CEPHALEXIN

Cephalexin, USP is a semisynthetic cephalosporin antibiotic intended for oral administration. It is 7-(D-α-amino-α-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid, monohydrate. Cephalexin has the following structural formula: C 16 H 17 N 3 O 4 S•H 2 O M.W. 365.41 The nucleus of cephalexin is related to that of other cephalosporin antibiotics. The compound is a zwitterion; i.e., the molecule contains both a basic and an acidic group. The isoelectric point of cephalexin in water is approximately 4.5 to 5. The crystalline form of cephalexin which is available is a monohydrate. It is a white crystalline solid having a bitter taste. Solubility in water is low at room temperature; 1 or 2 mg/mL may be dissolved readily, but higher concentrations are obtained with increasing difficulty. The cephalosporins differ from penicillins in the structure of the bicyclic ring system. Cephalexin has a D -phenylglycyl group as substituent at the 7-amino position and an unsubstituted methyl group at the 3-position. Each capsule contains cephalexin monohydrate equivalent to 250 mg (720 μmol) or 500 mg (1,439 μmol) of cephalexin. Inactive Ingredients: CAPSULES: magnesium stearate, silicon dioxide, and sodium starch glycolate. Capsule Shell and Print Constituents: black iron oxide, D&C Yellow #10 Aluminum Lake, FD&C Blue #1 Aluminum Lake, FD&C Blue #2 Aluminum Lake, FD&C Red #40 Aluminum Lake, gelatin, pharmaceutical glaze modified in SD-45, silicon dioxide or carboxymethylcellulose sodium, sodium lauryl sulfate, titanium dioxide and may contain propylene glycol. In addition, the 250 mg capsule shell contains yellow iron oxide. After mixing, each 5 mL of cephalexin for oral suspension USP will contain cephalexin monohydrate equivalent to 125 mg (360 μmol) or 250 mg (720 μmol) of cephalexin. Inactive Ingredients: SUSPENSION: FD&C Red #40, cherry mixed fruit flavor (artificial flavors, benzyl alcohol, maltodextrin, and modified corn starch), silicon dioxide, sodium benzoate, sugar (fruit granulated), and xanthan gum. Each tablet contains cephalexin monohydrate equivalent to 250 mg (720 μmol) or 500 mg (1,439 μmol) of cephalexin. Inactive Ingredients: TABLETS: hypromellose, magnesium stearate, microcrystalline cellulose, polyethylene glycol, polysorbate 80, sodium starch glycolate, and titanium dioxide. cephalexin structural formula

Cephalexin is indicated for the treatment of the following infections when caused by susceptible strains of the designated microorganisms: Respiratory tract infections caused by Streptococcus pneumoniae and Streptococcus pyogenes (Penicillin is the usual drug of choice in the treatment and prevention of streptococcal infections, including the prophylaxis of rheumatic fever. Cephalexin is generally effective in the eradication of streptococci from the nasopharynx; however, substantial data establishing the efficacy of cephalexin in the subsequent prevention of rheumatic fever are not available at present.) Otitis media due to Streptococcus pneumoniae, Haemophilus influenzae , Staphylococcus aureus , Streptococcus pyogenes , and Moraxella catarrhalis Skin and skin structure infections caused by Staphylococcus aureus and/or Streptococcus pyogenes Bone infections caused by Staphylococcus aureus and/or Proteus mirabilis Genitourinary tract infections, including acute prostatitis, caused by Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae Note —Culture and susceptibility tests should be initiated prior to and during therapy. Renal function studies should be performed when indicated. To reduce the development of drug-resistant bacteria and maintain the effectiveness of cephalexin capsules, cephalexin for oral suspension, cephalexin tablets, and other antibacterial drugs, cephalexin capsules, cephalexin for oral suspension, and cephalexin 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.

Cephalexin is administered orally. Adults The adult dosage ranges from 1 to 4 g daily in divided doses. The 333 mg and 750 mg strengths should be administered such that the daily dose is within 1 to 4 grams per day. The usual adult dose is 250 mg every 6 hours. For the following infections, a dosage of 500 mg may be administered every 12 hours: streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis in patients over 15 years of age. Cystitis therapy should be continued for 7 to 14 days. For more severe infections or those caused by less susceptible organisms, larger doses may be needed. If daily doses of cephalexin greater than 4 g are required, parenteral cephalosporins, in appropriate doses, should be considered. Pediatric Patients The usual recommended daily dosage for pediatric patients is 25 to 50 mg/kg in divided doses. For streptococcal pharyngitis in patients over 1 year of age and for skin and skin structure infections, the total daily dose may be divided and administered every 12 hours. Cephalexin Suspension Weight 125 mg/5 mL 250 mg/5 mL 10 kg (22 lb) 1/2 to 1 tsp q.i.d. 1/4 to 1/2 tsp q.i.d. 20 kg (44 lb) 1 to 2 tsp q.i.d. 1/2 to 1 tsp q.i.d. 40 kg (88 lb) 2 to 4 tsp q.i.d. 1 to 2 tsp q.i.d. Or Weight 125 mg/5 mL 250 mg/5 mL 10 kg (22 lb) 1 to 2 tsp b.i.d. 1/2 to 1 tsp b.i.d 20 kg (44 lb) 2 to 4 tsp b.i.d. 1 to 2 tsp b.i.d. 40 kg (88 lb) 4 to 8 tsp b.i.d. 2 to 4 tsp b.i.d. In severe infections, the dosage may be doubled. In the therapy of otitis media, clinical studies have shown that a dosage of 75 to 100 mg/kg/day in 4 divided doses is required. In the treatment of β-hemolytic streptococcal infections, a therapeutic dosage of cephalexin should be administered for at least 10 days. Directions for Mixing 250 mg per 5 mL (200 mL when mixed): Prepare suspension at time of dispensing. Add to the bottle a total of 140 mL of water. For ease in preparation, tap bottle to loosen powder, add the water in 2 portions, shaking well after each addition. The resulting suspension will contain cephalexin monohydrate equivalent to 250 mg cephalexin in each 5 mL (teaspoonful). * After mixing, store in refrigerator. May be kept for 14 days without significant loss of potency.

Cephalexin is contraindicated in patients with known allergy to the cephalosporin group of antibiotics.

Gastrointestinal Onset of pseudomembranous colitis may occur during or after antibacterial treatment (see WARNINGS ). Nausea and vomiting have been reported rarely. The most frequent side effect has been diarrhea. It was very rarely severe enough to warrant cessation of therapy. Dyspepsia, gastritis, and abdominal pain have also occurred. As with some penicillins and some other cephalosporins, transient hepatitis and cholestatic jaundice have been reported rarely. Hypersensitivity AlIergic reactions in the form of rash, urticaria, angioedema, and, rarely, erythema multiforme, Stevens-Johnson syndrome, or toxic epidermal necrolysis have been observed. These reactions usually subsided upon discontinuation of the drug. In some of these reactions, supportive therapy may be necessary. Anaphylaxis has also been reported. Other reactions have included genital and anal pruritus, genital moniliasis, vaginitis and vaginal discharge, dizziness, fatigue, headache, agitation, confusion, hallucinations, arthralgia, arthritis, and joint disorder. Reversible interstitial nephritis has been reported rarely. Eosinophilia, neutropenia, thrombocytopenia, hemolytic anemia, and slight elevations in AST and ALT have been reported. In addition to the adverse reactions listed above that have been observed in patients treated with cephalexin, the following adverse reactions and altered laboratory tests have been reported for cephalosporin class antibiotics: Adverse Reactions Fever, colitis, aplastic anemia, hemorrhage, renal dysfunction, and toxic nephropathy. Several cephalosporins have been implicated in triggering seizures, particularly in patients with renal impairment when the dosage was not reduced (see INDICATIONS AND USAGE and PRECAUTIONS , General ). If seizures associated with drug therapy should occur, the drug should be discontinued. Anticonvulsant therapy can be given if clinically indicated. Altered Laboratory Tests Prolonged prothrombin time, increased BUN, increased creatinine, elevated alkaline phosphatase, elevated bilirubin, elevated LDH, pancytopenia, leukopenia, and agranulocytosis. To report SUSPECTED ADVERSE EVENTS, contact FDA at 1-800-FDA-1088 or www.fda.gov.

Metformin In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin mean C max and AUC increased by an average of 34% and 24%, respectively, and metformin mean renal clearance decreased by 14%. No information is available about the interaction of cephalexin and metformin following multiple doses of either drug. Although not observed in this study, adverse effects could potentially arise from coadministration of cephalexin and metformin by inhibition of tubular secretion via organic cationic transporter systems. Accordingly, careful patient monitoring and dose adjustment of metformin is recommended in patients concomitantly taking cephalexin and metformin. Probenecid As with other β-lactams, the renal excretion of cephalexin is inhibited by probenecid.