메틸렌 블루

해독제 / 티아진 염료

메틸렌 블루는 **티아진 염료**로, 주로 반추동물에서 질산염이나 염소산염과 같은 산화제에 의해 유발된 **메트헤모글로빈혈증**을 치료하는 **해독제**로 사용됩니다. 또한 시안화물 중독의 보조 또는 대체 요법으로도 간혹 사용됩니다. 소동물 의학에서는 개 췌장의 **췌도세포종(인슐린종)**을 우선적으로 염색하기 위한 수술 중 정맥 내 염색제로 독특하게 사용되어 외과적 절제를 돕습니다. **임상 요점:** * 메틸렌 블루는 역설적인 용량 의존적 효과를 가집니다. 저용량에서는 메트헤모글로빈혈증을 치료하는 환원제로 작용하지만, 고용량에서는 산화제로 작용하여 오히려 메트헤모글로빈혈증을 *유발*할 수 있습니다. * 고양이는 이 약물로 인한 산화적 손상에 매우 민감하므로, 고양이 환자에서의 사용은 논란의 여지가 많으며 일반적으로 금기로 간주됩니다.

작용 기전: Methylene blue acts as an artificial electron acceptor and donor in red blood cells. * **Reduction Pathway:** In the tissues, methylene blue interacts with the enzyme **NADPH-methemoglobin reductase**. It is rapidly reduced to **leucomethylene blue**. * **Hemoglobin Conversion:** Leucomethylene blue serves as a reducing agent (electron donor) → converts **methemoglobin (Fe3+)** back to functional oxygen-carrying **hemoglobin (Fe2+)**. * **Oxidation Pathway (High Doses):** Methylene blue is inherently an oxidizing agent. If administered at high doses (species dependent), it overwhelms the reduction pathway and directly oxidizes hemoglobin → **causes methemoglobinemia**.

동물 종별 용량

Sheep

For methemoglobin-producing toxins (nitrites, nitrates, chlorates) · 4-15 mg/kg (Using a 1% solution) · IV · q6h · As needed
For cyanide toxicity · 4-6 grams per 454 kg (1000 lb.) of body weight · IV · Once · Once

Goats

For methemoglobin-producing toxins (nitrites, nitrates, chlorates) · 4-15 mg/kg (Using a 1% solution) · IV · q6h · As needed
For cyanide toxicity · 4-6 grams per 454 kg (1000 lb.) of body weight · IV · Once · Once

Cats

Methemoglobinemia secondary to phenol exposure · 1.5 mg/kg · IV · Single, slow infusion · Once · May use with 20 mg/kg ascorbic acid PO.
Methemoglobinemia · 1-1.5 mg/kg · IV · one time only · Once
Severe methemoglobinemia · 1 mg/kg as a 1% solution · IV · given slowly over several minutes · May be repeated if necessary · Use cautiously (can cause Heinz body anemia). Measure hematocrit for 3 days.

Cattle

For methemoglobin-producing toxins (nitrites, nitrates, chlorates) · 4-15 mg/kg (Using a 1% solution) · IV · q6h · As needed
For nitrate poisoning · 5-15 mg/kg as a 1% solution in physiologic saline · IV · Once · Repeat treatment at a lower dose may be required in severe cases · In animals that do not succumb, recovery occurs by 24 hours.

투여 경로

금기

Cats (considered contraindicated by most clinicians due to severe sensitivity)
Renal insufficiency
Hypersensitivity to methylene blue
Intraspinal (intrathecal) injection
Lactating dairy animals
Severe renal impairment
Patients with G6PD deficiency (can cause severe hemolysis)
Use with extreme caution in cats due to high susceptibility to Heinz body formation

이상반응

Heinz body anemia
Red cell morphological changes
Methemoglobinemia (at high doses)
Decreased red blood cell life span
Necrotic abscesses (if injected SC or extravasated IV)
Green-blue discoloration of urine
Heinz body anemia (especially in cats)
Paradoxical methemoglobinemia (at high doses)
Tissue necrosis (if extravasated)
Blue/green discoloration of urine, feces, and mucous membranes
Nausea and vomiting

약물 상호작용

SSRIs (e.g., Fluoxetine) · Methylene blue is a potent reversible monoamine oxidase inhibitor (MAOI); concurrent use can precipitate fatal serotonin syndrome. · major
Tricyclic Antidepressants (TCAs) · Increased risk of serotonin toxicity. · major

모니터링

Methemoglobinemia levels
Red cell morphology
Red cell indices
Hematocrit
Hemoglobin
Methemoglobin levels
Complete Blood Count (CBC) for Heinz bodies and hemolysis
Arterial blood gas (ABG)
Renal function
Signs of serotonin syndrome if on concurrent serotonergic drugs

과용량

The LD50 for IV administered 3% methylene blue is approximately 43 mg/kg in sheep. High doses can paradoxically cause methemoglobinemia due to the drug's inherent oxidizing properties.

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