Penicillins
Penicillins have several things in common:
- Penicillins have very short half-lives (<2 hours) and must be dosed multiple times per day. The half-lives of most of them are prolonged in the presence of renal dysfunction.
- Like other beta-lactams, penicillins can cause hypersensitivity reactions. If a patient has a true hypersensitivity reaction to a penicillin, other penicillins should be avoided, even if they are from different classes of penicillins. If the reaction is not severe (that is, not anaphylactoid), cephalosporins and carbapenems may be useful.
- Many penicillins are relatively poorly absorbed, even those available as oral formulations. This can lead to diarrhea when oral therapy is needed. Pay attention to the dosing of oral versus intravenous penicillins-often, a conversion from intravenous to oral therapy means there will be a substantial decrease in the amount of active drug in the body.
Many penicillins were developed after the natural penicillins became available. Until researchers developed beta-lactamase inhibitors, development primarily focused on either improved activity against staphylococci (MSSA) or Gram-negative rods.