They are also, therefore, referred to as being penicillinase-resistant. Broad-spectrum antibiotics
This group of antibiotics is called "broad-spectrum" because they are active against a wide range of Gram-negative bacteria such as Escherichia coli and Salmonella typhi, for which penicillin is not suitable. However, resistance in these organisms is now common. Ampicillin
AmoxicillinThere are many ampicillin precursors in existence. These are inactive compounds that are broken down in the gut to release ampicillin. None of these pro-drugs of ampicillin are in current use: 

Pivampicillin (pivaloyloxymethyl ester of ampicillin)
Bacampicillin
Metampicillin (formaldehyde ester of ampicillin)
Talampicillin
Hetacillin (ampicillin conjugated to acetone)Epicillin is an aminopenicillin that has never seen widespread clinical use. Antipseudomonal antibiotics
The Gram-negative species, Pseudomonas aeruginosa, is naturally resistant to many antibiotic classes. There were many efforts in the 1960s and 1970s to develop antibiotics that are active against Pseudomonas species. There are two chemical classes within the group: carboxypenicillins and ureidopenicillins. All are given by injection: none can be given by mouth. Carboxypenicillins
Carbenicillin
Ticarcillin
Temocillin

Ureidopenicillins
Mezlocillin
Piperacillin
Azlocillin

β-lactamase inhibitors
Clavulanic acid
Sulbactam
Tazobactam

Medical usage
The term "penicillin", when used by itself, may refer to either of two chemical compounds, penicillin G or penicillin V.

Penicillin G
Penicillin G is destroyed by stomach acid, so it cannot be taken by mouth, but doses as high as 2.4 g can be given (much higher than penicillin V). It is given by intravenous or intramuscular injection. It can be formulated as an insoluble salt, and there are two such formulations in current use: procaine penicillin and benzathine benzylpenicillin, which are used only in the treatment of syphilis.
He confirmed this observation with a new experiment on 28 September 1928. He published his experiment in 1929, and called the antibacterial substance (the fungal extract) penicillin.C. J. La Touche identified the fungus as Penicillium rubrum (later reclassified by Charles Thom as P. notatum and P. chrysogenum, but later corrected as P. rubens). Fleming expressed initial optimism that penicillin would be a useful antiseptic, because of its high potency and minimal toxicity in comparison to other antiseptics of the day, and noted its laboratory value in the isolation of Bacillus influenzae (now called Haemophilus influenzae).Fleming did not convince anyone that his discovery was important. This was largely because penicillin was so difficult to isolate that its development as a drug seemed impossible. It is speculated that had Fleming been more successful at making other scientists interested in his work, penicillin would possibly have been developed years earlier.The importance of his work has been recognized by the placement of an International Historic Chemical Landmark at the Alexander Fleming Laboratory Museum in London on 19 November 1999.