Penicilline

Penicillin is a group of beta-lactam antibiotics produced by certain species of Penicillium fungi. They inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins and blocking the transpeptidase enzymes that cross-link peptidoglycan. The beta-lactam ring is essential for activity. Industrial production now relies on strains of Penicillium chrysogenum.

Penicillin G and related natural penicillins are effective mainly against many gram-positive cocci and some gram-positive bacilli. They have limited activity against most gram-negative bacteria due to permeability barriers and beta-lactamases. Structural families include natural penicillins (penicillin G, penicillin V), penicillinase-resistant penicillins (oxacillin, nafcillin, dicloxacillin), and broad-spectrum aminopenicillins (amoxicillin, ampicillin). In clinical practice, combinations with beta-lactamase inhibitors extend activity to beta-lactamase–producing organisms (for example, amoxicillin-clavulanate, piperacillin-tazobactam).

Clinical use and administration vary by its type. Natural penicillins are used for streptococcal infections and syphilis; penicillin G is typically given by injection, while penicillin V is oral. To treat beta-lactamase–producing bacteria, penicillins are combined with beta-lactamase inhibitors or used with broader-spectrum agents when appropriate.

Resistance and safety. Resistance arises mainly via beta-lactamase production and altered penicillin-binding proteins; methicillin-resistant Staphylococcus aureus (MRSA) is resistant to most penicillins. Adverse effects include allergic reactions ranging from rash to anaphylaxis, gastrointestinal upset, and rare superinfections. Penicillins are generally considered safe in pregnancy, but should be avoided in individuals with a severe allergy.