$re = '/^val:\s*([^-\n]*?)(?:\s*-[^-]*-\s*(.*))?$/m';
$str = 'val: 1.25MG - OM - PO/TUBE
val:2.5 MG - OM - PO/TUBE
val: 18 UNITS(S)
val: 850 MG - TDS AFTER FOOD - SC (SUBCUTANEOUS)
val: 75 MG - OM - PO/TUBE';
preg_match_all($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