<?php

$string =
'<ul>
<li>
<a href="/nalcrom">Nalcrom</a>
        (Sodium Cromoglicate)
</li>
<li>
<a href="/alimemazine">Alimemazine</a>
</li>
<li>
<a href="/xolair">Xolair</a>
        (Omalizumab)
</li>
</ul>';

preg_match_all('%">(.*?)</a>\s+(\(.*?\))?%i', $string, $match, PREG_PATTERN_ORDER);
for ($i = 0; $i < count($match[0]); $i++) {
    echo  $match[1][$i] . " ". $match[2][$i] ."\n";
}