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Urolastic — In-Situ Polymerizing PDMS (PDMS-U)

Urolastic is a nonbiodegradable, in-situ polymerizing polydimethylsiloxane (PDMS) silicone gel urethral bulking agent for female SUI. CE-marked in Europe; not FDA-approved in the US.[1] It is distinguished from other PDMS products by its unique mechanism — injected as a liquid/gel that polymerizes and solidifies in situ within the periurethral tissues.

Composition & Material Properties​

  • Active: medical-grade PDMS silicone elastomer.[1]
  • Form: injected as a viscous liquid / gel that cross-links and solidifies after injection — unlike Macroplastique, which consists of pre-formed solid PDMS macroparticles in a PVP carrier.
  • Non-particulate: forms a continuous solid mass after polymerization — distinct from particulate Macroplastique, Durasphere, and Coaptite.
  • No carrier gel — does not require a biodegradable carrier.
  • Nonbiodegradable, non-immunogenic (no skin testing required); permanent once polymerized.

The in-situ polymerization was designed to allow injection through smaller needles, conformation to tissue contours before solidifying, and — theoretically — reduced migration via a continuous mass rather than discrete particles.

Mechanism​

Periurethral injection of PDMS gel followed by in-situ cross-linking converts the viscous liquid to a solid elastomeric implant within the submucosa, producing permanent, non-migrating periurethral bulk that augments coaptation during rises in abdominal pressure.[1][2]

Injection Technique​

Periurethral injection under local anesthesia, typically without cystoscopic guidance:[3][2]

  • Setting: office / outpatient; ~15–30 minutes.
  • Sites: 4 periurethral injections — typically 10, 2, 4, and 8 o'clock.
  • Volume: 0.5–1.25 mL per site (~2–5 mL total per session).
  • Cystoscopy: not routinely required (contrast with Bulkamid / Coaptite).
  • Operator: physicians must be PDMS-U certified.[4]
  • Reinjection: needed in 16.7–35% (pooled 20%, 95% CI 15–24%).[5]

Indications​

Female SUI, particularly in patients who are not optimal MUS candidates:[2][5]

  • Recurrent SUI after prior anti-incontinence surgery.
  • Prior oncologic gynecologic surgery.
  • Neurologic disease with voiding dysfunction.
  • Low maximum flow rate.

Clinical Efficacy​

Capobianco 2018 Systematic Review & Meta-Analysis​

The only dedicated systematic review (5 studies, 6–24 mo follow-up):[5]

  • Pooled objective success: 57% (95% CI 38–75%; I² = 82.3%) — wide range 32.7–67.0%.
  • PGI-I subjective improvement: > 80% in 2 cohorts (assessed in only 40% of studies).
  • Pooled secondary injection rate: 20% (95% CI 15–24%; I² = 0%).

Individual Studies​

StudyDesignnFollow-upOutcome
Futyma 2015Open multicenter (primary + recurrent SUI)6012 moPad weight ↓ ~70–75% from baseline.[6]
Futyma 2016Prospective, recurrent SUI6624 mo32.7% objective success; 22.4% dry; ITT 24.2% cure / 16.7% dry; 4.5% intravesical material; 25.8% complication rate.[3]
Kowalik 2018Prospective, non-MUS candidates206 mo90% subjective improvement; 56% subjective cure; 65% objective cure; 40% abnormal PVR (> 150 mL).[2]
Casteleijn 2020Cross-sectional (87 revisited)11025 mo median51% satisfaction; 46% subjective cure; 47% objective cure; 22% retention; 15% pain; 15% dyspareunia; 7% exposure; 5% erosion; 18% required excision.[7]

Casteleijn 2023 — PDMS-U vs MUS (Two-Arm Cohort)​

Prospective comparison, n = 131 PDMS-U vs n = 153 MUS:[8]

  • Subjective cure: MUS 90% vs PDMS-U 46% (adjusted OR 4.9).
  • Objective cure: MUS 90% vs 63% (adjusted OR 5.4).
  • Mean total cost: PDMS-U €3,567 vs MUS €6,688.
  • At a €25,000 willingness-to-pay threshold, MUS was 84% likely cost-effective using disease-specific QoL (IIQ QALY); PDMS-U was 99% likely cost-effective using generic QoL (EQ-5D-5L QALY).

Safety Profile — The Defining Concern​

Urolastic carries a notably higher complication burden than other bulking agents — particularly for erosion, exposure, and excision requirement.[3][7][9]

Casteleijn 2020 (n = 110)[7]​

  • Urinary retention 22% (most common AE)
  • Pain 15%, dyspareunia 15%
  • Exposure 7%, erosion 5%
  • Excision required 18% — by far the highest among bulking agents.

Erosion — Up to 24.6%​

The Hoe 2021 systematic review documented erosion with Macroplastique, Coaptite, and Urolastic, with rates as high as 24.6% in one Urolastic study — by far the highest erosion rate reported for any urethral bulking agent and a marked contrast to Bulkamid, which has no reported erosions.[9]

Intravesical Material Migration​

Futyma 2016 reported 4.5% of patients had oval-shaped Urolastic material inside the bladder — a unique complication not reported with other bulking agents.[3]

Casteleijn 2023 Learning Curve (n = 203, 9 physicians)[4]​

  • Most physicians did not reach acceptable failure rates for complications, retention, or excision.
  • Only 2 of 5 physicians who performed ≥ 20 procedures reached competence (at procedures 20 and 40).
  • No significant association between procedure number and complications.
  • Large inter-physician variability.
  • Authors' conclusion: physician experience did not influence safety outcomes.

Overall Complication Rate​

25.8% in the Futyma series.[3]

Urolastic vs Other Bulking Agents​

ParameterUrolasticBulkamidMacroplastiqueCoaptite
FormIn-situ polymerizing gelHomogeneous hydrogelPDMS macroparticlesCaHA microspheres
MechanismIn-situ polymerizationCollagen infiltrationForeign-body encapsulationFibrous encapsulation
ParticulateNo (continuous mass)NoYes (> 100 μm)Yes (75–125 μm)
Cystoscopy requiredNo (periurethral)YesOptional (MIS)Yes
Objective cure (12–24 mo)32.7–65%47–63.7%37–49%63.4%
Subjective cure (12–24 mo)46–56%63.7–81.8%47.6%—
ErosionUp to 24.6%0%2.4%Rare
Excision required18%RareRareRare
Urinary retention22–40%~3.1%~7.2%~34.2%
Intravesical material4.5%Not reportedNot reportedNot reported
FDA approvalNoYes (2020)Yes (2006)Yes (2005)
CE markedYesYesYesYes

Guideline Position​

The AUA/SUFU 2023 guideline does not specifically mention Urolastic — likely because it is not FDA-approved and is unavailable in the US. The guideline highlights CaHA, PDMS, and PAHG as having documented long-term persistence and explicitly notes that erosions were not noted with PAHG as with other bulking agents.[10]

Regulatory Status​

  • CE-marked in Europe.[1]
  • Not FDA-approved — never underwent PMA, unavailable in the US.
  • CE marking historically required less stringent clinical evidence than FDA PMA.[11]
  • Devices approved first in the EU have an increased risk of post-marketing safety alerts and recalls (adjusted HR 2.9; 95% CI 1.4–6.2) vs devices approved first in the US.[12]

Advantages​

  • Unique in-situ polymerization mechanism.
  • No cystoscopy required — office-based periurethral injection under local.
  • Non-particulate — theoretically avoids particle migration.
  • Lower acquisition cost than MUS (€3,567 vs €6,688).[8]
  • Useful in patients not optimal for MUS.
  • Does not preclude future surgery.

Limitations​

  • Not FDA-approved.[1]
  • Highest erosion rate of any urethral bulking agent — up to 24.6%.[9]
  • 18% excision rate — highest among bulking agents.[7]
  • Intravesical material migration in 4.5% — unique complication.[3]
  • High urinary retention (22–40%) and dyspareunia (15%).
  • Overall complication rate 25.8%.[3]
  • Poor long-term efficacy in recurrent SUI (32.7% objective at 24 mo; ITT 24.2%).[3]
  • Learning-curve study: physician experience did not improve safety — and most physicians did not reach acceptable failure rates.[4]
  • Inferior to MUS (subjective cure 46% vs 90%; objective 63% vs 90%).[8]
  • Removal is technically difficult — polymerized silicone is firm and adherent.
  • Limited evidence base; no RCTs vs other bulking agents.

Current Position​

Urolastic occupies a limited and declining niche in the European market. The erosion and excision signals, the failed learning curve, the lack of FDA approval, and the rise of Bulkamid (no erosion, longest documented persistence at 96 months) have substantially eroded the rationale for its use. The Hoe 2021 systematic review concluded that Bulkamid and Macroplastique are the preferred bulking agents, with Bulkamid having the most favorable safety profile.[9][10]

See also: Bulkamid, Macroplastique, Coaptite, Durasphere, Urethral Bulking Agents (procedure).

References​

1. Hussain SM, Bray R. Urethral Bulking Agents for Female Stress Urinary Incontinence. Neurourology and Urodynamics. 2019;38(3):887-892. doi:10.1002/nau.23924

2. Kowalik CR, Casteleijn FM, van Eijndhoven HWF, Zwolsman SE, Roovers JWR. Results of an Innovative Bulking Agent in Patients With Stress Urinary Incontinence Who Are Not Optimal Candidates for Mid-Urethral Sling Surgery. Neurourology and Urodynamics. 2018;37(1):339-345. doi:10.1002/nau.23299

3. Futyma K, Nowakowski Ł, Gałczyński K, Miotła P, Rechberger T. Nonabsorbable Urethral Bulking Agent — Clinical Effectiveness and Late Complications Rates in the Treatment of Recurrent Stress Urinary Incontinence After 2 Years of Follow-Up. European Journal of Obstetrics, Gynecology, and Reproductive Biology. 2016;207:68-72. doi:10.1016/j.ejogrb.2016.10.011

4. Casteleijn F, Latul Y, van Eekelen R, Roovers JP. A Clinical Learning Curve Study of Polydimethylsiloxane Urolastic for Stress Urinary Incontinence: Does Safety Improve When Expertise Grow? Gynecologic and Obstetric Investigation. 2023;88(4):240-248. doi:10.1159/000530666

5. Capobianco G, Azzena A, Saderi L, et al. Urolastic®, a New Bulking Agent for Treatment of Stress Urinary Incontinence: A Systematic Review and Meta-Analysis. International Urogynecology Journal. 2018;29(9):1239-1247. doi:10.1007/s00192-018-3703-6

6. Futyma K, Miotła P, Gałczyński K, et al. An Open Multicenter Study of Clinical Efficacy and Safety of Urolastic, an Injectable Implant for the Treatment of Stress Urinary Incontinence: One-Year Observation. BioMed Research International. 2015;2015:851823. doi:10.1155/2015/851823

7. Casteleijn FM, Kowalik CR, Berends C, et al. Patients' Satisfaction and Safety of Bulk Injection Therapy Urolastic for Treatment of Stress Urinary Incontinence: A Cross-Sectional Study. Neurourology and Urodynamics. 2020;39(6):1753-1763. doi:10.1002/nau.24417

8. Casteleijn FM, de Vries AM, Tu LM, et al. Cost-Effectiveness of Urethral Bulking Polydimethylsiloxane-Urolastic® Compared With Mid-Urethral Sling Surgery for Stress Urinary Incontinence: A Two-Arm Cohort Study. BJOG. 2023;130(6):674-683. doi:10.1111/1471-0528.17396

9. Hoe V, Haller B, Yao HH, O'Connell HE. Urethral Bulking Agents for the Treatment of Stress Urinary Incontinence in Women: A Systematic Review. Neurourology and Urodynamics. 2021;40(6):1349-1388. doi:10.1002/nau.24696

10. Kobashi KC, Vasavada S, Bloschichak A, et al. Updates to Surgical Treatment of Female Stress Urinary Incontinence (SUI): AUA/SUFU Guideline (2023). The Journal of Urology. 2023;209(6):1091-1098. doi:10.1097/JU.0000000000003435

11. Greer SL, Hervey TK, Mackenbach JP, McKee M. Health Law and Policy in the European Union. Lancet. 2013;381(9872):1135-1144. doi:10.1016/S0140-6736(12)62083-2

12. Hwang TJ, Sokolov E, Franklin JM, Kesselheim AS. Comparison of Rates of Safety Issues and Reporting of Trial Outcomes for Medical Devices Approved in the European Union and United States: Cohort Study. BMJ. 2016;353:i3323. doi:10.1136/bmj.i3323