Medication Overview: Keflex

Keflex, a first-generation cephalosporin antibiotic, is commonly used to treat infections caused by bacteria. In the market, it is available in various forms including capsules, tablets, and oral suspension. The active ingredient, cephalexin, works by disrupting the synthesis of the bacterial cell wall, leading to cell lysis. It is prescribed for bacterial infections such as respiratory tract infections, otitis media, skin and soft tissue infections, and urinary tract infections.

Mechanism of Action

Keflex interferes with the biosynthesis of peptidoglycan, a vital component of the bacterial cell wall. This disruption inhibits the final transpeptidation step of peptidoglycan synthesis, leading to weak cell walls that can rupture easily. The bactericidal activity of cephalexin is most effective against actively growing gram-positive bacteria such as Streptococcus pneumoniae and Streptococcus pyogenes. However, it also acts against select gram-negative organisms like Escherichia coli and Klebsiella pneumoniae.

Recommended Dosage

The usual adult dose is 250 mg to 1,000 mg taken every 6 hours. In some situations, an 8 or 12-hour dosing interval may be recommended. Pediatric dosages are often calculated based on bodyweight, usually 25 mg to 50 mg per kilogram of body weight per day, divided into a few doses. Duration of treatment commonly extends to about 7 to 14 days, depending on the type and severity of infection. Dose adjustments may be necessary for patients with impaired renal function.

Pharmacokinetic Properties

Cephalexin is well absorbed from the gastrointestinal tract and achieves peak plasma concentrations approximately 1 hour after oral administration. The plasma half-life is about 1 hour in individuals with normal renal function. The drug is widely distributed in body fluids and tissues, except for the central nervous system. It is primarily excreted by the kidneys, with the majority of an administered dose appearing unchanged in the urine within 6 hours.

Indications for Use

Keflex is indicated mainly for the treatment of infections caused by susceptible bacteria. These include upper respiratory tract infections, such as sinusitis and pharyngitis, and lower respiratory tract infections like bronchitis and pneumonia. It is also used for skin and soft tissue infections, including cellulitis and abscesses, and urinary tract infections causing cystitis and pyelonephritis. It is effective against bone infections such as osteomyelitis.

Contraindications

Keflex is contraindicated in patients with a known hypersensitivity to cephalexin or other cephalosporin antibiotics. It should not be administered to those with serious allergic reactions, such as anaphylaxis, to penicillin. Cross-reactivity in patients with severe penicillin allergies can occur. A detailed patient medical history and allergy profile should be reviewed before prescribing this medication.

Adverse Reactions

The most common adverse effects include gastrointestinal disturbances like diarrhea, nausea, vomiting, and abdominal pain. Allergic reactions, while less frequent, can range from mild rash to severe hypersensitivity reactions including anaphylaxis. Rare but serious side effects are cytopenias, interstitial nephritis, and pseudomembranous colitis. Patients should be monitored for symptoms of superinfection, as antibiotic treatment can disrupt normal flora.

Drug Interactions

Co-administration with probenecid can result in increased plasma concentrations of cephalexin due to reduced renal excretion. Concurrent use with oral anticoagulants like warfarin may enhance anticoagulant effects, necessitating careful monitoring of prothrombin time. The use of Keflex alongside aminoglycosides or potent diuretics should be approached cautiously due to potential nephrotoxicity risks.

Special Populations Considerations

In elderly patients, there may be a need for dosing adjustment due to the likelihood of age-related decrease in renal function. During pregnancy, Keflex should only be used if clearly needed, as controlled human studies have not been conducted. It is considered generally safe for use in lactating women, but cephalexin is secreted in small amounts in breast milk. Neonates and infants require careful dosing modifications based on their renal maturation.

Storage Guidelines

Capsules and tablets should be stored at room temperature, away from moisture and heat. Oral suspension, after reconstitution, should be refrigerated and discarded after 14 days. Ensure the medication is kept out of reach of children to avoid accidental ingestion. Each form of the medication must be stored in accordance with specific product labeling to maintain its efficacy.

Administration Instructions

Patients should be instructed to take Keflex orally, with or without food. Consistency regarding intake on a full or empty stomach should be maintained to optimize absorption. It is important to complete the full course of therapy to prevent the development of resistance, even if symptoms improve. Shaking the bottle well before each dose is advised for oral suspension to ensure proper dosing.

Monitoring Parameters

Monitoring renal function is essential, especially in patients at risk of renal impairment. Regular assessment for the resolution of infection symptoms is necessary to evaluate the therapeutic response. In patients under anticoagulant therapy, blood warfarin levels should be checked regularly. Watching for signs of allergic reactions or gastrointestinal distress can help manage adverse effects promptly.

Resistance Concerns

Bacterial resistance to cephalexin may develop in certain strains due to prolonged use, typically by fragmentation of the beta-lactam ring. Methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus species are generally not susceptible. Prescribing Keflex should always involve consideration of local bacterial resistance patterns and confirmation of strain susceptibility to prevent ineffective treatment and resistance acceleration.