All penicillin family antibiotics have the beta-lactam ring and are therefore also called beta-lactam antibiotics. The penicillins are bactericidal.
Beta-Lactam Antibiotics
MOA: Inhibits bacterial cell wall synthesis by competitive inhibiting the transpeptidase enzyme. All of the follow PCNs including aztreonam and the carbapenems work by inhibiting bacterial cell wall synthesis and are thus bactericidal.
Below, we review the 7 subgroups of the Beta-lactam family.
| Drugs | Group Properties | Common Uses | Comments | |
| Original Penicillins | Penicllin G – IM, IV Penicillin V – Po |
Sensitive to beta-lactamase (penicillinase) enzyme. | Strep throat (Streptococcal pharyngitis caused by GAS) Syphilis (Treponema pallidum) |
|
| Aminopenicillins | Amoxicillin Ampicillin |
Sensitive to beta-lactamase (penicillinase) enzyme.
|
Sinusitis, Otitis Media, Bronchitis. Drug of choice for Listeria. Amp + Gent combo for broad gm- coverage. |
|
| Penicillinase-Resistant Penicillins | Methi-, Naf-, Oxa-, Cloxa-, dicloxa- -cillin |
Resistant to penicillinase enzyme. | Nafcillin is the drug of choice for serious staphylococcus aureus infections such as cellulitis, endocarditis, and sepsis. | |
| Anti-Pseudomonal Penicillins | Piperacillin, Carbenicillin, Ticarcillin, Mezlocillin |
Sensitive to penicillinases and thus, most Staphylococcus aureus are resistant. This issue is solved by combining them with beta-lactamase inhibitors like tazobactam, clavulanic acid, and sulbactam. Covers Pseudomonas, many Gram negatives, Anaerobes, and many Gram positives. |
For: Pseudomonas coverage. Anaerobic coverage. Very broad coverage e.g. for HAP |
Pip/ tazo (Zosyn) covers staff b/c of the tazobactam that is a beta-lactamase inhibitor. |
| Cephalosporins (Read her for Cephalosporins) |
Resistant to penicillinase enzyme. Unfortunately, cephalosporinases have crept up! 10% of pts allergic to PCN will have a reaction to Cephalosporins. |
See Cephalosporins link | ||
| Carbapenems | Imipenem, Meropenem, Doripenem, Ertapenem | Have some of the broadest coverage. Resistant to Beta-Lactamases. Resistant to ESBL. Imipenem has the broadest coverage of all antibiotics known to man! It covers Gm negs, Gm pos, Pseudomonas, Anaerobes. ** Ertapenem doesn’t cover pseudomonas (a bug other carbapenems all cover.) |
MRSA, some species of Pseudomonas and bacteria without peptidoglycan cell walls (mycoplasma) are still resistant to imipenem. A normal kidney has a dihydropeptidase the breaks down imipenem, so Cilastatin, an inhibitor of this didhyropeptidase is given with imipenem. Meropenem and doripenem are stable against dihydropeptidase, so cilastatin is not needed.10% of pts allergic to PCN will have a reaction to imipenem.10% of pts allergic to PCN will have a reaction to imipenem.Imipenem lowers seizure threshold and makes seizures more likely. Avoid this drug in patients with a hx of seizures, meningitis, prior strokes, or evidence of brain masses. Meropenem and doripenem have less potential for causing seizures than imipenem. |
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| Aztreonam | Aztreonam | Kills all Gram Negatives. Little cross reactivity with PCN allergic pts, so you can use in pts with PCN allergies. |
It’s a beta-lactam but differs from all others in that it’s a monobactam. It doesn’t bind to the transpeptidases of GM+ or anaerobic bacteria, only to the transpeptidases of gram-negative bacteria. Because it only kills GM-negs, you use it in combination with something else that kills gram positives. Vanc + Aztreonam Clinda + Aztreonam |
Kills the tough hospital acquired MDR, gram-negative bacteria including Pseudomonas. |
ESBL = Extended Spectrum Beta-lactamases.
Beta-lactamase inhibitors (Clavulanic acid, Sulbactam, and Tazobactam).
These are penicillanic acid derivatives that inhibit beta-lactamase. They are combined with penicillins to create beta-lactamase resistant combinations. E.g. Amoxicillin/Clavulanic acid = Augmentin; Ampicillin/Sulbactam = Unasyn; Piperacillin/Tazobactam = Zosyn; Ticarcillin/Clavulanic acid = Timentin
These combinations produce coverage against beta-lactamase producing gram positives (staph aureus), gram-negatives (Haemophilus influenza), and anaerobes (Bacteroides fragilis).
** A lot of staph aureus strains produce penicillinase. So, the empiric treatment that includes coverage for staph aureus needs to cover penicillinase.
Note that MRSA trumps penicillinase-resistant penicillins.