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/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]
Biocompatibility does not make allergic reactions, granuloma or tissue injury impossible. Similarly, CaHA used in an aesthetic filler does not make that product interchangeable with Coaptite for urethral injection. Do not substitute a dermal-filler formulation or its administration instructions.
Selection and Label Safety
The US label contraindicates treatment with a significant unresolved history of urinary tract infections, current/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. Previous continence surgery therefore requires assessment of tissue viability; it is not by itself a reason to choose Coaptite.[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.
- Pregnancy/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
Use the current supplied instructions and product training for preparation, needles, injection depth and endpoint. The intended US route is transurethral, submucosal injection at the bladder neck; published periurethral experience does not change the label's precaution about that route.[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, and the study's permitted number of sessions is not an automatic treatment schedule. 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
| Source | Population and endpoint | Result and interpretation |
|---|---|---|
| Pivotal randomized trial, 2007 | 296 women allocated to CaHA or bovine collagen; 231 had 12-month data | At 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. These are improvement rates among patients with follow-up, not complete-dryness rates for all randomized women.[3] |
| Post-approval study in the September 2025 US IFU | Single-arm study of 459 women at 20 US sites, followed to 36 months; 458 in the effectiveness analysis | At 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. Attrition and additional treatment matter when counseling about durability.[1] |
| Cochrane urethral-injection review, 2017 | 14 trials involving 2,004 women across different agents/interventions; search through November 2010 | Limited, heterogeneous trials did not establish a clearly superior injectable agent. This review predates several modern bulking trials and is not a current head-to-head comparison of Coaptite with Bulkamid.[4] |
The AUA's cited persistence of CaHA benefit at approximately six years is evidence that some patients remain improved, not a guarantee of six years of continence after one injection. Follow-up duration should not be used to rank the durability of different products studied in different populations.[2]
Ultrasound and Volume Change
A prospective study of 20 women found mean implant-volume reductions of approximately 41–46% at three months, with less symptom improvement associated with greater volume reduction. This small observational study does not establish a universal rate of CaHA resorption, prove the cause of treatment failure, or define a reinjection threshold.[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. These categories are not interchangeable.[1]
Older studies and reviews reported different retention frequencies. They do not support a precise safety ranking against Bulkamid or Macroplastique because surveillance, repeat treatment and adverse-event definitions differ. The current label includes obstruction, tissue erosion and other potentially consequential events; its study findings should not be summarized as “only transient complications.”[1]
Foreign-body granuloma is a reported complication. In a two-patient report, excision relieved pain but stress incontinence recurred in both patients. The report establishes a possible explanation for a symptomatic periurethral mass, not its population incidence.[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. It does not establish US approval for pediatric VUR, and its results cannot be compared directly with cure percentages from unrelated Deflux or Macroplastique cohorts. The Coaptite label states that pediatric safety/effectiveness have not been established.[1][7]
See also: Bulkamid, Macroplastique, Durasphere.
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