Les vasodilatateurs sont des médicaments qui dilatent et augmentent le calibre des vaisseaux sanguins. Ils permettent de réduire la pression artérielle. Leur principale indication est donc l’hypertension artérielle. Ils sont aussi employés chez l’homme pour traiter des dysfonctionnements urologiques ou érectiles. Explications.
Définition : qu’est-ce qu’un médicament vasodilatateur ?
Les vasodilatateurs regroupent un ensemble hétérogène de médicaments qui ont pour principal effet de dilater les vaisseaux sanguins et donc d’augmenter le calibre de ces derniers. “Leur principale indication est le traitement de l’hypertension artérielle (hta) qui est la maladie chronique la plus répandue en France qui concerne 1 adulte sur 3.
Les vasodilatateurs les plus connus et les plus souvent prescrits sont les inhibiteurs calciques”, d’après Samuel Ouaknine, docteur en pharmacie et directeur de laboratoire HT26.
Pourquoi prendre des vasodilatateurs ? Dans quelles indications ?
Le principal effet des médicaments vasodilatateurs est de diminuer la pression artérielle. Ainsi leur principale indication est le traitement de l’hypertension artérielle systémique .
Ils sont aussi prescrits pour :
- améliorer certains troubles cardiaques et vasculaires comme l’insuffisance cardiaque et coronaire (angine de poitrine ou angor) ou encore la maladie de Raynaud ;
- contre l’impuissance sexuelle ou les troubles urologiques chez l’homme.
Les vasodilatateurs peuvent en effet avoir une action spécifique sur certains vaisseaux tels que :
- les coronaires (insuffisance cardiaque, angor, infarctus du myocarde) ;
- les artères cérébrales (AVC, AIT, vertiges, migraines…) ;
- les artères des membres inférieurs (artériopathie oblitérante des membres inférieurs) ;
- les vaisseaux des capillaires(syndrome de Raynaud, alopécie androgénique) ;
- les vaisseaux oculaires (hypertension oculaire) ;
- les vaisseaux des voies génitales et urinaires (hypertrophie bénigne de la prostate, impuissance masculine).
Quels sont les différents types de médicaments vasodilatateurs ?
Il existe plusieurs classifications de vasodilatateurs. La plus utilisée est celle qui les classe en fonction de leur site d’action. On distingue ainsi les vasodilatateurs à prédominance veineuse des vasodilatateurs qui agissent sur les artères de ceux qui agissent sur ces deux types de vaisseaux (vasodilatateurs mixtes).
Les vasodilatateurs à prédominance veineuse (dérivés nitrés, sydonimines), sources de monoxyde d’azote
- Les dérivés nitrés (trinitrine, dinitrate d’isosorbide, nitroglycérine, mononitrate d’isosorbide, tétranitrate de pentaérythrityle.…) qui sont des donneurs de monoxyde d’azote (NO).
- ” Ces subbstances conduisent à une relaxation des fibres musculaires vasculaires lisses”, selon Samuel Ouaknine. Par voie systémique, la trinitrine est utilisée dans la prise en charge de l’angor, l’insuffisance ventriculaire, l’ischémie myocardique, l’œdème aigu du poumon. Par voie locale, la trinitrine est utilisée dans la prise en charge des fissures anales.
- Lessydnonimines (molsidomine) qui sont aussi des donneurs de NO. Ils sont administrés pour traiter l’angine de poitrine (angor).
Les vasodilatateurs à prédominance artérielle (inhibiteurs calciques, vasodilatateurs directs, alpha-bloquants, antihypertenseurs centraux)
- Les inhibiteurs calciques (nifédipine, nicardipine, amlodipine, félodipine, isradipine, diltiazem, vérapamil…) : “ils agissent au niveau des canaux calciques en freinant l’entrée du calcium dans les cellules musculaires vasculaires lisses et les cardiomyocytes.
- Ils sont indiqués dans le traitement de troubles cardiaques divers tels que l’angine de poitrine, les arythmies ou l’hypertension artérielle”, développe le scientifique Samuel Ouaknine.
- Les vasodilatateurs directs (hydralazine, dihydralazine, monoxidil…) qui ont pour effet exclusif de relâcher le muscle lisse de la paroi artérielle. Ils sont efficaces contre l’hypertension artérielle. Appliqué localement le monoxidil permet de traiter l’alopécie.
- Les alphabloquants ou alpha-adrénolytiques (prazosine, urapidil…) sont des médicaments qui s’opposent aux effets vasoconstricteurs de l’adrénaline et de la noradrénaline. Ils ont d’abord été employés en cardiologie comme antihypertenseurs. Aujourd’hui, ils sont aussi utilisés en urologie pour diminuer les symptômes de l’adénome prostatique appelé hypertrophie bénigne de la prostate.
- Les antihypertenseurs centraux (clonidine, méthyldopa, moxonidine, rilménidine…) qui sont des traitements de troisième ou quatrième intention de l’hypertension artérielle essentielle et qui s’utilisent en association avec d’autres antihypertenseurs. Ils sont souvent prescrits en cas d’hypertension gravidique (au cours de la grossesse).
- Ces médicaments sont des agonistes présynaptiques de type alpha-2 agissant sur les centres bulbaires cardiomodérateurs et ils ont tous un effet sympatholytique central plus ou moins marqué.
Les vasodilatateurs mixtes (inhibiteurs de l’enzyme de conversion, antagonistes des récepteurs de l’angiotensine 2)
- Les inhibiteurs de l’enzyme de conversion ou IEC (captopril, énalapril, lisinopril, ramipril…) sont utilisés notamment dans le traitement de l’hypertension artérielle, de la maladie coronarienne et de l’insuffisance cardiaque chronique.
- Ces médicaments sont des inhibiteurs de l’enzyme de conversion de l’angiotensine qui est un élément d’une cascade régulant la pression artérielle.
- Les antagonistes des récepteurs de l’angiotensine 2 ou ARA 2 (candesartan, éprosartan, irbesartan, losartan, telmisartan et valsartan…) qui bloquent l’action d’une enzyme appelée angiotensine II qui cause le resserrement des vaisseaux sanguins.
- Ils sont indiqués, seuls ou en association avec un diurétique thiazidique, dans le traitement de l’hypertension artérielle de l’adulte.
Mode d’action : comment agissent les vasodilatateurs ?
Un vasodilatateur peut agir :
- d’un effet direct sur les cellules musculaires lisses (par stimulation de leurs récepteurs vasodilatateurs, par inhibition de l’influx calcique, par activation de canaux potassiques ou encore par leur action sur le métabolisme de l’AMP ou du GMP cycliques) ;
- d’un effet indirect via la libération de facteurs dits “endothéliaux” (NO, prostacycline, facteurs hyperpolarisants) ;
- de l’inhibition de la formation de vasoconstricteurs endogènes (inhibiteurs de l’enzyme de conversion de l’angiotensine) ou de leurs effets.
Dans tous les cas de figure, l’effet est le même : le diamètre des vaisseaux sanguins est augmenté. “Cette vasodilatation a donc pour effet de diminuer la pression artérielle. Elle augmente également l’afflux sanguin dans les vaisseaux et entraîne l’accélération du rythme cardiaque”, d’après l’expert.
Vasodilatateurs : existe-t-il des contre-indications ?
La principale contre-indication à la prise de ces médicaments est une hypotension artérielle importante. En outre, des précautions sont à prendre en cas de prise d’anticoagulants (puisque les vasodilatateurs augmentent alors le risque hémorragique). Enfin, une surveillance particulière, notamment de la tension artérielle et de la fréquence cardiaque, doit être de mise pendant toute la durée du traitement par vasodilatateur .
Quels sont les effets secondaires des vasodilatateurs ?
Comme la plupart des médicaments, les vasodilatateurs sont susceptibles d’entraîner des effets secondaires.
Ces derniers dépendent du type de vasodilatateurs administrés, de la posologie et du profil du patient. Les principaux effets indésirables répertoriés sont :
- une hypotension (diminution de la tension artérielle) ;
- des vertiges ;
- des malaises et évanouissements ;
- une hypotension orthostatique (baisse de la tension artérielle en se levant rapidement) ;
- des maux de tête (céphalées) ;
- des bouffées de chaleur et rougeurs du visage (flushs) ;
- des palpitations cardiaques ;
- une arythmie (tachycardie ou bradycardie) ;
- une congestion nasale (nez bouché) ;
- des troubles digestifs (maux de ventre, nausées…).
Certains vasodilatateurs peuvent provoquer des effets indésirables plus graves comme des ulcérations buccales, des œsophagites, des troubles cutanés ou encore des atteintes rénales (lithiase rénale) ou hépatiques. La consommation d’alcool, qui est aussi un puissant vasodilatateur, peut intensifier ces effets.
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