伊維菌素
伊維菌素是一種典型的**阿維菌素類 (avermectin)** 抗寄生蟲藥物，廣泛應用於多種獸醫物種。它是一種巨環內酯類衍生物，對廣泛的線蟲和節肢動物具有高度療效。 **主要臨床重點：** * **FDA 核准用途：** 犬貓的心絲蟲預防；牛、豬、馬、馴鹿和野牛的胃腸道線蟲、肺蟲、牛皮蠅蛆、蝨子和蟎蟲治療。 * **標示外用途：** 微絲蟲殺滅劑、緩慢殺滅成蟲療法（通常與多西環素併用），以及小動物的全身性毛囊蟲症和疥癬治療。 * **基因敏感性：** 對於帶有 **ABCB1-1Δ（原稱 MDR1）** 基因突變的犬種（例如牧羊犬、澳洲牧羊犬、喜樂蒂牧羊犬、長毛惠比特犬等）需極度謹慎。這些犬隻的血腦屏障缺乏具功能的 P-醣蛋白幫浦，在用於治療疥癬或微絲蟲的常規劑量下，可能導致嚴重甚至致命的中樞神經系統毒性。 * **毒性概況：** 在低劑量的心絲蟲預防用藥下通常是安全的（即使是 MDR1 突變犬隻），但在高劑量或與 P-醣蛋白抑制劑併用時，神經毒性風險會顯著增加。
作用機制: Ivermectin exerts its antiparasitic effect by binding selectively and with high affinity to **glutamate-gated chloride channels** which occur in invertebrate nerve and muscle cells. * **Primary Mechanism:** Binds to glutamate-gated chloride channels → increases cell membrane permeability to chloride ions → hyperpolarization of the nerve or muscle cell → flaccid paralysis and death of the parasite. * **Secondary Mechanism:** Enhances the release of **gamma-aminobutyric acid (GABA)** at presynaptic neurons. GABA acts as an inhibitory neurotransmitter → blocks post-synaptic stimulation → paralysis. > **Pharmacology Pearl:** Because flukes (trematodes) and tapeworms (cestodes) do not utilize GABA as a peripheral nerve transmitter and lack glutamate-gated chloride channels, ivermectin is completely ineffective against these parasites. Mammals generally lack glutamate-gated chloride channels, and mammalian GABA receptors are confined to the CNS, which ivermectin does not readily cross (unless the P-glycoprotein pump is defective or overwhelmed), providing a wide margin of safety.
各物種劑量
- As a preventative for heartworm · 0.024 mg/kg (24 micrograms/kg) PO every 30-45 days · PO · every 30-45 days · Also controls hookworms at this dosage.
- For Aelurostrongylus abstrusus · 0.4 mg/kg SC once · SC · once
- Ear mites · 1 mg/g ear gel · topical · Not specified · Not specified · Otimectin Vet. Do not use in kittens under 16 weeks.
- For susceptible parasites · 300 micrograms/kg (0.3 mg/kg) SC in the neck immediately behind the ear · SC · once
- For general control of endo- and ectoparasites in potbellied pigs · 300 micro-grams/kg SC or IM once for internal parasites and repeated in 10-14 days for external parasites · SC/IM · once, repeat in 10-14 days · Only partially effective against whipworms.
- For prevention of heartworm disease · 0.02 mg/kg PO monthly · PO · monthly
- To treat heartworm disease using the very slow protocol · 50 micrograms PO once a month. · PO · once a month
- For nasal bot infection · 200 micrograms/kg · SC/PO · once
- For susceptible parasites · 200 micrograms/kg SC for one dose · SC · once
給藥途徑
禁忌症
- Foals less than 4 months old (manufacturer recommendation)
- Puppies less than 6 weeks old
- Breeds susceptible to ABCB1-1Δ (MDR1) mutation at high doses (unless tested normal)
- Chelonians (turtles, tortoises)
- Indigo snakes
- Skinks
- Lactating dairy animals (no milk withdrawal established)
- Females of breeding age (cattle/swine, per label)
- Dogs with the MDR1 (ABCB1) gene mutation (unless using strictly at low heartworm preventative doses)
- Chelonians (turtles and tortoises) - causes fatal flaccid paralysis
- Kittens under 16 weeks of age (for topical ear gel)
- Use of concentrated livestock formulations in small animals
不良反應
- Horses: Ventral midline swelling and pruritus (hypersensitivity to dying Onchocerca microfilariae)
- Dogs: Shock-like reaction (when used as microfilaricide), depression, hypothermia, vomiting
- Dogs (MDR1/Toxicity): Ataxia, lethargy, hypersalivation, mydriasis, tremors, seizures, blindness, coma
- Cats: Agitation, vocalization, anorexia, mydriasis, rear limb paresis, tremors, disorientation, blindness
- Cattle: Paralysis/staggering or salivation/bloat (if Hypoderma bovis larvae are killed in vital areas), injection site swelling
- Birds: Lethargy, anorexia, death (especially in finches and budgerigars)
- Neurotoxicity (ataxia, tremors, mydriasis, blindness, coma, death) - especially in MDR1-mutant dogs
- Hypersalivation
- Vomiting
- Lethargy
- Bradycardia
藥物相互作用
- Benzodiazepines · Effects may be potentiated by ivermectin; concurrent use is not advised.
- Ketamine · Avoid ivermectin in reptiles within 10 days of ketamine administration.
- Spinosad · Increased risk of neurotoxicity; do not use with high extra-label doses of ivermectin. · major
- Amiodarone · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity.
- Carvedilol · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity.
- Clarithromycin · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity.
- Cyclosporine · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity. · moderate
- Diltiazem · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity.
- Erythromycin · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity.
- Itraconazole · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity.
- Ketoconazole · Strong P-glycoprotein inhibitor; should never be used with ivermectin in dogs. · moderate
- Quinidine · P-glycoprotein inhibitor; increases risk of ivermectin CNS toxicity.
監測
- Clinical efficacy (resolution of parasites, negative skin scrapes, etc.)
- Adverse effects/toxicity (especially neurologic signs: ataxia, mydriasis, tremors)
- MDR1 (ABCB1) genotype (prior to use in susceptible breeds)
- Neurological signs (ataxia, mydriasis, tremors)
- Resolution of parasitic infection
過量
**Clinical Signs of Toxicity:** * **Dogs:** Vomiting, ataxia, lethargy, tachycardia, hypersalivation, mydriasis, tremors, and seizures. In non-sensitive breeds, signs rarely occur at ≤ 1 mg/kg. Mydriasis occurs at 2.5 mg/kg, tremors at 5 mg/kg, severe tremors/ataxia at 10 mg/kg. LD50 is 80 mg/kg. In MDR1-sensitive breeds, severe signs can develop within 4 hours at much lower doses. * **Cats:** Agitation, vocalization, anorexia, mydriasis, rear limb paresis, tremors, disorientation, blindness, head pressing, wall climbing. Margin of safety is narrower in kittens (signs seen at 300 mcg/kg). * **Large Animals:** Horses show visual impairment, depression, ataxia at 2 mg/kg. Cattle show ataxia and listlessness at 8 mg/kg. Swine show lethargy, ataxia, tremors, lateral recumbency at 30 mg/kg. **Treatment:** * **Decontamination:** Emptying the gut should be considered for recent massive oral ingestions. Repeated doses of activated charcoal are advised to interrupt enterohepatic recirculation. * **Supportive Care:** Symptomatic and supportive therapy for CNS, GI, and cardiovascular effects. * **Advanced Therapy:** **Intravenous Lipid Emulsion (IVFE)** therapy has been used successfully to facilitate clearance of ivermectin due to its highly lipophilic nature.
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