Complex sentence: The standard abbreviation µL for a microlitre has the disadvantage that it can be misread as mL (a unit 1000 times larger), and in pharmaceutical use no abbreviation for a microlitre is considered safe; recommended practice is to write "microlitre" in full.
Split into simpler sentences: The standard abbreviation µL for a microlitre has the disadvantage that it can be misread as mL (a unit 1000 times larger). The recommended practice is to write "microlitre" in full.