Does treating a patient with Mast Cell Activation Syndrome (MCAS) with systemic antihistamines (e.g. loratadine) and H2 blockers (e.g. ranitidine) help manage symptoms?

From the Guidelines

Treating a patient with Mast Cell Activation Syndrome (MCAS) with systemic antihistamines like loratadine and H2 blockers like ranitidine can effectively help manage symptoms, as supported by the most recent and highest quality study 1. The standard approach typically involves a combination of H1 antihistamines (such as loratadine 10mg daily, cetirizine 10mg daily, or fexofenadine 180mg daily) along with H2 blockers (such as ranitidine 150mg twice daily or famotidine 20mg twice daily). These medications work by blocking different histamine receptors that are involved in the allergic and inflammatory responses triggered when mast cells inappropriately release mediators. H1 antihistamines help control symptoms like itching, hives, and nasal congestion, while H2 blockers address gastrointestinal symptoms such as abdominal pain, heartburn, and diarrhea. For optimal symptom control, these medications should be taken regularly rather than as needed. Some patients may benefit from adding mast cell stabilizers like cromolyn sodium or ketotifen to their regimen, as suggested by 1 and 1. The effectiveness varies between individuals, so medication types and dosages often need adjustment to find the optimal combination. Patients should also identify and avoid personal triggers that may provoke mast cell activation, such as certain foods, medications, temperature extremes, or stress, as recommended by 1. It is essential to note that the treatment of MCAS is highly individualized and targeted to bothersome symptoms and the underlying pathology, as stated in 1. Other coexisting medical conditions need to be treated by an appropriate specialist, and patients at risk for systemic anaphylaxis should carry an epinephrine autoinjector, as advised by 1. Overall, the use of systemic antihistamines and H2 blockers, along with other medications and lifestyle modifications, can help improve the quality of life for patients with MCAS, as supported by the evidence from 1, 1, and 1.

From the Research

Treatment of Mast Cell Activation Syndrome (MCAS)

• Systemic antihistamines (e.g. loratadine) and H2 blockers (e.g. ranitidine) are commonly used to manage symptoms of MCAS 2, 3, 4.
• These medications can help block the effects of mast cell mediators, such as histamine, and reduce symptoms like itching, flushing, and gastrointestinal issues 2, 3.
• A study published in 2015 found that treatment with the H1-antihistamine rupatadine resulted in significant improvements in quality of life, symptom control, and reduction in itching and whealing in patients with cutaneous and systemic mastocytosis 2.
• Another study published in 2019 noted that symptoms of MCAS can be managed by blockade of mediator receptors, including H1 and H2 antihistamines, and that a combination of these approaches may be effective 3.
• Gastrointestinal symptoms, which are common in MCAS, can be refractory to symptom-targeted prescription medications, but may respond to therapies that modulate mast cell activation and the effects of mediators, including over-the-counter medications like antihistamines and H2 blockers 5.

Management of MCAS Symptoms

• Treatment of MCAS often involves a multi-faceted approach, including avoidance of triggers, use of medications to modulate mast cell activation, and management of symptoms 3, 4, 6.
• Antihistamines, including H1 and H2 blockers, are a key component of this approach, and can help reduce symptoms and improve quality of life for patients with MCAS 2, 3, 4.
• It is essential for healthcare providers to be aware of MCAS and its treatment options, as delayed diagnosis and misdiagnosis are common 6.