Metiltioninio Cloruro S.A.L.F. (Methylthioninium Chloride)

• Methylthioninium chloride is used in conditions where rapid reduction of oxidized hemoglobin or detoxification of cyanide is required. It also serves as an antiseptic and staining agent.
• Methemoglobinemia: restores normal hemoglobin by reducing methemoglobin to functional hemoglobin.
• Cyanide poisoning: binds cyanide to form a less toxic complex that can be eliminated.
• Urinary tract infections: provides topical antiseptic activity in the urinary tract.
• Diagnostic staining: used to highlight tissues or fluids for laboratory analysis.

• Methylthioninium chloride acts as an electron carrier that donates electrons to methemoglobin, converting it back to hemoglobin, and simultaneously inhibits nitric oxide synthase, reducing nitric oxide production. In cyanide poisoning, it forms a cyanomethemoglobin complex that is more readily excreted, thereby detoxifying cyanide.

Methylthioninium chloride may cause a range of adverse reactions, from mild to severe.

Common Side Effects

• Nausea: mild gastrointestinal upset occurring shortly after infusion.
• Headache: transient headache reported in some patients.
• Urine discoloration: blue‑green coloration of urine without clinical significance.
• Mild hypertension: temporary increase in blood pressure during administration.

Serious or Rare Side Effects

• Hemolysis in G6PD deficiency: can trigger severe red blood cell destruction.
• Serotonin syndrome: risk when combined with serotonergic drugs, leading to agitation and hyperthermia.
• Anaphylaxis: rare allergic reaction requiring immediate medical intervention.
• Severe hypertension or hypertensive crisis: abrupt rise in blood pressure that may be life‑threatening.

Prior to administration, clinicians should assess patient-specific risk factors and monitor for adverse events.

• G6PD deficiency: avoid use due to risk of hemolysis.
• Pregnancy: safety unknown; use only if potential benefit justifies the risk.
• Serotonergic agents: monitor closely for signs of serotonin syndrome.
• Renal or hepatic impairment: adjust monitoring and consider dose modification.
• Store at ambient temperature: keep in original container, protect from light and moisture.

Methylthioninium chloride can interact with several drug classes, requiring caution.

Major Interactions (Avoid)

• Selective serotonin reuptake inhibitors (SSRIs): increased risk of serotonin syndrome.
• Monoamine oxidase inhibitors (MAOIs): may precipitate hypertensive crisis.
• Phenothiazine antipsychotics: can diminish the drug's efficacy.

Moderate Interactions (Monitor Closely)

• Antihypertensive agents: potential additive blood pressure lowering effect.
• General anesthetics: may enhance hypotensive response during surgery.
• Chemotherapeutic agents: possible interference with drug metabolism.
• Diuretics: monitor electrolyte balance and blood pressure.