Levothyroxine (L-Thyroxine) Dosage Calculator
Estimate initial Levothyroxine dosage based on body weight and patient condition (Elderly, Cardiac, Pregnancy) using ATA guidelines.
About
Levothyroxine dosing requires high precision due to the drug's narrow therapeutic index. The American Thyroid Association (ATA) recommends weight-based estimation for initiating therapy in hypothyroidism. However, a standard calculation often fails for special populations. The elderly and those with cardiac history require significantly lower starting coefficients to prevent thyrotoxicosis or arrhythmias, while pregnant patients often require increased dosages to support fetal development.
This tool synthesizes lean body mass estimates and specific condition multipliers to recommend a starting daily dose. It matches the calculated value to the nearest commercially available tablet strength (color-coded by industry standard), reducing the cognitive load of manually adjusting theoretical numbers to pharmacy reality.
Formulas
The calculator uses condition-specific coefficients (k) applied to the patient's weight.
Dosedaily = Weightkg × k
The result is then snapped to the nearest valid set element S where S = {25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200}.
Reference Data
| Tablet Strength | Standard Color | Coeff: Adult | Coeff: Elderly |
|---|---|---|---|
| 25 mcg | Orange | 1.6 mcg/kg | 0.5 mcg/kg |
| 50 mcg | White | 1.6 mcg/kg | 0.5 mcg/kg |
| 75 mcg | Violet | 1.6 mcg/kg | Titrate |
| 88 mcg | Olive | 1.6 mcg/kg | Titrate |
| 100 mcg | Yellow | 1.6 mcg/kg | Titrate |
| 112 mcg | Rose | 1.6 mcg/kg | Titrate |
| 125 mcg | Brown | 1.6 mcg/kg | Titrate |
| 137 mcg | Turquoise | 1.6 mcg/kg | Titrate |