Spectrum and indications
Cephalexin is a first-generation cephalosporin, one of the earliest representatives of a class developed as an alternative to penicillins. Its mechanism of action, like other β-lactam antibiotics, is inhibition of bacterial cell wall synthesis, leading to cell lysis and death. Although newer cephalosporins cover a broader spectrum, cephalexin retains an important place in outpatient therapy because of its oral availability, predictable safety, and effectiveness against common community pathogens.
Its spectrum is strongest against Gram-positive bacteria. It is highly active against Streptococcus pyogenes, Streptococcus pneumoniae, and methicillin-sensitive Staphylococcus aureus (MSSA). This makes it suitable for skin and soft tissue infections such as cellulitis, impetigo, and uncomplicated abscesses when the organism is not resistant.
Cephalexin also covers selected Gram-negative organisms, including Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae. This allows its use in certain urinary tract infections and mild respiratory infections, provided resistance is not present. It is less reliable against organisms like Haemophilus influenzae or Neisseria gonorrhoeae, for which higher-generation cephalosporins or other drug classes are preferred.
Clinically, cephalexin is prescribed for:
- Skin and soft tissue infections, particularly cellulitis and wound infections.
- Respiratory tract infections such as bacterial sinusitis, pharyngitis, and mild bronchitis.
- Otitis media in children, though resistance in some pathogens may limit its use.
- Uncomplicated urinary tract infections, especially when culture confirms susceptibility.
- Dental infections, when penicillins are unsuitable.
It is not suitable for severe systemic infections, meningitis, or cases where resistant organisms such as MRSA are suspected. For broader or more complex coverage, physicians select later-generation cephalosporins or alternative antibiotics.
In short, cephalexin is best understood as a reliable first-line oral antibiotic for mild to moderate infections caused by susceptible organisms. Its effectiveness depends on correct indication and attention to local resistance trends, as outlined in Indications by condition.
Cephalexin is a dependable first-line oral option for mild to moderate infections when organisms are susceptible and indications are chosen correctly.
Forms and administration
Cephalexin is formulated exclusively for oral use, which differentiates it from many other cephalosporins that also have injectable preparations. This makes it especially practical for outpatient treatment, where hospital admission is unnecessary.
The most common dosage forms are capsules and tablets, typically available in strengths of 250 mg and 500 mg. These are suitable for adults and older children who can swallow solid medicines. In addition, oral suspension are widely used in pediatrics, supplied as powders that must be reconstituted with water. Standard concentrations include 125 mg/5 mL and 250 mg/5 mL. Once mixed, suspensions should be stored according to instructions, usually refrigerated, and shaken before each dose to ensure accuracy.
Since cephalexin is only available orally, patient adherence is crucial. Unlike single-dose therapies such as azithromycin, cephalexin often requires dosing several times per day, which increases the risk of missed doses. Consistency ensures stable blood concentrations and effective bacterial clearance. Food has little effect on absorption, so tablets and suspensions can be taken with or without meals. However, taking them with food may reduce the likelihood of stomach upset. Patients should follow the schedule precisely, as skipping doses weakens therapeutic impact and encourages bacterial survival. Further practical advice on dosage forms and their handling is provided in Forms.
In outpatient settings, cephalexin’s oral-only nature is an advantage: it allows early treatment without hospital resources. But it also limits its role in severe infections, where intravenous agents are necessary. Thus, it is best seen as a reliable home-treatment antibiotic for well-defined, mild to moderate infections.
Dosages and regimens
Cephalexin dosing is straightforward but must be tailored to the infection’s severity, the site of infection, and the patient’s age and weight. Because the drug is eliminated primarily by the kidneys, dosing intervals are structured to maintain adequate concentrations in the blood and tissues without accumulation.
In adults, typical regimens are 250–500 mg every six hours or 500 mg every twelve hours, depending on the condition and physician preference. In more severe infections, doses may be increased to a total daily maximum of 4 g, divided across the day. For example, cellulitis or severe respiratory infections may require 500 mg every six hours, while milder pharyngitis can often be controlled with 250 mg every six hours.
In children, dosing is calculated by weight, usually 25–50 mg/kg/day, divided into doses every six or twelve hours. For more severe infections, the daily dose can be increased up to 100 mg/kg, not exceeding the adult maximum. Suspensions allow precise adjustment, but accurate measuring devices are essential, as emphasized in
Dosing children.
Course length varies according to indication. Pharyngitis is typically treated for 10 days to prevent complications such as rheumatic fever. Skin infections may require 7–14 days, depending on depth and response. Uncomplicated urinary tract infections often respond to shorter courses, but therapy should always be based on culture results when available. One of the most important rules is to complete the prescribed course, even if symptoms improve early. Stopping too soon allows bacteria to survive and potentially develop resistance. Guidance on managing missed doses, food intake, and course completion is provided in How to take. For adults, general dosing principles are outlined in Dosing adults, which reinforce the importance of precise intervals.
Overall, cephalexin’s regimens are flexible but require discipline. Regular intake at the prescribed intervals is essential to ensure that infections are cured and that resistance is not promoted.
Safety profile and tolerability
Cephalexin is generally well tolerated and has a safety record that supports its use in both adults and children. The majority of adverse effects are mild and reversible, but patients should still be aware of potential complications.
The most common issues are gastrointestinal. Diarrhea, abdominal discomfort, and mild nausea occur in some patients, usually resolving after the course is finished. These effects are linked to disruption of gut flora, a risk shared by all antibiotics. While usually minor, persistent diarrhea can signal a more serious condition such as Clostridioides difficile–associated colitis. Patients who develop severe watery diarrhea should stop treatment and seek medical care immediately. Skin reactions are another possible side effect. Rashes may appear during therapy, but not all represent true allergies. In some cases, the rash is mild and transient; in others, it may indicate hypersensitivity. Rarely, severe allergic reactions such as hives, swelling, or even anaphylaxis occur, particularly in patients with a history of penicillin allergy.
Other reported but less frequent effects include dizziness, fatigue, headache, or vaginal candidiasis due to disturbance of the natural microbiome. Very rarely, liver enzyme abnormalities or blood count changes are observed.
Compared with many other antibiotics, cephalexin has a favorable tolerability profile. Its long-standing use in pediatric practice underscores its reliability, especially in uncomplicated infections. Parents should nevertheless monitor children closely for rash, diarrhea, or unusual fatigue during therapy.
A more comprehensive overview of antibiotic-related side effects, including how to distinguish mild reactions from emergencies, is available in Side effects overview.
Contraindications and interactions
Cephalexin is contraindicated in patients with a known allergy to cephalosporins or a history of severe hypersensitivity to other β-lactams, such as penicillins. Cross-reactivity is possible, meaning a patient who has experienced anaphylaxis to penicillin should avoid cephalexin as well. For patients with only mild, non-allergic rashes, the decision must be individualized by a physician.
Renal impairment warrants caution, since cephalexin is excreted mainly unchanged by the kidneys. In such patients, dosing intervals may need adjustment to prevent accumulation and toxicity. Close monitoring is recommended for older adults or those with reduced kidney function.
Drug interactions, while less extensive than with some antibiotics, still matter. Cephalexin can enhance the effects of anticoagulants such as warfarin, raising bleeding risk. Concomitant use with metformin may increase the risk of lactic acidosis by reducing its renal clearance, though this is rare. As with other antibiotics, cephalexin can also interfere with the efficacy of oral typhoid vaccines, which should not be administered during or shortly after antibiotic therapy.
Patients should always inform their healthcare provider about other medications they are taking, since interactions, even if infrequent, can alter safety. Broader discussion of drug compatibility is available in Drug interactions.
Buying cephalexin safely online
Since cephalexin is a common first-line antibiotic, it is widely advertised on the internet, often without requiring a prescription. This ease of access may appear convenient, but it carries significant risks. Counterfeit or substandard cephalosporins are a persistent problem in unregulated online markets. Tablets may contain too little active ingredient, no antibiotic at all, or even harmful substances. Such products not only fail to treat infections but also encourage resistance by exposing bacteria to ineffective doses.
Legally, cephalexin is a prescription-only medication. This rule is not bureaucratic formality but a safeguard: only a physician can determine whether cephalexin is appropriate for the infection, the right dose, and the necessary course length. Self-diagnosis and self-purchase bypass these safeguards, increasing the risk of misuse and complications.
The safe way to access cephalexin online is through telemedicine services, where a patient completes a health questionnaire and, if appropriate, receives an electronic prescription. This prescription is then filled by a licensed pharmacy, ensuring authenticity and correct labeling. The legal framework is outlined in Is it legal, and a practical verification guide for online pharmacies is provided in Checklist – safe pharmacy.
Patients should also keep in mind that cephalexin is not always the best choice. For instance, in uncomplicated urinary tract infections, alternatives such as Nitrofurantoin may be more effective. Professional evaluation is crucial to match the antibiotic to the infection.
In total, buying cephalexin online is safe only when done with a prescription and through regulated pharmacies. Any shortcut exposes the patient to ineffective or dangerous drugs and contributes to the global problem of resistance.