Vomiting often is the protective act directed to release of a stomach from the irritating and toxic substances which got to it. In such cases it is physiological process for which acceleration the use of special drugs for vomiting - vomitives can be necessary.
However in some cases vomiting is the accompanying process worsening a condition of an organism. Quite often vomiting develops as a result of the general toxicosis caused by receipt in an organism (not only through a stomach, but also a parenteral way) toxic products, including medicines (for example, cytostatic antineoplastic drugs, etc.). Vomiting can be caused by various diseases, surgeries, contagious excitation, etc. Radiation therapy usually is complicated by vomiting. Quite often vomiting is caused by overexcitation of the labyrinth device (for example, at sea and airsickness). In these and other cases the use of the means calming vomiting and facilitating it a state is often necessary.
Vomiting is controlled by special structures of a medulla: emetic center and so-called hemoretseptorny starting (trigger) zone. Vomiting develops at excitement of the emetic center that can come by immediate effect on it toxic or medicinal substances, its reflex excitement from centripetal ways and also at receipt of impulses in it from chemoceptors of a starting zone. This zone is especially sensitive to effect of chemicals, and emetic as well as antiemetic, effect of many medicinal substances is implemented by primary excitement or braking of this zone. From medicinal substances morphine and other narcotic analgetik, Apomorphinum, antineoplastic drugs, etc. have direct central effect (resorptive way) on a starting zone.
Affect with a reflex way the emetic center of substance, the irritating receptors of a mucous membrane of a stomach, such as copper sulfate, zinc sulfate, etc. Cardiac glycosides can cause vomiting (at overdose), affecting directly a starting zone of a medulla and also a reflex way.
The main use as medicinal vomitive has Apomorphinum. The act of vomiting is preceded by nausea and a number of the effects accompanying it, including strengthening of a sialosis and bronchial secretion. These effects are observed also at use of vomitives in small doses, and some of them are used in this regard as expectorants (see).
The substances influencing different links of nervous control can have antiemetic effect. If vomiting is caused by local irritation of a stomach, then after removal of the irritating substances enveloping also astringents in case of need can be applied. Reduction of excitability of receptors of a stomach and suppression of nausea and vomiting can be reached by prescribing of local anesthetics (see Anaesthesin, Novocaine).
For removal of excitement of the emetic center sedative and sleeping medicines had earlier main use. Significant progress in receiving more specific, highly effective antiemetics of the central action is connected with development of works on studying cholinolytic, antihistaminic and especially antipsychotic drugs and antagonists of dopamine.
Antiemetic effect of various neurotropic drugs is substantially connected with their influence on the neuromediator systems of the emetic center and a hemoretseptorny starting zone. The Hemoretseptorny zone contains dopamine receptors, in different kernels of the emetic center are available cholinergic (muskarinovy), histamine (N) and. serotoninovy 5-NTz-receptors. Cholinergic and histamine receptors (N) contain also in a lateral vestibular nucleus. Cholinolytic drugs (see the tablets "Aeronum") found the greatest application in prevention and treatment sea and airsickness, Menyer's disease.
As vomiting medicine antihistaminic drugs are widely used: Dimedrol, isopromethazine, etc. In the mechanism of effect of these drugs a part is played also by their sedation and a cholinolytic component.
Very effective antiemetics are the antipsychotic drugs of group of a fenotiazin and phenyl propyl ketone operating on dofaminergichesky systems. Their action is connected mainly with the braking influence on a hemoretseptorny starting zone. Have high antiemetic activity among derivatives of a fenotiazin etaperazin, Metherazinum, Triphtazinum, ftorfenazin, etc., among phenyl propyl ketones - a haloperidol, etc.
To the derivatives of a fenotiazin which are possessing strong and more selective antiemetic effect, than other neuroleptics, and not causing therefore the side effects connected with the general antipsychotic activity drug thiethylperazine (Torecanum) belongs.
Recently the antiemetic activity of antagonists serotoninovy 5-HT - receptors is established. One of the new antiemetic drugs used for prevention of the vomiting caused by chemotherapeutic means is tropisetron (see). Believe that at use of antineoplastic drugs there is a release of serotonin from enterokhromaffinny cells of a mucous membrane of intestines that causes an emetic reflex.
Due to the complexity of the neurochemical organization of the emetic act the most significant antiemetic effect can be observed at the combined use of the substances influencing different mediator systems (for example, neuroleptics and antihistaminic drugs, etc.).
Antagonists of dopamine receptors are Metoclopramidum, domperidon, dimetpramid, also applied as antiemetics.