Antibiotic Penicillin

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Penicillin -lactam drugBy: Peshawa Mohammed Ibrahim


What is penicillinPenicillin is one of the most commonly prescribed antibiotics. It is part of a family of antibiotics known as beta lactams, and there are many individual medications in this family: Penicillin G, nafcillin, oxacillin, cloxacillin and dicloxacillin, ampicillin, amoxicillin, carbenicillin, ticarcillin, and piperacillin.

Acting of penicillin Penicillin act by inhibiting transpeptidases, the enzymes that catalyze the final cross-linking step in the synthesis of peptidoglycan, penicillin can bind to the active site of the transpeptidase and inhibit its activity.


Two additional factors are involved in the action of penicillin(1) The first is that penicillin binds to a variety of receptors in the bacterial cell, membrane and cell wall, called penicillin-binding proteins (PBPs). Some PBPs are, transpeptidases; the others function in the synthesis of peptidoglycan. Changes in PBPs are in part responsible, for an organisms becoming resistant to penicillin.

(2) The second factor is that autolytic enzymes called murein hydrolases (murein is a synonym for peptidoglycan) are activated in penicillin-treated cells and degrade the peptidoglycan. Some bacteria (e.g., strains of S. aureus) are tolerant to the action of penicillin, because these autolytic enzymes are not activated. A tolerant organism is one that is inhibited but not killed by a drug that is usually bactericidal, such as penicillin

Mutation of bacteriaAntibiotic act by binding proteins, but Some bacteria undergo mutation so antibiotic cant recognize because of that antibiotic cant bind bacteria

Penicillin is bactericidal, but it kills cells only when they are growing. When cells are growing, new peptidoglycan is being synthesized, and transpeptidation occurs. However, in no growing cells, no new cross-linkages are required, and penicillin is inactive. Penicillin are therefore more active during the log phase of bacterial cell growth than during the stationary phase

-lactam ring Penicillin are called -lactam drugs because of the importance of the -lactam ring . An intact ring structure is essential for antibacterial activity; cleavage of the ring by penicillinases (-lactamases) inactivates the drug.

Disadvantages of penicillin 1- they where effective for gram positive bacteria.2- they where defective for gram negative bacteria.3- hydrolysis by gastric acids, so that it cannot be taken orally.4- inactivation by -lactamases.5- The fifth disadvantage common to all penicillins that has not been overcome is hypersensitivity.

Nowadays we can take penicillin orally and it can be activate against B-lactum by clavulanic acid and sulbactam they are inhibitors of b-lactum. Combinations, such as amoxicillin and clavulanic acid(Augmentin), are in clinical use.

Penicillins are usually nontoxic at clinically effective levels. The major disadvantage of these compounds is hypersensitivity, which is estimated to occur in 1% to 10% of patients. The hypersensitivity reactions include anaphylaxis, skin rashes, hemolytic anemia, nephritis, and drug fever

Penicillin allergy Penicillin allergy is an abnormal reaction of your immune system to the antibiotic drug penicillin. Penicillin is prescribed for treating various bacterial infections.Common signs and symptoms of penicillin allergy include hives, rash and itching. Severe reactions include anaphylaxis, a life-threatening condition that affects multiple body systems.

Side effect of penicillinThe more common side effectsof this drug include nausea, vomiting, upset stomach, diarrhea, and a black, hairy tongue.In some cases, penicillin can cause serious side effects. These include severe allergic reactions and diarrhea.

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