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ADVERSE REACTIONS TO CONTRASTS OF IODINE
DENOMINATION DEFINITION FREQUENCY YOU CAUSE REACTIONS TO SEE TO CONSULT

OTHER NAMES

  • Reactions to contrasts,
  • Reactions to the iodine,
  • Allergy to contrasts,
  • Reactions to MCR.

DEFINITION

The means of radiological contrasts (MCR) are substances got artificially in the organism to increase the differences of absorption of radiation between organs.

Most of them (MONOMEROS IONICOS) have a common basic structure: The acidic benzoic triyodado (a ring bencénico sustituído with iodine in three positions), presented in salt which catión is the Na (sodium), or the sugar meglumina (N-metilglucamina), or a miscellany of both salt.
In watery solution (when IV are injected), they dissociate in an iodized anion typical of the compound and one of the cationes: the Na (sodium) or the metilglucamina.

To reach a concentration adapted for use intravascular, I/ml needs a content in iodine of at least 200 mg, and to reach this necessary iodine concentration, they must be administered in hypertonic forms (aprox. 5 times) with regard to the vascular space.

In last decade there have got called "MCR isoosmóticos", which are of two types:

  • MONOMEROS not IONICOS (Metrizamida, iohexol, ioversol and iopamadol): They do not dissociate, that is to say, they do not need to turn into an iodized anion, and this characteristic of not be ionizing diminishes them osmolaridad.
  • DIMERO IONICO: IOXAGLATO (Hexabrix ®). It dissociates, but on having taken double iodine quantity, he needs half of molecules to produce the same effect contrast, therefore he behaves like the not iónicos as for osmolaridad.
  • All these contrasts "isoosmolares" present a much minor incidence of adverse reactions, especially of minor type. The frequency with which they provoke these reactions has not been established safely, but also they can provoke reactions anafilactoides.

    FREQUENCY OF ADVERSE REACTIONS

    Of 5 to 8 % of the patients to which there is administered a way of X-ray contrast (MCR) they suffer adverse reaction, which in 0,1 % of the cases is serious and in 1 of 40.000 - 50.000 fatal (certain authors gave a proportion of 1 of every 10.000).

    The clinical declarations can qualify for the type of reaction (anafilactoides, cardiopulmonares and diverse), also for his gravity (minor or major). To consult the table 1 (Contrasts: Clinical declarations). These reactions, excepted the renal insufficiency, usually take place in the 3 to 10 minutes following the injection. Certain illnesses can increase the risk that reactions take place opposite to certain contrast means, see table 2 (Contrasts: Factors of Risk). Although these reactions can take place with any exhibition route, they are especially frequent with the administration intravascular.

    CAUSES OF THE REACTIONS TO MCR

    Although many reactions to contrast means resemble the come up ones by IgE (Allergy), there exist few indicative proofs that the above mentioned reactions have an immune mediation. The most probable explanation (although not demonstrated), in case of the reactions anafilactoides, is that the MCR provokes not immune mediators liberation in the capable patients. The possible causes of other reactions comprise the effects quimiotóxicos direct, not immune activation of the complement, the effects hemodinámicos of the hypertonic solution, the stimulation vagal or others.

    Most of the deaths that take place as a result of the administration of MCR do not go accompanied by the clinical characters not anatomopatológicos of the anafilaxia, and in the autopsies the immediate cause of the death is not discovered usually. Consequently, most of the fatal reactions to MCR is considered of unknown cause.

    THEORIES OF THE REACTIONS TO MCR

    1. Activation of the complement

      The MCR activate the complement, with significant falls in the complement levels in big percentages of subjects that receive them, although these falls are not related consistentemente to the presence of reactions anafilactoides. Predilection for these reactions does not also exist in the illnesses that they study with activation of the complement.

      The MCR activate the complement by means of the only interactions not related to the classic or alternative routes.

      • The agents iónicos can activate the Complement of not sequential form, with simultaneous depression of classic and alternate components, well across the induction of a system enzimático lítico (that might be the system plasminógeno-plasmina), or for direct effect on C3 and C4, producing péptidos C3b-like ó C4b-like.
      • The monómeros not iónicos (type Metrizamida) induce activation of the Complement across the alternate route, by means of the generation of a factor C3b - they do not act on C4 - and by means of the unactivation of the inhibiting system of the alternate route (the factors H and I-C3b-inactivador), allowing alternate activity of the Complement without brake.
    2. Direct histamine liberation for mastocitos and basófilos The MCR liberate mastocitos histamine and basófilos so many living in as in vitro, what can owe to (four theories):
      • Direct effect on mastocitos and basófilos across interaction with a membrane recipient.
      • Generation of secondary anafilotoxinas to activation of the Complement.
      • Liberation due to hiperosmolaridad.
      • Liberation due to interaction IgE-Antigen.
    3. Recruiting of multiple mediators of the inflammation
    4. Reactions Ag-Ac. Very rare cases.
    TO SEE ALSO

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    • Writing: Medical equipment   Update: June, 2009
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