Ulipristal and Selective Progesterone Receptor Modulators
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Direct answer
Ulipristal and selective progesterone receptor modulators bind progesterone receptors with mixed agonist and antagonist activity. Ulipristal acetate is effective as emergency contraception for up to five days after unprotected intercourse, and it is more effective than levonorgestrel in women with higher body weight. In gynaecology it is also used to shrink fibroids before surgery, but rare serious liver injury has led to restricted long-term use in several regions.
What you must remember
- Mechanism: ulipristal acetate is a selective progesterone receptor modulator with mixed activity, which blocks progesterone action and can delay or prevent ovulation.
- Emergency contraception: ulipristal works up to 120 hours after unprotected intercourse and is more effective than levonorgestrel, particularly at a body mass index of 30 or more.
- Fibroid use: short courses before myomectomy reduce fibroid size and bleeding, and the drug has been used before surgery in many settings.
- Hepatic safety: serious liver injury was rarely reported with the repeated 5 mg fibroid courses, not the single 30 mg emergency dose, so liver function is monitored in fibroid use and the drug is avoided in liver disease.
- Endometrial changes: reversible endometrial thickening and other changes need monitoring with repeated use.
- Interactions and pregnancy: enzyme inducers such as rifampicin and St John's wort reduce efficacy, pregnancy must be excluded, and mifepristone is a different modulator used for medical termination.
A stepwise approach to emergency contraception at 96 hours
A 27-year-old woman presents 96 hours after unprotected intercourse and asks about emergency contraception. Her choice depends on timing, body weight, drug interactions and whether she plans ongoing hormonal contraception. The steps below follow the usual order of decision-making.
- Confirm the time window: Ulipristal is effective up to five days after unprotected sex, so timing is the first check, with levonorgestrel less effective when taken late.
- Exclude pregnancy: An established pregnancy rules out ulipristal as a treatment, since it is not a means of ending an existing pregnancy.
- Check interactions: Enzyme inducers such as rifampicin, some anticonvulsants and St John's wort reduce its effect, so these are asked about first.
- Choose the method: Ulipristal is preferred over levonorgestrel when body weight or delay is a concern, and a copper intrauterine device is the most effective option where it can be placed.
- Plan ongoing contraception: Hormonal contraception should be started about five days after ulipristal, because the drug can block progestogen action in the interval.
- Monitor fibroid use: If prescribed for fibroids, liver function and the endometrium are checked, and the drug is stopped if liver injury appears.
Where the exam tries to catch you
Examiners test whether you choose emergency contraception by timing and weight and recognise the liver and interaction cautions.
- Trap: Treat ulipristal and levonorgestrel as interchangeable at 96 hours. Correct: Levonorgestrel loses efficacy with delay and with higher body weight, whereas ulipristal retains its effect up to five days.
- Trap: Start a combined pill the same day after ulipristal. Correct: Wait about five days, because the drug's progesterone receptor blockade can reduce the effect of progestogen.
- Trap: Assume ulipristal is safe for repeated fibroid therapy everywhere. Correct: Regulators have restricted repeated courses after reports of liver injury, so local labelling and liver monitoring must be followed.
- Trap: Confuse ulipristal with mifepristone. Correct: Both are progesterone receptor modulators, but mifepristone is used for medical termination, while ulipristal is used for emergency contraception and fibroids.
Frequently asked questions
How long after unprotected intercourse is ulipristal effective?
Ulipristal acetate is effective for up to five days, or 120 hours, after unprotected intercourse. This longer window is its main advantage over levonorgestrel, which becomes less effective when taken late.
Why is ulipristal preferred over levonorgestrel in women with higher body weight?
Ulipristal is preferred over levonorgestrel in women with higher body weight because levonorgestrel efficacy falls as body mass index rises. Ulipristal retains better efficacy in this group, which makes it the preferred pill when weight is a concern.
What liver problem is linked with ulipristal used for fibroids?
Serious liver injury is rarely reported with ulipristal used for fibroids, which led regulators to restrict repeated use in several regions. Liver function monitoring is advised whenever ulipristal is used for fibroid therapy.
When can hormonal contraception be started after ulipristal?
Hormonal contraception should be started about five days after ulipristal, to avoid reduced efficacy from progesterone receptor blockade. Condoms bridge the interval, as per local guidance on ulipristal use.