Doses - MEGESTROL ACETATE
Dogs: 
For estrus control: a) To halt cycle in proestrus: 2.2 mg/kg once daily for 8 days starting during the first 3days of proestrus. While the timing of the next cycle is variable, it may be prolongedwith 2.2 mg/kg/day for 4 days, then 0.55 mg/kg/day for 16-20 days.
To postpone an anticipated cycle: 0.55 mg/kg/day for 32 days, beginning at least 7 daysprior to proestrus (Burke 1985)
b) For suppression during proestrus (first 3 days): 2.2 mg/kg once daily for 8 days (92%efficacy). Bitch must be controlled until behavioral signs of estrus disappear. If matingoccurs during first 3 days of therapy, stop treatment and consider mismating therapy.
There is a an increased likelihood of pyometra developing if progestins are usedconcomitantly with estrogens. If mating occurs after 3 or more days of therapy continueat a dosage rate of 3-4 mg/kg PO.
To delay an anticipated heat during anestrus: 0.55 mg/kg PO for 32 days initiated 7days prior to proestrus. Recommend doing vaginal cytology prior to therapy. If noerythrocytes are seen, initiate therapy if cycle time frame is appropriate. If erythrocytesare seen, delay therapy until proestrus therapy can be instituted. Do not repeat therapymore often than once every 6 months. (Woody 1988)
For pseudocyesis (false pregnancy):
a) 0.5 mg/kg PO once daily for 8 days (Barton and Wolf 1988)
To prevent vaginal hyperplasia development:
a) 2.2 mg/kg PO for 7 days early in proestrus (Wykes 1986)
For treatment of severe galactorrhea:
a) 0.55 mg/kg PO once daily for 7 days (Olson and Olson 1986)
For adjunctive treatment of aggressive or unacceptable masculine behavior:
a) 1.1 - 2.2 mg/kg PO once daily for 2 weeks, then 0.5 - 1.1 mg/kg once daily for 2 weeks.
Should be used with behavior modification. (Voith and Marder 1988a)
Cats: 
For suppression of estrus: a) If in behavioral estrus, signs may be inhibited by giving 5 mg/day PO until estrus stops(generally within 3-5 days), then 2.5 - 5.0 mg PO once weekly for 10 weeks.
Postponement of estrus (if started during diestrus): 2.5 mg PO daily for 8 weeks.
Postponement of estrus (if started during anestrus): 2.5 mg PO once weekly for up to18 months. Recommend allowing cat to have a cycle (unmedicated) before beginninganother treatment cycle. (Woody 1988)
b) If started in diestrus: 2.5 mg per day PO for up to 2 months.
If started in anestrus: 2.5 mg per week for up to 18 months.
For prevention of estrus: 5 mg daily PO for 3 days as soon as behavioral signs of estrusare seen; next estrus period will occur in approximately 4 weeks. (Romatowski 1989)(derived from package inserts; Ovarid®¯Glaxovet)
For treatment of idiopathic feline miliary dermatitis:
a) 2.5 - 5 mg once every other day, followed by weekly maintenance dosages. May benecessary to treat for animal's lifetime. Reserve use for severe cases; explain risks toowner and do not exceed 2.5 mg per week during maintenance phase. (Kwochka 1986)
As an alternative treatment for immune-mediated skin diseases:
a) 2.5 - 5.0 mg PO once daily for 10 days, then every other day (Giger and Werner 1988)
For adjunctive therapy of eosinophilic granulomas:
a) 0.5 mg/kg PO once daily for 2 weeks, then twice weekly prn (Coppoc 1988)
For eosinophilic ulcers:
a) Alone or in combination with methylprednisolone acetate (Depo-Medrol®): 5 - 10 mg
PO every other day for 10-14 doses, then every 2 weeks prn (DeNovo, Potter, and Woolfson 1988)
For eosinophilic keratitis (feline proliferative keratitis):
a) 0.5 mg/kg PO daily until a response is noted, then reduce dose to 1.25 mg PO 2-3 timesweekly as required. (Nelson 1986)
For feline plasma cell gingivitis:
a) 2.5 mg PO once daily for 10 days, then once every other day for 5 treatments, then prn(Morgan 1988)
As a secondary therapy (thyroid hormone replacement first choice) for treatment of felineendocrine alopecia (FEA):
a) 5 mg PO every second to third day initially, then 2.5 mg PO once to twice weekly(Thoday 1986)
For feline psychogenic alopecia and dermatitis:
a) 2.5 - 5 mg every other day initially, then taper to the lowest maintenance dosage possible, given weekly prn. (Walton 1986)
For adjunctive therapy (with urine acidification, increased urine crystalloid solubility, andantispasmodics if required) for persistent hematuria and urethritis in a non-obstructed cat:
a) 2.5 - 5 mg PO once daily to every other day (with prednisone: 2.5 - 5.0 mg PO daily).(Lage, Polzin, and Zenoble 1988)
For urine marking, intraspecies aggression, anxiety:
a) 5 mg PO once daily for 5-7 days, then once weekly (Morgan 1988)
b) 2 mg/kg/day for 5 days, then 1 mg/kg/day for 5 days, then 0.5 mg/kg/day for 5 days.(Romatowski 1989) (derived from package inserts; Ovarid®¯Glaxovet)
Monitoring Parameters -
Client Information - The client should fully understand the potential risks of therapy (see
Adverse effects above) before starting therapy and should report changes in mammary glands orother symptoms of adverse reactions (e.g., PU/PD, extreme lethargy, behavior changes, etc.) to theveterinarian.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times - Veterinary-Approved Products:
Megestrol Acetate Oral Tablets 5 mg, 20 mg; available in bottles of 100 & 250 tablets and in 30foil strips of 8 and packaged in cartons of 240 tablets; Ovaban® (Schering); (Rx) Approvedfor use in dogs only.
Human-Approved Products:
Megestrol Acetate Oral Tablets 20 mg, 40 mg; Megace® (Bristol-Myers Oncology);Generic(Rx)MELARSOMINE
Chemistry/
Storage, Stability, Compatibility
An organic arsenical compound, melarsomine dihydrochloride has a molecular weight of 501 and is freely soluble in water. The unreconstitutedpowder should be stored upright at room temperature. Once reconstituted, the solution should bekept in the original container and kept refrigerated for up to 24 hours. Do not freeze. Do not mixwith any other drug.Pharmacology
While melarsomine is an arsenical compound, its exact mechanism of action isnot known. Both laboratory and field studies have demonstrated that melarsomine is 90-99% effective in killing adult and L5 larvae of D. immitis in dogs at recommended dosages.Uses, Indications
Melarsomine is indicated for the treatment of stabilized class I, II and IIIheartworm disease caused by immature (4 month old, stage L5) to mature adult infections of D.immitis in dogs. When compared with thiacetarsamide, melarsomine appears to be more efficacious, less irritating to tissues and does not cause hepatic necrosis.Pharmacokinetics
The drug is reportedly rapidly absorbed after IM injection. The time to peakplasma concentration is about 11 minutes after IM injection. The apparent volume of distribution isabout 0.7 l/kg. Terminal half life is approximately 3 hours.Contraindications, Precautions, Reproductive Safety
Melarsomine is contraindicated in dogswith class IV (very severe) heartworm disease. Class IV is having caval syndrome (heartwormspresent in venae cavae and right atrium). Melarsomine is reportedly very toxic to cats and its usecannot be recommend for this species at this time.Safety has not been established for use in pregnant, lactating or breeding dogs. Risks versus potential benefits of therapy should be weighed before use.
Adverse Effects, Warnings
Approximately 1/3 of dogs show signs of injection site reactions(pain, swelling, tenderness, reluctance to move) after receiving melarsomine. Most of these signsresolve within weeks, but rarely severe injection reactions can occur. Firm nodules at the injectionsite can persist indefinitely. SubQ or IV injections must be avoided.Other reactions reported in 5% or more dogs treated include: coughing/gagging (22% incidence;average day of onset after treatment = 10); depression/lethargy (15% incidence; average day ofonset after treatment = 5); anorexia/inappetence (13% incidence; average day of onset aftertreatment = 5); fever (7%); lung congestion (6%); vomiting (5%). There is significant interpatientvariance in both the date of onset and duration for the above effects.
Animals not exhibiting adverse effects after the first dose or course of therapy may demonstratethem after the second dose or course of therapy.
A plethora of other adverse effects in dogs have been noted for melarsomine with reported incidences less than 3%; some of these however are serious. Refer to the package insert for specifics.
Do NOT give IV or SubQ; significant toxicity or tissue damage may occur. Administer only deep IM as directed (lumbar epaxial muscles (L3-L5). Do not administer at any other site.
While all dogs with heartworm disease are at risk for post-treatment pulmonary thromboembolism, those with severe pulmonary artery disease are at increased risk for post treatment morbidity and mortality. Dogs should be exercise restricted after treatment.
Wash hands after use or wear gloves. Avoid contact with animal's eyes; if exposed wash withcopious amounts of water. Avoid human exposure. If human exposure occurs, contact a physician.
Overdosage - There is low margin of safety with melarsomine dosages. A 3X dose (7.5 mg/kg) inhealthy dogs have demonstrated respiratory inflammation and distress, excessive salivation, restlessness, panting, vomiting, edema, tremors, lethargy, ataxia, cyanosis, stupor and death. Signs ofdiarrhea, excessive salivation, restlessness, panting, vomiting and fever have been noted in infecteddogs who have received inadvertent overdoses (2X).
Treatment with dimercaprol (BAL in Oil) may be considered to treat melarsomine overdoses.
Clinical efficacy of melarsomine may be reduced, however.