Characteristics of Antibiotic Classes: Penicillins

The basic structure of penicillin (consisting of a beta lactam ring) is susceptible to beta-lactamases (enzymes that break down the penicillin). Thus, many penicillin-class ABs are combined with a beta-lactamase inhibitor (Amox is one such brand name). The penicillins have limited gram negative coverage. The allergic potential is relatively greater (though rare if given orally, most allergies are from the parenteral route). They are the dental first-line agents (infections usually respond within 5-7 days). There is a 10-15% chance of allergic cross reactivity with some Cephalosporins, so concurrent administration of penicillin and Cephalosporin is a relative contraindication. Penicillins are cleared from the body via the renal route (in WWII when penicillin was rare, pts who were given penicillin had their urine collected so that it could be filtered out for reuse).


You should always choose the AB agent with the narrowest spectrum that will do the job (ie. choose Pen VK instead of other more broad spectrum ABs).

Category: Pharmacology Notes