The newest FDA-approved bulking agent is Durasphere. It consists of pyrolytic carbon-coated zirconium oxide beads suspended in an approximately 50% vol/vol water-based carrier gel containing glucan. The targeted radio-opaque bead size originally ranged from 250 to 300 microns in diameter, but now consists of non-radio-opaque beads measuring between 100 to 200 microns. This size reduction was made to facilitate the technical aspects of injection without risking particle migration associated with agents less than the known 80-micron threshold. This synthetic bulking agent is permanent and nonreactive. The potential advantages over other injectable bulking agents include nonimmunogenicity (eliminating the need for skin testing before implantation) and a bead diameter size of more than 80 microns (decreasing the risk of potential macrophage phagocytosis and migration).

The short-term results of Durasphere seem to be comparable to those of other established bulking agents. Lightner et al.6 reported prospective results in 355 women randomized to receive Durasphere or Contigen for the treatment of ISD. At 12 months after injection, 80.3% of patients in the Durasphere group had improvement in continence grade versus 69.1% in the bovine collagen group. Improvement in urine loss, as measured by reduction in pad weight, was 27.9 g for the Durasphere group versus 26.4 g for the Contigen group. Mean total volume injected was 7.55 mL for Durasphere versus 9.58 mL for collagen. An increase in durability was not proven, because Durasphere required a mean of 1.69 injections versus 1.55 for collagen.

Complications associated with Durasphere are similar to those associated with Contigen. However, the incidence of self-limited acute urinary retention and urgency are higher with Durasphere (24.7% and 16.9%,respectively) than with Contigen (11.9% and 3.4%, respectively).

Although Durasphere is reported as being nonmigra-tory, some controversy regarding this issue was generated early on in the clinical use of this agent. In 2001, Pannek et al.7 described 20 patients with ISD who underwent transurethral submucosal injection of Durasphere. They reported six cases with evidence of distant migration of the Durasphere particles on X-ray. The authors could not explain the reason for bead migration or its clinical implications, yet it seemed that all these patients were males injected under a general anesthetic using large amounts of material in excess of typical volumes used for the treatment of female SUI. This invariably led to venous injection and extravasation of the material.

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