Erythromycin (oral)

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# Overview
Erythromycin (oral) is an antibacterial antibiotic that is FDA approved for the treatment of upper respiratory tract infections, lower respiratory tract infections, listeriosis ,pertussis, skin and skin structure infections, diphtheria, erythrasma, syphilis, intestinal amebiasis, acute pelvic inflammatory disease, conjunctivitis of the newborn, pneumonia of infancy, urogenital infections during pregnancy, nongonococcal urethritis and legionnaires' disease.   Common adverse reactions include nausea, vomiting, abdominal pain, diarrhea and anorexia.

# Adult Indications and Dosage

## FDA-Labeled Indications and Dosage (Adult)
- Upper respiratory tract infections of mild to moderate degree caused by Streptococcus pyogenes, Streptococcus pneumoniae, or Haemophilus influenzae (when used concomitantly with adequate doses of sulfonamides, since many strains of H. influenzae are not susceptible to the erythromycin concentrations ordinarily achieved).
- The usual dose is 250 mg four times daily in equally spaced doses. The 333 mg tablet is recommended if dosage is desired every 8 hours. If twice-a-day dosage is desired, the recommended dose is 500 mg every 12 hours. Dosage may be increased up to 4 g per day according to the severity of the infection. However, twice-a-day dosing is not recommended when doses larger than 1 g daily are administered.
- Lower respiratory tract infections of mild to moderate severity caused by Streptococcus pneumoniae or Streptococcus pyogenes.
- The usual dose is 250 mg four times daily in equally spaced doses. The 333 mg tablet is recommended if dosage is desired every 8 hours. If twice-a-day dosage is desired, the recommended dose is 500 mg every 12 hours. Dosage may be increased up to 4 g per day according to the severity of the infection. However, twice-a-day dosing is not recommended when doses larger than 1 g daily are administered.
- caused by Listeria monocytogenes.
- The usual dose is 250 mg four times daily in equally spaced doses. The 333 mg tablet is recommended if dosage is desired every 8 hours. If twice-a-day dosage is desired, the recommended dose is 500 mg every 12 hours. Dosage may be increased up to 4 g per day according to the severity of the infection. However, twice-a-day dosing is not recommended when doses larger than 1 g daily are administered.
- Pertussis (whooping cough) caused by Bordetella pertussis. Erythromycin is effective in eliminating the organism from the nasopharynx of infected individuals rendering them noninfectious. Some clinical studies suggest that erythromycin may be helpful in the prophylaxis of pertussis in exposed susceptible individuals.
- Although optimal dosage and duration have not been established, doses of erythromycin utilized in reported clinical studies were 40 to 50 mg/kg/day, given in divided doses for 5 to 14 days.
- The usual dose is 250 mg four times daily in equally spaced doses. The 333 mg tablet is recommended if dosage is desired every 8 hours. If twice-a-day dosage is desired, the recommended dose is 500 mg every 12 hours. Dosage may be increased up to 4 g per day according to the severity of the infection. However, twice-a-day dosing is not recommended when doses larger than 1 g daily are administered.
- Skin and skin structure infections of mild to moderate severity caused by Streptococcus pyogenes or Staphylococcus aureus (resistant staphylococci may emerge during treatment).
- The usual dose is 250 mg four times daily in equally spaced doses. The 333 mg tablet is recommended if dosage is desired every 8 hours. If twice-a-day dosage is desired, the recommended dose is 500 mg every 12 hours. Dosage may be increased up to 4 g per day according to the severity of the infection. However, twice-a-day dosing is not recommended when doses larger than 1 g daily are administered.
- Infections due to Corynebacterium diphtheriae, as an adjunct to antitoxin, to prevent establishment of carriers and to eradicate the organism in carriers.
- The usual dose is 250 mg four times daily in equally spaced doses. The 333 mg tablet is recommended if dosage is desired every 8 hours. If twice-a-day dosage is desired, the recommended dose is 500 mg every 12 hours. Dosage may be increased up to 4 g per day according to the severity of the infection. However, twice-a-day dosing is not recommended when doses larger than 1 g daily are administered.
- In the treatment of infections due to Corynebacterium minutissimum.
- The usual dose is 250 mg four times daily in equally spaced doses. The 333 mg tablet is recommended if dosage is desired every 8 hours. If twice-a-day dosage is desired, the recommended dose is 500 mg every 12 hours. Dosage may be increased up to 4 g per day according to the severity of the infection. However, twice-a-day dosing is not recommended when doses larger than 1 g daily are administered.
- caused by Treponema pallidum: Erythromycin is an alternate choice of treatment for primary syphilis in penicillin-allergic patients. In primary syphilis, spinal fluid examinations should be done before treatment and as part of follow-up after therapy.
- 30 to 40 g given in divided doses over a period of 10 to 15 days.
- caused by Entamoeba histolytica (oral erythromycins only). Extraenteric amebiasis requires treatment with other agents.
- 500 mg every 12 hours, 333 mg every 8 hours or 250 mg every 6 hours for 10 to 14 days.
- Acute pelvic inflammatory disease caused by Neisseria gonorrhoeae: Erythromycin lactobionate for injection, USP followed by erythromycin base orally as an alternative drug in treatment of acute pelvic inflammatory disease caused by N. gonorrhoeae in female patients with a history of sensitivity to penicillin. Patients should have a serologic test for syphilis before receiving erythromycin as treatment of gonorrhea and a follow-up serologic test for syphilis after 3 months.
- 500 mg Erythrocin Lactobionate-I.V. (erythromycin lactobionate for injection, USP) every 6 hours for 3 days, followed by 500 mg of erythromycin base orally every 12 hours, or 333 mg of erythromycin base orally every 8 hours for 7 days.
- Erythromycins are indicated for the treatment of the urogenital infections during pregnancy. When tetracyclines are contraindicated or not tolerated, erythromycin is indicated for the treatment of uncomplicated urethral, endocervical, or rectal infections in adults due to Chlamydia trachomatis.
- Although the optimal dose and duration of therapy have not been established, the suggested treatment is 500 mg of erythromycin by mouth four times a day or two erythromycin 333 mg tablets orally every 8 hours on an empty stomach for at least 7 days. For women who cannot tolerate this regimen, a decreased dose of one erythromycin 500 mg tablet orally every 12 hours, one 333 mg tablet orally every 8 hours or 250 mg by mouth four times a day should be used for at least 14 days.
- For adults with uncomplicated urethral, endocervical, or rectal infections caused by Chlamydia trachomatis, when tetracycline is contraindicated or not tolerated: 500 mg of erythromycin by mouth four times a day or two 333 mg tablets orally every 8 hours for at least 7 days.
- When tetracyclines are contraindicated or not tolerated, erythromycin is indicated for the treatment of nongonococcal urethritis caused by Ureaplasma urealyticum.
- 500 mg of erythromycin by mouth four times a day or two 333 mg tablets orally every 8 hours for at least seven days.
- Legionnaires' disease caused by Legionella pneumophila. Although no controlled clinical efficacy studies have been conducted, in vitro and limited preliminary clinical data suggest that erythromycin may be effective in treating Legionnaires' Disease.
- Although optimal dosage has not been established, doses utilized in reported clinical data were 1 to 4 g daily in divided doses.
- Prevention of Initial Attacks of Rheumatic Fever
- Penicillin is considered by the American Heart Association to be the drug of choice in the prevention of initial attacks of rheumatic fever (treatment of Streptococcus pyogenes infections of the upper respiratory tract, e.g., tonsillitis or pharyngitis). Erythromycin is indicated for the treatment of penicillin-allergic patients. The therapeutic dose should be administered for ten days.
- Prevention of Recurrent Attacks of Rheumatic Fever
- Penicillin or sulfonamides are considered by the American Heart Association to be the drugs of choice in the prevention of recurrent attacks of rheumatic fever. In patients who are allergic to penicillin and sulfonamides, oral erythromycin is recommended by the American Heart Association in the long-term prophylaxis of streptococcal pharyngitis (for the prevention of recurrent attacks of rheumatic fever).
- To reduce the development of drug-resistant bacteria and maintain the effectiveness of Erythromycin Delayed-release Capsules and other antibacterial drugs, Erythromycin Delayed-release Capsules should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

## Off-Label Use and Dosage (Adult)

### Guideline-Supported Use
- Developed by: CDC/NIH/IDSA
- Class of Recommendation: Class IIb
- Strength of Evidence: Category C
- Dosing Information
- Erythromycin 500 mg orally or IV every 6 hours for at least 3 months.
- Developed by: CDC
- Class of Recommendation: Class IIa
- Strength of Evidence: Category C
- Dosing Information
- Erythromycin base 500 mg orally three times daily for 7 days.
- Developed by: CDC
- Class of Recommendation: Class IIb
- Strength of Evidence: Category C
- Dosing Information
- Erythromycin base 500 mg orally four times daily for at least 3 weeks and until all lesions have healed completely.
- Developed by: The Infectious Diseases Society of America
- Class of Recommendation: Class IIb
- Strength of Evidence: Category C
- Dosing Information
- Erythromycin 500 mg PO QID.
- Developed by: CDC/NIH/IDSA GUIDELINES
- Class of Recommendation: Class IIb
- Strength of Evidence: Category C
- Dosing Information
- Erythromycin base 500 mg orally four times a day for 21 days.

### NonGuideline-Supported Use
- Dosing Information
- Erythromycin 250 mg 4 times daily in adults.
- Dosing Information
- Erythromycin 250 mg.

# Pediatric Indications and Dosage

## FDA-Labeled Indications and Dosage (Pediatric)
- Conjunctivitis of the Newborn Caused by Chlamydia trachomatis.
- Oral erythromycin suspension 50 mg/kg/day in 4 divided doses for at least 2 weeks.
- Pneumonia of Infancy Caused by Chlamydia trachomatis.
- Although the optimal duration of therapy has not been established, the recommended therapy is oral erythromycin suspension 50 mg/kg/day in 4 divided doses for at least 3 weeks.
- Age, weight, and severity of the infection are important factors in determining the proper dosage. The usual dosage is 30 to 50 mg/kg/day, in equally divided doses. For more severe infections, this dose may be doubled but should not exceed 4 g per day.
- In the treatment of streptococcal infections of the upper respiratory tract (e.g., tonsillitis or pharyngitis), the therapeutic dosage of erythromycin should be administered for at least ten days.
- The American Heart Association suggests a dosage of 250 mg of erythromycin orally, twice a day in long-term prophylaxis of streptococcal upper respiratory tract infections for the prevention of recurring attacks of rheumatic fever in patients allergic to penicillin and sulfonamides.4
- 30 to 50 mg/kg/day in divided doses for 10 to 14 days.

## Off-Label Use and Dosage (Pediatric)

### Guideline-Supported Use
There is limited information regarding Off-Label Guideline-Supported Use of Erythromycin in pediatric patients.

### NonGuideline-Supported Use
There is limited information regarding Off-Label NonGuideline-Supported Use of Erythromycin in pediatric patients.

# Contraindications
- Erythromycin is contraindicated in patients with known hypersensitivity to this antibiotic.
- Erythromycin is contraindicated in patients taking terfenadine, astemizole, cisapride, pimozide, ergotamine, or dihydroergotamine.

# Warnings
- Hepatotoxicity
- There have been reports of hepatic dysfunction, including increased liver enzymes, and hepatocellular and/or cholestatic hepatitis, with or without jaundice, occurring in patients receiving oral erythromycin products.
- QT Prolongation
- Erythromycin has been associated with prolongation of the QT interval and infrequent cases of arrhythmia. Cases of torsades de pointes have been spontaneously reported during postmarketing surveillance in patients receiving erythromycin. Fatalities have been reported. Erythromycin should be avoided in patients with known prolongation of the QT interval, patients with ongoing proarrhythmic conditions such as uncorrected hypokalemia or hypomagnesemia, clinically significant bradycardia, and in patients receiving Class IA (quinidine, procainamide) or Class III (dofetilide, amiodarone, sotalol) antiarrhythmic agents. Elderly patients may be more susceptible to drug-associated effects on the QT interval.
- Syphilis in pregnancy
- There have been reports suggesting that erythromycin does not reach the fetus in adequate concentration to prevent congenital syphilis. Infants born to women treated during pregnancy with oral erythromycin for early syphilis should be treated with an appropriate penicillin regimen.
- Clostridium difficile-associated diarrhea
- Clostridium difficile-associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including Erythromycin Delayed-release Capsules, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of C. difficile.
- C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.
- If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated.
- Drug Interactions
- Serious adverse reactions have been reported in patients taking erythromycin concomitantly with CYP3A4 substrates. These include colchicine toxicity with colchicine; rhabdomyolysis with simvastatin, lovastatin, and atorvastatin; and hypotension with calcium channel blockers metabolized by CYP3A4 (for example, verapamil, amlodipine, diltiazem).
- There have been post-marketing reports of colchicine toxicity with concomitant use of erythromycin and colchicine. This interaction is potentially life-threatening, and may occur while using both drugs at their recommended doses.
- Rhabdomyolysis with or without renal impairment has been reported in seriously ill patients receiving erythromycin concomitantly with lovastatin. Therefore, patients receiving concomitant lovastatin and erythromycin should be carefully monitored for creatine kinase (CK) and serum transaminase levels.

### Precautions
- Prescribing Erythromycin Delayed-release Capsules in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.
- Since erythromycin is principally excreted by the liver, caution should be exercised when erythromycin is administered to patients with impaired hepatic function.
- Exacerbation of symptoms of myasthenia gravis and new onset of symptoms of myasthenic syndrome has been reported in patients receiving erythromycin therapy.
- There have been reports of infantile hypertrophic pyloric stenosis (IHPS) occurring in infants following erythromycin therapy. In one cohort of 157 newborns who were given erythromycin for pertussis prophylaxis, seven neonates (5 percent) developed symptoms of non bilious vomiting or irritability with feeding and were subsequently diagnosed as having IHPS requiring surgical pyloromyotomy. A possible dose-response effect was described with an absolute risk of IHPS of 5.1 percent for infants who took erythromycin for 8 to 14 days and 10 percent for infants who took erythromycin for 15 to 21 days.5 Since erythromycin may be used in the treatment of conditions in infants which are associated with significant mortality or morbidity (such as pertussis or neonatal Chlamydia trachomatis infections), the benefit of erythromycin therapy needs to be weighed against the potential risk of developing IHPS. Parents should be informed to contact their physician if vomiting or irritability with feeding occurs.
- Prolonged or repeated use of erythromycin may result in an overgrowth of nonsusceptible bacteria or fungi. If superinfection occurs, erythromycin should be discontinued and appropriate therapy instituted.
- When indicated, incision and drainage or other surgical procedures should be performed in conjunction with antibiotic therapy.

# Adverse Reactions

## Clinical Trials Experience
- The most frequent side effects of oral erythromycin preparations are gastrointestinal and are dose-related. They include nausea, vomiting, abdominal pain, diarrhea and anorexia. Symptoms of hepatitis, hepatic dysfunction and/or abnormal liver function test results may occur.
- Onset of pseudomembranous colitis symptoms may occur during or after antibacterial treatment.
- Erythromycin has been associated with QT prolongation and ventricular arrhythmias, including ventricular tachycardia and torsades de pointes.
- Allergic reactions ranging from urticaria to anaphylaxis have occurred. Skin reactions ranging from mild eruptions to erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis have been reported rarely.
- There have been reports of interstitial nephritis coincident with erythromycin use.
- There have been reports of pancreatitis and convulsions.
- There have been isolated reports of reversible hearing loss occurring chiefly in patients with renal insufficiency and in patients receiving high doses of erythromycin.

## Postmarketing Experience
There is limited information regarding Postmarketing Experience of Erythromycin in the drug label.

# Drug Interactions
- Theophylline
- Erythromycin use in patients who are receiving high doses of theophylline may be associated with an increase in serum theophylline levels and potential theophylline toxicity. In case of theophylline toxicity and/or elevated serum theophylline levels, the dose of theophylline should be reduced while the patient is receiving concomitant erythromycin therapy.
- There have been published reports suggesting that when oral erythromycin is given concurrently with theophylline there is a significant decrease in erythromycin serum concentrations of approximately 35 percent. The mechanism by which this interaction occurs is unknown. The decrease in erythromycin concentrations due to co-administration of theophylline could result in subtherapeutic concentrations of erythromycin.
- Hypotension, bradyarrhythmias, and lactic acidosis have been observed in patients receiving concurrent verapamil, belonging to the calcium channel blockers drug class.
- Concomitant administration of erythromycin and digoxin has been reported to result in elevated digoxin serum levels.
- There have been reports of increased anticoagulant effects when erythromycin and oral anticoagulants were used concomitantly. Increased anticoagulation effects due to interactions of erythromycin with oral anticoagulants may be more pronounced in the elderly.
- Erythromycin is a substrate and inhibitor of the 3A isoform subfamily of the cytochrome P450 enzyme system (CYP3A). Co-administration of erythromycin and a drug primarily metabolized by CYP3A may be associated with elevations in drug concentrations that could increase or prolong both the therapeutic and adverse effects of the concomitant drug. Dosage adjustments may be considered, and when possible, serum concentrations of drugs primarily metabolized by CYP3A should be monitored closely in patients concurrently receiving erythromycin.
- The following are examples of some clinically significant CYP3A based drug interactions. Interactions with other drugs metabolized by the CYP3A isoform are also possible. The following CYP3A based drug interactions have been observed with erythromycin products in post-marketing experience:
- Ergotamine/dihydroergotamine
- Post-marketing reports indicate that co-administration of erythromycin with ergotamine or dihydroergotamine has been associated with acute ergot toxicity characterized by vasospasm and ischemia of the extremities and other tissues including central nervous system. Concomitant administration of erythromycin with ergotamine or dihydroergotamine is contraindicated.
- Triazolobenzodiazepines (such as triazolam and alprazolam) and related benzodiazepines
- Erythromycin has been reported to decrease the clearance of triazolam and midazolam, and thus, may increase the pharmacologic effect of these benzodiazepines.
- HMG-CoA Reductase Inhibitors
- Erythromycin has been reported to increase concentrations of HMG-CoA reductase inhibitors (for example, lovastatin and simvastatin). Rare reports of rhabdomyolysis have been reported in patients taking these drugs concomitantly.
- Sildenafil (Viagra)
- Erythromycin has been reported to increase the systemic exposure (AUC) of sildenafil. Reduction of sildenafil dosage should be considered.
- There have been spontaneous or published reports of CYP3A based interactions of erythromycin with carbamazepine, cyclosporine, tacrolimus, alfentanil, disopyramide, bromocriptine, rifabutin, quinidine, methylprednisolone, cilostazol, and vinblastine.
- Concomitant administration of erythromycin with cisapride, pimozide, astemizole, or terfenadine is contraindicated.
- In addition, there have been reports of interactions of erythromycin with drugs not thought to be metabolized by CYP3A, including hexobarbital, phenytoin, and valproate.
- Erythromycin has been reported to significantly alter the metabolism of the nonsedating antihistamines terfenadine and astemizole when taken concomitantly. Rare cases of serious cardiovascular adverse events, including electrocardiographic QT/QTc interval prolongation, cardiac arrest, torsades de pointes, and other ventricular arrhythmias have been observed. In addition, deaths have been reported rarely with concomitant administration of terfenadine and erythromycin.
- There have been post-marketing reports of drug interactions when erythromycin was co-administered with cisapride, resulting in QT prolongation, cardiac arrhythmias, ventricular tachycardia, ventricular fibrillation, and torsades de pointes, most likely due to the inhibition of hepatic metabolism of cisapride by erythromycin. Fatalities have been reported.
- Colchicine
- Colchicine is a substrate for both CYP3A4 and the efflux transporter P-glycoprotein (P-gp). Erythromycin is considered a moderate inhibitor of CYP3A4. A significant increase in colchicine plasma concentration is anticipated when co-administered with moderate CYP3A4 inhibitors such as erythromycin. If co-administration of colchicine and erythromycin is necessary, the starting dose of colchicine may need to be reduced, and the maximum colchicine dose should be lowered. Patients should be monitored for clinical symptoms of colchicine toxicity.

# Use in Specific Populations

### Pregnancy
Pregnancy Category (FDA): B
- Pregnancy Category B
- There was no evidence of teratogenicity or any other adverse effect on reproduction in female rats fed erythromycin base (up to 0.25 percent of diet) prior to and during mating, during gestation, and through weaning of two successive litters. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Pregnancy Category (AUS):
- Australian Drug Evaluation Committee (ADEC) Pregnancy Category
There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Erythromycin in women who are pregnant.

### Labor and Delivery
- The effect of erythromycin on labor and delivery is unknown.

### Nursing Mothers
- Erythromycin is excreted in human milk. Caution should be exercised when erythromycin is administered to a nursing woman.

### Pediatric Use
There is no FDA guidance on the use of Erythromycin with respect to pediatric patients.

### Geriatic Use
- Clinical studies with Erythromycin Delayed-release Capsules did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of the decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.
- Elderly patients may be more susceptible to development of torsades de pointes arrhythmias than younger patients.
- Elderly patients may experience increased effects of oral anticoagulant therapy while undergoing treatment with erythromycin.
- Erythromycin Delayed-release Capsules (250 mg) do not contain sodium or potassium.

### Gender
There is no FDA guidance on the use of Erythromycin with respect to specific gender populations.

### Race
There is no FDA guidance on the use of Erythromycin with respect to specific racial populations.

### Renal Impairment
There is no FDA guidance on the use of Erythromycin in patients with renal impairment.

### Hepatic Impairment
There is no FDA guidance on the use of Erythromycin in patients with hepatic impairment.

### Females of Reproductive Potential and Males
There is no FDA guidance on the use of Erythromycin in women of reproductive potentials and males.

### Immunocompromised Patients
There is no FDA guidance one the use of Erythromycin in patients who are immunocompromised.

# Administration and Monitoring

### Administration
- Oral

### Monitoring
There is limited information regarding Monitoring of Erythromycin in the drug label.

# IV Compatibility
There is limited information regarding IV Compatibility of Erythromycin in the drug label.

# Overdosage

## Acute Overdose
- In case of overdosage, erythromycin should be discontinued. Overdosage should be handled with the prompt elimination of unabsorbed drug and all other appropriate measures should be instituted.
Erythromycin is not removed by peritoneal dialysis or hemodialysis.

## Chronic Overdose
There is limited information regarding Chronic Overdose of Erythromycin in the drug label.

# Pharmacology

## Mechanism of Action
- Erythromycin acts by inhibition of protein synthesis by binding 50 S ribosomal subunits of susceptible organisms. It does not affect nucleic acid synthesis.

## Structure
- Erythromycin Delayed-release Capsules contain enteric-coated pellets of erythromycin base for oral administration.
- Each Erythromycin Delayed-release Capsule contains 250 mg of erythromycin base.
- Inactive Ingredients
- Cellulosic polymers, citrate ester, D&C Red No. 30, D&C Yellow No. 10, magnesium stearate and povidone. The capsule shell contains FD&C Blue No. 1, FD&C Red No. 3, gelatin, and titanium dioxide.
- Erythromycin is produced by a strain of Saccharopolyspora erythraea (formerly Streptomyces erythraeus) and belongs to the macrolide group of antibiotics. It is basic and readily forms salts with acids but it is the base which is microbiologically active. Erythromycin base is (3R*, 4S*, 5S*, 6R*, 7R*, 9R*, 11R*, 12R*, 13S*, 14R*)-4--14-ethyl-7,12,13-trihydroxy-3,5,7,9,11,13-hexamethyl-6-oxy]oxacyclotetradecane-2,10-dione.

## Pharmacodynamics
There is limited information regarding Pharmacodynamics of Erythromycin in the drug label.

## Pharmacokinetics
- Orally administered erythromycin base and its salts are readily absorbed in the microbiologically active form. Interindividual variations in the absorption of erythromycin are, however, observed, and some patients do not achieve acceptable serum levels. Erythromycin is largely bound to plasma proteins, and the freely dissociating bound fraction after administration of erythromycin base represents 90% of the total erythromycin absorbed. After absorption, erythromycin diffuses readily into most body fluids. In the absence of meningeal inflammation, low concentrations are normally achieved in the spinal fluid, but the passage of the drug across the blood-brain barrier increases in meningitis. The drug is excreted in human milk. The drug crosses the placental barrier, but fetal plasma levels are low. Erythromycin is not removed by peritoneal dialysis or hemodialysis.
- In the presence of normal hepatic function erythromycin is concentrated in the liver and is excreted in the bile; the effect of hepatic dysfunction on biliary excretion of erythromycin is not known. After oral administration, less than 5% of the administered dose can be recovered in the active form in the urine.
- The enteric coating of pellets in Erythromycin Delayed release Capsules protects the erythromycin base from inactivation by gastric acidity. Because of their small size and enteric coating, the pellets readily pass intact from the stomach to the small intestine and dissolve efficiently to allow absorption of erythromycin in a uniform manner. After administration of a single dose of a 250 mg Erythromycin Delayed-release Capsule, peak serum levels in the range of 1.13 to 1.68 mcg/mL are attained in approximately 3 hours and decline to 0.30 to 0.42 mcg/mL in 6 hours. Optimal conditions for stability in the presence of gastric secretion and for complete absorption are attained when erythromycin is taken on an empty stomach.
- Mechanism of Resistance
- The major route of resistance is modification of the 23S rRNA in the 50S ribosomal subunit to insensitivity, while efflux can also be significant.
- Interaction with other Antimicrobials
- Antagonism exists in vitro between erythromycin and clindamycin, lincomycin, and chloramphenicol. Erythromycin has been shown to be active against most isolates of the following bacteria both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.
- Gram-positive bacteria:
- Corynebacterium diphtheriae
- Corynebacterium minutissimum
- Listeria monocytogenes
- Staphylococcus aureus
- Streptococcus pneumoniae
- Streptococcus pyogenes
- Gram-negative bacteria:
- Bordetella pertussis
- Haemophilus influenzae
- Legionella pneumophila
- Neisseria gonorrhoeae
- Other Microorganisms:
- Chlamydia trachomatis
- Entamoeba histolytica
- Mycoplasma pneumoniae
- Treponema pallidum
- Ureaplasma urealyticum
- Susceptibility Test Methods
- When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drugs used in resident hospitals to the physician as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting an antibacterial drug for treatment.
- Dilution techniques
- Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized test method1,2 (broth and/or agar). The MIC values should be interpreted according to criteria provided in Table 1.
- Diffusion techniques
- Quantitative methods that require measurement of zone diameters can also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The zone size provides an estimate of the susceptibility of bacteria to antimicrobial compounds. The zone size should be determined using a standardized test method.2,3 This procedure uses paper disks impregnated with 15 mcg erythromycin to test the susceptibility of microorganisms to erythromycin. The disc diffusion interpretive criteria are provided in Table 1.
- A report of Susceptible indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations at the site of infection necessary to inhibit growth of the pathogen. A report of Intermediate indicates that the result should be considered equivocal, and, if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated or in situations where a high dosage of drug can be used. This category also provides a buffer zone which prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of Resistant indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations usually achievable at the infection site; other therapy should be selected.
- Quality Control
- Standardized susceptibility test procedures require the use of laboratory controls to monitor and ensure the accuracy and precision of supplies and reagents used in the assay, and the techniques of the individuals performing the test.1,2,3,4 Standard erythromycin powder should provide the following range of MIC values noted in Table 2. For the diffusion technique using the erythromycin 15 mcg disk the criteria in Table 2 should be achieved.

## Nonclinical Toxicology
There is limited information regarding Nonclinical Toxicology of Erythromycin in the drug label.

# Clinical Studies
There is limited information regarding Clinical Studies of Erythromycin in the drug label.

# How Supplied
- Erythromycin Delayed-release Capsules, USP, are clear and opaque maroon capsules bearing the Product Code ER with pink and yellow particles containing 250 mg of erythromycin supplied in bottles of 100 (NDC 24338-120-13)
- Recommended storage
- Store at 20 to 25C (68 to 77F) 
- Protect from moisture and excessive heat.

## Storage
There is limited information regarding Erythromycin (oral) Storage in the drug label.

# Images

## Drug Images

## Package and Label Display Panel

# Patient Counseling Information
- Patients should be counseled that antibacterial drugs including Erythromycin Delayed-release Capsules should only be used to treat bacterial infections. They do not treat viral infections (for example, the common cold). When Erythromycin Delayed-release Capsules are prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by Erythromycin Delayed-release Capsules or other antibacterial drugs in the future.
- Diarrhea is a common problem caused by antibiotics which usually ends when the antibiotic is discontinued. Sometimes after starting treatment with antibiotics, patients can develop watery and bloody stools (with or without stomach cramps and fever) even as late as two or more months after having taken the last dose of the antibiotic. If this occurs, patients should contact their physician as soon as possible.

# Precautions with Alcohol
- Alcohol-Erythromycin interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.

# Brand Names
- ERYTHROMYCIN

# Look-Alike Drug Names
There is limited information regarding Erythromycin (oral) Look-Alike Drug Names in the drug label.

# Drug Shortage Status

# Price