Methylene Blue
Also known as: Azul Metile, Collubleu, Desmoidpillen, Vitableu, Urolene Blue, Zumetil, Methylene Blue, Proveblue
* **Professional Supervision:** Because of the potential toxicity of this agent and the seriousness of methemoglobin-related intoxications, this drug should be used with close professional supervision only. * **Staining:** Methylene blue may severely stain clothing or skin. Removal may be accomplished using hypochlorite solutions (bleach). * **Urine Color:** Pet owners should be aware that the animal's urine may turn a green-blue color during treatment.
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
What it is used for
- For methemoglobin-producing toxins (nitrites, nitrates, chlorates)
- For cyanide toxicity
- For methemoglobin-producing toxins (nitrites, nitrates, chlorates)
- For cyanide toxicity
- Methemoglobinemia secondary to phenol exposure
- Methemoglobinemia
- Severe methemoglobinemia
- For methemoglobin-producing toxins (nitrites, nitrates, chlorates)
- For nitrate poisoning
- For cyanide toxicity
- Methemoglobinemia secondary to chlorate toxicity
- To preferentially stain islet-cell tumors of the pancreas
- Methemoglobinemia secondary to phenol exposure
How it is given
Possible side effects
- 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
Cautions & contraindications
- 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
- > **WARNING:** Cats are highly sensitive to methylene blue and can rapidly develop **Heinz body anemia** and methemoglobinemia. Dogs and horses can also develop these effects at relatively low dosages. * **Administration:** Must be given IV. Extravasation or subcutaneous injection can cause severe necrotic abscesses. * **Efficacy:** Considered relatively ineffective in reducing methemoglobin in horses. * **Food Animal Residues:** FARAD recommends a minimum milk withdrawal time of 4 days. Meat withdrawal is conservatively recommended at 180 days due to carcinogenicity concerns, though some data suggest 14 days may be sufficient. * **Pregnancy:** FDA Category C. Safe use during pregnancy has not been demonstrated.
Drug interactions
- SSRIs (e.g., Fluoxetine): Methylene blue is a potent reversible monoamine oxidase inhibitor (MAOI); concurrent use can precipitate fatal serotonin syndrome.
- Tricyclic Antidepressants (TCAs): Increased risk of serotonin toxicity.
Frequently asked questions
What is Methylene Blue used for in pets?
* **Professional Supervision:** Because of the potential toxicity of this agent and the seriousness of methemoglobin-related intoxications, this drug should be used with close professional supervision only. * **Staining:** Methylene blue may severely stain clothing or skin. Removal may be accomplished using hypochlorite solutions (bleach). * **Urine Color:** Pet owners should be aware that the animal's urine may turn a green-blue color during treatment.
Is Methylene Blue safe for my pet?
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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