Page 5 - Diagnosing and managing urinary incontinence in dogs

related to the degree of urethral coaptation, it may be related to an increased force of sphincter
muscle contraction secondary to stretching of the sarcomere following the bulking agent
implantation; vascular smooth muscle and striated muscle are known to exert increased contractile
force when stretched (Byron JVIM 2011). Client satisfaction was excellent despite a variable
duration and degree of improvement of the urinary incontinence.

The duration of improvement following collagen implantation is variable and there are no identified
factors that will predict the degree or duration of improvement in any individual dog. Five dogs in this
study had a second series of collagen injections. Often these injections are placed into the previous
injection sites to augment the degree of urethral coaptation. Loss of the beneficial effect following
collagen implantation occurs in some dogs possibly due to loss of volume as absorption of the
phosphate buffer occurs; occasionally there is complete loss of the implanted collagen into the
urethral lumen.

There are a variety of other urethral bulking agents that have been used in human medicine but
none have been reported in the veterinary literature– collagen has been the most commonly used
agent in dogs. Contigen® (Bard) has been the gold standard for urethral bulking in veterinary
medicine for a long time, but Bard stopped manufacturing this product in 2011.

RegGain® (Avalon Medical; Stillwater, MN) was formulated for veterinary use as a direct
replacement for Contigen®. This preparation was previously available only in a research formulation
but will begin marketing as a fully available retail product in October 2011. ReGain® contains a
higher concentration of collagen in suspension compared to the Bard product (42 mg/ml vs 35 mg/ml
); this could mean more bulking per ml of suspension delivered to the urethral submucosa. ReGain®
does not require refrigeration as did Contigen® and the company claims to have improved the
collagen crosslinking technology compared to Contigen.

Use of this formulation of collagen has yet to be reported in veterinary medicine. ReGain® is
substantially less expensive than the human product ($250 for 2.5 ml in a prefilled syringe).
Researchers at the University of Tennessee are currently in the process of evaluating
®
polydimethylsiloxane (PDMS; Macroplastique -Uroplasty, Inc Minnetonka, MN) in a clinical study of
female dogs with PSMI. This product has used to treat European women with stress induced urinary
incontinence since 1991 and was FDA approved for use in the USA in 2006. PDMS outperforms
collagen urethral bulking in studies of humans with urinary incontinence. In an interim report on 22

dogs with PSMI, 17 were fully continent without other medications and 3 were improved 1 month
following urethral implantation with PDMS.

Three dogs experienced blepharedema and urticarial as an allergic reaction attributed to the PVP
gel component of the PDMS injection– all responded to antihistamine treatment; one dog