March 30th, 2019
Antibiotics Pharmacology | Cell Wall Synthesis Inhibitors
Antibiotics pharmacology is prominent with clinical pharmacy exams, including the NAPLEX exam. Infections are among the most common conditions that patients experience.
It’s up to clinicians to know how to deal with each infection and what management approach works best. It’s not always easy to know what infection the patient has. Further testing may be required. In the meantime, then, clinicians and pharmacists should determine, based on patient symptoms to date, what the most likely cause is, until such time that further evidence is presented.
Mechanism of action matters, too. Knowing what infection the patient has leads the clinician or pharmacist to determine what type of organism is involved. Whether the organism is Gram-positive or Gram-negative matters. Whether the organism is aerobic or anaerobic also matters.
Below, we’ve put together a quick review guide of antibiotics pharmacology as it relates to cell wall synthesis inhibitors. These are important drug classes.
The class includes:
Let’s go through each of these antibiotic drug classes in turn.
Cell Wall Synthesis Inhibitors
Cell wall synthesis inhibitors include drugs such as carbapenems, penicillins, cephalosporins, glycopeptides and monobactams.
Let’s go through each of these drug classes in turn – learning more about their mechanisms, side effects and drug interactions.
|Imipenem is always co-administered with cilastatin – an excipient that prevents its degradation by the renal enzyme dehydropeptidase 1.|
All active against Pseudomonas aeruginosaexcept ertapenem.
Bactericidal, broad-spectrum drugs.
Identified through the suffix -penem.
|Amoxicillin is taken with beta-lactamase inhibitor clavulanic acid. Sulbactam is used with ampicillin and tazobactam with piperacillin. Tazobactam is taken with piperacillin.|
Flucloxacillin is beta-lactamase resistant due to an acyl side-chain that protects the beta-lactam ring from degradation.
Piperacillin is active against P. aeruginosa.
Penicillins reduce renal excretion of methotrexate, increasing toxicity risk.
Identified through the suffix –cillin.
|Active against aerobic / anaerobic Gram-positive bacteria. Active against MRSA.|
Work by inhibiting peptidoglycan synthesis.
Side effects include thrombophlebitis, red man syndrome, nephrotoxicity, ototoxicity and blood disorders such as neutropenia and thrombocytopenia.
|Earlier cephalosporin generations have greater activity against Gram-positives than later generations. Fifth-generation drugs have similar activity against Gram-positives as first-generation drugs.|
GI upset and nausea are common side effects.
As with other beta-lactams, they interrupt synthesis of the peptidoglycan layer of bacterial cell walls.
|Monobactams||Aztreonam||Used to treat Gram-negative infections, including Pseudomonas aeruginosa infections.|
When given by injection, common side effects include injection site pain, vomiting and rash.
When given by inhalation, common side effects include wheezing, cough and vomiting.
High affinity for penicillin-binding protein-3.
Aztreonam is bactericidal.
How to Memorize Cephalosporins
Many people find it tough to remember cephalosporin generations.
There is a reason to remember the generations, though. What generation a drug belongs to lets you know more about what spectrum of activity that drug has. There are many different cephalosporins. Knowing how to differentiate between each cephalosporin generation, and the drugs within each generation, adds enormously to your clinical knowledge.
Here are the top 7 ways to remember some of the fundamental facts about cephalosporins that you need to know.
1. Earlier generations use the prefix cefa- more. Cefradine is the only first-generation drug that breaks this rule.
2. Later generations have more activity against Gram-negative organisms than earlier generations, which have more activity against Gram-positive organisms.
3. Cefoperazone and ceftazidime are both third-generation drugs with a difference – namely, that both are active against P. aeruginosa.
4. Fifth-generation drugs are active against MRSA. Examples include ceftaroline and ceftobiprole.
5. Fourth-generation drugs, such as cefepime, are active against P. aeruginosa.
6. Use ‘furry fox for tea’ to identify second-generation drugs – cefuroxime, cefoxitin, cefaclor and cefotetan.
7. Many third-generation drugs have ‘t’ within their names: ceftazidime, ceftriaxone and cefotaxime. Other drugs include the ‘fix me dinner’ drugs – cefixime and cefdinir.
Antibiotics pharmacology doesn’t need to be difficult.
There will be many NAPLEX questions on antibacterial drugs. There is no doubt about it. You must know about each drug class – how they work, what members they include, what side effects they have and what prominent drug interactions you need to know.
Of course, cell wall synthesis inhibitors are just one class. Just one class, but an important class at that.
There are many others, which we explore in future NAPLEX blogs. Check back to our blog soon for even more facts about antibiotics pharmacology that you need to know. NAPLEX Study Guide – helping you become a qualified pharmacist!