Metiltioninio Cloruro Bioindustria L.I.M. (Methylthioninium Chloride)

Methylthioninium chloride is used in clinical settings to address conditions involving abnormal hemoglobin oxidation and certain toxic exposures.

• Methemoglobinemia: rapidly reduces methemoglobin to functional hemoglobin, restoring oxygen delivery.
• Cyanide poisoning: acts as an antidote by facilitating detoxification pathways in acute exposure.
• Urinary tract infections: employed as a topical antiseptic for diagnostic staining and bacterial suppression.
• Diagnostic staining: used to color urinary sediments and tissues for microscopic examination.

• Methylthioninium chloride functions as an electron carrier that accepts electrons from cellular reductases and transfers them to ferric (Fe³⁺) iron in methemoglobin, converting it back to ferrous (Fe²⁺) hemoglobin. The reduced form also inhibits nitric oxide synthase and soluble guanylate cyclase, diminishing nitric oxide signaling. These actions together lower methemoglobin levels and counteract the toxic effects of cyanide and other oxidizing agents.

Methylthioninium chloride may be associated with a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Nausea: mild gastrointestinal upset.
• Vomiting: occasional emesis.
• Headache: transient cranial discomfort.
• Dizziness: light‑headed sensation.
• Injection site pain: local discomfort at the IV site.
• Mild hypotension: slight drop in blood pressure.

Serious or Rare Side Effects

• Severe hypotension: marked blood pressure decline requiring intervention.
• Anaphylaxis: acute allergic reaction with airway compromise.
• Hemolysis: rapid destruction of red blood cells, especially in G6PD deficiency.
• Methemoglobinemia paradoxical increase: worsening of methemoglobin levels.
• Renal impairment: acute kidney injury in susceptible patients.
• Severe allergic reaction: skin rash, bronchospasm, or angioedema.

When using methylthioninium chloride, clinicians should observe several safety precautions to minimize risk.

• Indication verification: confirm methemoglobinemia or cyanide poisoning before administration.
• G6PD deficiency screening: avoid or adjust dose in patients with glucose‑6‑phosphate dehydrogenase deficiency.
• Methemoglobin monitoring: measure levels before and after treatment to assess response.
• Hypersensitivity assessment: discontinue if signs of allergic reaction appear.
• Renal/hepatic impairment: use caution and consider dose adjustment in organ dysfunction.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Methylthioninium chloride can interact with several agents, influencing its efficacy or safety profile.

Major Interactions (Avoid)

• Nitrites: co‑administration can exacerbate methemoglobinemia.
• Phenazopyridine: additive effect on methemoglobin formation.
• Dapsone: increases risk of severe methemoglobinemia.
• Prilocaine and other oxidizing local anesthetics: may potentiate methemoglobin levels.
• Methylenediamine: concurrent use may cause unpredictable redox reactions.

Moderate Interactions (Monitor Closely)

• Anticoagulants: monitor for bleeding if high‑dose therapy is prolonged.
• Renally excreted drugs: adjust dosing as renal function may affect clearance.
• Hepatotoxic agents: observe liver function during treatment.
• Diuretics: watch for electrolyte shifts with hypotension.
• Other redox‑active compounds: assess for cumulative oxidative stress.