Table 2.
Pharmacology and pharmacokinetics of antithyroid drugs
| MMI | PTU | |
|---|---|---|
| Absorption | rapid | rapid |
| Bioavailability | ~100% | ~100% |
| Peak serum level | 60–120 min | 60 min |
| Serum half-life | 6–8 h | 90 min |
| Thyroid concentration | 5 × 105 mol/L | unknown |
| Thyroid turnover | slow | moderate |
| Duration of action | >24 h | 8–12 h |
| Serum protein binding | nil | >75% |
| Crosses placenta | + + | + |
| Levels in breast milk | + + | + |
| Volume of distribution | 40 L | 20 L |
| Excretion | renal | renal |
| Metabolism during illness | ||
| Renal | nil | nil |
| Liver | prolonged | nil |
| Potency | 10× | 1× |
| Normalization T3/T4 | 6 weeks | 12 weeks |
| Adverse events | 15% | 20% |
| Agranulocytosis | 0.6% | 1–1.5% |
| Cross-reaction of adverse events | 13.8% | 15.2% |
| Compliance | high | fair |
| Costs | low | moderate |
MMI, methimazole; PTU, propylthiouracil.