Introduction

Tetracyclines were first discovered in the 1940s and, still today, they remain an important pillar in the antibacterial family of medicines.

As part of your NAPLEX exam, or other clinical pharmacy exam, candidates are expected to have a thorough knowledge of each antibacterial drug class. Below, then, we’ve put together the most convenient summary to help you commit the essential facts to memory.

Of course, tetracyclines are not just used to treat antibacterial infections. Drugs such as demeclocycline are, for example, used to treat SIADH – syndrome of inappropriate antidiuretic hormone secretion. Tetracyclines are also widely used in veterinary medicine, too.

Let’s get started.

Facts about Tetracyclines

1 – Tetracyclines are broad-spectrum antibacterials effective in the treatment of acne, Lyme disease, malaria, chlamydia, Rickettsia infections, and syphilis.

2 – They are protein synthesis inhibitors – inhibiting the 30S ribosomal subunit – inhibiting the binding of aminoacyl-tRNA to the mRNA translation complex.

3 – Side effects include tooth discoloration and enamel hypoplasia, hence these drugs should be avoided in children and those who are pregnant.

4 – Demeclocycline inhibits antidiuretic hormone and so is an effective treatment option for SIADH.

5 – Other side effects include photosensitivity, esophageal irritation, and GI effects – nausea, vomiting, diarrhea.

6 – Tetracyclines are usually formulated as capsules or tablets. For this reason, they should be swallowed with a whole glass of water while standing/sitting, to avoid any irritation to the throat.

7 – Tetracyclines bind to divalent ions which interferes with absorption. They should not be taken within 2 hours of calcium, antacids or iron.

8 – Tetracyclines enhance the anticoagulant effect of warfarin by killing normal gut flora which otherwise synthesizes vitamin K.

9 – Intracranial hypertension is a rare adverse effect that leads to headache and visual disturbances.

10 – Tetracyclines may be divided according to their half-lives:

• Short-acting drugs (half-life 6-8 hours): such as lymecycline and oxytetracycline and tetracycline (“LOT” drugs).
• Intermediate-acting drugs (half-life around 12 hours): such as demeclocycline (intermediate – demeclocycline’
• Long-acting drugs (half-life 16 hours or more): such as doxycycline and minocycline and tigecycline (“Do More Time” drugs)

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