多拉菌素
多拉菌素 (Doramectin) 是一種屬於阿維菌素 (avermectin) 類的**大環內酯類**抗寄生蟲藥物。 - **經濟動物用途**：FDA 核准用於牛和豬的注射液及外用澆潑劑，可治療多種胃腸道線蟲、肺蟲、眼蟲、牛皮蠅蛆、蝨子和疥蟎。 - **伴侶動物用途**：在犬貓主要作為標示外使用 (extra-label)，用於治療**全身性毛囊蟲症**和犬食道蟲症 (spirocercosis)。 > **臨床要點**：雖然非常有效，但其在小動物的使用完全屬於標示外，且具有嚴重的神經毒性風險，特別是在帶有 MDR1 (ABCB1) 基因突變的牧羊犬品種中。
作用機制: Doramectin exerts its antiparasitic effect by binding to **glutamate-gated chloride channels** found in invertebrate nerve and muscle cells. - **Mechanism**: Binding → increases membrane permeability to chloride ions → cellular hyperpolarization → **flaccid paralysis and death** of the parasite. - It also enhances the release of **gamma-aminobutyric acid (GABA)** at presynaptic neurons, further inhibiting nerve transmission. - **Mammalian Safety**: Mammals lack glutamate-gated chloride channels, and avermectins typically do not cross the intact mammalian blood-brain barrier (where GABA receptors reside) due to the **P-glycoprotein efflux pump**. Toxicity occurs when this pump is deficient (e.g., MDR1 mutation) or overwhelmed by massive overdoses.
各物種劑量
- Feline demodicosis (D. cati, D. gatoi) · 600 micrograms/kg (0.6 mg/kg) · SC · once per week · Extra-label. Get informed consent from owner. Alternative treatments include Lime sulfur dips or amitraz.
- Labeled indications (Injectable) · 200 micrograms/kg (1 mL per 110 lb. body weight) · SC/IM · once · Beef Quality Assurance guidelines recommend SC administration as the preferred route.
- Labeled indications (Pour-on) · 500 micrograms/kg (1 mL per 22 lb. body weight) · topical · once · Administer topically along the mid-line of the back in a narrow strip between the withers and tailhead.
- Labeled indications · 300 micrograms/kg (1 mL per 75 lb. body weight) · IM · once · Intramuscular injections should be administered into the muscular region of the neck.
- P. cuniculi infestations (Rabbits) · 200 micrograms/kg · IM · once · once
- Treatment of generalized demodicosis · 600 micrograms/kg · PO · once daily · Until 60 days without improvement · Extra-label. If improvement is not seen after 60 days, an alternative therapy should be used.
- Treatment of generalized demodicosis · 600 micrograms/kg (0.6 mg/kg) · SC · once per week · Extra-label. Get informed consent from owner.
給藥途徑
禁忌症
- Dogs with MDR1-allele mutations (relative/absolute depending on dose)
- Female dairy cattle 20 months of age or older
- Calves to be processed for veal
不良反應
- Injection site blemishes (IM administration)
- Pupil dilation (mydriasis) in dogs
- Lethargy
- Blindness
- Coma (especially in MDR1-mutant dogs)
監測
- Clinical efficacy (resolution of parasites/lesions)
- Signs of neurotoxicity in off-label species (dogs/cats)
過量
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.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。