Ketotifen fumarate (HC 20511 fumarate) is a cycloheptathiophene blocker of histamine H1 receptors and release of inflammatory mediators.

Ketotifen (HC 20-511) is a second-generation, orally active noncompetitive histamine 1 (H1) receptor antagonist and mast cell stabilizer. It inhibits 6-phosphogluconate dehydrogenase (PGD) in vitro and displays antiviral activity against SARS-CoV-2 and the Influenza virus. Additionally, Ketotifen is utilized in researching autoimmune encephalomyelitis (EAE) and preventing asthma attacks.

Picumast dihydrochloride is a prophylactically active anti-allergic compound which combines inhibition of mediator release and action. The activity profile of PDH differs clearly from that of known prophylactic anti-allergic drugs such as DSCG and ketotifen.