Durasphere — Carbon-Coated Beads
Durasphere EXP is a permanent particulate urethral bulking implant indicated in the United States for adult women with stress urinary incontinence due to intrinsic sphincter deficiency (ISD). Current EXP labeling must be distinguished from the original zirconium-oxide formulation studied before the product's first FDA approval in September 1999.[1][2]
For clinical treatment selection and operative context, see Urethral Bulking Agents.
Material and Imaging: Identify the Formulation
| Feature | Original pivotal-trial material | Current US EXP instructions |
|---|---|---|
| Beads | Pyrolytic carbon-coated zirconium oxide, 212–500 μm | Pyrolytic carbon-coated graphite, 90–212 μm |
| Carrier | Water-based gel containing beta-glucan | Water-based gel containing beta-glucan |
| Imaging | Zirconium-containing deposits can be radiopaque | The label states graphite-containing EXP is not visible on X-ray and identifies MRI for visualization |
The current DFU explicitly describes the original material in its clinical-trial section. Do not infer that every implant called Durasphere has the same X-ray appearance or that the original trials separately establish all outcomes for the later formulation.[1][3]
The beads provide bulk and improve coaptation after submucosal injection. Permanent material does not guarantee permanent continence, and particle size does not guarantee absence of migration or inflammation.
Current US Safety Restrictions
Do not inject in the presence of acute cystitis, urethritis or another acute genitourinary infection. Correct bladder-neck or urethral strictures before use. Intravascular injection can cause vascular occlusion, infarction or embolic injury.[1]
Pregnancy safety and effects on later pregnancy/delivery are unknown. Assess reproductive plans when counseling. Use viable mucosa, maintain sterility and do not resterilize or reuse the product. No skin-test requirement should be interpreted as a guarantee against local inflammatory complications.[1]
The March 2026 DFU specifies compatible CMT 890-XXX injection needles, with additional syringe/needle restrictions in its supply table. It describes both transurethral and periurethral approaches; check the exact product and delivery-system instructions. Avoid forcing injection against resistance: intramuscular placement can prevent bead flow while carrier gel is forced into tissue, causing clogging and inappropriate deposition.[1]
Study-average volumes are not mandatory doses. Use the label's anatomy and coaptation endpoint, then assess emptying. Patients should remain under observation until they can void; retention may require catheterization. The label prohibits retreatment within seven days, but that minimum interval is not a recommendation for scheduled weekly injections.[1]
Delivery-system update: FDA cleared the InjecSURE Injection System on March 31, 2026 as a cystoscopic accessory for delivering injectable material into urethral tissues. This accessory clearance does not establish improved Durasphere continence outcomes or broaden the implant's indication.[4]
Evidence: Keep Timepoint and Denominator Visible
Original Randomized Trial
The multicenter double-blind trial treated 355 women, 178 with Durasphere and 177 with collagen. The published cohort used an abdominal leak-point pressure below 90 cmH₂O, an eligibility criterion rather than a universal diagnostic definition of ISD.[2][1]
| Analysis | Result | What it means |
|---|---|---|
| DFU, 12-month follow-up | 76/115 (66%) improved at least one continence grade; 36/115 (31%) dry | Available follow-up from 178 treated women; improvement is not dryness. |
| Published analysis, one year after last treatment | 49/61 (80.3%) improved versus 47/68 (69.1%) with collagen, p=0.162 | A smaller denominator and different treatment-anchored timepoint; not 80% cure among all 355 women. |
| Injection burden | DFU reports mean initial volume 4.8 mL, total volume 7.6 mL, and mean 1.7 treatments | Course total, initial injection and later sessions must not be interchanged. |
These data did not establish superior clinical efficacy over collagen. The absence of a significant difference is insufficient to rank Durasphere against contemporary agents that were studied with different endpoints and follow-up.[2][1]
Longer Follow-up
The label's post-approval study invited only the 76 initial 12-month responders; 70 enrolled. At an average 5.2 years, 38/70 (54.3%) reported maintenance of their prior continence grade and six were dry. This is selected-responder durability, not a 54% five-year cure rate among all patients initially treated.[1]
In a separate institutional comparison, 43 of 56 Durasphere-treated women were available for extended telephone follow-up. Nine of those 43 reported continuing effectiveness at a median 51 months. Outcomes declined with both Durasphere and collagen, with no significant adjusted difference in time to failure. This cohort supports frank retreatment counseling; it does not establish that Durasphere has the worst durability of every modern bulking agent.[5]
The AUA/SUFU 2023 guideline finds inadequate comparative data to recommend one injectable over another. A missing product from a guideline's illustrative persistence list does not mean no long-term study exists. The 2017 Cochrane review likewise found insufficient evidence for clear agent superiority; its trial search ended in November 2010.[6][7]
Complications and Follow-up
Interpret Label Frequencies Correctly
The original 178-patient trial table includes both treatment-related and unrelated events. Any urinary urgency was reported in 44/178 (24.7%), whereas investigator-attributed treatment-related urgency occurred in 23/178 (13%). The 24.7% should not be called a pooled mean of new-onset urgency or a proven highest risk among current products. Similarly, all reported UTIs (53/178) differ from treatment-related UTIs (16/178).[1]
Retention can be transient or prolonged. The label separately records treatment-related retention lasting up to seven days in 29/178 and longer than seven days in 10/178; these categories should not be added without knowing whether patients overlap. Persistent obstruction, pain, irritative symptoms or recurrent infection warrants evaluation.[1]
Migration and Delayed Local Complications
A small early series of 13 women and seven men documented carbon-coated bead migration to lymph nodes and urethral mucosa. This demonstrates that large particle size is not a reliable no-migration guarantee, but the series does not provide a general incidence estimate for current EXP use.[8]
A retrospective series identified four periurethral masses among 135 treated women, presenting 12–18 months after injection. Cases required drainage or excision; the authors explicitly considered the true incidence uncertain. Chronic outlet obstruction requiring endoscopic evacuation has also been reported a year after injection.[3][9]
Document the product generation and prior injections. Explain that improvement can diminish despite retained material and that uncommon delayed complications may need intervention. Comparisons with other products should use comparable populations and endpoints, not side-by-side rates drawn from unrelated series.
Male and Fecal Incontinence
Male incontinence and anal injection are outside the current US Durasphere indication. For incontinence after prostate treatment, AUA/GURS/SUFU 2024 recommends counseling that urethral-bulking efficacy is low and cure is rare; choose among the male-incontinence pathways based on the patient's condition.[1][10]
Small anal-injection trials and cohorts do not establish routine use. The 2013 Cochrane review found limited, methodologically weak evidence, and ASCRS 2023 does not routinely recommend anal bulking injections, a conditional recommendation based on low-quality evidence. See Fecal Incontinence.[11][12]
See also: Bulkamid, Macroplastique, Coaptite.
References
1. Carbon Medical Technologies. Durasphere EXP Directions for Use. 51013(1), March 2026. Current US instructions.
2. Lightner D, Calvosa C, Andersen R, et al. A New Injectable Bulking Agent for Treatment of Stress Urinary Incontinence: Results of a Multicenter, Randomized, Controlled, Double-Blind Study of Durasphere. Urology. 2001;58(1):12-15. doi:10.1016/s0090-4295(01)01148-7
3. Madjar S, Sharma AK, Waltzer WC, Frischer Z, Secrest CL. Periurethral Mass Formations Following Bulking Agent Injection for the Treatment of Urinary Incontinence. The Journal of Urology. 2006;175(4):1408-1410. doi:10.1016/S0022-5347(05)00679-8
4. US Food and Drug Administration. InjecSURE Injection System, K253598. Cleared March 31, 2026. FDA record; 510(k) summary.
5. Chrouser KL, Fick F, Goel A, et al. Carbon Coated Zirconium Beads in Beta-Glucan Gel and Bovine Glutaraldehyde Cross-Linked Collagen Injections for Intrinsic Sphincter Deficiency: Continence and Satisfaction After Extended Followup. The Journal of Urology. 2004;171(3):1152-1155. doi:10.1097/01.ju.0000103688.83606.06
6. 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
7. Kirchin V, Page T, Keegan PE, et al. Urethral Injection Therapy for Urinary Incontinence in Women. Cochrane Database of Systematic Reviews. 2017;7:CD003881. doi:10.1002/14651858.CD003881.pub4
8. Pannek J, Brands FH, Senge T. Particle Migration After Transurethral Injection of Carbon Coated Beads for Stress Urinary Incontinence. The Journal of Urology. 2001;166(4):1350-1353. PubMed.
9. Hartanto VH, Lightner DJ, Nitti VW. Endoscopic Evacuation of Durasphere. Urology. 2003;62(1):135-137. doi:10.1016/s0090-4295(03)00249-8
10. AUA/GURS/SUFU. Incontinence after Prostate Treatment Guideline. Amended 2024, statement 25. Guideline.
11. Maeda Y, Laurberg S, Norton C. Perianal Injectable Bulking Agents as Treatment for Faecal Incontinence in Adults. Cochrane Database of Systematic Reviews. 2013;(2):CD007959. doi:10.1002/14651858.CD007959.pub3
12. Bordeianou LG, Thorsen AJ, Keller DS, et al. The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Fecal Incontinence. Diseases of the Colon and Rectum. 2023;66(5):647-661. doi:10.1097/DCR.0000000000002776