Pseudoallergic reactions Medical Assignment Help

In some susceptible patients, substances mimic the allergic reactions described under dose-independent reactions but without the same immunological mechanisms occurring. Unlike allergic reactions they occur on first contact with a drug rather than after previous sensitizing exposure. Susceptibility to such a reaction appears to be determined by genetic and environmental factors. These reactions are produced by compounds that are able to release histamine and other mediators directly from mast cells without involving an antigen-antibody reaction. Examples are:
• Itching, bronchospasm and vasodilatation due to histamine release by morphine
• The flushing, urticaria, angie-oedema, conjunctivitis, rhinitis, bronchial asthma, hypotension and even fatal shock produced by aspirin.
It is probable that reactions to many other drugs are also due to this mechanism. An interesting example is the anaphylactic response produced by aspirin in one patient with urticaria pigmentosa and generalized mastocytosis.
If use of the particular drug to which the pseudoallergic reaction occurs cannot be avoided, its dose should be kept as low as possible, or, in the case of intravenous administration, it should be given by slow infusion rather than rapid injection. Sometimes it is possible to desensitize a patient by starting with a small dose of the drug and gradually increasing it under supervision.

Agents that are believed to be capable

Agents that are believed to be capable

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