All of the following statements about penicillin G are true EXCEPT :
Penicillin act by inhibiting bacterial cell wall synthesis via the inhibition of transpeptidation reaction.
Penicillin G is the drug of choice for:

- Gram +ve bacteria (like Streptococcus, Pneumococcus, non-beta-lactamase producing Staphylococcus, Clostridium and other gram-positive rods)
- Gram-negative bacteria (like Meningococci, Enterococci and non-β-lactamase producing gram-negative anaerobic bacteria)
- Actinomycetes and Treponema pallidum (syphilis)

Penicillin is rapidly excreted by the kidney. 90% excretion is by tubular secretion whereas 10% is by glomerular filtration. Probenecid competes with tubular secretion and prolongs the duration of action.
Penicillin G is less effective by oral route due to destruction by hydrochloric acid in the stomach. Penicillin V is acid stable and thus can be given orally. Mostly penicillin G is administered parenterally (i.m. or i.v.) but it can be administered orally for mild infections. Katzung Pg. 742, in preparations available, also shows the oral and parenteral preparations.
Thus "penicillin is never administered orally" is not a true statement because it can be used orally but commonly used parenterally.
It is actively secreted in tubules
It is never administered orally
It is effective, against gram positive as well as some gram negative bacteria
It acts by inhibiting cell wall synthesis