Are alprostadil and sildenafil (viagra) effective in the treatment of all types of erectile impotence?

No: Nothing works all the time. That is certainly true of these agents. For instance, if the blood vessels that are responsible for creating an erection are damaged then these medications probably won't work.

No: These medications do not necessarily help all men with erectile dysfunction. These medications help draw more blood into the erectile chambers of the penis. If men's arterial inflow is too compromised, or their venous circulation permits leakage of blood from the chambers, these medications might not work as well. Men also must have intact pelvic nerves for medications like viagra (sildenafil) to work.