Continuing Education Activity

Erythromycin has traditionally been used for various respiratory infections (i.e., community-acquired pneumonia, Legionnaires disease), prophylaxis of neonatal conjunctivitis, and chlamydia. It is also FDA approved for treating skin infections, intestinal amebiasis, rheumatic fever, prophylaxis, syphilis, and pelvic inflammatory disease (PID). In addition, if mixed with tretinoin cream or benzoyl peroxide, it is effective for treating acne. This activity will highlight the mechanism of action, adverse event profile, pharmacology, monitoring, and relevant interactions of erythromycin, pertinent for members of the interprofessional team in the treatment of patients with infections and other conditions where this agent is indicated.

Objectives:

• Describe the mechanism of antibacterial action for erythromycin.
• Outline the infectious and non-infectious indications for erythromycin.
• Review the potential adverse events associated with erythromycin.
• Explain the importance of improving care coordination among the interprofessional team to enhance the delivery of care for patients when using erythromycin.

Indications

Erythromycin is a macrolide antibiotic initially discovered in 1952. It is useful for treating various infections and also has an indication for a non-infectious pathology.

Traditionally, its use has been for various respiratory infections (i.e., community-acquired pneumonia, Legionnaires disease),[1] prophylaxis of neonatal conjunctivitis, and chlamydia. It is also FDA approved for treating skin infections, intestinal amebiasis, rheumatic fever, prophylaxis, syphilis, and pelvic inflammatory disease (PID).[2] If mixed with tretinoin cream or benzoyl peroxide, it is effective for treating acne.[3] During pregnancy, it can be used for the prevention of Group B streptococcal infection in the newborn.[4] Some literature shows specific forms of erythromycin may not be fully safe in pregnant women. Erythromycin is also used off-label for treating gastroparesis, also known as delayed gastric emptying. However, the treatment of gastroparesis is a non-FDA-approved indication.[5] 

Erythromycin is active against gram-positive bacteria, gram-negative bacteria, and several other organisms. The gram-positive bacteria include Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Listeria monocytogenes, Corynebacterium minutissimum, Corynebacterium diphtheria. The gram-negative bacteria include Legionella pneumophila, Neisseria gonorrhoeae, Haemophilus influenzae, and Bordetella pertussis. Other microorganisms covered by erythromycin include Chlamydia trachomatis, Entamoeba histolytica, Mycoplasma pneumoniae, Treponema pallidum, and Ureaplasma urealyticum.[2]  

Mechanism of Action

Erythromycin is a bacteriostatic antibiotic, which means it prevents the further growth of bacteria rather than directly destroying it. This action occurs by inhibiting protein synthesis. Erythromycin binds to the 23S ribosomal RNA molecule in the 50S subunit of the bacterial ribosome; this causes a blockage in the exiting of the peptide chain that is growing. Humans have the 40S and 60S subunits and do not have 50S subunits, so erythromycin does not affect protein synthesis in human tissues.[6][7][8][9] Resistance can develop against erythromycin. This occurs via modification of the 23S rRNA found in the 50S rRNA. The erythromycin cannot bind to the ribosome, and the bacteria can continue protein synthesis.[10][11] 

Aside from being a bacteriostatic macrolide antibiotic, erythromycin is a pro-motility drug. It is an agonist to motilin, which increases motility in the gut.[12] As erythromycin gets deactivated by gastric acid, oral tablets must either contain an ester or stable salt as part of the molecular structure or be enteric-coated. Once erythromycin is orally administered, it is easily absorbed through the gastrointestinal system. Following absorption via the gastrointestinal system, it diffuses into various tissues and phagocytes. As phagocytes circulate in the blood and induce phagocytosis of harmful bacteria, erythromycin gets released during this process.  Erythromycin is largely bound to plasma proteins, but erythromycin readily diffuses into most bodily fluids. Erythromycin is concentrated in the liver and is later excreted in bile. The liver metabolizes most of the administered erythromycin. It undergoes demethylation through the cytochrome P450 system, specifically the enzyme CYP3A4, and undergoes elimination through bile. A tiny percentage of the drug undergoes renal excretion. Erythromycin has a half-life of 1.5 hours to 2 hours. Optimal blood levels are reached when the patient takes it in a fasting state. Peak plasma concentration(Cmax) is achieved in four hours when administered with food.[13]

Administration

Routes of Administration

Erythromycin Base Filmtab tablets (erythromycin tablets, USP) are supplied as pink, unscored oval tablets. Erythromycin can also be administered intravenous, topical, and ophthalmic route.

Adults

The oral form of the medication is available in 250-mg tablets and 500-mg tablets.  For maximal absorption and minimal side effects, the patient should avoid alcohol, take on an empty stomach (1 hour before or 2 hours after meals), take a full glass of water, and avoid taking with grapefruit juice.[14] The maximum recommended oral dose is 4 grams per day. 

Children

The usual dosage is 30 to 50 mg/kg/day, in equally divided doses. For more severe infections, the maximum recommended dosage is 4 grams per day.

Pregnancy

For urogenital infections during pregnancy, the recommended dose is 500 mg of erythromycin by mouth four times a day on an empty stomach for at least 7 days.[15]

Adverse Effects

Erythromycin comes in various forms. Pregnant women should not use the form of erythromycin estolate as it may cause hepatotoxicity. It may also increase the risk of pyloric stenosis in the newborn. All antibiotics carry a significant risk of nausea, vomiting, abdominal pain, and diarrhea. Erythromycin is a motilin agonist, and this increases the likelihood of gastrointestinal side effects compared to other antibiotics.[16] All macrolide antibiotics cause QT prolongation. Azithromycin causes clinically insignificant QT prolongation. Clarithromycin causes greater QT prolongation. Erythromycin is known to cause major prolongation of the QT interval and carries a risk of torsades de pointes. This arrhythmia may cease on its own, or it may degenerate into ventricular fibrillation, which can be fatal.[17][18][19] There also exists a risk of rash, allergic reaction, and reversible deafness. Rare side effects include Stevens-Johnson syndrome, toxic epidermal necrolysis, and cholestasis.[20] Erythromycin is a cytochrome P-450 inhibitor; this means it carries the potential to interact with a broad range of medications. Given it is an inhibitor of cytochrome P-450, drugs that get metabolized via the cytochrome P-450 system would have increased concentrations, leading to an increased risk of toxicity.[21]

Contraindications

Patients who have a prolonged QT interval on an electrocardiogram (ECG) should not use erythromycin. A normal QTc interval would be less than 440 ms in males and less than 460 ms in females. Anyone using a medication that prolongs the QT interval should be very cautious and monitored if adding erythromycin. Similarly, patients diagnosed with long QT syndrome (LQTS) should not use erythromycin. Patients who have had an episode of torsades de pointes in the past should avoid QT-prolonging drugs such as erythromycin. Erythromycin is contraindicated in patients taking terfenadine, astemizole, or cisapride. [17] As erythromycin may cause serious rashes in a small number of patients, anyone who has experienced similar symptoms in the past should avoid future use of the drug. Pregnant women should avoid using erythromycin estolate as it may precipitate hepatotoxicity. Erythromycin is contraindicated in patients with known hypersensitivity to this drug.

Monitoring

Erythromycin has significant promotility activity and is used in patients with gastroparesis. The clinician should monitor the development of microbial resistance to erythromycin following its long-term use as a pro-motility agent. Liver function tests require monitoring because of the potential for rare but serious hepatic failure.[22] QT interval prolongation is a possible adverse effect and requires careful vigilance in patients with heart conditions or who take antiarrhythmic or interacting drugs. Pseudomembranous colitis has been reported with erythromycin and may range in severity from mild to life-threatening; the clinician should consider this diagnosis in patients present with severe diarrhea after its administration.[23]

Toxicity

Macrolide antibiotics have varying levels of cardiotoxicity. Erythromycin carries the most prominent risk of cardiotoxicity among the more commonly used macrolide antibiotics. It induces QT prolongation and increases the risk of the potentially deadly heart rhythm known as torsades de pointes. Careful monitoring of the QTc interval on the ECG is recommended to minimize risk. Patients at higher risk should also have their potassium, magnesium, and calcium levels monitored. There is no known reversal agent for erythromycin.[17]

Enhancing Healthcare Team Outcomes

Erythromycin causes common adverse drug reactions such as nausea, vomiting, diarrhea, and serious adverse drug reactions such as QT prolongation and pseudomembranous colitis. The clinician who is prescribing erythromycin should monitor the patient for QT prolongation. Torsades de pointes require the immediate cessation of therapy, referral to a cardiologist, and prompt treatment. Pseudomembranous colitis requires referral to a gastroenterologist. Pharmacists should check for potential drug-drug interactions as erythromycin is a known enzyme inhibitor. Pharmacists should also ensure proper medication reconciliation. The nurses can play a vital role in medication administration and patient education. 

The interprofessional team approach that includes clinicians, mid-level practitioners, nurses, and pharmacists, would maximize therapeutic efficacy, minimize the risk of adverse drug reactions, and ultimately achieves the best possible patient outcome. [Level 5]