Metiltioninio Cloruro Monico (Methylthioninium Chloride)

• Methylthioninium chloride is used in conditions where rapid reduction of oxidized hemoglobin or detoxification of cyanide is required.
• Methemoglobinemia: rapid conversion of methemoglobin back to functional hemoglobin, restoring oxygen delivery.
• Cyanide poisoning: facilitates conversion of cyanide to less toxic metabolites, supporting cellular respiration.
• Urinary tract infection: exhibits antimicrobial activity that can aid in adjunctive treatment of certain bacterial infections.

• Methylthioninium chloride acts as an electron carrier that donates electrons to methemoglobin, reducing it to hemoglobin, and simultaneously inhibits nitric oxide synthase. In cyanide poisoning, it forms a complex with cyanide, allowing conversion to thiocyanate via endogenous pathways, thereby reducing toxicity. The compound also displays antimicrobial and antimalarial properties through oxidative mechanisms.

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

Common Side Effects

• Nausea or vomiting: gastrointestinal discomfort following administration.
• Headache or dizziness: transient neurological sensations.
• Mild hypertension: temporary increase in blood pressure.
• Blue‑green discoloration of urine: harmless coloration due to the dye.

Serious or Rare Side Effects

• Hemolysis in patients with G6PD deficiency: rapid destruction of red blood cells.
• Severe hypertension or hypertensive crisis: marked elevation of blood pressure requiring intervention.
• Serotonin syndrome: risk when combined with serotonergic agents, presenting with agitation, hyperreflexia, and fever.

• Methylthioninium chloride requires careful consideration of patient-specific factors and handling conditions.
• G6PD deficiency: avoid use due to risk of hemolysis.
• Pregnancy: limited data; use only if potential benefit outweighs risk.
• Concurrent serotonergic drugs: monitor for signs of serotonin syndrome.
• Renal impairment: assess renal function and monitor for accumulation.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Methylthioninium chloride can interact with several drug classes, necessitating vigilance.

Major Interactions (Avoid)

• Selective serotonin reuptake inhibitors (SSRIs): increased risk of serotonin syndrome.
• Monoamine oxidase inhibitors (MAOIs): heightened potential for serotonin toxicity.

Moderate Interactions (Monitor Closely)

• Antihypertensive agents: possible additive blood pressure effects.
• Local anesthetics such as prilocaine: may exacerbate methemoglobinemia.
• Other oxidizing agents: monitor methemoglobin levels closely.