Now, if they can just find a way to get rid of the pesky delayed backache side effect! Ever wonder why pharma don't issue updated versions of their meds? It is not uncommon for vitamin companies to update to "new and improved" yet Pharma's would rather issue a whole new drug. I guess that has to due with the long approval required?
In this case, I imagine it's because the market is already saturated with ED pills, and it wouldn't be a quick fix to eliminate that side effect. All three of the main ones have back pain as a potential side effect, so it looks like it may actually have something to do with its mechanism of action, although I can't think of what part of its mechanism would affect that. So this may mean that scientists would have to find a new class of drugs to treat ED.
But drug companies would much prefer to wait until the patent has expired, or nearly expired to release a new version of their drug, as they don't want two drugs that they have produced competing with each other for market share. Lately, the most common way to do this is to separate out racemic mixtures of drugs to only the active isomer. (Layman's terms: you have a box of gloves, only the left-handed gloves (as an example) are active in the body, the right-handed ones are inactive or cause adverse effects. (Famous example:
thalidomide)) By purifying the drug to only include one isomer (glove), the drug is considered a new entity, and is eligible for a new patent. More recently:
Lexapro released when Celexa was losing its patent
Nexium from Prilosec
Kapidex from Prevacid
Xyzal from Zyrtec
Clarinex from Claritin
Although, with the exception of Lexapro and Nexium, both of which have been out longer than the rest, insurance doesn't like paying for the newer versions, since evidence is limited (or non-existent) that they work any better than their predecessors.