Penicillins

Penicillins carry a beta-lactam ring that binds and inactivates penicillin-binding proteins (PBPs), the enzymes that cross-link peptidoglycan in the bacterial cell wall. The weakened wall gives way and dividing bacteria burst, so penicillins are bactericidal. Bacteria resist them by making beta-lactamases (penicillinases) or by changing their PBPs.

• BenzylpenicillinThe long-acting benzathine salt treats early syphilis with one intramuscular dose and is used to stop rheumatic fever coming back.
• AmoxicillinCombined with clavulanic acid (co-amoxiclav) to overcome beta-lactamases, and with clarithromycin and a proton pump inhibitor to clear H. pylori.
• FlucloxacillinIt has no US label. Like oxacillin, cloxacillin and dicloxacillin it is an isoxazolyl penicillin, and like them it does not work against MRSA.
• PiperacillinTazobactam shields it from many beta-lactamases, so the combination also covers beta-lactamase-producing staphylococci, E. coli, Klebsiella and Bacteroides.

• Strep throat
• Pneumonia and other chest infections
• Middle ear infections (otitis media)
• Skin and soft tissue infections
• Urinary tract infections
• Syphilis

• Allergic reactions (penicillin allergy)Known forSerious
• AnaphylaxisKnown forSerious
• Rash
• Diarrhea
• Nausea and vomiting
• C. difficile diarrhea and colitisSerious
• Severe skin reactions (SJS, TEN, DRESS)Serious
• Seizures with very high dosesSerious
• Kidney inflammation (interstitial nephritis)Serious
• Liver injury, including cholestatic jaundiceSerious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Penicillin allergy: avoid every penicillin; people with serious reactions may also react to cephalosporins and carbapenems.
• Kidney impairment: penicillins are cleared by the kidneys, so doses are reduced to avoid build-up and seizures.
• Probenecid blocks their secretion by the kidney tubules and raises their levels; they also slow the clearance of methotrexate.
• Glandular fever (infectious mononucleosis): amoxicillin often causes a widespread red rash.

Written for biofideX in plain words, after checking these references:

• Penicillin Antibiotic (NCI Thesaurus)
• Penicillin G potassium for injection: label (DailyMed)
• Amoxicillin capsules, tablets and oral suspension: label (DailyMed)
• Benzylpenicillin sodium 600 mg powder for injection: SmPC (emc)
• Who can and cannot take amoxicillin (NHS)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.