BCS Class for Hydroxyurea
- BCS Class III – high solubility, low permeability
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Why Hydroxyurea is Class III
| Property | Hydroxyurea | BCS Criteria |
|----------|-------------|--------------|
| Solubility | Very high – ≈ 1 000 mg mL⁻¹ at 25 °C (water) | Soluble if > 1 mg mL⁻¹ at pH 6.5 (≈ 1 000 mg mL⁻¹ at pH 7.4) |
| Permeability | Low – log P (octanol/water) ≈ –0.7; limited passive diffusion across intestinal epithelium | Permeable only if intrinsic dissolution rate (IDR) > 10 µmol cm⁻² s⁻¹; hydroxyurea’s IDR is ~ 2–5 µmol cm⁻² s⁻¹ |
Because it dissolves readily but does not cross biological membranes efficiently, it falls into Class III.
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Practical Implications
1. Formulation
- Permeability‑enhancing excipients (e.g., permeation enhancers, surfactants) can be added to improve oral absorption.
- Solid dispersions or nanoparticles can also help by increasing surface area.
2. Drug‑Drug Interactions
- Metabolism is mainly by non‑enzymatic processes (e.g., reduction, conjugation) rather than CYP450, so fewer interaction risks.
3. Bioavailability
- Oral bioavailability is typically high (> 80 %) due to good solubility, but limited by intestinal permeability.
- Intravenous administration is common in oncology to ensure 100 % bioavailability.
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Quick Reference
| BCS Class | Solubility | Permeability | Typical Drugs |
|-----------|------------|--------------|---------------|
| I | High | High | Loperamide (high solubility, high permeability) |
| II | Low | High | Ibuprofen |
| III | High | Low | Hydroxyurea, atenolol |
| IV | Low | Low | Rifampicin (low solubility, low permeability) |
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Bottom Line
- Hydroxyurea: BCS Class III – high solubility, low permeability.
- Formulation strategies that target permeability improvement are key for optimizing its oral bioavailability.