Treating Systemic Mastocytosis: From Antihistamines to Targeted Therapy

In this episode, "Treating Systemic Mastocytosis: From Antihistamines to Targeted Therapy," the expert pharmacists explored the following questions:

How do treatment goals differ in indolent vs. advanced systemic mastocytosis?

Before covering chronic treatment of systemic mastocytosis, how are patients managed acutely with anaphylactic reactions, and what is the role of the pharmacist in the acute setting?

What is the role of H1 and H2 antihistamines, cromolyn sodium, and leukotriene receptor antagonists in the symptomatic management of indolent systemic mastocytosis?

What are the strengths and limitations of these therapies?

When should patients escalate to tyrosine kinase-targeted therapy in clinical practice?

What is the role of pharmacists here?

The panelists examined how treatment goals differ between indolent and advanced systemic mastocytosis (SM) — the former focused on symptom control and quality of life, the latter also targeting disease modification to reduce mast cell burden and organ damage — and outlined the pharmacist's role in acute anaphylaxis management, including patient education on epinephrine use and antihistamine dosing. Lewis-Gonzalez and Smith detailed the stepwise symptomatic approach for indolent SM, beginning with dual H1/H2 antihistamine blockade, followed by cromolyn sodium for gastrointestinal-predominant symptoms and leukotriene receptor antagonists, noting the boxed warning for neuropsychiatric effects associated with the latter, before escalating to the tyrosine kinase inhibitor avapritinib for refractory disease. They emphasized the pharmacist's central role in monitoring drug interactions, particularly with CYP3A4 substrates, supporting medication adherence amid significant polypharmacy, and serving as a patient advocate throughout care.

Throughout the conversation, the experts provided a comprehensive reflection on the field and the factors that may shape how clinicians approach care moving forward.

The next episode in this series, "From Rationale to Results: Tyrosine Kinase Inhibitors in Systemic Mastocytosis," features the panelists advancing their conversation on systemic mastocytosis and focusing on the clinical rationale for targeting the KIT pathway, PIONEER trial data supporting avapritinib in indolent disease, and strategies to improve survival in advanced SM complicated by secondary malignancies.