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vulvar discharge, mammary nodules or liver/kidney insufficiency should not be treated. Pregnant females
or pseudopregnant bitches should not be treated. Also, treatment during oestrus to suppress an unwanted heat should be done with caution and only with short-acting drugs for short periods of time, as progestongens side effects are likely to be amplified by previous estrogen exposure. Table n° 1 shows the suggested dosages
of the most commonly used progestogen-based compounds in bitches and queens. The lowest effective dose should be used even if this may cause an earlier return to oestrus. Treatment durations of more than one year are probably adequate for young, healthy females, while shorter treatments should be considered for middle age females who may have subclinical uterine or mammary conditions. The use of progestogens in older females should be discouraged.
3, 5 and 7 post breeding27. No short-term side effects have been reported following this protocol. However, in a retrospective study done in the UK the incidence of pyometra in the 4 months after the administration of low doses of estradiol benzoate was 8.7%, whereas the incidence of that condition in a practice situation was estimated to be < 2.0%28.
Urinary incontinence
Long-acting synthetic compounds such as diethylstilbestrol, estradiol, estrone and other esther compounds are characterized by a dangerous action
on bone marrow and uterus because of their prolonged nuclear occupance time in estrogen receptors of target tissues29. The following is a list of estrogens which have been used to treat canine urinary incontinence.
Your Singapore, the Tropical Garden City
17-b estradiol Estradiol benzoate Estradiol valerate Diethylstilbestrol Estriol
Conjugated estrogens
0.01 mg/kg MID sc/im for 3 days 0.01-1.0 mg MID per os
1.0 mg/10 kg bw
0.06 mg MID, tapering out to 0.01 mg 0.5-2.0 mg
0.02 mg/kg
 Suggested Dosage
 Bitch
  Queen
   Megestrol Acetate
 Oestrus suppression
<2.0 mg/kg for 8 days in proestrus
Oestrus postponement 0.05 to 0.01 mg/kg daily per os up to 1 yr
   Oestrus postponement 0.02 to 0.09 mg/kg/day per os up to 1 year
   Medroxy- progesterone Acetate
Oestrus postponement
1.5-2.0 mg/kg SC or IM every 13 weeks
2.5-3.0 mg/kg SC or IM every 4-5 mos 0.05 mg/kg/day per os up to 1 year
  Oestrus postponement 0.01- 0.05 mg/kg/day for up 1 year
 Proligestone
  Oestrus postponement
10-33 mg/kg SC every 3,7,5,5 months
  Oestrus postponement 25-30 mg/kg SC every 5 months
 Table n° 1 – Suggested dosages of the 3 most commonly used progestogen compounds in bitches for the control of reproduction. The dosage for proligestone in bitches should be intended 10 mg/kg in large size dogs and up to 33 mg/kg in medium to small size dogs
ESTROGENS
Estrogens have always been considered as potentially dangerous drugs for small animals because of their role in inducing mammary neoplasia, endometrial hyperplasia, pyometra and bone marrow aplasia in bitches 25. However, such dangerous side effects are a feature of long-acting compounds, while short-acting estrogens such as estriol are not associated with development of full (late) estrogenic effects. Estrogens have historically been used for contraception and for the treatment of urinary incontinence.
Unwanted pregnancy
Several estrogenic compounds have been used for
this purpose, but for most of them the risk of side
effects has discouraged their clinical application26. As
a consequence, estrogens are no longer considered
a safe choice for canine pregnancy termination. Only estradiol benzoate, when given at low doses has proven to be fairly efficacious and relatively safe. A compound with estradiol benzoate is marketed for veterinary use in mismated bitches in some European countries, which is to be administered at the dose of 10 mcg/kg SC on day
Of all the estrogenic compounds listed above, estriol
is the only one considered as a safe drug due to its short-action which is characterized by short nuclear occupance time and minimal metabolism following absorption. Estriol does not bind to sex-hormone binding globulin, which helps in preventing development of full (late) estrogenic effects such as endometrial hyperplasia, pyometra and bone marrow suppression. Estriol is available for human use as hormone replacement therapy for women in menopause, and is marketed in several European countries as a veterinary preparation to treat canine urinary incontinence. The current formulation is in 1.0 mg pills to be given once daily for
1 week, and then either gradually increase (in case of little or no response) or decrease (in case of a very good response), with the goal being to find the lowest possible dosage Its efficacy after 42 days of 2.0 mg/day treatment was 85% in a multicentric clinical trial recently performed on 129 bitches in 4 european countries30. Hematological abnormalities are not observed when using dosages
of 0.5-1.0 mg/day even for years, nor have they been reported in mid-term (3 months) chronic toxicity studies using 2.0, 6.0 and 10 mg doses31. Vulvar swelling and male attractiveness was occasionally observed in bitches treated with estriol doses of >1.5 mg/day. Some signs of estrus can be observed in bitches administered higher dosages 31
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