The pill debossed with “TEVA 3147” (or “93 3147”) is a 500 mg oral formulation of Cephalexin Monohydrate, a first-generation cephalosporin antibiotic manufactured by Teva Pharmaceuticals. It is primarily prescribed to treat a broad range of susceptible bacterial infections.
Pill Identification
Attribute – Specification
- Imprint – TEVA 3147 (or 93 3147)
- Active Ingredient – Cephalexin Monohydrate (500 mg)
- Color – Red / Dark Orange-Red / Maroon
- Shape – Capsule or Capsule-shaped tablet (Oblong)
- Manufacturer – Teva Pharmaceuticals USA / Teva Canada
- Drug Class – First-Generation Cephalosporin Antibiotic (lactam)
- Prescription Status – Rx-only (Not a controlled substance)
Mechanism of Action
Cephalexin is a bactericidal lactam antibiotic:
- Inhibition of Cell Wall Synthesis: Cephalexin binds to specific penicillin-binding proteins (PBPs) located inside the bacterial cell wall.
- Lysis: This binding prevents the final transpeptidation step of peptidoglycan chain cross-linking, compromising structural integrity. Osmotic pressure causes the bacterial cell wall to rupture, resulting in bacterial cell death.
- Spectrum of Activity:
- Gram-Positive: Staphylococcus aureus (methicillin-susceptible strains only), Streptococcus pneumoniae, and Streptococcus pyogenes.
- Gram-Negative: Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae.
- Note: It is inactive against MRSA, Enterococcus species, Pseudomonas aeruginosa, and viral pathogens (e.g., influenza, common cold).
Indications and Dosage
Cephalexin 500 mg is used for susceptible respiratory tract infections, otitis media, skin and soft tissue infections (e.g., cellulitis, folliculitis), bone infections, and uncomplicated urinary tract infections (UTIs).
- Standard Adult Dosage:
- Mild to Moderate Infections / Uncomplicated UTIs: 500 mg orally every 12 hours.
- Severe or Deep-Tissue Infections: 500 mg orally every 6 hours (up to 4 g/day in severe cases).
- Pediatric Dosing: Typically 25 to 50 mg/kg/day divided into 2 to 4 doses (up to 75–100 mg/kg/day for otitis media), usually administered via oral suspension rather than 500 mg solid pills.
- Renal Impairment: Dosing intervals must be extended in patients with reduced creatinine clearance.
- Administration: Swallow whole with a glass of water. It may be taken with or without meals; taking it with food reduces gastrointestinal irritation.
Side Effects
Common Side Effects
- Gastrointestinal: Diarrhea, nausea, vomiting, indigestion, and abdominal cramps.
- Genital: Vaginal candidiasis (yeast infection) and vaginal discharge.
- Central Nervous System: Mild dizziness, fatigue, and headache.
Serious Adverse Reactions
- Clostridioides difficile-Associated Diarrhea (CDAD): Severe, persistent watery or bloody diarrhea, severe stomach cramping, and fever occurring during or weeks after treatment.
- Severe Hypersensitivity / Anaphylaxis: Hives, angioedema (facial/throat swelling), bronchospasm, or severe cutaneous reactions such as Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN).
- Hematologic & Hepatic Effects: Transient neutropenia, hemolytic anemia, eosinophilia, or elevated liver enzymes (AST/ALT) / cholestatic jaundice.
- Nephrotoxicity: Acute interstitial nephritis (rare).
Precautions and Drug Interactions
- Penicillin Allergy Cross-Reactivity: Cephalosporins should be used with caution in individuals with a documented penicillin allergy; cross-reactivity occurs in approximately 1% to 5% of patients. It is contraindicated in patients with a history of severe, immediate penicillin-induced anaphylaxis.
- Metformin Interaction: Cephalexin competes with metformin for renal tubular secretion, potentially increasing metformin plasma concentrations and elevating the risk of adverse effects.
- Probenecid: Co-administration inhibits the renal excretion of cephalexin, leading to higher and more prolonged serum concentrations.
- Diagnostic Test Interference: May cause false-positive urine glucose results when using copper sulfate tests (Benedict’s solution or Clinitest) and can produce a positive direct Coombs’ test.
- Pregnancy and Breastfeeding: FDA Pregnancy Category B. It crosses the placenta and is excreted in breast milk in low concentrations; generally considered safe under medical supervision.
Critical Warnings
- Finish Full Course: Even if symptoms resolve within a few days, the full prescribed regimen must be completed. Premature discontinuation promotes the emergence of antibiotic-resistant bacteria.
- Do Not Self-Treat Diarrhea: Anti-peristaltic drugs (like loperamide) should not be used if severe diarrhea occurs during or after therapy, as this can worsen C. difficile toxicity.
- Bacterial Specificity: Cephalexin is ineffective against viral illnesses; improper use increases future antimicrobial resistance risks.