Cromolyn Sodium

Cromolyn sodium is the classic pharmaceutical mast cell stabilizer. It prevents Degranulation by blocking chloride channels on the mast cell membrane, which prevents the calcium influx that triggers granule fusion and mediator release.

How It Works

The exact molecular mechanism is not fully characterized, but the best-supported model: cromolyn blocks calcium-activated chloride channels on the mast cell surface. Without chloride flux, the intracellular calcium signaling cascade that drives Degranulation is interrupted. The cell receives the activation signal but can’t complete the release sequence.

Pharmacology

Oral (Gastrocrom/generic): Very poorly absorbed from the GI tract — bioavailability is approximately 1%. This is actually a feature, not a bug, for GI-predominant MCAS: the drug stays in the gut lumen and stabilizes mast cells in the intestinal wall locally. It doesn’t reach systemic circulation in meaningful amounts.

Inhaled (Intal): Delivered directly to airway mast cells. Used for mast cell-driven respiratory symptoms.

Ophthalmic: Stabilizes conjunctival mast cells. Used for allergic eye symptoms.

Nasal spray: For nasal mast cell symptoms.

Clinical Use in MCAS

For GI-predominant MCAS, oral cromolyn is often a cornerstone therapy. Typical dosing is 4 times daily (before meals and at bedtime) because its duration of action is limited.

Key points:

• Must be taken consistently — it’s preventive, not rescue. Starting and stopping sporadically won’t show benefit.
• Takes days to weeks of consistent use before full effect
• Extremely safe due to minimal systemic absorption
• Start low and titrate up — some patients are sensitive to the excipients or have initial GI adjustment
• Not effective for systemic (non-GI) mast cell symptoms at standard oral doses, because it doesn’t reach systemic mast cells

Limitations

Oral cromolyn addresses gut mast cells only. A person with significant skin, respiratory, neurological, or cardiovascular mast cell symptoms needs additional interventions targeting those tissue populations. See Medications Overview.