processes.
• Side Effects: Nausea, headache, drowsiness, numbness/tingling (rarely, sensory neuropathy with high doses).
• Contraindications: Hypersensitivity to pyridoxine hydrochloride.
• Drug Interactions: Levodopa, anticonvulsants, isoniazid, cycloserine, penicillamine, oral contraceptives.
• Pregnancy & Breastfeeding: Generally safe at recommended doses.
• Dosage: Varies depending on indication and age.
• Monitoring Parameters: Monitor for signs of sensory neuropathy with high-dose, long-term use.

Popular Combinations

Pyridoxine is sometimes combined with doxylamine for the treatment of nausea and vomiting in pregnancy, though this usually involves pyridoxine hydrochloride, not pyridoxamine dihydrochloride.

Precautions

• General Precautions: Assess for pre-existing B6 deficiency.
• Specific Populations: Standard precautions for pregnant/breastfeeding women and elderly patients.
• Lifestyle Considerations: No specific lifestyle restrictions.

FAQs (Frequently Asked Questions)

Q1: What is the recommended dosage for Pyridoxamine dihydrochloride?

A: The dosage varies depending on the reason for treatment and the patient’s age. Typical adult doses for deficiency range from 50mg to 150mg daily, sometimes up to 600mg. Pediatric and other specific dosages should be checked in appropriate guidelines.

Q2: What are the main uses of Pyridoxamine dihydrochloride?

A: It’s primarily used for preventing and treating vitamin B6 deficiency and specific B6-dependent seizures.

Q3: How is Pyridoxamine dihydrochloride different from other forms of Vitamin B6?

A: While all forms are eventually converted to the active PLP, they have slightly different pharmacological properties. Pyridoxamine dihydrochloride is specifically indicated for B6 deficiency and dependency syndromes. Other forms (like pyridoxine hydrochloride) are more commonly used in other conditions like nausea in pregnancy.

Q4: Are there any serious side effects I should be aware of?

A: The most serious side effect is sensory neuropathy, generally seen only with high doses taken over a prolonged period.

Q5: Can Pyridoxamine dihydrochloride be used during pregnancy?

A: Yes, at recommended doses it is considered safe during pregnancy. Avoid high doses.

Q6: Does this medication interact with other drugs?

A: Yes. It can interact with levodopa, anticonvulsants, isoniazid, cycloserine, penicillamine, and oral contraceptives.

Q7: How should I monitor patients taking Pyridoxamine dihydrochloride?

A: Monitor for any signs of neuropathy, especially with long-term, high-dose therapy. Regular blood tests might be indicated to assess vitamin B6 levels.

Q8: What should I do if a patient experiences side effects?

A: For mild side effects, symptomatic treatment may be sufficient. For severe reactions or signs of neuropathy, discontinue the medication and consult a specialist.

Q9: Can I prescribe this for nausea and vomiting in pregnancy?

A: While other B6 forms are commonly used in pregnancy for nausea, pyridoxamine dihydrochloride is primarily indicated for B6 deficiency. Pyridoxine hydrochloride, often combined with doxylamine, is more commonly used for pregnancy-related nausea.