CLINICAL PHARMACOLOGY SECTION.

CLINICAL PHARMACOLOGY. Orally administered erythromycin ethylsuccinate tablets are readily and reliably absorbed under both fasting and nonfasting conditions.Erythromycin diffuses readily into most body fluids. Only low concentrations are normally achieved in the spinal fluid, but passage of the drug across the blood-brain barrier increases in meningitis. In the presence of normal hepatic function, erythromycin is concentrated in the liver and excreted in the bile; the effect of hepatic dysfunction on excretion of erythromycin by the liver into the bile is not known. Less than percent of the orally administered dose of erythromycin is excreted in active form in the urine.Erythromycin crosses the placental barrier, but fetal plasma levels are low. The drug is excreted in human milk.MicrobiologyErythromycin acts by inhibition of protein synthesis by binding 50 ribosomal subunits of susceptible organisms. It does not affect nucleic acid synthesis. Antagonism has been demonstrated in vitro between erythromycin and clindamycin, lincomycin, and chloramphenicol.Many strains of Haemophilus influenzae are resistant to erythromycin alone but are susceptible to erythromycin and sulfonamides used concomitantly.Staphylococci resistant to erythromycin may emerge during course of therapy.Erythromycin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.Gram-positive organismsCorynebacterium diphtheriaeCorynebacterium minutissimumListeria monocytogenesStaphylococcus aureus (resistant organisms may emerge during treatment)Streptococcus pneumoniaeStreptococcus pyogenesGram-negative organismsBordetella pertussisLegionella pneumophilaNeisseria gonorrhoeaeOther microorganismsChlamydia trachomatisEntamoeba histolyticaMycoplasma pneumoniaeTreponema pallidumUreaplasma urealyticumThe following in vitro data are available, but their clinical significance is unknown.Erythromycin exhibits in vitro minimal inhibitory concentrations (MICs) of 0.5 mcg/mL or less against most (>= 90%) strains of the following microorganisms; however, the safety and effectiveness of erythromycin in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials.Gram-positive organismsViridans group streptococciGram-negative organismsMoraxella catarrhalisSusceptibility TestsDilution TechniquesQuantitative 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 standardized procedure. Standardized procedures are based on dilution method1 (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of erythromycin powder. The MIC values should be interpreted according to the following criteria:MIC (mcg/mL)Interpretation <= 0.5Susceptible (S)1-4Intermediate (I)>= 8Resistant (R)A report of Susceptible indicates that the pathogen is likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable. 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 high dosage of drug can be used. This category also provides buffer zone which prevents small uncontrolled technical factors from causing major discrepancies in interpretation. report of Resistant indicates that the pathogen is not likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable; other therapy should be selected.Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures. Standard erythromycin powder should provide the following MIC values:MicroorganismMIC (mcg/mL) S. aureus ATCC 292130.12-0.5E. faecalis ATCC 292121-4Diffusion TechniquesQuantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure2 requires the use of standardized inoculum concentrations. This procedure uses paper disks impregnated with 15-mcg erythromycin to test the susceptibility of microorganisms to erythromycin.Reports from the laboratory providing results of the standard single-disk susceptibility test with 15-mcg erythromycin disk should be interpreted according to the following criteria:Zone Diameter (mm)Interpretation >= 23Susceptible (S)14-22Intermediate (I)<= 13Resistant (R)Interpretation should be as stated above for results using dilution techniques. Interpretation involves correlation of the diameter obtained in the disk test with the MIC for erythromycin.As with standardized dilution techniques, diffusion methods require the use of laboratory control microorganisms that are used to control the technical aspects of the laboratory procedures. For the diffusion technique, the 15-mcg erythromycin disk should provide the following zone diameters in these laboratory test quality control strains:MicroorganismZone Diameter (mm)S. aureus ATCC 2592322-30.

DOSAGE & ADMINISTRATION SECTION.

DOSAGE AND ADMINISTRATION. Erythromycin ethylsuccinate tablets may be administered without regard to meals. To avoid unpleasant taste, the 400 mg tablets should not be chewed.ChildrenAge, weight, and severity of the infection are important factors in determining the proper dosage. In mild to moderate infections the usual dosage of erythromycin ethylsuccinate for children is 30 to 50 mg/kg/day in equally divided doses every hours. For more severe infections this dosage may be doubled. If twice-a-day dosage is desired, one-half of the total daily dose may be given every 12 hours. Doses may also be given three times daily by administering one-third of the total daily dose every hours.The following dosage schedule is suggested for mild to moderate infections:Body WeightTotal Daily DoseUnder 10 lbs30-50 mg/kg/day15-25 mg/lb/day10 to 15 lbs200 mg16 to 25 lbs400 mg26 to 50 lbs800 mg51 to 100 lbs1200 mgover 100 lbs1600 mgAdults400 mg erythromycin ethylsuccinate every hours is the usual dose. Dosage may be increased up to g per day according to the severity of the infection. If twice-a-day dosage is desired, one-half of the total daily dose may be given every 12 hours. Doses may also be given three times daily by administering one-third of the total daily dose every hours.For adult dosage calculation, use ratio of 400 mg of erythromycin activity as the ethylsuccinate to 250 mg of erythromycin activity as the stearate, base or estolate.In the treatment of streptococcal infections, therapeutic dosage of erythromycin ethylsuccinate should be administered for at least 10 days. In continuous prophylaxis against recurrences of streptococcal infections in persons with history of rheumatic heart disease, the usual dosage is 400 mg twice day.For Treatment of Urethritis Due to C. trachomatis or U. urealyticum 800 mg three times day for days. For Treatment of Primary Syphilis Adults48 to 64 given in divided doses over period of 10 to 15 days. For Intestinal Amebiasis Adults400 mg four times daily for 10 to 14 days. Children30 to 50 mg/kg/day in divided doses for 10 to 14 days. For Use in PertussisAlthough 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 to 14 days. For Treatment of Legionnaires DiseaseAlthough optimal doses have not been established, doses utilized in reported clinical data were those recommended above (1.6 to g daily in divided doses.).

INDICATIONS & USAGE SECTION.

INDICATIONS AND USAGE. To reduce the development of drug-resistant bacteria and maintain the effectiveness of erythromycin ethylsuccinate tablets and other antibacterial drugs, erythromycin ethylsuccinate tablets 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.Erythromycin ethylsuccinate tablets are indicated in the treatment of infections caused by susceptible strains of the designated organisms in the diseases listed below: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). (See appropriate sulfonamide labeling for prescribing information.)Lower-respiratory tract infections of mild to moderate severity caused by Streptococcus pneumoniae or Streptococcus pyogenes .Listeriosis caused by Listeria monocytogenes.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.Respiratory tract infections due to Mycoplasma pneumoniae .Skin and skin structure infections of mild to moderate severity caused by Streptococcus pyogenes or Staphylococcus aureus (resistant staphylococci may emerge during treatment).Diphtheria: Infections due to Corynebacterium diphtheriae as an adjunct to antitoxin, to prevent establishment of carriers and to eradicate the organism in carriers.Erythrasma: In the treatment of infections due to Corynebacterium minutissimum.Intestinal amebiasis caused by Entamoeba histolytica (oral erythromycins only). Extraenteric amebiasis requires treatment with other agents.Acute pelvic inflammatory disease caused by Neisseria gonorrhoeae: As an alternative drug in treatment of acute pelvic inflammatory disease caused by N. gonorrhoeae in female patients with history of sensitivity to penicillin. Patients should have serologic test for syphilis before receiving erythromycin as treatment of gonorrhea and follow-up serologic test for syphilis after months.Syphilis 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.Erythromycins are indicated for the treatment of the following infections caused by Chlamydia trachomatis: Conjunctivitis of the newborn, pneumonia of infancy, and 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.When tetracyclines are contraindicated or not tolerated, erythromycin is indicated for the treatment of nongonococcal urethritis caused by Ureaplasma urealyticum.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.ProphylaxisPrevention of Initial Attacks of Rheumatic FeverPenicillin 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.3 The therapeutic dose should be administered for 10 days.Prevention of Recurrent Attacks of Rheumatic FeverPenicillin 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).3.

PRECAUTIONS SECTION.

PRECAUTIONS. GeneralPrescribing erythromycin ethylsuccinate tablets in the absence of proven or strongly suspected bacterial infection or 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. (See CLINICAL PHARMACOLOGY and WARNINGS sections.)There have been reports that erythromycin may aggravate the weakness of patients with myasthenia gravis.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%) developed symptoms of non-bilious vomiting or irritability with feeding and were subsequently diagnosed as having IHPS requiring surgical pyloromyotomy. possible dose-response effect was described with an absolute risk of IHPS of 5.1% for infants who took erythromycin for 8-14 days and 10% for infants who took erythromycin for 15-21 days.4 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.Information for PatientsPatients should be counseled that antibacterial drugs including erythromycin ethylsuccinate tablets should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When erythromycin ethylsuccinate tablets is prescribed to treat 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 ethylsuccinate tablets or other antibacterial drugs in the future.Drug InteractionsErythromycin 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.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 various oral anticoagulants may be more pronounced in the elderly.Erythromycin is substrate and inhibitor of the 3A isoform subfamily of the cytochrome p450 enzyme system (CYP3A). Coadministration of erythromycin and 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/dihydroergotamineConcurrent use of erythromycin and ergotamine or dihydroergotamine has been associated in some patients with acute ergot toxicity characterized by severe peripheral vasospasm and dysesthesia.Triazolobenzodiazepines (Such as Triazolam and Alprazolam) and Related BenzodiazepinesErythromycin has been reported to decrease the clearance of triazolam and midazolam, and thus, may increase the pharmacologic effect of these benzodiazepines.HMG-CoA Reductase InhibitorsErythromycin has been reported to increase concentrations of HMG-CoA reductase inhibitors (e.g., 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. (See Viagra package insert.)There have been spontaneous or published reports of CYP3A based interactions of erythromycin with cyclosporine, carbamazepine, tacrolimus, alfentanil, disopyramide, rifabutin, quinidine, methylprednisolone, cilostazol, vinblastine, and bromocriptine.Concomitant administration of erythromycin with cisapride, pimozide, astemizole, or terfenadine is contraindicated. (See CONTRAINDICATIONS .)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. (See CONTRAINDICATIONS.) 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 coadministered 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. (See CONTRAINDICATIONS.)Drug/Laboratory Test InteractionsErythromycin interferes with the fluorometric determination of urinary catecholamines.Carcinogenesis, Mutagenesis, Impairment of FertilityLong-term (2-year) oral studies conducted in rats with erythromycin ethylsuccinate and erythromycin base did not provide evidence of tumorigenicity. Mutagenicity studies have not been conducted. There was no apparent effect on male or female fertility in rats fed erythromycin (base) at levels up to 0.25% of diet.PregnancyTeratogenic Effects.Pregnancy Category BThere is no evidence of teratogenicity or any other adverse effect on reproduction in female rats fed erythromycin base (up to 0.25% 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.Labor and DeliveryThe effect of erythromycin on labor and delivery is unknown.Nursing MothersErythromycin is excreted in human milk. Caution should be exercised when erythromycin is administered to nursing woman.Pediatric UseSee INDICATIONS AND USAGE and DOSAGE AND ADMINISTRATION sections.

REFERENCES SECTION.

REFERENCE. National Committee for Clinical Laboratory Standards, Method for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically, Third Edition. Approved Standard NCCLS Document M7-A3, Vol. 13, No. 25. NCCLS, Villanova PA, December 1993.National Committee for Clinical Laboratory Standards, Performance Standards for Antimicrobial Disk Susceptibility Tests, Fifth Edition. Approved Standard NCCLS Document M2-A5, Vol. 13, No. 24. NCCLS, Villanova PA, December 1993.Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease of the Council on Cardiovascular Disease in the Young, the American Heart Association: Prevention of Rheumatic Fever. Circulation. 78(4):1082-1086, October 1988.Honein, M.A., et. al.: Infantile hypertrophic pyloric stenosis after pertussis prophylaxis with erythromycin: case review and cohort study. The Lancet 1999; 354(9196):2101-5.. National Committee for Clinical Laboratory Standards, Method for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically, Third Edition. Approved Standard NCCLS Document M7-A3, Vol. 13, No. 25. NCCLS, Villanova PA, December 1993.. National Committee for Clinical Laboratory Standards, Performance Standards for Antimicrobial Disk Susceptibility Tests, Fifth Edition. Approved Standard NCCLS Document M2-A5, Vol. 13, No. 24. NCCLS, Villanova PA, December 1993.. Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease of the Council on Cardiovascular Disease in the Young, the American Heart Association: Prevention of Rheumatic Fever. Circulation. 78(4):1082-1086, October 1988.. Honein, M.A., et. al.: Infantile hypertrophic pyloric stenosis after pertussis prophylaxis with erythromycin: case review and cohort study. The Lancet 1999; 354(9196):2101-5.. Abbott LaboratoriesNorth Chicago, IL 60064, U.S.A.Relabeling and Repackaging by:Physicians Total Care, Inc.Tulsa, OK 74146.

WARNINGS SECTION.

WARNINGS. There have been reports of hepatic dysfunction, including increased liver enzymes, and hepatocellular and/or chloestatic hepatitis, with or without jaundice, occurring in patients receiving oral erythromycin products.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.Pseudomembranous colitis has been reported with nearly all antibacterial agents, including erythromycin, and may range in severity from mild to life threatening. Therefore, it is important to consider this diagnosis in patients who present with diarrhea subsequent to the administration of antibacterial agents.Treatment with antibacterial agents alters the normal flora of the colon and may permit overgrowth of clostridia. Studies indicate that toxin produced by Clostridium difficile is primary cause of antibiotic-associated colitis.After the diagnosis of pseudomembranous colitis has been established, therapeutic measures should be initiated. Mild cases of pseudomembranous colitis usually respond to discontinuation of the drug alone. In moderate to severe cases, consideration should be given to management with fluids and electrolytes, protein supplementation, and treatment with an antibacterial drug clinically effective against Clostridium difficile colitis.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. (See package insert for lovastatin.).