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Coaptite — Calcium Hydroxylapatite (CaHA)

Coaptite is a particulate urethral bulking implant for stress urinary incontinence caused by intrinsic sphincter deficiency in adult women. Its US instructions describe submucosal injection at the bladder neck. The September 2025 instructions identify Merz as manufacturer and distributor; use that product-specific labeling when selecting and handling the implant.[1] For choosing bulking versus a sling or other continence operation, see Urethral Bulking Agents.

Material and Mechanism​

Coaptite contains 75–125 μm calcium hydroxylapatite particles in an aqueous carrier of sodium carboxymethylcellulose, water and glycerin. The carrier dissipates after injection, while the particles provide tissue bulk and urethral coaptation. The implant is supplied sterile for single use.[1]

Coaptite is particulate, like Macroplastique, and contrasts with the homogeneous Bulkamid hydrogel. Allergic reactions, granuloma and tissue injury can occur with Coaptite.[1] CaHA is also used as an aesthetic dermal filler (Radiesse) for facial volume loss; that is a separate product.[8]

Selection and Label Safety​

Contraindications and tissue integrity

The US label contraindicates treatment with a significant unresolved history of urinary tract infections, current or acute cystitis or urethritis, or fragile urethral mucosa. Correct urethral or bladder-neck strictures before considering injection.[1]

The label also warns to avoid nonviable or substantially compromised tissue, including tissue affected by significant pelvic irradiation or multiple pelvic operations. It cautions against use in a very short urethra after multiple SUI operations.[1] Previous continence surgery therefore requires assessment of tissue viability.[1]

  • Tracking through tissue can cause erosion requiring corrective surgery or elevation of the bladder wall with ureteral obstruction.
  • Peripheral vascular disease together with previous pelvic surgery may increase erosion risk.
  • Overcorrection may obstruct the urethra; intravascular injection may cause vascular occlusion.
  • Safety and effectiveness of periurethral injection, male or pediatric use, and several comorbid populations have not been established in the US labeling. Its list includes bladder neuropathy, detrusor instability, diabetes and immunosuppressive disorders; these are precautions, distinct from the listed contraindications.[1]
  • Pregnancy and lactation safety and the effects of subsequent pregnancy and delivery are unknown.[1]

The AUA/SUFU 2023 bulking section supports this treatment category for women who prefer a less invasive procedure, want shorter recovery, or have insufficient improvement after a previous continence intervention. It also stresses the likelihood of repeat injections and the lack of adequate evidence to select one agent as universally superior.[2]

Administration Principles​

The labeled route is transurethral submucosal injection, typically through a 35 cm cystoscopic needle with a 10 mm, 21-gauge tip. The injection site is usually 1 to 1.5 cm distal to the bladder neck; each site is injected until the bleb reaches the urethral midline or maximum tissue compliance, and further sites are added until the lumen coapts. Overcorrection can cause retention. Safety and effectiveness of periurethral injection have not been established.[1]

The pivotal study used a mean 2.2 mL initially and 4.0 mL over the treatment course. The course total is not a recommended single-session dose. Retreatment was common. Avoid passing the cystoscope back through a newly coapted area, confirm satisfactory voiding before discharge, and have a plan for catheterization if emptying is impaired.[1]

Evidence and Expected Outcomes​

SourcePopulation and endpointResult and interpretation
Pivotal randomized trial, 2007296 women with intrinsic sphincter deficiency and without associated urethral hypermobility were allocated to CaHA or bovine collagen; 231 had 12-month dataAt least one Stamey-grade improvement occurred in 83/131 (63.4%) CaHA recipients and 57/100 (57.0%) collagen recipients; the difference was not statistically significant.[3]
Post-approval study in the September 2025 US IFUSingle-arm study of 459 women at 20 US sites, followed to 36 months; 458 in the effectiveness analysisAt 36 months, improvement of at least one Stamey grade was 199/329 (60.5%) among observed patients, versus 199/458 (43.4%) with baseline carried forward for missing data. More than half received at least two injections; 116/459 discontinued and approximately 10% received an alternative incontinence treatment.[1]
Mayer 2001 (pilot)10 women; 12 monthsMean total volume 3.9 mL. Seven women reported substantial improvement (three used no pads), mean 24-hour pad weight fell from 104.9 to 1.5 g and mean Valsalva leak point pressure rose from 39 to 46 cm H2O.[9]
Griffin 2016 (retrospective)60 women treated by one surgeon; 37 provided questionnaires and 38 provided pad counts; mean age 75 among respondents; short termAmong questionnaire respondents, overall AUASS improved in 67.6%, AUASS QOL in 54.8% and M-ISI in 61.3%. Daily pad use fell by 1.7 among those with pad counts (p = 0.006), and 19% had transient urinary retention.[10]
Cochrane urethral-injection review, 201714 trials involving 2,004 women across different agents/interventions; search through November 2010Limited, heterogeneous trials did not establish a clearly superior injectable agent.[4]

In the pivotal trial, 38.0% of CaHA patients (60) needed only one injection, compared with 26.1% of collagen patients (36) (p = 0.034), and mean total volume was 4.0 mL versus 6.6 mL (p < 0.0001).[3] AUA/SUFU 2023 notes that long-term data on bulking agents are limited, cites persistence of effect at 73.2 months for CaHA, 83 months for polydimethylsiloxane and 96 months for polyacrylamide hydrogel, and states that no comparative study has shown one agent superior.[2] A qualitative systematic review reported long-term success of 60 to 75% for Coaptite, 42 to 70% for Bulkamid and 21 to 80% for Macroplastique, and noted no direct comparisons of bulking agents.[11]

Ultrasound and Volume Change​

A prospective study of 20 women found mean implant-volume reductions of approximately 41 to 46% at three months and a 39.5% reduction in coaptation. Ninety percent reported 50% or greater improvement (45% reported 90% or greater). Women with the least improvement had the greatest volume reduction. Injected volume, percent coaptation and number of vials were not associated with symptoms.[5]

Adverse Events and Follow-up​

Retention, UTI, dysuria, hematuria and discomfort should be discussed before treatment. In the 459-woman post-approval label dataset, 66/459 (14.4%) had urinary retention recorded as a treatment-emergent event; 60/459 (13.1%) had retention classified as treatment-related. UTI figures also differ by attribution: 136/459 (29.6%) treatment-emergent, versus 13/459 (2.8%) treatment-related.[1]

Older studies and reviews reported different retention frequencies. A systematic review found temporary acute retention more commonly with Coaptite than with other agents (mean 34.2%), and reported erosion with Coaptite, Macroplastique and Urolastic but none with Bulkamid.[11] In the post-approval study, cystoscopy identified erosion in 1/459 (0.2%) women, and serious treatment-related urinary retention occurred in 39/459 (8.5%).[1]

Foreign-body granuloma is a reported complication. In a two-patient report, excision relieved pain but stress incontinence recurred in both patients.[6]

Assess inability to void promptly. Persistent pain, recurrent infection, hematuria, obstructed flow or a new periurethral mass warrants evaluation for an injection-related complication. Document the agent and injection history for future clinicians and imaging interpretation.

Pediatric Reflux Is a Separate, Off-label Use​

A historical multicenter study evaluated CaHA injection for VUR in 98 children with 155 refluxing ureters, with substantial follow-up attrition. Of 98 enrolled children, 74 had 1-year assessments and 46 completed 2-year endpoints. The authors reported 24/74 (32%) as cured "at 1 and 2 years," with ureteral cure rates of 46% at 1 year and 40% at 2 years.[7] At the highest-volume center (35 treated patients; 85% compliance with the required 2-year VCUG), 2-year cure was 66% of patients and 72% of ureters, and the authors concluded that results improved with experience.[7] Pediatric VUR remains outside Coaptite's US approval. The Coaptite label states that pediatric safety and effectiveness have not been established.[1][7]

See also: Bulkamid, Macroplastique, Durasphere.

Guideline Position​

AUA/SUFU 2023 lists bulking agents among the options to discuss with index patients considering surgery for SUI and among the options clinicians may offer for SUI with a fixed, immobile urethra .[2]

References​

1. Merz. Coaptite Injectable Implant: Instructions for Use. IN00259-01, September 2025. Manufacturer labeling.

2. 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

3. Mayer RD, Dmochowski RR, Appell RA, et al. Multicenter Prospective Randomized 52-Week Trial of Calcium Hydroxylapatite Versus Bovine Dermal Collagen for Treatment of Stress Urinary Incontinence. Urology. 2007;69(5):876-880. doi:10.1016/j.urology.2007.01.050

4. 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

5. Unger CA, Barber MD, Walters MD. Ultrasound Evaluation of the Urethra and Bladder Neck Before and After Transurethral Bulking. Female Pelvic Medicine & Reconstructive Surgery. 2016;22(2):118-122. doi:10.1097/SPV.0000000000000250

6. Gafni-Kane A, Sand PK. Foreign-Body Granuloma After Injection of Calcium Hydroxylapatite for Type III Stress Urinary Incontinence. Obstetrics and Gynecology. 2011;118(2 Pt 2):418-421. doi:10.1097/AOG.0b013e3182161953

7. Mevorach RA, Hulbert WC, Rabinowitz R, et al. Results of a 2-Year Multicenter Trial of Endoscopic Treatment of Vesicoureteral Reflux With Synthetic Calcium Hydroxyapatite. The Journal of Urology. 2006;175(1):288-291. doi:10.1016/S0022-5347(05)00013-3

8. Lorenc ZP, Bass LM, Fitzgerald R, Goldberg DJ, Graivier MH. Physiochemical Characteristics of Calcium Hydroxylapatite (CaHA). Aesthetic Surgery Journal. 2018;38(suppl_1):S8-S12. doi:10.1093/asj/sjy011

9. Mayer R, Lightfoot M, Jung I. Preliminary Evaluation of Calcium Hydroxylapatite as a Transurethral Bulking Agent for Stress Urinary Incontinence. Urology. 2001;57(3):434-438. doi:10.1016/s0090-4295(00)01098-0

10. Griffin MA, Janosek-Albright KJ, Diaz-Insua M, Elshatanoufy S, Atiemo HO. Quality of Life Outcomes in Peri-Urethral Calcium Hydroxylapatite Injection. International Urogynecology Journal. 2016;27(12):1879-1887. doi:10.1007/s00192-016-3053-1

11. 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