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Clinician’s Corner: MACROLIDES


Erythromycin was first isolated in 1952.

Mechanism: may be bactericidal OR bacteriostatic.

Most common uses: Upper Respiratory Infection, Community Acquired Pneumonia, Chlamydia, atypicals. They are also used for other lung infections.


Gastrointestinal distress (nausea, vomiting & diarrhea) occurs with all Erythromycins.

Allergies are rare, may see skin eruptions, fever, and eosinophilia

Erythromycins can block the liver metabolism of other drugs. May increase the effects of warfarin, digoxin & theophylline, some cholesterol drugs (Zocor, Lipitor).  Your Thompson Pharmacist will always monitor for drug interactions. Azithromycin (Zithromax) does NOT interact with these drugs.

Side effects:

Pseudomembranous colitis.

GI upset because it stimulates GI motility & increase pain and cramping.

Drug Interactions:  Erythromycin and clarithromycin block metabolism of some drugs.

Azithromycin is excreted through the feces and does not undergo liver metabolism to a great extent.

Patient Education:

Take with food

Take course until completed

Watch for signs of liver dysfunction (pale stools, muscle cramps, yellowing of skin etc.)

Most common Drugs & dosage of this class

  • Erythromycin base (Erytab) (Erythrocin) (old drug—extremely expensive $10-$17/tablet)
  • Azithromycin (Zithromax®)

Pregnancy Category B

Azithromycin has a half-life of 63 hours, so coverage occurs for 5 days after the last dose.

  • NOT metabolized by the liver enzyme system
  • No dosage adjustment needed if poor kidney function
  • Caution: may affect the heart rhythm.
  • RESISTANCE: is a major problem with azithromycin. The current resistance rate for Strep pneumo (respiratory infections) for azithromycin (Z-pak) is around 47% in Altoona, PA.
  • Clarithromycin (Biaxin®)

Clarithromycin was developed in the 1970s.  Clarithromycin was developed to overcome the acid instability of erythromycin.

Pregnancy Category: C

** more effective than Erythromycins against staph & strep.

Given with Prevacid (lansoprazole) & Prilosec (omeprazole) to eradicate Helicobacter pylori, a bacteria that causes stomach ulcers.

  • Causes metallic taste in mouth
  • Caution: cause heart arrhythmias.

POTENT blocker of CYP450-3A4, and P-glycoprotein

Increases warfarin (Coumadin ®) levels—may cause increase bleeding risk.

Macrolide resistance is a real problem.  Unnecessary antibiotic use causes a lot of resistance, so be sure to ask your Thompson Pharmacist for advice to help decrease the risk of resistance.  Go Ahead and ASK, at Thompson Pharmacy it’s ALL for YOU!