🦋 Levothyroxine Dose Titration Simulator

Diagnosing the Untreated Hypothyroid State

Placeholder lead: thyroid gland underproduces hormone, pituitary TSH climbs.

• 18.4 mIU/L: Baseline TSH (Placeholder: markedly elevated above normal.)
• 0.55 ng/dL: Baseline Free T4 (Placeholder: below the reference interval.)
• 0.4–4.0: Normal TSH range (Placeholder: typical adult reference range.)
• Hashimoto's: Common cause (Placeholder: autoimmune thyroiditis, most frequent cause.)

Feedback loop breakdown

Placeholder: pituitary senses low T4, raises TSH output sharply.

Presenting symptoms

Placeholder: fatigue, cold intolerance, weight gain, bradycardia commonly seen.

Placeholder highlight: untreated hypothyroidism raises cardiovascular and metabolic risk over time.

Weight-Based Starting Dose Selection

Placeholder lead: starting dose scaled to body weight and cardiac risk.

• ~1.6 mcg/kg: Standard starting dose (Placeholder: full replacement in healthy adults.)
• ~0.8 mcg/kg: Elderly/cardiac start (Placeholder: lower dose, start low go slow.)
• 12.5 mcg: Tablet increments (Placeholder: smallest practical dose adjustment step.)
• Empty stomach: Absorption note (Placeholder: take dose fasting for consistency.)

Weight-based calculation

Placeholder: dose (mcg/day) equals weight in kg times factor.

Cardiac risk caution

Placeholder: rapid full-dose replacement can provoke angina, arrhythmia.

Placeholder highlight: elderly and cardiac patients start conservative and titrate slowly upward.

Waiting for Steady State Before Rechecking TSH

Placeholder lead: levothyroxine has a long half-life, needs weeks to equilibrate.

• ~7 days: Half-life (Placeholder: long half-life delays steady state.)
• 6–8 weeks: Recheck interval (Placeholder: minimum wait before dose reassessment.)
• ~5 half-lives: Steady state reached (Placeholder: roughly five weeks to equilibrium.)
• False signal: Early recheck risk (Placeholder: checking too soon misleads titration.)

Why the wait matters

Placeholder: premature labs reflect prior dose, not current one.

What gets measured

Placeholder: TSH primary marker, free T4 confirms direction of change.

Adjusting the Dose Up or Down

Placeholder lead: TSH result drives the next dose adjustment decision.

• Increase dose: TSH high → action (Placeholder: raise by one tablet increment.)
• Decrease dose: TSH low → action (Placeholder: reduce to avoid overtreatment.)
• Tachycardia: Overdose sign (Placeholder: resting heart rate rises with excess hormone.)
• Bone loss: Long-term overdose risk (Placeholder: chronic suppression accelerates osteoporosis.)

Titration step size

Placeholder: smaller, slower steps used in elderly cardiac patients.

Overdose risk signals

Placeholder: suppressed TSH plus symptoms flags over-replacement.

Placeholder highlight: atrial fibrillation risk and bone density loss rise with chronic over-replacement.

Reaching Target Range and Ongoing Monitoring

Placeholder lead: stable maintenance dose found, monitoring continues periodically.

• 0.5–4.5 mIU/L: Target TSH range (Placeholder: euthyroid maintenance target window.)
• Every 6–12 mo: Maintenance recheck (Placeholder: once stable, less frequent testing.)
• Years: Dose stability (Placeholder: maintenance dose often stable long-term.)
• Weight, pregnancy: Recheck triggers (Placeholder: major changes prompt earlier recheck.)

Confirming stability

Placeholder: two consecutive normal TSH values confirm maintenance dose.

Long-term follow-up

Placeholder: annual TSH checks catch drift from weight or age.