© 2003-17 Susan K. Mikota DVM and Donald C. Plumb, Pharm.D. Published by
Elephant Care International
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Chemistry/Storage/Stability/Compatibility – An avermectin antiparasitic compound, doramectin is isolated from fermentations from the soil organism Streptomyces avermitilis. The commercially available injectable solution is a colorless to pale yellow, sterile solution. The injectable solution should be stored below 86°F (30°C).
Pharmacology – The primary mode of action of avermectins like doramectin is to affect chloride ion channel activity in the nervous system of nematodes and arthropods. Doramectin binds to receptors that increase membrane permeability to chloride ions. This inhibits the electrical activity of nerve cells in nematodes and muscle cells in arthropods and causes paralysis and death of the parasites. Avermectins also enhance the release of gamma amino butyric acid (GABA) at presynaptic neurons. GABA acts as an inhibitory neurotransmitter and blocks the post-synaptic stimulation of the adjacent neuron in nematodes or the muscle fiber in arthropods. Avermectins are generally not toxic to mammals as they do not have glutamategated chloride channels and these compounds do not readily cross the blood-brain barrier where mammalian GABA receptors occur.
Uses/Indications – Doramectin injection is indicated for the treatment and control of the following endo- and ectoparasites in cattle: roundworms (adults and some fourth stage larvae)—Ostertagia ostertagi (including inhibited larvae), O. lyrata, Haemonchus placei, Trichostrongylus axei, T. colubriformis, T. longispicularis, Cooperia oncophora, C. pectinata, C. punctata, C. surnabada (syn. mcmasteri), Bunostomum phlebotomum, Strongyloides papillosus, Oesophagostomum radiatum, Trichuris spp.,; lungworms (adults and fourth stage larvae)—Dictyocaulus viviparus; eyeworms (adults)—Thelazia spp.; grubs (parasitic stages)—Hypoderma bovis, H. lineatum ; lice—Haematopinus eurysternus, Linognathus vituli, Solenopotes capillatus; and mange mites—Psoroptes bovis, Sarcoptes scabiei.
The manufacturer states the doramectin protects cattle against infection or reinfection with Ostertagia ostertagi for up to 21 days.
Pharmacokinetics – After subcutaneous injection, the time to peak plasma concentration in cattle is about 5 days. Bioavailability is for practical purposes, equal with subQ and IM injections.
Contraindications/Precautions/Reproductive Safety – The manufacturer warns to not use in other animal species as severe adverse reactions, including fatalities in dogs, may result.
Studies performed in breeding animals (bulls, and cows in early and late pregnancy), at a dose of 3X recommended had no effect on breeding performance.
Adverse Effects/Warnings – No listed adverse effects. Intramuscular injections may have a higher incidence of injection site blemishes at slaughter than do subcutaneous injections.
Overdosage – In field trials, no toxic signs were seen in cattle given up to 25X the recommended dose. In breeding animals (bulls, and cows in early and late pregnancy), a dose 3 times the recommended dose had no effect on breeding performance.
Drug Interactions – None noted.
For labeled indications: 200 mcg/kg (1 ml per 110 lb. body weight)) SubQ or IM. Injections should be made using 16 to 18 gauge needles. Subcutaneous injections should be administered under the loose skin in front of or behind the shoulder. Intramuscular injections should be administered into the muscular region of the neck. Beef Quality Assurance guidelines recommend subcutaneous administration as the preferred route. (Label Directions; Dectomax®—Pfizer)
Monitoring Parameters – Efficacy
Client Information/Withdrawal Times – Cattle must not be slaughtered for human consumption within 35 days of treatment. Not for use in female dairy cattle 20 months of age or older. A withdrawal period has not been established for this product in pre-ruminating calves. Should not be used in calves to be processed for veal.
Dosage Forms/Preparations/FDA Approval Status –
Human-Approved Products: None
Doramectin 10 mg/ml Injectable Solution in 100 ml, 250 ml, and 500 ml multi-dose vials; Dectomax® (Pfizer); (OTC). Approved for use in cattle (see limitations in Client Information above).