$re = '/^value:\s?(\S+(?:\s[^-\n]+)?)(?:\s-\s.*?-([^-\n]*)(?:-.*)?)?$/m';
$str = 'value: 1.25MG - OM - PO/TUBE - ashaf
value:2.5 MG - OM - PO/TUBE -test
value: 18 UNITS(S)
value: 850 MG - TDS AFTER FOOD - SC (SUBCUTANE)
value: 75 MG - OM - PO/TUBE';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php