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Penicillin Antibiotics Classification - Uses and Side Effects

Antibiotics are specific chemical substances derived from or produced by living organisms that are capable of inhibiting the life processes of other organisms. Penicillins are a group of closely related antibiotics used to treat a wide variety of bacterial infections occurring in the body.

Penicillin, the world's first antibiotic, was discovered by British scientist Alexander Fleming in 1928 on accident. The penicillins were the first antibiotics discovered as natural products from the mold Penicillium.

Over the years, this family of antibiotics has grown, and the antimicrobial activity has expanded. Today there are at least 20 kinds of penicillin antibiotics. However, despite the discovery of many new antibiotics, the penicillins have remained a primary choice for treatment of a wide variety of bacterial infections. They are used to treat ear, nose and throat infections, respiratory and urinary tract infections, prostate infections, and certain sexually transmitted diseases.

Penicillins disadvantages:

* acid lability - most of these drugs are destroyed by gastric acid
* short duaration of action - because of this short half-life, the penicillins must be administered at short intervals, usually every 4 hours

* lack of activity against most Gram-negative organisms
* drug hypersensivity - about 10% of population has allergy
* many patients experience GI upset
* painful if given intramuscularly

Penicillins advantages:

* bactericidal against sensitive strains
* relatively nontoxic
* have excellent tissue penetration
* efficacious in the treatment of infections
* relatively inexpensive in comparison with other antibiotics.

Newer penicillins are resistant to stomach acid, such as penicillin V, or have a broader spectrum, such as ampicillin and amoxicillin.

Classification of Penicillins

There are 4 classes of penicillins, based upon their ability to kill various types of bacteria. From narrow to broad range of effectiveness they include:
* Natural Penicillins (Penicillin G, Procaine, Penicillin G, Penicillin V, Benzathine). The natural penicillins were the first agents in the penicillin family to be introduced for clinical use. The natural penicillins are based on the original penicillin-G structure. They are effective against gram-positive strains of streptococci, staphylococci, and some gram-negative bacteria such as meningococcus. Penicillin V is the drug of choice for the treatment of streptococcal pharyngitis. It is also useful for anaerobic coverage in patients with oral cavity infections.
* Penicillinase-Resistant Penicillins (Cloxacillin, Dicloxacillin, Methicillin, Nafcillin, Oxacillin). Methicillin was the first member of this group, followed by oxacillin, nafcillin, cloxacillin and dicloxacillin. The penicillinase-resistant penicillins have a more narrow spectrum of activity than the natural penicillins. Their antimicrobial efficacy is aimed directly against penicillinase-producing strains of gram-positive cocci, particularly Staphylococcal species and these drugs are sometimes called anti-staphylococcal penicillins.
* Aminopenicillins (Ampicillin, Amoxicillin, Bacampicillin). The aminopenicillins were the first penicillins discovered to be active against gram-negative bacteria (such as E. coli and H. influenzae). Aminopenicillins are acid-resistant so administered orally. Orally administered amoxicillin and ampicillin are used primarily to treat mild infections such as otitis media, sinusitis, bronchitis, urinary tract infections and bacterial diarrhea. Amoxicillin is the agent of choice for the treatment of otitis media.
* Extended Spectrum Penicillins (sometimes called anti-pseudomonal penicillins). Extended Spectrum Penicillins include both alpha-carboxypenicillins (carbenicillin and ticarcillin) and acylaminopenicillins (piperacillin, azlocillin, and mezlocillin). These agents have similar spectrums of activity as the aminopenicillins but with additional activity against several gram negative organisms of the family Enterobacteriaceae, including many strains of Pseudomonas aeruginosa. Like the aminopenicillins, these agents are susceptible to inactivation by beta-lactamases. These agents may be used alone or in combination with Aminoglycosides.

Mode of action

All penicillin derivatives produce their bacteriocidal effects by inhibition of bacterial cell wall synthesis. Penicillins prevent bacteria from using a substance that is necessary for the maintenance of the bacteria?s outer cell wall. Unable to use this substance for cell wall maintenance, the bacteria swell, rupture, assume unusual shapes, and finally die.

The penicillins may be bactericidal (kill the bacteria) or bacteriostatic (stop the growth of bacteria). They are bactericidal against sensitive microorganisms provided there is an adequate concentration of penicillin in the body. An inadequate concentration of penicillin may produce bacteriostatic activity, which may or may not control the infection.

Conditions treated with penicillins, indications & uses

Penicillins may be used to treat infections such as urinary tract infections, septicemia, meningitis, intra-abdominal infection, gonorrhea, syphilis, pneumonia, respiratory infections, ear, nose and throat infections, skin and soft tissue infections. Examples of infectious microorganisms (bacteria) that may respond to penicillin therapy include gonococci, staphylococci, streptococci, and pneumococci.

Penicillins are used to prevent bacterial infection before, during and after surgery and to prevent Group A streptococcus ("strep") infections in people with a history of rheumatic heart disease.

Most penicillins work best when taken on an empty stomach (either one hour before meals or two hours after) with an 8-ounce glass of water. The water helps prevent the medicine from irritating the delicate lining of the esophagus and stomach. However, some types of penicillin can be taken on either a full or empty stomach. These include amoxicillin, penicillin V, and the tablet form of bacampicillin.

Penicillins work best when there is a constant amount circulating in the body. So it's important not to miss a dose. Also, it's best to take doses at evenly spaced intervals, both day and night.

Side effects

Although most penicillins are safe for the majority of people, some people may experience side effects.

Allergic or hypersensitivity reactions are thought to be the most frequently occurring side effect. An estimated 3-10% of the general population are allergic to penicillin. Once an individual is allergic to one penicillin, he or she is most likely allergic to all of the penicillins. Those allergic to penicillin also have a higher incidence of allergy to the cephalosporin antibiotics.

The most serious allergic reaction is anaphylaxis, a severe allergic reaction that can cause skin rash, hives, itching, difficulty breathing, shock, and unconsciousness. An early sign of anaphylaxis is a feeling of warmth and flushing. If any of these occurs, the medicine should be stopped and emergency help sought immediately. Anaphylactic shock occurs more frequently after parenteral administration but can occur with oral use.

Other most common side effects are mild diarrhea, vomiting, headache, vaginal itching and discharge, sore mouth or tongue, or white patches in the mouth or on the tongue. These problems usually go away as the body adjusts to the drug and do not require medical treatment unless they continue or they are bothersome. Occasionally, certain types of penicillin may cause the tongue to darken or discolor. This condition is temporary and will go away when the medicine is stopped.

On rare occasions some types of penicillin may cause severe abdominal or stomach cramps, pain, or bloating or severe or bloody diarrhea. Other rare side effects include fever, increased thirst, severe nausea or vomiting, unusual tiredness or weakness, weight loss, seizures, or unusual bleeding or bruising.