AbobotulinumtoxinA casts tinge of hope for erectile dysfunction
The addition of abobotulinumtoxinA (aboBTX-A) – one of three commercial preparations of botulinum toxin (BTX) type A – to phosphodiesterase type 5 inhibitors (PDE5-Is) or prostaglandin E1 (PGE1) led to favourable outcomes in men with erectile dysfunction (ED), a new study shows.
Approximately 35 percent of men with ED respond poorly to PDE5-Is despite its efficacy, said the researchers. “[Furthermore,] failure to achieve successful intercourse after using the maximum recommended dose of PDE5-Is is always a problem if the patient does not desire alternative treatments … such as vacuum constriction devices, vasoactive agents, and implantation of penile prostheses.”
Therefore, local pharmacological therapies should be considered for PDE5-I non-responders to improve erectile function, they added. [J Sex Med 2010;7:3572-3588] Previous evidence has suggested the potential of BTX as ‘a local aphrodisiac’ given its ability to reduce the contractile power of penile arterioles, allowing men to easily achieve and maintain erections. [Nature 1989;340:348]
Intracavernosal injections of aboBTX-A 250 or 500 units (U)/mL were administered in 47 men with ED (mean age 55.1 years, average ED duration 8.4 years) as an adjunct to their current PDE5-Is or PGE1 regimen. ED was categorized as severe, moderate, or mild (43 percent, 21 percent, and 36 percent, respectively). Participants were advised to engage in sexual activity while under pharmacologic treatment prior to follow-up. [Toxins (Basel) 2019;doi:10.3390/toxins11050283]
At 6 weeks, overall response rates following the administration of aboBTX-A 250 and 500 U/mL were 54.5 percent and 52.9 percent, respectively, which according to the researchers, were “quite high”.
When stratified according to ED severity, men with mild ED had higher response rates (70.0 percent and 74.8 percent for 250 and 500 U/mL, respectively) than those with moderate (57.2 percent and 33.3 percent, respectively) or severe ED (43.8 percent and 33.4 percent, respectively).
Moreover, IIEF-EF* domain scores at 6 weeks increased by 4.7 and 5.6 in the 250 and 500 U/mL arms, respectively.
“AboBTX-A [could have enhanced] the efficacy of oral or injectable agents by eliciting a decrease in tone of resistant vessels thereby enhancing penile blood flow and inhibiting persistent cavernosal smooth muscle tone,” said the researchers. “[AboBTX-A facilitates] long-acting cavernosal smooth muscle relaxation [by modifying] the balance within the erectile tissue between the permanent contractile tone applied onto cavernosal smooth muscle cells and the relaxed state of the same cells elicited by the activation of the NO-cGMP** pathway,” they continued.
Only two patients reported mild post-injection pain. There were no reports of ejaculatory disorder, urinary retention, pelvic floor muscle weakness, or priapism (ie, prolonged erection). “This is reassuring [in terms of] the general and locoregional safety of aboBTX-A,” said the researchers.
“[Taken together, our findings reflect the potential of] aboBTX-A as an add-on therapy [to] maximize the response rate to PDE5-Is with an acceptable safety,” said the researchers.
The findings also hint at a potential new indication for aboBTX-A, [Sex Med Rev 2018;6:135-142] which has initially been approved by the US Food and Drug Administration in 2009 for muscle spasticity, cervical dystonia, and certain cosmetic purposes. Future randomized trials are thus necessary to ascertain the therapeutic potential of aboBTX-A in this setting, said the researchers.