Stress urinary incontinence (SUI) is a common and debilitating condition, predominantly affecting women. Through injecting a bulking agent into the submucosal tissues of the urethra or bladder neck to elevate the urethral mucosa, UBAs aim to replace loss of coaptation function. Although Contigen® was once the most widely used injectable in clinical practice, it has now been superseded by new synthetic non-absorbable UBAs. Currently marketed UBAs include polyacrylamide hydrogel (Bulkamid®) polydimethylsiloxane (Macroplastique®), carbon-coated zirconium oxide (Durasphere®), calcium hydroxylapatite (Coaptite®), with the latest product being a polydimethylsiloxane silicone gel that polymerises when injected (Urolastic®). Despite the common use of UBAs, clinical data comparing outcomes are limited. The aim of this systematic review is to assess and compare the efficacy and safety profile of all UBAs available for the treatment of SUI in women.

This systematic review was conducted in accordance with the PRISMA guideline. A systematic search was conducted using the Ovid Medline, Embase and PubMed databases. All studies involving women who underwent urethral bulking injections for SUI or mixed urinary incontinence (MUI) in primary or recurrent settings, with either Bulkamid®, Macroplastique®, Durasphere®, Coaptite® and Urolastic® were included. The primary outcome assessed in this study is treatment efficacy. Secondary outcomes assessed are duration of efficacy and adverse events. Short term outcomes were defined as a follow-up duration of <24-months, and long-term outcomes >24-months. Given the heterogeneity of patient cohorts across studies and the variability in outcomes reported, quantitative analyses combining the outcomes of different studies were not performed.  583 articles were screened with 56 articles included. A qualitative analysis was performed.

The newer synthetic UBAs are not inferior to Contigen®, with variable mean success rates of 30%-80% in the short-term. Better long-term success rates were found with Bulkamid® (42%-70%), Coaptite® (60%-75%), and Macroplastique® (21%-80%) on qualitative review. Urinary tract infection rates were similar between bulking agents (4%-10.6%) although temporary acute urinary retention was more commonly associated with Coaptite® (mean 34.2%), and de novo urgency in Durasphere® (mean 24.7%). Significant complications such as migration into lymph nodes was reported with Durasphere®. Erosion was reported with Macroplastique®, Coaptite® and Urolastic®, with a rate as high as 24.6% in one study of Urolastic®.

The synthetic UBAs were not inferior to Contigen® in the short-term. Available data supports the use of Bulkamid® and Macroplastique®, which has shown a short-term efficacy of 30%-90% and 40%-85% respectively, and long-term efficacy of 42%-70%, and 21%-80% respectively. Bulkamid® appears to have a more favourable safety profile, with no cases of erosion or migration of product associated with its use. Direct comparisons of UBAs have not been performed.

Overall, there are more data to support the use of Bulkamid® and Macroplastique®. Additionally, Bulkamid® appears to have a more favourable safety profile, with no significant complications being reported. Further studies are required to directly compare the efficacy of currently available UBAs in addition to assessing the long-term outcome and durability of each UBA. Furthermore, a minimum set of outcome measures is required in future publications to standardise these comparative analyses to better understand these therapies.