It would be helpful to know why the prostate was removed because its a little different ballgame when its removed due to constant enlargement & inflammation, versus when its removed during cancer treatment (especially if radiation or hormone therapy was used, and/or still in use).
Before you do something as drastic as a penile implant, he might try something a lot cheaper, and a lot less invasive: High dose Losartan + Aspirin.
I'm fairly certain that this will still work with the prostate gland removed, and it does work for a large number of men with ED when drugs like viagra fail. There is a growing body of evidence that this combination can help sustain erections even when there is nerve injury
, and does increase interest (slightly) in men. It also doesn't have the heart attack risks that drugs like viagra have. Benicar, and Losartan generally make it easier for the heart to do its job, rather than the other way around.
While no drug(s) can replace the smooth muscle tissue lost from removal of the prostate gland, and its not going to change the dry ejaculation issue (thats just physical with the prostate removed), a combination of high dose (100mg to 200mg) losartan (Cozaar is the brand name in the US) split into morning & evening doses, and taken daily, plus 325mg to 1g of aspirin taken an hour or two before sex can significantly help ED. Depending upon the cause, even aspirin alone can help, but the combination is better than either of them apart. Big plus, losartan is now generic. (ARB's are hideously expensive as far as BP drugs go.) It has been expressed to me that some people find an extra 50mg an hour before sex, or timing their medication so that it is taken an hour before sexual activity seems to have an additive benefit for them.
The harder part is finding a doctor that knows about the off label use of losartan & a few select other ARB's for ED, and making sure it plays nice with any other conditions he may have, or other medications he may be taking (in particular steroids, adrenal/hormone supplements, other blood pressure drugs, drugs for treating bone density, heart medications, and other nsaids).
What if he doesn't have high blood pressure or pre-hypertension? Wont this lower his blood pressure too much?
Losartan does have some side effects, but even if his blood pressure is in the normal range it is unlikely to lower it to levels that would be problematic (though it will drop harder the first couple days, and dizziness is a frequent initial side effect the first day or two). If it does drop it too much, try something else.
What if he does have hypertension?
If he is already on a BP drug, he might get enough relief switching it to losartan; and since quite a few of the other BP drugs contribute to ED problems he might end up with a double benefit from switching if the other drug is contributing to the ED issues.
Higher doses of Olmesartan (brand name Benicar), another ARB, can also help, but can be a lot more problematic with side effects (extreme sensitivity to light is a fairly common one at high doses). Might be worth investigating if losartan helps, but doesn't help enough. I would put it last on the list to try because of side effects, cost, and the likelihood of having to battle an insurance company to get it covered. This is also a very off label use of an ARB. This works best for ED at dose ranges far exceeding those used for controlling blood pressure, and does not have the same amount of evidence to back up its effectiveness for ED as Losartan does. However it binds more strongly to the things that should help ED than losartan does. Its effect on blood pressure pretty much stops at 40-60mg a day; so taking 40mg every 6 hours doesn't have any additive effect on decreasing BP. To be honest, its just not very impressive as a blood pressure drug; it has a lot of other uses it is quite good for though (such as treating congestive heart failure). Again, works better in combination with aspirin for ED issues.
Benicar is also hideously expensive at these doses, and no generic on the US market. Insurance companies will likely balk at this, but will gladly cough up $10 a day for other ED treatments. I don't consider $10 a day cheap by any means. I don't make the rules!
The reason for the higher & every 6 hour dosing of benicar, as opposed to the 20-40mg a day people take for general hypertension treatment has to do with its effects on inflammation at higher doses, its effects on the steroid system at higher doses, and on sex hormones at higher doses. The other effects which are also beneficial for treating ED have a much shorter life (6-8hrs) than the drugs effect on hypertension, and it takes a lot more of the drug to activate those receptors in the body. He might still get a benefit from 40mg taken in the evening an hour or two before sex, but its far less likely to be as helpful.
(Just like losartan: need to make sure it will play nice with any other medication he is on. In particular other BP meds, heart drugs, NSAIDS, hormone treatments, adrenal supplements...etc)
Notes for both of the above: These also come as a combination drug for blood pressure containing hydrochlorothiazide; you don't want that kind for the high doses used here. Those will be marked drug+HCT, or in the case of losartan/cozaar - the HCT version is hyzaar.
Any time you combine an ARB with aspirin (or pretty much any NSAID) they have the potential to spike potassium. Its a simple blood test to check electrolytes, and liver function, but it needs to be done if they are used in combination frequently at the higher doses of aspirin (600mg to 1g per day). Electrolytes should also be checked at least once while concurrently taking both the aspirin & ARB at the time the blood is drawn
if he requires the full 1g dose of aspirin in concert to make things work for him. Its not likely to be a problem, but it can be serious if he is sensitive to either drug causing elevated potassium. Because of the higher doses of each of these, these effects can happen quicker. First couple months electrolytes need to be monitored.
One more off label option, and this will get an eyebrow raised from the doc as its very commonly used to treat enlarged prostate problems -- Cardura (drug name Doxazosin). You might also have a fight with insurance over this one because of its chief use if he doesn't have concurrent high blood pressure, or pre-hypertension. This is more likely to work in the lower ranges of 2mg-8mg a day if its going to help. Cardura is in another class of blood pressure drugs called alpha blockers. Not at all ironically, one of the more serious, and thankfully rare side effects of this drug is priapism (an erection lasting for hours that wont go away). This one doesn't play nice with aspirin, and there is no additive benefit from combining them.
The main way all of these these drugs help is by increasing the amount of blood flow available to the penis to become erect. The penis both needs to be able to get blood flow to become erect, and to be able to retain that blood to stay erect. (The latter is why most blood pressure drugs can cause difficulties maintaining an erection, they take away the ability for the penis to decrease that outward flow of blood.)
Benicar & Losartan also have some effect on the steroid, and hormone systems in the body. They activate (weakly) some of those receptors in ways that make up for some of the lost hormones, either directly, or by the bodies tendency to tightly regulate, and use sex hormones to counter balance steroid metabolism.
Aspirin primarily reduces inflammation, reduces blood clotting, and thins the blood slightly allowing blood to more easily penetrate into the fine capillaries, and tissues of the penis.
Cardura works for ED by a combination of increasing blood flow available to the penis, and by opening up fine capillaries, and pathways in tissues in the penis to allow increased blood flow.
There are other options out there yet still ...
As always, the standard legal disclaimer applies. I'm not a doctor, this isn't to be considered medical advice, some results are based on imperfect and/or limited data, knowledge of research that is ongoing, always check with your doctor first, pay your taxes, wear a helmet while riding, and I'm too broke to sue.