Histamin - Modifiers of metabolism
Certain drugs and certain compounds can modify the synthesis and the release of histamine.
Tritoqualine inhibits histidine decarboxylase but, to obtain this inhibition, it is necessary to use high dosage, 2 to 10 tablets of 100 mg per day. It is very little used and only in two or three countries.
Some drugs inhibit the release of histamine and other inflammatory mediators such as serotonin, prostaglandins, leukotrienes, mediators called autacoids, and are called mast-cells stabilisers. Numerous mechanisms have been evoked to explain this stabilisation. Probably an inhibition of Ca2+ penetration into cells could be implicated.,
The first effective product in this field, and the most used, is cromoglicate, also written cromoglycate and called cromolyn. Its discovery is due to serendipity, because during animal investigations, it appeared that it prevented bronchospasm.
Cromoglicate is practically not absorbed by the digestive route and is administered by local routes, bronchial, nasal, ocular and digestive (it acts on digestive mucous membranes without being absorbed). There are various presentations of cromoglicate corresponding to specific therapeutic uses, the most important being prevention of asthma attacks.
Cromoglicate has little adverse effects: sometimes bronchial irritations and eosinophilia.
Nedocromil inhibits synthesis and release of various autacoids. Its properties and its therapeutic uses resemble, cromoglycate
Ketotifen is both a mast-cell stabiliser and a H1-antihistamine with an anti-PAF effect (platelet activating Factor). Contrary to cromoglycate, it is absorbed by the digestive tract and thus has general effects. It is used in prophylactic treatment of asthma and applied locally as eye drops. Its principal secondary effects are drowsiness, an oral dryness, digestive dizziness and increased appetite.
Lodoxamide is a mast-cell stabiliser used in treatment of allergic conjunctivitis in ophthalmic solution.
- Olopatadine, has properties close to those of lodoxamide.
Certain drugs can, in certain circumstances, elicit as adverse effect an excessive histamine release. They are essentially atropine, morphine, dextran, polyvinylpyrrolidone and neuromuscular blocking agents. Other compounds (basic polypeptides, venoms) also do it.