Hetacillin is a beta-lactam antibiotic that is part of the aminopenicillin family.

It is a prodrug and has no antibacterial activity itself,[1] but quickly splits off acetone in the human body to form ampicillin,[2] which is active against a variety of bacteria.

[4] It is sold under the trade name Hetacin for intramammary injection in veterinary use.

[5] Hetacillin was withdrawn from the market for human use when the discovery was made that it had no advantages over ampicillin.

In aqueous solutions it is unstable, with a half life of 15 to 30 minutes at 37 °C (99 °F) and pH 7, quickly releasing acetone again.