Vet360 Vet360 Vol 05 Issue 02 | Page 28

UROLOGY
be considered . The aim of medical management is to either increase the sensitivity of alpha-receptors , increase the number of alpha-receptors in the urethral sphincter or both .
Alpha-adrenergic drugs
• Phenylpropanolamine Many clinicians consider phenylpropanolamine ( PPA ) to be the first choice in the treatment of USMI . PPA is an alpha-adrenergic agonist which is associated with treatment success rates of 75- 90 %. The dosage for individual animals may vary quite widely but starting doses of 1.0-1.5 mg / kg per os every 8-12 hours appears to be effective in most cases . Over time the response to treatment may decrease and increases in dosage may be required . A 2011 study showed that once daily dosing may be adequate . A single daily dose of 1.5 mg / kg was successful in controlling incontinence in 88.9 % of clinical cases in this study . It was shown in healthy beagles that PPA reached therapeutic levels 2 hours after a single dose and then progressively decreased to baseline by 24 hours . Despite higher plasma levels of PPA with more frequent dosage , urethral pressure profiles were not significantly different . The reasons for clinical efficacy is not clearly understood , but it may be possible that certain individuals can be managed with once daily dosing which is more convenient and cost effective for owners .
In South Africa PPA can be used in the form of a cold and flu mixture sold as Rinex ®. Rinex ® contains phenylpropanolamine hydrochloride , chlorpheniramine maleate ( an antihistamine ) and phenylephrine hydrochloride ( another alphaadrenergic agonist ). The drug is available in capsules ( 30mg PPA per capsule ), syrup ( 1mg PPA per ml ) and paediatric syrup ( 0.5 mg / ml ). Most patients have some kind of response to this drug . The dosage may need to be increased over time as the drug does seem to become less effective over time . Side effects may include restlessness , hypertension , aggressiveness , changes in sleeping patterns and gastrointestinal side effects . These can usually be limited by decreasing the dose .
Contraindications for the use of PPA include preexisting cardiac disease , chronic kidney disease , protein losing nephropathy , hyperthyroidism and hypertension . Although hypertension does not seem to develop to a clinically significant degree in dogs receiving PPA it is recommended that blood pressure is monitored regularly . In many cases PPA is combined with oestrogen drugs and there seems to be a synergistic effect when these two drugs are used together .
PPA is also usually prescribed in incontinent male dogs . Some clinicians combine PPA with testosterone , but efficacy of this approach has not been well documented . Approximately 43 % of male dogs are responsive to PPA , much lower than what is seen in female dogs .
• Phenylephrine This drug is an alpha-adrenergic agonist which is used to treat hypotension . It is usually used as a constant rate infusion to improve peripheral vascular resistance and increase mean arterial pressure . The drug is compounded and sold as an oral solution to treat USMI in incontinent dogs . In South Africa it is compounded by Kyron laboratories as a syrup which contains 20 mg / ml . The recommended dose is 1.2 mg / kg three times daily . As with PPA , it is contraindicated in cases with cardiac disease , renal disease or hypertension . It is advisable to monitor blood pressure regularly .
Oestrogens
Oestrogens can be administered less frequently than PPA which may be more convenient for most owners . However , with some formulations response rate is lower than with PPA and only 60-65 % of patients respond to treatment with diethylstilboesterol . For the newer oestriol formulation a response rate of up to 80 % or higher was reported .
Oestrogens increase the sensitivity of the urethral alpha-adrenergic receptors to catecholamines and possibly also increase the number of alpha-adrenergic receptors . Diethylstilboesterol ( DES ) and oestriol are the most commonly used oestrogens .
Side effects of oestrogen therapy could include signs of oestrus such as mammary gland enlargement , vulvar swelling and attractiveness to intact males ; perineal alopecia and bone marrow suppression . In most cases bone marrow suppression is not a clinically significant complication unless dosages of around 10 times the recommended doses are used and it is not listed as a side effect for oestriol . It is recommended that as a precaution a complete blood count should be performed prior to treatment and repeated a month after initiating treatment and again at 3 months and 5 months . Its use is contraindicated in intact female dogs and the drug should be used with extreme caution in male dogs as it could result in prostatic metaplasia .
• Diethylstilboesterol DES is compounded by compounding pharmacies such as V-Tech . DES is dosed at 0.1-1 mg ( 0.02 mg / kg ) per dog perios for 3-5 days and then every 3-7 days depending on the response . Once a week dosing may be more convenient for some owners . After two months the dosing frequency can be decreased to once every 10 days , and in some cases even to every 14 days . The formulations available from V-Tech in South Africa include 30 vet360
Issue 02 | MAY 2018 | 28