<?php
$re = '/\b\d+(?:\.\d+)?(?=mcg\b)/';
$str = 'some text 0.25mcg some more text some text 25mcg some more text';
preg_match_all($re, $str, $matches);
print_r($matches[0]);
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
Array
(
[0] => 0.25
[1] => 25
)