Classification of Penicillin

Penicillin is derived from a fungi named Penicillium. They are a group of Beta-lactam antibiotics, which are used in the treatment or prevention of bacterial infections originated by susceptible, particularly gram-positive, organisms. They are usually bactericidal in action.

Classification of Penicillin

Based upon Penicillin’s ability to execute or destroy bacterium and effectiveness (ranging from limited to extensive), they can be classified into following four classes.

Natural Penicillins (Penicillin V, Penicillin G, Benzathine, Procaine Penicillin)

Picture of Streptococcus Pneumoniae
Streptococcus Pneumoniae
Source: Nathan Reading, CC-BY-2.0, via Flickr
In the penicillin family, antibiotics of natural penicillin class were the first innovative agents, which were launched for clinical purposes. The original structure of penicillin-G is the basis of natural Penicillins. Antibiotics from this particular class of Penicillin are mainly useful against gram (+) strains of staphylococci and streptococci and a few gram (-) bacteria (for example, meningococcus). Additionally, you need to know that Penicillin V is not only useful for anaerobic coverage in patients who are suffering infections of oral cavity, but also it is considered as the agent of choice for treating streptococcal pharyngitis.

Penicillinase-Resistant Penicillins (Oxacillin, Dicloxacillin, Cloxacillin, Methicillin, Nafcillin)

Picture of Staphylococcus Aureus
Staphylococcus Aureus
Source: Nathan Reading, CC-BY-2.0, via Flickr
The first drug of this class was Methicillin. After that, one by one oxacillin, nafcillin, cloxacillin and dicloxacillin were added in this class. Penicillins of this class don't possess broad spectrum activity as compared to previous class of penicillin. Particularly, the antimicrobial efficacy of Penicillinase-Resistant Penicillins are aimed straightly against penicillinase-creating strains of gram (+) cocci, more specifically against staphylococcal species. For this reason, these penicillins are often called as anti-staphylococcal penicillins.

Aminopenicillins (Amoxicillin, Bacampicillin, Ampicillin)

Amoxicillin Powder for Suspension
Source: Isafmedia, CC-BY-2.0, via Flickr
The aminopenicillins were the first class of penicillins, which were discovered as active agents against several gram (-) bacteria (e.g. H. influenzae and E. coli). This class of penicillins have acid resistant properties, and for this reason they are available in oral dosage forms. Orally administered drugs (amoxicillin, Bacampicillin and ampicillin) of this class are usually used in several mild infections, including sinusitis, tonsillitis, otitis media, bronchitis, bacterial diarrhea and UTIs. In addition, you need to know that for the otitis media treatment, Amoxicillin is considered as the drug of choice.

Extended Spectrum Penicillins

Extended Spectrum Penicillins are also called as anti-pseudomonal penicillins. They include both acylaminopenicillins (mezlocillin, piperacillin, and azlocillin) and alpha-carboxypenicillins (ticarcillin and carbenicillin). The antibiotics of this class penicillin have similar spectrum of anti-bacterial activity as compared to aminopenicillins. However, these penicillins have an additional anti-bacterial activity against many organisms (gram-negative) of the Enterobacteriaceae family, including several strains of Pseudomonas aeruginosa. The antibiotics of this class may be administered alone or in combination with Aminoglycosides. In addition, you need to know that like the aminopenicillins, drugs of this class are also vulnerable to inactivation by beta-lactamases.

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