Pharmacology for Technicians PTCB Test Prep

Antibacterial Drugs Pharmacology!

Jul 16th, 2020
antibacterial drugs for the ptcb exam

Introduction to Antibacterial Drugs

Anti-infective agents are an important knowledge domain for the 2020 PTCB syllabus. Here, we review the major kinds of antibacterial drug pharmacology, mechanism of action, and examples of each kind of class.

Anti-infective agents are among the most widely prescribed medicines – drugs used in the treatment of infections.

Of course, infections itself is a wide term. It includes:

  • Bacterial infections
  • Fungal infections
  • Viral infections
  • Parasitic infections

Here, we focus on antibacterial drugs. In later articles, we will discuss antifungal, antiviral, and antiparasitic drugs.

At the outset, it is worth emphasizing that antibacterial drugs (also called “antibiotics”) cannot be used to treat other kinds of infection – such as fungal infections or viral infections. Often, antibacterial drugs are prescribed to treat viral infections, such as the common cold, but this is not an effective treatment option. Antibacterial drugs have no effectiveness against viral infections – and vice versa. If anything, overuse of antibacterial drugs is harmful because it increases drug resistance.

There are a few exceptions to this general rule. For example: metronidazole (Flagyl) is used to treat a wide range of both bacterial and some parasitic infections.

For the PTCB exam, students should understand the differences between the major antibacterial drug classes and what they are used to treat, and to be able to identify members of these drug classes. At first, this can seem difficult and overwhelming but, by taking as many PTCB practice test questions and by knowing the theory, things become much easier over time.

Antibacterial Drugs Pharmacology

In the case of antibacterial drugs, it is worth making a distinction between drugs that kill microbes from those drugs that suppress bacterial growth.

  • Bactericidal drugs – are drugs that actively kill microorganisms, thereby reducing the level of infection in the body.
  • Bacteriostatic drugs – are drugs that suppress bacterial growth and replication. By suppressing replication, this prevents further growth and allows the body to fight off the infection.

Antibacterial drugs are also divided in terms of their spectrum of activity.

Spectrum of activity refers to the range of microorganisms against which the antibacterial drug is effective. Bacteria are divided into Gram-positive organisms and Gram-negative organisms. That’s because bacteria are structurally different. And with different structures comes different drugs to meet these challenges.

  • Gram-positive organisms – are bacteria that have a thick outer wall (made of peptidoglycan) and have no outer lipid (fat) membrane. Staphylococci, streptococci, and Clostridium are examples of Gram-positive organisms.
  • Gramnegative organisms – are bacteria that have a think outer wall (made of peptidoglycan) and an outer lipid (fat) membrane. E. coli, Helicobacter pylori, and Pseudomonas aeruginosa are examples of Gram-negative organisms.

Some drugs are effective at penetrating the thick outer wall of Gram-positive organisms but are ineffective against Gram-negative organisms. Therefore, it is often important to correctly identify what organism is causing the patient’s infection. That way, a tailored treatment plan can be developed to effectively combat the infection. When the infection or disease is not known, a broad range of drugs may be administered to the patient to cover as wide a base as possible until test results of the organism come back.

Drug/Drug ClassExamplesMechanism of action
Cell wall synthesis inhibitors
Cell wall synthesis inhibitors
Cell wall synthesis inhibitors
Protein synthesis inhibitors
Protein synthesis inhibitors
Protein synthesis inhibitors
DNA synthesis inhibition
GlycopeptideVancomycinCell wall synthesis inhibitor
OxazolidinoneLinezolidProtein synthesis inhibitor
Folate antagonistTrimethoprim
Inhibition of folate synthesis
LipopeptideDaptomycinDNA/RNA synthesis inhibition
LincosamideClindamycinProtein synthesis inhibitor
NitrofuransNitrofurantoinDamages bacterial DNA

Beta-Lactamase Inhibitors

Some drug classes are co-administered with beta-lactamase inhibitors.

Beta-lactam antibiotics include drug classes such as penicillins and cephalosporins. These drug classes contain a 4-membered ring in their chemical structures – known as the beta-lactam ring. This ring is responsible for their antibacterial properties and, without it, the drugs become ineffective.

Bacteria learn to know this – and so develop enzymes (called beta-lactamases) to break down the ring inside the drug. However, drug manufacturers have developed beta-lactamase inhibitors to prevent the enzyme from breaking down the ring. These beta-lactamase inhibitors are co-administered with the drug. For example – the penicillin, amoxicillin, is co-administered with the clavulanic acid, the beta-lactamase inhibitor. Clavulanic acid is the shield that protects the beta-lactam ring inside amoxicillin from attack from bacterial beta-lactamase enzymes.

Not all penicillins or cephalosporins or carbapenems are co-administered with beta-lactamase inhibitors, but some are. These include:

  • Clavulanic acid – with amoxicillin or ticarcillin
  • Sulbactam – with ampicillin or cefoperazone
  • Tazobactam – with piperacillin
  • Avibactam – with ceftazidime
  • Relebactam – with imipenem/cilastatin
  • Vaborbactam – with meropenem

Note that beta-lactamase inhibitor drugs always contain the suffix -bactam, except clavulanic acid.


Students preparing for the PTCB exam must have a comprehensive knowledge of these antibacterial drug classes. Always note the suffixes of each drug class and allow that to help you identify drugs.

For instance:

  • fluoroquinolones end in –floxacin
  • penicillins end in –cillin
  • cephalosporins begin with the suffix cef-, ceph-, or ceft
  • tetracyclines end in the suffix -cycline

…and so on. This makes categorization easier. It does not cover all medicines, but it is at least a starting point. From there, you can build your knowledge of antibacterial drugs further. Learning by mechanism of action is also useful, too. For instance – most antibacterial drug classes can be split into:

  • Protein synthesis inhibitors – macrolides, aminoglycosides, tetracyclines
  • Cell wall synthesis inhibitors – penicillins, cephalosporins, glycopeptides
  • Folate synthesis inhibitors – such as trimethoprim
  • DNA synthesis inhibitors – such as fluoroquinolones

Whilst drug classes, mechanisms of action, and drug identification are important parts to cover for the Medications knowledge domain of the PTCB exam, it is also important to know indications, side effects, and drug interactions too – to provide a thorough, rounded knowledge of this important subject area.

Check back to our PTCB Test Prep blood soon for even more theory, PTCB practice test questions, and more on the life and work of pharmacy technicians.