Prescribing Unithroid (Levothyroxine)
The recommended starting dosage of Unithroid (levothyroxine) for adults with primary hypothyroidism is 1.6 mcg/kg/day, with lower starting doses for elderly patients or those with cardiac conditions, and dosage titration based on periodic TSH monitoring until euthyroid status is achieved. 1, 2
Initial Dosing Protocol
The initial dosing of Unithroid depends on several patient-specific factors:
Adult Patients
- Standard adult dosing: 1.6 mcg/kg/day 2
- Adults at risk for atrial fibrillation or with cardiac disease: Lower starting dose (25-50 mcg/day) 1, 2
- Elderly patients: Lower starting dose (25-50 mcg/day) 1, 2
Pediatric Patients
Dosing varies by age:
- 0-3 months: 10-15 mcg/kg/day
- 3-6 months: 8-10 mcg/kg/day
- 6-12 months: 6-8 mcg/kg/day
- 1-5 years: 5-6 mcg/kg/day
- 6-12 years: 4-5 mcg/kg/day
12 years but growth incomplete: 2-3 mcg/kg/day
- Growth and puberty complete: 1.6 mcg/kg/day 2
Administration Instructions
- Administer as a single daily dose
- Give on an empty stomach, 30-60 minutes before breakfast
- Take with a full glass of water to avoid choking
- Separate administration by at least 4 hours from medications that interfere with absorption 2
Dosage Titration
Primary Hypothyroidism
- Standard adult titration: Increase by 12.5-25 mcg every 4-6 weeks until euthyroid 2
- Cardiac patients/elderly: Titrate more slowly, every 6-8 weeks 1, 2
- Target TSH range:
- General population: 0.5-2.0 mIU/L
- Elderly patients: 1.0-4.0 mIU/L 1
Secondary/Tertiary Hypothyroidism
- TSH is not reliable for monitoring
- Use free T4 levels to guide therapy
- Target free T4 in upper half of normal range 2
Special Populations
Pregnant Patients
- Increase weekly dosage by 30% (take one extra dose twice weekly)
- Monitor TSH every 4 weeks during pregnancy
- Maintain TSH within trimester-specific reference range
- Return to pre-pregnancy dose immediately after delivery 1, 2
Cardiac Patients
- Start with lower doses (25-50 mcg/day)
- Titrate more slowly (every 6-8 weeks)
- Monitor for cardiac symptoms 1, 2
Monitoring Protocol
- Initial TSH and free T4 within 4-6 weeks of starting therapy
- Once stable, check TSH every 6-12 months
- Adjust dosage based on clinical response and laboratory parameters
- Peak therapeutic effect may not be reached for 4-6 weeks after dosage change 1, 2
Common Pitfalls to Avoid
- Overtreatment: Can increase risk of atrial fibrillation and osteoporosis, particularly in elderly patients 1
- Inadequate absorption: Ensure patient takes medication on empty stomach and separates from interfering medications 2
- Failure to adjust for pregnancy: Pregnancy requires prompt dose adjustment 2
- Inappropriate monitoring: For secondary/tertiary hypothyroidism, free T4 (not TSH) should guide therapy 2
- Dosages >200 mcg/day: Rarely required and may indicate poor compliance, malabsorption, or drug interactions 2
Remember that the peak therapeutic effect of Unithroid may not be attained for 4-6 weeks after initiating therapy or changing dosage 2.