Pharmacology for Technicians PTCB Test Prep

PTCB Guide to Tetracyclines!

Jun 10th, 2023
ptcb guide to tetracyclines

What are Tetracyclines?

Tetracyclines are a widely used antibacterial drug class. Over the course of this PTCB guide to tetracyclines, we will learn the essential details that get tested for this drug class on the PTCB exam.

Tetracyclines are used in the treatment of many different bacterial infections and, for that reason, they are classified as having a relatively broad-spectrum of activity.

Indications of tetracyclines include:

  • Acne vulgaris.
  • Lower respiratory tract infections (LRTIs).
  • Chlamydial infection, including pelvic inflammatory disease.
  • Other infections including typhoid, malaria, and Lyme disease.

Given that over 25 million prescriptions are written for tetracyclines each year, it’s essential that pharmacy technicians have a thorough understanding of this drug class.

Common brands and examples to know include:

TetracyclineCommon Brands

How do tetracyclines work?

Tetracyclines work as protein synthesis inhibitors.

By inhibiting the production of new proteins inside bacterial cells, tetracyclines disrupt many of the fundamental processes that keep that bacterial cell alive – and so the bacteria die. By slowing the rate of bacterial reproduction, it gives the immune system an opportunity an opportunity to kill any remaining bacteria from the body.

That said, many bacteria have developed the means to defend themselves against tetracyclines. Bacterial resistance to these drugs continues to rise. This makes tetracyclines less effective than when they were first introduced, but they still have significant clinical activity that warrants their continued use in medicine.

Side Effects

Tetracyclines are generally well-tolerated medicines.

Possible side effects include:

  • Nausea and vomiting
  • Diarrhea
  • Hypersensitivity reactions, such as skin rash
  • Esophageal irritation and ulceration
  • Photosensitivity – an increased risk of sunburn

Tetracyclines can also cause tooth discoloration and tooth enamel hypoplasia (thin or absent enamel).

Tetracyclines are contraindicated in pregnancy (and children younger than 12-years) due to the risk of tetracyclines binding to teeth and bones.

Taking expired tetracyclines can cause Fanconi syndrome – a defect in the kidneys that causes poor absorption of electrolytes, such as sodium and potassium.

Tetracyclines are typically formulated as capsules or tablets. To minimize side effects – particularly esophageal irritation – they should be taken with a full glass of water while sitting or standing upright.

Drug Interactions

Tetracyclines bind to multivalent ions, including:

  • Magnesium ions
  • Aluminum ions
  • Zinc ions
  • Calcium ions
  • Iron ions

Therefore, taking foods or medicines – including antacids and dairy products – that contain any of these ions can disrupt the absorption of tetracyclines. These foods and medicines should be avoided within 2-hours of taking tetracyclines.

Tetracyclines can also enhance the anticoagulant effects of warfarin. That’s because gut bacteria produce vitamin K, and this vitamin opposes the effects of warfarin. Tetracyclines kill gut bacteria, reducing vitamin K production – and so this increases the anticoagulant effects of warfarin.


Over the course of this revision guide, we have learned that:

  • Tetracyclines are an antibacterial drug class used to treat a broad-range of infections – from acne to pneumonia to malaria.
  • Widely dispensed examples include doxycycline, minocycline, tetracycline, and demeclocycline.
  • Tetracyclines work as protein synthesis inhibitors.
  • Bacterial resistance continues to rise, but tetracyclines remain an effective antimicrobial drug class.
  • Tetracyclines are well-tolerated drugs, but they can cause photosensitivity, tooth discoloration and enamel hypoplasia.
  • To reduce the risk of esophageal irritation or ulceration, tetracyclines should be taken with a full glass of water whilst sitting or remaining upright.
  • Foods or medicines that contain multivalent ions – such as calcium or magnesium – can impair tetracycline absorption. This includes dairy products and antacids.
  • Tetracyclines can enhance the anticoagulant effects of warfarin (increasing the risk of bleeding).
  • Tetracyclines are avoided in pregnancy and children younger than 12-years due to the drug binding to teeth and bones.

We hope you found this PTCB guide to tetracyclines helpful. Check back to our blog soon for more exclusive content to help you study and pass the pharmacy technician exam.

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PTCB Test Prep Author


Elaine Walker

Elaine joined PTCB Test Prep in 2017, currently serving as the lead product development manager overseeing both course development and quality improvement. Mrs. Walker is a graduate of California State University and has worked as a pharmacy technician for over twenty years – with particular interests in pediatric pharmacy, extemporaneous compounding, and hospital pharmacy. Over the past 8-years, she has helped prepare thousands of students for the PTCB examination.