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Coaptite — Calcium Hydroxylapatite (CaHA)

Coaptite (BioForm Medical, now Merz Pharmaceuticals) is a particulate, non-immunogenic urethral bulking agent of calcium hydroxylapatite (CaHA) microspheres in an aqueous gel carrier. FDA-approved in 2005 for female stress urinary incontinence (SUI) due to intrinsic sphincter deficiency (ISD).[1]

Composition & Material Properties​

  • Active: synthetic CaHA microspheres, 75–125 μm diameter.[1]
  • Carrier: sodium carboxymethylcellulose aqueous gel — gradually absorbed.
  • Non-immunogenic — CaHA is a normal constituent of bone; no skin testing required (unlike the now-discontinued Contigen collagen).[1][2]
  • Particulate — like Macroplastique; contrasts with homogeneous Bulkamid hydrogel.
  • Radiopaque — visible on plain film / CT; useful for implant localization but a potential imaging pitfall.
  • Rheology: comparatively high elastic modulus (G'), providing structural support and resistance to compression.[3]

The same CaHA material is marketed as Radiesse for aesthetic dermal volume augmentation — a far larger market than the urologic indication.[3]

Mechanism​

CaHA microspheres create immediate periurethral volume expansion and improve urethral coaptation. The aqueous gel carrier is absorbed; the microspheres become encapsulated by a fibrous tissue response, with new collagen deposition around the particles maintaining the bulking effect.[2][4]

A defining feature of Coaptite is substantial volume loss over time. Translabial ultrasound shows ~40–46% mean volume reduction at 3 months post-injection, with the degree of shrinkage correlating with reduced clinical efficacy.[5]

Injection Technique​

Transurethral, cystoscopic guidance:[2][4]

  • Anesthesia: local (periurethral lidocaine); sedation or GA optional.
  • Setting: office / outpatient; ~15–30 minutes.
  • Sites: submucosal injection at the proximal urethra / bladder neck, typically 2–4 sites.
  • Volume: mean 3.9–4.0 mL per treatment course — significantly less than collagen (6.6 mL, p < 0.001).[4]
  • Sessions: up to 5 sessions permitted in the first 6 mo of the pivotal trial; 38% needed only 1 injection (vs 26.1% collagen, p = 0.034).[4]

Indications​

Female SUI due to ISD without significant urethral hypermobility.[1][4] Particularly suited to:[6][7]

  • ISD with a well-supported urethra.
  • Patients who wish to avoid more invasive surgery.
  • Elderly / medically unfit (mean age 68–75 yr across series).
  • Recurrent SUI after failed prior anti-incontinence procedure.
  • Patients who cannot tolerate anesthesia or more invasive surgery.

Clinical Efficacy​

Pivotal RCT (Coaptite vs Contigen collagen)​

Multicenter, randomized, single-blind, n = 296 women with ISD:[4]

  • ≥ 1 Stamey-grade improvement at 12 mo: 63.4% CaHA vs 57.0% collagen (p = 0.34, NS).
  • Fewer injections required: 38% vs 26.1% needed only 1 (p = 0.034).
  • Less total volume: 4.0 mL vs 6.6 mL (p < 0.001).
  • Cochrane analysis noted a non-significant trend favoring CaHA on Stamey grade (RR 0.85; 95% CI 0.62–1.17) and a significant QoL advantage.[1]

Short / Medium-Term Outcomes​

StudyDesignnFollow-upOutcome
Mayer 2001Prospective pilot1012 mo70% substantial improvement; pad weight ↓ > 90%; VLPP 39 → 46 cmH₂O.[2]
Mayer 2007RCT vs Contigen29612 mo63.4% ≥ 1 Stamey-grade improvement; 38% with single injection.[4]
Griffin 2016Retrospective QoL60Short-termAUASS improved in 67.6%; M-ISI improved in 61.3%; pad use ↓ 1.7/d (p = 0.006).[8]
Unger 2016Prospective ultrasound203 mo90% ≥ 50% improvement; 45% ≥ 90%; 40–46% volume loss on US.[5]

Long-Term​

AUA/SUFU 2023 notes CaHA has demonstrated persistence of effect at 73.2 months (~6.1 yr) — among the longest-documented (behind PAHG at 96 mo, comparable to PDMS at 83 mo).[9] Systematic review reports long-term success 60–75%.[10]

Coaptite vs Other Bulking Agents​

ParameterCoaptite (CaHA)Bulkamid (PAHG)Macroplastique (PDMS)
CompositionCaHA in aqueous gel2.5% polyacrylamide in waterSilicone macroparticles in PVP
Particle-basedYes (75–125 μm)No (homogeneous gel)Yes (> 100 μm)
ImmunogenicityNon-immunogenicNon-immunogenicNon-immunogenic
Volume per course~4.0 mL~2–4 mL total~5–6.3 mL
12-mo improvement63.4%66–89.7%73%
Persistence of effect73.2 mo96 mo83 mo
Long-term success60–75%42–70%21–80%
Transient retention~34–41%~3.1%~7.2%
Erosion reportedYes (rare)NoYes (2.4%)
GranulomaYes (case reports)NoRare
FDA approval200520202006

The standout safety difference is transient urinary retention — 34–41% with Coaptite in the pivotal trial, the highest among bulking agents and several-fold higher than Bulkamid (~3%) or Macroplastique (~7%). Likely reflects the immediate volume effect of CaHA particles; typically resolves spontaneously.[1][10]

Safety Profile​

Common:[4][1][10]

  • Transient urinary retention 34–41% (highest among bulking agents).
  • UTI: 4–10.6%.
  • Transient dysuria, injection-site discomfort.

Uncommon / notable:

  • Vaginal erosion reported in the pivotal trial (1 treatment-related SAE).[1]
  • Tracking of injectate under the trigone with obscuration of the ureteric orifice — 1 SAE.[1]
  • Foreign-body granuloma — case reports of periurethral mass; excision relieved pain but caused SUI recurrence in both reported cases. Granuloma described as "not the normative response" but should be considered for periurethral mass after CaHA.[11]
  • Volume loss (~40–46% at 3 mo on US) correlates with reduced clinical efficacy.[5]

AUA/SUFU specifically notes that erosions were not noted with PAHG (Bulkamid) as with other bulking agents — implicitly including CaHA among agents where erosion has been reported.[9]

Pediatric Vesicoureteral Reflux​

Multicenter prospective trial (n = 98 patients, 155 ureters, grades II–IV VUR):[12]

  • 1-year cure: 32% of patients (46% of ureters).
  • 2-year cure: 32% of patients (40% of ureters).
  • At the highest-experience center, 2-yr cure 66% patients / 72% ureters — strongly operator-dependent.

These results are notably lower than Macroplastique (90% ureteral cure) and Deflux (81%), suggesting CaHA is less effective for VUR.[12]

Guideline Position​

AUA/SUFU 2023: bulking agents have a role in patients who wish to avoid more invasive surgery, prioritize shorter recovery, or have insufficient improvement after a prior anti-incontinence procedure. Inadequate data to recommend one injectable over another, but CaHA has documented 73.2-mo persistence. Erosions reported with some agents (including CaHA), not with PAHG.[9]

ACOG: improvement rates 63–80% at 1 yr; urethral bulking agents are less effective than sling surgery.[6]

Regulatory Status​

  • FDA-approved 2005 for female SUI due to ISD.[1]
  • No skin testing required.
  • Not a mesh product — unaffected by FDA mesh restrictions.
  • Same CaHA marketed as Radiesse for aesthetic indications.[3]

Advantages​

  • Non-immunogenic; no skin testing.
  • Less volume than collagen (4.0 mL vs 6.6 mL).
  • Fewer sessions than collagen (38% with a single injection).
  • Persistence to 73.2 months.
  • Long-term success 60–75%.
  • Radiopaque — implant localization on imaging.

Limitations​

  • Highest transient retention rate among bulking agents (~34–41%).[10]
  • ~40–46% volume loss at 3 months with corresponding efficacy decline.[5]
  • Erosion reported (unlike Bulkamid).
  • Granuloma reported.[11]
  • Shorter persistence than Bulkamid (73.2 vs 96 mo).
  • Limited long-term prospective data beyond the 12-mo pivotal RCT.
  • No head-to-head RCT vs Bulkamid or Macroplastique.
  • Inferior for pediatric VUR vs Macroplastique / Deflux.
  • Pivotal comparator (Contigen) is no longer marketed.

Current Market Position​

Coaptite occupies a diminishing niche. It remains FDA-approved and commercially available, but several factors have reduced its utilization: Bulkamid's favorable safety profile (no erosion, no granuloma, low retention), Macroplastique's longer evidence base, the practical disadvantage of high transient retention in the office, and ultrasound evidence of substantial volume loss.[9][10]

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

References​

1. 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

2. 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

3. 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

4. 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

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. Committee on Practice Bulletins—Gynecology and the American Urogynecologic Society. ACOG Practice Bulletin No. 155: Urinary Incontinence in Women. Obstetrics and Gynecology. 2015;126(5):e66-e81. doi:10.1097/AOG.0000000000001148

7. Shah SM, Gaunay GS. Treatment Options for Intrinsic Sphincter Deficiency. Nature Reviews Urology. 2012;9(11):638-651. doi:10.1038/nrurol.2012.177

8. 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

9. 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

10. 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

11. 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

12. 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