Why would a provider ever pair the two?
A provider pairs them when neither one alone gives a firm enough erection. Pills are the usual starting point, but the AUA guideline notes that PDE5 inhibitors are ineffective in about 40% of men, and that some men who respond at first lose that response as ED progresses. Injections such as Trimix are the next step for many of them.
A smaller group gets only a partial result from injections, too. For those men, adding a pill is a recognized salvage approach. In a study of 93 men whose home trials of high-dose alprostadil and a three-drug injection had both failed:
| Result | Men | Share |
|---|---|---|
| Responded to sildenafil alone | 32 | 34% |
| Responded only to sildenafil plus injection | 29 | 31% |
| Responded to neither | 32 | 34% |
The men who needed the combination all took 100 mg of sildenafil alongside the injection. That is a meaningful rescue for a hard-to-treat group, but it was done in a specialist center with doses chosen for each man.
What are the risks of combining them?
The same study recorded the cost. Of the 41 men given the combination, 20 reported side effects: penile pain, headache, facial flushing, indigestion, nasal congestion and dizziness in 12 of them. One man fainted.
One plausible contributor to the dizziness is blood pressure. Phentolamine, one of the three drugs in Trimix, is an alpha-blocker, a class that relaxes blood vessels throughout the body. The Viagra label asks that men on alpha-blockers be stable before starting sildenafil and begin at 25 mg, because the two together can lower blood pressure. Our page on phentolamine in Trimix covers what it does in the mix.
The approved alprostadil injections take a cautious line as well. The Caverject label says the safety and effectiveness of combining it with other vasoactive agents have not been established and that such combinations are not recommended.
Why does doing it unsupervised raise priapism risk?
Your Trimix dose was set in the office, without a pill on board. Add sildenafil and the same injection is working on tissue that is already primed for blood flow, so the erection can be stronger and last longer than the dose was designed to produce.
That matters because priapism is the most serious side effect of injection therapy, according to the AUA. The AUA/SMSNA priapism guideline lists recent penile injections among the common causes, defines priapism as an erection lasting more than four hours, and notes that smooth muscle damage can begin as early as six hours.
An erection still firm at four hours is an emergency. Call 911 or go to the nearest emergency room and tell the staff you used an ED injection and a pill. Our page on an erection lasting more than 4 hours explains what happens next.
Related question: is it safe to use them on different days?
Often, but the spacing depends on which pill. Sildenafil has a terminal half-life of about 4 hours, so most of it clears within a day. Tadalafil is another matter: the Cialis label reports improved erections for up to 36 hours after a dose, which means yesterday’s tablet can overlap with today’s injection. Your provider sets the gap, and the Trimix versus pills comparison covers how men often use each.
How Ultimate Male handles a partial response
When injections fall short, the first questions are simpler than adding a second drug. Is the technique right? Was the vial stored cold and in date? Is the dose at the level your test injection supported? Is an untreated problem, such as low testosterone, part of the picture? Fixing one of those often solves the problem.
If it does not, a PA-C or MD at our San Gabriel or Downey clinic may consider a stronger mix such as Quadmix or, for selected men, a planned combination with exact doses, timing and clear instructions for a long erection. Learn more on the ED medications page or the sildenafil medication page, or talk it through on a free 10-minute call.
