Levothyroxine in Pediatric Medicine
Levothyroxine
Key Points
- Essential hormone replacement for thyroid disorders
- Narrow therapeutic index medication
- Critical for growth and neurodevelopment
- Requires precise dosing and monitoring
- Brand consistency is important
Overview
Levothyroxine (L-thyroxine, T4) is a synthetic thyroid hormone that serves as the cornerstone of thyroid hormone replacement therapy in pediatrics. Its proper administration is crucial for normal growth, development, and metabolic function in children.
Mechanism of Action
Physiological Basis
- Hormone Action
- Conversion to active T3 in peripheral tissues
- Nuclear receptor binding and activation
- Regulation of gene transcription
- Influence on cellular metabolism
- Systemic Effects
- Growth and skeletal development
- Brain development and function
- Cardiovascular function
- Energy metabolism
- Protein synthesis
Pharmacological Properties
- Absorption
- Variable absorption (40-80%)
- Best absorbed on empty stomach
- Multiple drug interactions
- Food interactions affect bioavailability
- Distribution
- High protein binding (99%)
- Long half-life (7 days)
- Steady state in 4-6 weeks
- Crosses placental barrier
Clinical Indications
Primary Indications
- Congenital Hypothyroidism
- Thyroid dysgenesis
- Dyshormonogenesis
- Central hypothyroidism
- Newborn screening positive cases
- Acquired Hypothyroidism
- Autoimmune thyroiditis
- Post-surgical
- Post-radiation
- Infiltrative disorders
- Special Situations
- Thyroid cancer management
- Goiter with hypothyroidism
- Secondary hypothyroidism
- Subclinical hypothyroidism (selected cases)
Administration & Dosing
Dosing Guidelines
- Congenital Hypothyroidism
- Initial: 10-15 μg/kg/day
- Severe cases: may need higher doses
- Early initiation critical
- Frequent adjustments in infancy
- Age-Based Dosing
- 0-3 months: 10-15 μg/kg/day
- 3-6 months: 8-10 μg/kg/day
- 6-12 months: 6-8 μg/kg/day
- 1-5 years: 5-6 μg/kg/day
- 6-12 years: 4-5 μg/kg/day
- >12 years: 2-3 μg/kg/day
Administration Guidelines
- Timing
- Once daily dosing
- 30-60 minutes before meals
- Consistent timing daily
- Separate from other medications
- Formulation Considerations
- Maintain consistent brand
- Tablets can be crushed/suspended
- Liquid formulations available
- Avoid switching between brands
Monitoring & Safety
Laboratory Monitoring
- Congenital Hypothyroidism
- TSH and FT4 at 2 weeks after initiation
- Every 2 weeks until normalized
- Every 1-3 months in first year
- Every 2-4 months in second year
- Acquired Hypothyroidism
- TSH and FT4 4-6 weeks after dose changes
- Every 3-6 months when stable
- More frequent in rapid growth periods
- Annual thyroid antibodies
Clinical Monitoring
- Growth Parameters
- Height and weight every visit
- Growth velocity calculation
- Body proportions
- Pubertal development
- Development Assessment
- Developmental milestones
- School performance
- Behavioral changes
- Physical activity level
Management Challenges
- Common Issues
- Poor compliance
- Absorption problems
- Drug interactions
- Growth spurts affecting needs
- Special Situations
- Acute illness
- Surgery preparation
- Concurrent medications
- Sports participation
