UROLOGY
dogs were actually lower than FSH and LH in
spayed continent dogs. GnRH analogues had no
effect on maximum urethral closing pressure and
urethral pressure profiles compared to PPA and
oestrogens.
mg capsules and a syrup which contains 1mg/ml.
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Oestriol
Oestriol (Incurin®) is a naturally occurring short
acting oestrogen which is registered for use
in dogs. Each tablet contains 1 mg oestriol. It is
dosed at 1 tablet per dog per day for 1-2 weeks
after which the dose is reduced to the lowest
controlling/effective daily dose, usually ½ tablet
per dog per day. After this stage, alternate day
dosing can be implemented. Dose is not related
to body weight and needs to be adjusted for the
individual animal. In cases that do not respond
to 1 tablet per day the dose can be doubled to 2
tablets per dog per day. If this regimen still has no
effect on the incontinence the diagnosis should
be reconsidered and a more intensive diagnostic
approach should be taken.
Conjugated oestrogens
Premarin® tablets (0.3 mg, 0.625 mg, 1.25 mg) is
a preparation used in postmenopausal women. It
is derived from pregnant mare urine and contains
conjugated oestrogens which are converted to
oestradiol. This drug can be dosed at 20µg/kg per
os every 3 or 4 days.
In a small group of dogs, a response rate of (7/11
dogs) 60% was seen when using leuprolide. The
fact that a response is seen clinically when using
the drug lead to the speculation than GnRH may
have a direct effect on the bladder which causes
detrusor muscle relaxation. The GnRH analogue,
leuprolide (Lupron®) can be used at 5-10 mg
intramuscularly every 3 months. This drug may
be useful in cases where oetrogens and PPA are
contraindicated.
Tricyclic antidepressants
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Testosterone analogues
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•
Testosterone cypionate
Testosterone injections have anecdotally been
reported to improve incontinence in male dogs.
It is given at 1.5 mg/kg every 4 weeks. The exact
mechanisms which result in an effect are unclear,
but could involve increased urethral smooth
muscle tone, improved tone in urethral supporting
structures and increased prostatic urethral
resistance. It is reported to be less effective than
PPA. Potential side effects in male dogs include
development of perianal adenomas and prostatic
enlargement. The use of testosterone in female
dogs cannot be recommended as its use may
lead to clitoral hypertrophy, masculinisation and
aggression. It is also contraindicated in dogs
with renal disease, cardiac disease and hepatic
insufficiency.
Gonadotropin releasing hormones
Although not often recommended and not
commonly
used,
gonadotropin
releasing
hormone (GnRH) analogues may be effective in
some cases of USMI. GnRH analogues decrease
follicle stimulating hormone (FSH) and luteinizing
hormone (LH) by down regulating gonadotropin
receptors in the pituitary gland. Because
spaying causes a decrease in oestrogens and a
subsequent increase in FSH and LH, GnRH may
have a role to play in the management of post
ovariohysterectomy USMI. This medication will
need further investigation as analysis to date
showed that FSH and LH in spayed incontinent
Imipramine
Imipramine (Tofranil®) is a norepinephrine
reuptake inhibitor and potential anticholinergic. It
is available in 10 mg, 25 mg and 50 mg tablets.
It indirectly increases alpha-receptor stimulation
in urethral sm ooth muscle and may lead to an
increase in bladder relaxation. It is dosed at 5-15
mg/dog ( ½ to 1 ½ of the 10mg tablets) per os
every 12 hours. It is not commonly used in the
treatment of PSMI. Side effects include vomiting,
diarrhoea, hyperexcitability, seizures and sedation.
It decreases the seizure threshold and should not
be used in epileptic animals.
Interventional procedures for USMI
A complete discussion on these procedures
are beyond the scope of this text as this paper
describes the medical management of USMI.
However, it is worth mentioning the surgical
options available for patients in South Africa.
Various surgical specialists can be contacted
regarding these procedures should a patient
require surgical intervention.
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Urethral bulking
This procedure involves the injection of bulking
agents such as bovine crosslinked collagen
submucosally into the proximal urethra during
cystoscopy. By bulking up the tissues an increase
in resting urethral pressure is achieved. There is
a variable response rate (50-80%) and duration
of effect with response periods varying from
8 months to 2 years. This procedure can be
combined with medical management and renders
PPA more effective.
See the article on Surgical Procedures for Urethral
Sphincter Mechanism Incompetence in Bitches on
page 30-34 in this edition
References on www.vetlink.vet360.co.za
Issue 02 | MAY 2018 | 29