From the Guidelines
Methylene blue is not classified as a carcinogen based on current scientific evidence. This synthetic dye has been used medically for over a century as a treatment for conditions like methemoglobinemia, urinary tract infections, and as a surgical marker, with no established link to cancer development in humans 1. While some laboratory studies have shown that methylene blue can cause DNA damage in test tubes, these effects have not translated to cancer formation in living organisms. The compound has undergone extensive safety testing due to its long history of medical use, and regulatory agencies like the FDA continue to approve it for various clinical applications. However, as with many medications, it should only be used when medically necessary and under appropriate supervision. Methylene blue does have other potential side effects and drug interactions, particularly with serotonergic medications where it can cause serotonin syndrome, but carcinogenicity is not considered a significant concern with this compound.
Key Points
- Methylene blue has been used medically for over a century with no established link to cancer development in humans.
- The compound has undergone extensive safety testing and is approved by regulatory agencies like the FDA for various clinical applications.
- Methylene blue can cause DNA damage in test tubes, but this effect has not translated to cancer formation in living organisms.
- The medication should only be used when medically necessary and under appropriate supervision due to potential side effects and drug interactions.
Recommendations
- Methylene blue is recommended for the treatment of methemoglobinemia 1.
- Patients with G6PD deficiency should be cautious when using methylene blue, as it may induce hemolysis and worsen methemoglobinemia 1.
- Methylene blue should be used with caution in pregnant women and patients with renal failure due to potential risks and side effects 1.
From the Research
Carcinogenicity of Methylene Blue
- The carcinogenic potential of methylene blue was investigated in a 2-year study in F344/N rats and B6C3F1 mice 2.
- In male rats, the incidences of pancreatic islet cell adenoma and adenoma or carcinoma (combined) were increased in all dosed groups, and were significantly increased in 25 mg/kg males 2.
- In male mice, the incidences of carcinoma and of adenoma or carcinoma (combined) of the small intestine occurred with a positive trend, and the incidence of malignant lymphoma exceeded the historical control range in 25 mg/kg males 2.
- Methylene blue trihydrate was mutagenic in Salmonella typhimurium strains TA98 and TA100 with and without rat or hamster liver S9 activation enzymes, and in Escherichia coli strain WP2 uvrA/pKM101 with and without rat liver S9 2.
- In cytogenetic tests with cultured Chinese hamster ovary cells, methylene blue trihydrate induced sister chromatid exchanges and chromosomal aberrations with and without S9 2.
Toxicity and Adverse Effects
- Methylene blue has been reported to cause severe central nervous system toxicity, including serotonin toxicity 3.
- The use of methylene blue has been associated with dose-dependent toxic effects, including hemolysis, methemoglobinemia, nausea, vomiting, chest pain, dyspnea, and hypertension 4.
- Methylene blue has been shown to induce serotoninergic toxicity, which clinically manifests as neuromuscular hyperactivity 4.
Other Studies
- A review of the literature on methylene blue found that its use is controversial due to the lack of preclinical data and the potential for adverse effects 4.
- Methylene blue has been used to treat various conditions, including methemoglobinemia, vasoplegic syndrome, and ifosfamide-induced encephalopathy 5, 6.