Cephalexin | Medical Uses and Indications


 Introduction to Cephalexin (Keflex)


Let's talk about cephalexin, also known by its brand name Keflex. This antibiotic was discovered in 1967 and first marketed in 1969, making it quite old. It is now available as a generic medication and is included on the World Health Organization list of essential medicines. Cephalexin is the fifth most commonly prescribed antibiotic in the United States and ranks as the 107th most prescribed drug. It is the most popular cephalosporin in Australia, where it is among the top 15 prescribed medicines.


 Improper Prescriptions and Bacterial Resistance


As an antibiotic, cephalexin is often prescribed for inappropriate reasons, with an estimated 40-60% of antibiotics used for non-appropriate indications such as viral infections. Cephalexin is effective against certain gram-positive bacteria like staph and strep, but there is an increasing problem with resistance due to overuse. It is useful against methicillin-susceptible staph but not methicillin-resistant staph (MRSA). It also has some efficacy against gram-negative bacteria such as E. coli, Proteus mirabilis, and Klebsiella pneumoniae.


 Cephalexin as a First-Generation Cephalosporin


Cephalexin belongs to the first generation of the cephalosporin family of antibiotics. Second, third, fourth, and even fifth-generation drugs offer different spectrums of activity. First-generation cephalosporins, including cephalexin, are similar to beta-lactam antibiotics, such as penicillin. They are bactericidal, killing a large number of organisms, but are inactive against anaerobes, fungi, and viruses.


 Medical Uses and Indications


Cephalexin is beneficial for treating otitis media (middle ear infection), skin and soft tissue infections like cellulitis and abscesses, certain forms of acne, respiratory infections like strep throat, and some cases of pneumonia. It can also be used to prevent bacterial infection of heart valves after dental procedures and treat urinary tract infections.


 Susceptibility and Bacterial Resistance Considerations


Determining the susceptibility of a bacteria to cephalexin requires knowledge of the local resistance patterns and sometimes a culture and sensitivity test. Resistance varies by location and can affect the choice of antibiotic.


 Interaction with Drug Metabolizing Enzymes


One advantage of cephalexin is its lack of interaction with drug-metabolizing enzymes in the liver, which means fewer cross-reactions with other drugs. It also achieves higher blood levels compared to most other antibiotics, with about 90% of the antibiotic remaining free and active in the system.


 Available Forms and Dosage


Cephalexin is available in capsules, tablets, and oral suspension in dosages of 250 mg, 500 mg, 333 mg, and 750 mg. It works by preventing peptidoglycan from forming a stable cell wall, causing bacteria to burst as they grow.


 Allergies and Adverse Reactions


The risk of allergy to cephalexin is low, but around 1-3% of penicillin-allergic individuals may have an adverse reaction to cephalexin. Those with severe penicillin allergies should avoid cephalexin. Adverse effects are generally rare, affecting around 3% of users.


 Potential Side Effects


Common side effects of cephalexin include gastrointestinal issues like diarrhea, nausea, and vomiting. Other potential effects include vaginitis or genital yeast infections, unpleasant taste, and difficulty swallowing due to the large capsule size.


Tendon Problems and Liver Enzymes


Cephalexin may rarely cause tendon problems and can increase liver enzymes. Prolonged use may lead to overgrowth of resistant bacteria.


 Clostridium Difficile-Associated Disease


A notable risk of using cephalexin and other antibiotics is the potential for C. difficile-associated disease, which can range from mild diarrhea to severe colitis.


 Overdose and Safety in Pregnancy


Overdosing on cephalexin usually causes mild symptoms such as nausea and vomiting. It appears safe for use during pregnancy and breastfeeding.


 Renal Function and Drug Interactions


Patients with decreased renal function should use cephalexin cautiously. Drug interactions with probenecid and other medications can affect cephalexin's blood levels and effectiveness.


 Conclusion: Generic Cephalexin as an Inexpensive Option


Generic cephalexin is an affordable option for treating minor bacterial infections such as staph, strep, middle ear infections, and urinary tract infections. Overuse of antibiotics leads to resistance issues, so cephalexin should only be used for susceptible bacterial infections and not for viruses or the common cold.

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