Very good questions. Again, I must say that I greatly appreciate your attention to detail in your questions. It is refreshing to have a pet owner so invested. Thank you.
Let me answer these questions in reverse order.
First, I think that before any of these medications are used, it is important to check the prostate to be sure that it is BPH, and not neoplasia, cyst, or prostatitis. These are all treated very differently. So, we need to be 100% sure before starting this protocol.
Castration would be recommended no matter what the cause of prostatic enlargement (neoplasia or BPH) and can be considered in prostatitis in an intact non-breeding male. Cysts, might not really make a difference either way.
3) I would actually not consider either of these medications as a superior treatment for BPH over castration. Castration has added benefits of reducing the risk of prostate cancer if indeed it is not already present. Yes, it reduces hyper activity for sure, and can lead to weight gain as well. But, that reduced risk in neoplasia is up for debate as well. For me it makes the best option. Because...
1) Osaterone acetate - does have a higher risk of side effects than does finasteride. Including :
- A transient increase in appetite occurs very commonly.
- Transient behavioral changes such as increased or decreased activity, or more sociable behavior, are common.
- Other adverse reactions, including transient vomiting and/or diarrhea, polyuria/polydipsia, lethargy or feminization syndrome including mammary gland hyperplasia occur uncommonly.
- A transient reduction in plasma cortisol occurs in most treated animals.
- Treatment does not usually need to be discontinued. In clinical trials, all dogs recovered without any specific therapy.
- Mammary gland hyperplasia was seen as a very rare adverse effect of osaterone during a laboratory study.
Osaterone was administered in test studies for one week, and compared to the regression rate after the same time period post castratio and found to be equivalent (roughly 60% reduction for both treatments after one week). Regression was measured about 6 months later (180 days) and enlargement had occured of the prostate. In some cases larger than previous before treatment.
So, your question 1b) has no definitive answer. Giving the medication will likely lead to a reduction in prostate equal to castration. When the medication stops, (for either medications you have mentioned) the prostate will begin to become enlarged again. Monitoring will be needed on an individual basis for either medical treatment you use. In some cases, the medication may need to be given life long in order to keep the hyperplasia to a minimum and to reduce the clinical signs.
So, monitoring at 2.5 months out may show enlargement or it might not. There is no definitive timeline that has been established. It sounds like a good model for experimentation, and you might even publish that! :) But, truthfully, my answer is we don't know.
2) Finesteride of the two is likely my favorite because secondary signs were mostly reverseable (with both drugs) but not as likely to happen with finesteride vs. osaterone. And it should be noted we can't be sure of long term effects of administration.
Finasteride specifically and totally inhibits 5-alpha-reductase. This enzyme is re sponsible for metabolizing testosterone to dihydrotestosterone (DHT) in the prostate, liver and skin. DHT is a potent androgen and is the primary hormone responsible for the development of the prostate
Keep in mind that for either drug or surgical castration you will be altering the natural hormonal balance of Ben. With castration, you are decreasing testosterone by removing the testicles. With osaterone you are using progesterone like hormones (feminine hormones) to alter your pet. This can lead to feminization signs like breast tissue enlargement, et al listed above). Finasteride again is less likely to cause these signs. One study done in dogs reported no adverse effects or irreversibility of effects after treating for 21 weeks at 1 mg/kg
AND, it is important to note that all of these studies have been used to treat EARLY stages of BPH. Later stages, it may no longer be effective. So, for long term treatment, we just don't know. Treatment might not be effective on sequential treatments. Castration however is a one time treatment with possible permanent solutions with a well established history of side effects and outcomes (maybe 100's of years of scientific evidence, and maybe thousands of human experience with castration of animals) versus newer hormonal treatment which isn't fully established and we don't know what all the long term side effects would be.
So, that is my best opinion after review of the available data.
Given only three options and having to chose for my own pet, by far I would chose castration as the best option. Followed by finasteride, and lastly osaterone.
Treating for a week, and then checking for regression at 2.5 months is also not likely to be an effective method either. Likely either medication will prove more effective at a once daily dose continuously in order to be effective.
Given once daily, both medications do appear to be legitamite choices for treatment of BPH. It remains to be seen if they are effective permanent solutions.