What is the appropriate dosing for oral (PO) replacement therapy?

Oral (PO) Medication Replacement Dosing Guidelines

For oral medication replacement therapy, dosing should follow specific guidelines based on the medication type, patient age, and clinical condition, with careful attention to monitoring parameters to ensure optimal therapeutic outcomes while minimizing adverse effects.

General Principles of PO Replacement Therapy

Thyroid Replacement

• Adults with hypothyroidism:

  • Standard starting dose: 1.6 mcg/kg/day of levothyroxine
  • For elderly or cardiac patients: Lower starting dose (<1.6 mcg/kg/day)
  • Titration: Increase by 12.5-25 mcg increments every 4-6 weeks until euthyroid 1

• Pediatric hypothyroidism: Age-based dosing

  • 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 complete: 1.6 mcg/kg/day 1

• Pregnant patients:

  • Pre-existing hypothyroidism: Increase dose by 12.5-25 mcg/day as needed
  • New onset (TSH ≥10 IU/L): 1.6 mcg/kg/day
  • New onset (TSH <10 IU/L): 1.0 mcg/kg/day 1

Corticosteroid Replacement

• Adrenal insufficiency:

  • Hydrocortisone: 15-20 mg/day in divided doses (preferred agent)
  • Physiologic maintenance therapy after tapering from higher doses 2

• Stress dosing for illness:

  • Education on stress dosing is essential for all patients on corticosteroid replacement
  • Emergency injectable medications should be prescribed
  • Medical alert bracelet recommended 2

Antiemetic Dosing for Chemotherapy

• High emetic risk chemotherapy:

  • Dexamethasone: 12 mg PO/IV on day 1, then 8 mg PO/IV daily on days 2-4
  • 5-HT3 antagonists (e.g., Ondansetron: 24 mg PO or 8-12 mg IV)
  • NK1-receptor antagonist (e.g., Aprepitant: 125 mg PO day 1, then 80 mg PO days 2-3) 2

• Moderate emetic risk:

  • Dexamethasone: 12 mg PO/IV day 1, then 8 mg PO/IV daily days 2-3
  • 5-HT3 antagonist (e.g., Granisetron: 1-2 mg PO or 1 mg PO twice daily) 2

• Low emetic risk:

  • Dexamethasone: 12 mg PO/IV daily 2

Acute Agitation Medication

• Benzodiazepines:

  • Adult standard dose: 2 mg PO/IM, may repeat every 30-60 minutes
  • Pediatric dose: 0.05-0.1 mg/kg PO/IM/IV 2

• Antipsychotics:

  • Adolescents: 5-10 mg PO (typical antipsychotics)
  • Children: 2.5 mg PO
  • May repeat PO doses every 30-45 minutes 2

Monitoring Parameters

Thyroid Replacement

• Adults: Monitor TSH 6-8 weeks after dose changes, then every 6-12 months if stable 1
• Pregnant patients: Monitor TSH every 4 weeks until stable, then each trimester 1

Corticosteroid Replacement

• Regular monitoring for symptoms of under or over-replacement
• Endocrinology consultation recommended for initial management 2

Antimicrobial Therapy

• Drug-specific monitoring required (e.g., vancomycin levels, renal function)
• Frequency depends on specific agent and duration of therapy 2

Special Considerations

Pediatric Dosing

• Never simply use "small adult" doses for children
• Consider age, size, and organ maturity when determining appropriate doses 3
• For medications without pediatric dosing guidelines, consultation with pediatric specialist is recommended

Pregnancy

• Many medications require dose adjustments during pregnancy
• Trimester-specific monitoring may be needed (e.g., thyroid function) 1

Renal Impairment

• Dose adjustment often required for renally excreted medications
• Software programs can assist with calculating appropriate doses based on creatinine clearance 4

Common Pitfalls to Avoid

1. Failure to adjust doses based on patient-specific factors (age, weight, organ function)
2. Inadequate monitoring of drug levels or clinical response
3. Not providing stress-dosing education for patients on corticosteroid replacement
4. Inappropriate dosing frequency that doesn't match the medication's pharmacokinetics
5. Overlooking drug interactions that may affect medication metabolism or clearance

By following these evidence-based guidelines for oral replacement therapy, clinicians can optimize therapeutic outcomes while minimizing adverse effects. Regular monitoring and appropriate dose adjustments are essential components of successful replacement therapy.