snakelize.js

function snake(string) {
     
    var my = string.replace(/([ ])/g, function($1) {
        //alert($1);
        return "_";
        
      });
    
    alert(my);
    
    return my.replace(/-/g, '');
}

alert(snake('Simeticona 125mg com 10 cápsulas gelatinosas - teuto - genérico'));