Hetacillin is a b-lactam antibiotic that is part of the aminopenicillin family. It is a prodrug and it has no antibacterial activity but quickly release acetone in the human body to form ampicillin.

Therapeutic use

Hetacillin is used in the treatment of bacterial infections caused by susceptible, usually gram-positive, organisms.  It has been withdrawn from the market since it has been discovered that it has no therapeutic advantage compared to ampicillin.


Dosage and Administration

Hetacillin can be administered orally.[1] The potassium salt, hetacillin potassium, is administered by injection, either intravenously or intramuscularly





Protein binding  
Cmax (mg/ml)  
tmax (hrs)  
Distribution volume Vd  








Mechanism of Action

Hetacillin is hydrolysed to ampicillin that binds to the penicillin binding proteins found in susceptible bacteria.

Other pharmacological effects


Medicinal Chemistry

CAS number: 3511-16-8  EINECS: 222-512-5

Molecular Formula:  C19H23N3O4S

Average mass: 389.469 Da

Monoisotopic mass:  389.140930 Da

Systematic name: (2S,5R,6R)-6-[(4R)-2,2-Dimethyl-5-oxo-4-phenyl-1-imidazolidinyl]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid

SMILES: (2S,5R,6R)-6-[(4R)-2,2-Dimethyl-5-oxo-4-phenyl-1-imidazolidinyl]-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid

Std. InChI: 1S/C19H23N3O4S/c1-18(2)13(17(25)26)21-15(24)12(16(21)27-18)22-14(23)11(20-19(22,3)4)10-8-6-5-7-9-10/h5-9,11-13,16,20H,1-4H3,(H,25,26)/t11-,12-,13+,16-/m1/s1

Density: 1.40.1 g/cm3 ACD/pKa (most basic): 5.090.60 (NH+)
Boiling Point: 648.455.0 C at 760 mmHg ACD/pKa (most acidic): 2.450.50 (OH)
Vapour Pressure: 0.02.0 mmHg at 25C ACD/LogP: 2.40
Enthalpy of Vaporization: 100.53.0 kJ/mol ACD/LogD (pH 5.5): -1.30
Flash Point: 345.931.5 C ACD/BCF (pH 5.5): 1.00
Index of Refraction: 1.673 ACD/KOC (pH 5.5): 1.00
Molar Refractivity: 102.10.4 cm3 ACD/LogD (pH 7.4): -2.20
#H bond acceptors: 7 ACD/BCF (pH 7.4): 1.00
#H bond donors: 2 ACD/KOC (pH 7.4): 1.00
#Freely Rotating Bonds: 3 Polar Surface Area: 115 2
# of Rule of 5 Violations: 0 Polarizability: 40.50.5 10-24cm3
Molar Volume: 272.35.0 cm3 Surface Tension: 69.55.0 dyne/cm

Major Impurities:

Appearance: Rectangular plates from water + methyl isobutyl ketone, dec. 182.8-183.9C; also reported as mp 189.2-191.0C.

Melting point: 190C

Optical rotation: +366 (pyridine).

Solubility: Practically insoluble in most organic solvents and water; soluble in diluted aqueous NaOH solution (pH 7-8), DMF, DMSO, pyridine, methanol (with decomposition).

logP: 2.35




Synthesis: Hetacillin is prepared from ampicillin and acetone. In aqueous solutions it ihas a half life of 15 to 30 minutes at 37 C and pH=7, quickly releasing acetone [2].


1. Sutherland, R., Robinson, O. P. "Laboratory and pharmacological studies in man with hetacillin and ampicillin". British Medical Journal 2, 804808, (1967). 

2. Faine, S., Harper, M. "Independent antibiotic actions of hetacillin and ampicillin revealed by fast methods". Antimicrobial agents and chemotherapy 3, 1518,  (1973).



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