Clinical use of penicillin antibiotics

Penicillin G is the drug of choice in infection caused by Pneumococci, Streptococci, Meningococci, Gonococci and Staphylococci (Non β-lactamase producing Staphylococci).
They are effective against Spirochaetes, Bacillus anthracis and other gram positive rods, Clostridium spp and other anaerobes but inactive against Bacteroides fragillis (gram –ve rod).
They are also active against Listeria spp and Actinomycetes.

Penicillin V is used for the treatment of mild respiratory tract infection such as Pharyngitis, otitis media, sinusitis etc.
It is oral drug.

Benzathine penicillin G is the insoluble salt of penicillin G and it is used for intramuscular injection. This is slow acting drug for prolong use.
A single dose of 1.2 million units of benzathine penicillin G is suitable for treatment of β-hemolytic Streptococcal pharyngitis.
4 million units of benzathine penicillin G injected once in 1-3 weeks in an appropriate proportion measure for primary and latent Syphilis.

Ampicillin is active against coli, Salmonella, Shigella and Haemophilus influenzae but not active against indole +ve Proteus (P.vulgaris), Pseudomonas, Klebsiella and Enterobacter.
Amphicillin and Amoxycillin are commonly used for treatment of common UTI caused by coliforms bacteria and for the treatment of mixed secondary bacterial infection of respiratory tract.
Ampicillin was a drug of choice in meningitis caused by influenzae but now a days Ceftriazone is used because of emergence of β-lactamase producing strain of H. influenzae.
Ampicillin and Amoxyccillin are alternative drug in typhoid fever but should not be used in non-invasive Salmonella gastroenteritis.
Carbenicillin is active against Pseudomonas and Proteus but not against Klebsiella.
Ticarcillin also active against Pseudomonas and proteus in lower dose than Carbenicillin.
Azolocillin, Mezlocillin and Piperacillin have greater activities against Pseudomonas than Carbenicillin.

These penicillins are used to prevent infection caused by β-lactamase producing streptococci.
These drugs are highly protein bound therefore they consumed 1 hour before and after meals.
Except Methicillin all β-lactamase resistant penicillin are suitable for oral administration. However methicillin is nephrotoxic and is not suitable for theurapeutic use.

β-lactamase inhibitors are also β-lactam group of antibiotics but with very little antimicrobial activity.
β-lactamase inhibitors are usually used in combination with β-lactam antibiotics (penicillin) to treat infection caused by β-lactamase producing strain of bacteria.
Commonly used β-lactamase inhibitors are; sulbactum, tazobactum and clavulanic acid.

Combination drugs commonly used are: