Histamine

Histamine

What process

• Mast cells

• Basophils

Histamine is stored and found in the highest amounts in —

• Energy- and Ca2+-dependent degranulation/immunologic/allergic reaction

• Energy- and Ca2+-dependent degranulation/chemical/mechanical reaction

Two processes by which HISTAMINE IS RELEASED

Energy- and Ca2+-dependent degranulation reaction

Energy- and Ca

2+ - independent release (displacement)

Recall

Recall histamine receptors

• R-alpha methylhistamine

• Betazole (Histalog)

• Impromidine

Histamine agonists identify

• H3 specific

• tenfold greater activity at H2-receptors than at H1-receptors

• investigational agent; its ratio of H2:H1 activity is about 10,000

• Pyrilamine

• Tripelennamine

Ethylaminediamines

• Clemastine

• Dimenhydrinate

• Doxylamine

• Diphenhydramine

• Carbonoxamine

Ethanolamines

• Hydroxyzine

• Meclizine

• Cyclizinw

Piperazines

• Brompheniramine

• Chlorpheniramine

Alkylamines

Promethazine

Phenothiazine

Cyproheptadine

Methylpiperidine

Terfenadine (Seldane) → Fexofenadine

Piperidine

• 30 mins

• 3-6 hours

• 3-24 hours

• Sedation

• GI upset, nandv, constipation

• Anticholinergic effects

Adverse effects of histamine blockers

• Cimetidine (Tagamet) - prototype

• Ranitidine (Zantec) - most prescribed

• Famotidine (Pepsid AC) - most potent

• Nizatidine (Axid) - most bioavailable

Enumerate H2 antagonists

gastric parietal cell

competitive antagonists at the H2-receptor, which predominates in the gastric parietal cell.

cimetidine

CYP1A2, CYP2C9, CYP2D6, and CYP3A4

Cimetidine is a potent enzyme inhibitor. It ointerferes with several important hepatic cytochrome

P450 drug metabolism pathways, including those catalyzed by

• Cromolyn (Ital)

• Nedocromil sodium (Tilade)

Enumerate histamine release inhibitors/mast cell stabilizers: