DISCUSSION
This new finding of methylene blue as an effective treatment for chemotherapy-induced oral mucositis in a pediatric patient outlines a potential alternative analgesic therapy for this common adverse event of cancer therapy, not explored before on this age population.
Methylene blue is a monoamine oxidase, nitric oxide synthase, and guanylate cyclase inhibitor [9]. When methylene blue and dye with biologic substrates are combined, they react with nucleic acids and damage proteins and lipid membranes of organisms [10]. It is not well understood how these properties translate to its analgesic properties, but there are several clinical and in vitro findings of methylene blue’s action on both peripheral and central neural pathways [9]. Methylene blue has the unique property of temporarily ablating nerve endings, which has been useful in the treatment of intractable pruritus ani [11]. In patients with open lumbar diskectomy, its anti-inflammatory mechanism has been shown to reduce lower back pain after surgery [12]. Deng et al. found that an injection of methylene blue within the disc for discogenic back pain led to decreased pain scores at 3 and 6 months (p < 0.05) [13]. Our report now adds to the literature on the therapeutic usefulness of topical methylene blue.
Methylene blue comes in several different formulations, including intravenous and tablet, and was most recently used in conjunction with photodynamic therapy. Its diverse methods of administration make it a prime anti-nociceptive agent for many types of patients and pain complaints. Unlike other therapies for oral mucositis–related pain that include the use of local anesthetics, this oral rinse formulation uses only methylene blue and normal saline. Without the sensation-dulling effect of local anesthetics, a patient’s sensation of taste can be preserved and therefore encouraging oral intake. For the pediatric population, this is paramount, as oral mucositis can lead to rapid weight loss and poor nutritional status.
When used systemically (e.g. oral or parenteral) methylene blue is not risk-free. Patients who are taking monoamine oxidase inhibitors, selective serotonin reuptake inhibitors, or serotonin and norepinephrine reuptake inhibitors are advised to use methylene blue with caution, given the increased risk of life-threatening serotonin syndrome [14] [15]. In addition, when given as an oral capsule may cause nausea, upset stomach, diarrhea, vomiting, or bladder irritation [16]. Despite its potential risk when used systemically, methylene blue appears to be safe and well tolerated in its oral rinse or topical formulation.