Anti-Estrogens and Antiprogestins – Reproductive Pharmacology

00:01 I'm Dr. Shukle.

00:02 We're going to cover a topic called Selective Estrogen Receptor Modulators.

00:07 This is a difficult concept for a lot of medical students.

00:10 So, we're going to take our time going over it, and try and get the understanding really up to a high level.

00:18 When we take a look at the overall armamentarium that we use in Gonadal hormone agonists and antagonists, you can see that the SERMs or Selective Estrogen Receptor Modulators fall under the receptor antagonists.

00:32 Why is that? Well, because from a pharmacological point of view, this is what we're using it for.

00:38 We're using it for its antagonistic action, not for its agonistic action.

00:44 Now have a look at this diagram. It's a really nice diagram.

00:47 After this lecture is over, I want you to pause the video and study it so that you can see where all of the drugs fit in.

00:53 The first of these SERMs that I want to talk about is probably the most famous of them, and it's used most commonly in breast cancer, and that is Tamoxifen.

01:02 Now, it acts as an estrogen antagonist in breast tissue, and that's why we're using it.

01:09 So it reduces the risk of high risk patient breast cancer, and it also reduces the risk that there's a recurrence once we've finished our treatment.

01:17 So a lot of times you'll see people being put on Tamoxifen, after they've had their chemotherapy, radiotherapy, and surgery from breast cancer.

01:26 One of the disadvantages of this particular drug is that it does work as an agonist in the endometrial tissue, so that can promote endometrial hyperplasia, and it can increase the risk of endometrial cancer.

01:40 So this is one of the great disadvantages of this medication.

01:44 Now, there are other agents within the drug class that has have less agonistic activity and therefore have lower endometrial risk factors.

01:56 Regarding its side effects as an antagonist, you increase the risk of hot flashes and other menopausal symptoms.

02:02 As an agonist, Tamoxifen decreases the risk of osteoporosis, but there is an increased risk in venous thromboembolism.

02:10 Raloxifene is a cousin of Tamoxifen.

02:14 It is also approved for the prevention of osteoporosis.

02:18 It is an antagonistic effect that reduces breast cancer risk.

02:23 It's agonistic effect does not have any significant estrogenic effects on the endometrail tissue, unlike Tamoxifen, which makes it a little bit better in terms of endometrial cancer risk.

02:35 So it's a very nice drug that's come along and starting to be picked up more and more in terms of use.

02:44 Another drug in this drug classes Bazedoxifene, which is also a cousin of Tamoxifen.

02:49 You can see that these agents all end in F-E-N-E except for tamoxifen, which the E was dropped for some reason that I can't explain.

03:00 But generally speaking, when you have that suffix, that's the class of drugs we're talking about.

03:05 This also is used for menopausal symptoms, and it's also used for osteoporosis prevention with estrogens.

03:14 Clomiphene is another example of a drug in this drug class.

03:17 It reduces the negative feedback loop in the pituitary.

03:22 What you end up having when you give this medication is you have an increase in the luteinizing hormone and follicular stimulating hormone.

03:30 Why would we ever want to do that? Well in patients who don't have ovulation or an ambulatory patients, it actually can induce ovulation.

03:42 Now let's move on to the full antagonists.

03:44 An example of the full antagonists include drugs like Fulvestrant.

03:50 It is a pure estrogen antagonist in all tissues, whether you're talking about breast or endometrium.

03:56 So it is used in breast cancer, in patients who are resistant to Tamoxifen.

04:02 And it is also used in patients who have breast cancer who also have high risk for endometrial cancer.

04:09 So although it isn't used as much as Tamoxifen, it is a very good drug.

04:13 And you can see where it fits on our pathway here it's right next to the Tamoxifens.

04:20 The next category of our drugs are the aromatase inhibitors.

04:23 They're also called synthesis inhibitors.

04:26 Why do we call them synthesis inhibitors? Because if you take a look at our diagram here, you'll see that aromatase is really responsible for the one of the last steps in the production of estrogen.

04:38 Now, these drugs are nonsteroidal competitive aromatase inhibitors.

04:44 They are used in the treatment of breast cancer for obvious reasons because we want to reduce the effects of estrogen on the breast cancer.

04:51 Another agent in this class is Exemestane.

04:55 which is an irreversible aromatase inhibitor.

04:59 Now, I put it in a slightly different category because it is irreversible.

05:03 It is also used in the treatment of breast cancer.

05:07 Let's move on to other drug classes specifically the gonadotropin releasing hormone agonists and antagonists, as well as danazol.

05:15 Now, this is a complicated drug.

05:17 And I'll tell you why.

05:19 Danazol is the prototypical drug in this drug class, there are others, but let's focus on Danazol.

05:24 Now this drug or this agent inhibits more than 45 different enzymes that are involved in not just gonadotropin synthesis, but other types of complex molecule synthesis as well.

05:36 So it's a very complicated drug.

05:37 It is metabolized by cytochrome p450 and you should be aware that it can have drug interactions.

05:45 It is a weak partial agonist of progestin, androgen, and glucocorticoid receptors.

05:52 So it's a complex set of effects here.

05:55 It is used in the treatment of endometriosis.

05:59 It is used in the treatment of fibrocystic disease of the breast, and it can be used in other dysmorphic diseases of the endometrium.

06:09 I'm going to move on to a slightly different category of drugs.

06:12 These are the gonadotropin-releasing hormone analogues, which means that they simulate the activity of gonadotropin releasing hormone.

06:21 The first of this that I'm going to talk about is Leuprolide.

06:25 Now, we have discussed this in a previous lecture, but I'll just mention it here for completeness sake.

06:33 This provides continuous stimulation of GnRH receptors, which actually end up suppressing secretion in the long run.

06:40 Why does that happen? Well think about teasing your little brother or your little sister, continuous teasing of your little brother or little sister eventually results in that sibling ignoring you.

06:52 It's kind of the same thing with the brain and with the body.

06:55 If you have continuous stimulation of certain types of receptors, eventually, the effect of that stimulation becomes less and less.

07:05 That happens through a process called Receptor-mediated endocytosis, also called downregulation.

07:11 So you end up taking in those receptors And you destroy them at a higher rate than you're producing them.

07:15 Eventually, you have fewer receptors to respond to your stimulus and you have less of an effect.

07:22 Now, the end result of using a drug like this is that it inhibits ovarian production of estrogen and progesterone.

07:28 So it is an anti estrogen and anti progesterone medication.

07:34 We use this in the treatment of precocious puberty in girls.

07:37 So if patients have high levels of estrogen and progesterone at a very young age, and they start to have early puberty, we can use this agent to delay puberty.

07:49 We also use this short term for the treatment of endometriosis.

07:52 We don't want to use it long term for obvious reasons.

07:55 And we can use it short term for the treatment of fibroids as well, which is kind of the same process as the endometriosis.

08:03 Let's move on now to the Gonadotropin-releasing hormone antagonists.

08:09 So Ganirelix is one of the first examples that we'll use.

08:12 And sometimes this is used for controlled ovarian hyperstimulation in patients who are anovulatory.

08:18 We can also use certain agents in prostate cancer in men, because again, you're antagonizing the effects of gonadotropin releasing hormone so it can be used in males.

08:29 Now, we can use it in females as well.

08:32 It is used in the first week of therapy with leuprolide in those patients.

08:37 We are less likely to cause a tumor flare with this combination.

08:41 The next category of drugs are the antiprogestins.

08:44 And the most famous of these is Mifepristone, which is also known as RU 486.

08:49 So you may remember this as being very controversial when it was first released onto the market.

08:54 It is an antagonist of progesterone and it is also an antagonist of glucocorticoids.

09:01 The use was for as an Abortifacient and it is also given in combination with misoprostol - with a 95% termination rate.

09:11 Side effects of this particular agent include nausea, vomiting, and diarrhea.

09:17 You can also get cramping and bleeding.

09:19 And you may have episodes of unusual infections like Clostridium for some unknown reason, and we can't really explain why that happens.

09:27 Okay, that's great.

09:29 We covered a couple of these medications.

09:32 Go to your exam, feel confident, and show them what you know.