## Progestin Classification and Structure **Key Point:** Progestins used in contraceptives are classified by their chemical origin: 19-nortestosterone derivatives, 17-hydroxyprogesterone derivatives, and others. ### 19-Nortestosterone Derivatives These are the most commonly used progestins in oral contraceptive pills (OCPs). They are derived from testosterone by removal of the 19-methyl group, making them structurally similar to androgens. **High-Yield:** Levonorgestrel is the prototype 19-nortestosterone progestin. Other members of this class include: - Norethisterone (norethindrone) - Norgestimate - Desogestrel - Gestodene ### Other Progestin Classes | Progestin Class | Examples | Notes | | --- | --- | --- | | 19-Nortestosterone | Levonorgestrel, norethisterone | Most potent; used in most OCPs | | 17-Hydroxyprogesterone | Medroxyprogesterone acetate (MPA) | Used in injectables (Depo-Provera) | | Progesterone derivatives | Dydrogesterone, megestrol acetate | Less commonly used in OCPs | **Clinical Pearl:** Levonorgestrel-containing OCPs are preferred in many countries due to extensive safety data and lower androgenic side effects compared to older formulations. **Mnemonic:** **LEND** — Levonorgestrel, Estrane derivatives (19-nortestosterone), Norethisterone, Desogestrel — all 19-nortestosterone progestins.
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