How to check admin right without include pluggable.php

Hi Guys,
What is the best way to check if the user has admin right?

We googling that the best way to do this is to check the current_user_can(‘manage_options’) but to do this I see that we need to include “pluggable.php”.

I also see that if you installed in a multisite this throws an error in authentication so we inserted the code like this return (is_multisite() || current_user_can(‘manage_options’));

BUT…
Including the file “pluggable.php” we will also define the wp_mail function so other plugins (like wpMandrill) will notify an error.

Below our current function

function isAdminUser() {
    if (!function_exists('wp_get_current_user')) {
        require_once(ABSPATH . 'wp-includes/pluggable.php');
    }
    return (is_multisite() || current_user_can('manage_options'));
}

There is a better way (compatible with multisite and without defining wp_mail) or we have to change our function like this ??

function isAdminUser() {
    return TRUE;
}

Thanks, Alex.