Synonyms: 4-Thia-1-azabicyclo[3.2.0]heptane-2-carboxylicacid, 6-(2-amino-2-phenylacetamido)-3,3-dimethyl-7-oxo-, hydroxymethyl esterpivalate (ester), D-(-)- (8CI); 4-Thia-1-azabicyclo[3.2.0]heptane-2-carboxylicacid, 6-[(aminophenylacetyl)amino]-3,3-dimethyl-7-oxo-,(2,2-dimethyl-1-oxopropoxy)methyl ester, [2S-[2a,5a,6b(S*)]]-;4-Thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid,6-[[(2R)-aminophenylacetyl]amino]-3,3-dimethyl-7-oxo-,(2,2-dimethyl-1-oxopropoxy)methyl ester, (2S,5R,6R)- (9CI); Ampicillin pivaloyloxymethylester; Hydroxymethyl6-(2-amino-2-phenylacetamido)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylatepivalate (ester); MK 191; Pivaloylampicillin; Pivaloyloxymethyl D-a-aminobenzylpenicillinate;Pivaloyloxymethyl ampicillinate; Pivampicillin