Penicilin

What class of antibiotics do penicillins belong to?

β-lactam antibiotics.

From which mold was penicillin first obtained?

Penicillium notatum.

What organism’s lysis led to the discovery of penicillin?

Staphylococcal organisms.

What is the nucleus common to all penicillins?

6-amino penicillanic acid.

What is the antibacterial nature of penicillins?

Bactericidal.

What bacterial structure do penicillins target?

The bacterial cell wall.

What is the bacterial cell wall mainly composed of?

Peptidoglycan.

What are peptidoglycans made of?

Glycan units joined by peptide cross-links.

Against which bacteria are penicillins most effective?

Rapidly multiplying bacteria.

Why do penicillins have little effect on non-dividing bacteria?

Because active cell wall synthesis is absent.

What step of cell wall synthesis is inhibited by penicillins?

The final transpeptidation or cross-linking step.

What happens when penicillins inhibit cell wall synthesis?

Osmotically unstable bacteria undergo lysis.

What enzymes may contribute to bacterial lysis in the presence of penicillins?

Autolysins.

Why are penicillins selectively toxic?

Mammalian cells lack peptidoglycan cell walls.

What are penicillin-binding proteins (PBPs)?

Bacterial enzymes involved in cell wall synthesis and maintenance.

What effect do penicillins have on PBPs?

They inactivate them.

What enzyme reaction is inhibited by penicillins during cell wall formation?

Transpeptidase reaction.

Why are peptide cross-links important in bacteria?

They maintain cell wall integrity.

What is the role of autolysins in bacterial cells?

Remodeling and degradation of the bacterial cell wall.

How do penicillins enhance autolysin activity?

Cell wall synthesis is inhibited while autolysins continue degrading existing wall.

Against which organisms are penicillins ineffective?

Mycobacteria, fungi, protozoa, and viruses.

Why are penicillins ineffective against viruses?

Viruses lack cell walls.

What is the clinical significance of penicillins?

They are widely effective and least toxic antibiotics.

What limits the use of penicillins today?

Increasing bacterial resistance.

Why should oral penicillins be taken away from meals?

To prevent food binding and acid inactivation.

How does probenecid increase penicillin levels?

By inhibiting tubular secretion of penicillin.

What is Benzyl penicillin also called?

Penicillin G.

Is Penicillin G acid stable?

No, it is acid labile.

Why is Penicillin G not very effective orally?

Gastric acid destroys it.

How is Penicillin G best administered?

Parenterally.

How quickly are peak plasma levels reached after parenteral Penicillin G?

About 30 minutes.

How is Penicillin G distributed in the body?

Mainly extracellularly.

How is CSF penetration of Penicillin G normally?

Poor unless meninges are inflamed.

Through which route is Penicillin G mainly excreted?

Urine.

In what forms is Penicillin G commonly administered intramuscularly?

Sodium or potassium salts.

Why is local application of Penicillin G discouraged?

Risk of sensitization.

What are the three major disadvantages of Penicillin G?

Rapid excretion, acid destruction, and narrow spectrum/resistance.

Why may Penicillin G require frequent administration?

It is rapidly absorbed and excreted.

What preparation prolongs penicillin blood levels for up to 24 hours?

Procaine penicillin.

Which long-acting penicillin preparations may last a week or more?

Benzathine penicillin and benethamine penicillin.

Which acid-resistant penicillin overcame gastric acid destruction?

Penicillin V (Phenoxymethyl penicillin).

What is the antibacterial spectrum of Penicillin G?

Mainly gram-positive cocci and some gram-positive bacteria.

Why were broad-spectrum penicillins developed?

To improve activity against gram-negative bacteria.

Give examples of acid-resistant penicillins.

Penicillin V, propicillin, phenethicillin, phenbenicillin.

Which acid-resistant penicillin is most useful orally?

Phenoxymethyl penicillin (Penicillin V).

Are acid-resistant penicillins destroyed by β-lactamase?

Yes.

What is Ampicillin?

A broad-spectrum aminopenicillin.

Which gram-negative organisms are sensitive to ampicillin?

Shigella, Salmonella, and Haemophilus influenzae.

Is ampicillin acid resistant?

Yes.

By which routes can ampicillin be administered?

Oral, IV, and IM routes.

Is ampicillin destroyed by β-lactamase?

Yes.

How much of oral ampicillin is absorbed?

About 30%.

Which drug is chemically related to ampicillin?

Amoxicillin.

What advantage does amoxicillin have over ampicillin?

Better absorption even in the presence of food.

Give examples of aminopenicillins.

Ampicillin, bacampicillin, amoxicillin.

Give examples of carboxypenicillins.

Carbenicillin and ticarcillin.

Give examples of ureidopenicillins.

Piperacillin and mezlocillin.

Which penicillin is especially active against Pseudomonas aeruginosa?

Ticarcillin.

Which penicillin has high potency against gram-negative organisms?

Piperacillin.

Which penicillin is active against both pseudomonas and klebsiella?

Azlocillin.

Are antipseudomonal penicillins well absorbed orally?

No.

What are penicillinase-resistant penicillins?

Penicillins resistant to β-lactamase destruction.

Give examples of penicillinase-resistant penicillins.

Methicillin, cloxacillin, flucloxacillin, nafcillin.

Why are penicillinase-resistant penicillins resistant to β-lactamase?

Their side chains protect the β-lactam ring.

Which penicillinase-resistant penicillins are acid resistant?

Cloxacillin and flucloxacillin.

Which penicillinase-resistant penicillin must be given parenterally?

Methicillin.

What are β-lactamase inhibitors?

Drugs that inhibit β-lactamase enzymes.

Give examples of β-lactamase inhibitors.

Clavulanic acid, sulbactam, tazobactam.

How do β-lactamase inhibitors work?

They bind covalently to β-lactamase enzymes and inhibit them.

Which organisms commonly produce β-lactamase?

Staphylococci, Neisseria gonorrhoeae, and Haemophilus influenzae.

Do streptococci produce β-lactamase?

No.

What are the two broad categories of adverse reactions to penicillins?

Allergic reactions and direct toxicity.

What severe allergic reaction can penicillins cause?

Anaphylactic shock.

What skin manifestations can penicillin allergy produce?

Pruritus and skin rashes.

What respiratory manifestation can occur in penicillin allergy?

Wheezing.

What swelling reaction may occur with penicillin allergy?

Angioneurotic edema.

What is the approximate incidence of penicillin allergic reactions?

1–10%.

Why are penicillins generally non-toxic to animal cells?

Animal cells lack bacterial cell walls.

What causes the direct toxicity of penicillins?

Irritation from high IM or IV concentrations.

What local reactions can occur after penicillin injection?

Pain and induration.

What nerve complication can occur accidentally during injection?

Nerve degeneration.

What is Augmentin?

Amoxicillin plus clavulanic acid.

What is Timentin?

Ticarcillin plus clavulanic acid.

What is Unasyn?

Ampicillin plus sulbactam.

What is Zosyn?

Piperacillin plus tazobactam.

Give examples of cephalosporins.

Ceftriaxone, cefuroxime, cephalexin, cefotaxime.

Give examples of carbapenems.

Imipenem, meropenem, ertapenem, doripenem.

What is an example of a monobactam?

Aztreonam.

Give examples of other cell wall inhibitors.

Vancomycin, bacitracin, daptomycin, telavancin.

What linkage in bacterial cell walls do penicillins block?

Peptide cross-linkage between peptidoglycan units.

What is the major antibacterial effect of β-lactam antibiotics?

Inhibition of bacterial cell wall synthesis.

Why do penicillins mainly affect growing bacteria?

Growing bacteria actively synthesize peptidoglycan.

What determines the success of penicillin antibacterial action?

The antibiotic’s size, charge, and hydrophobicity.