Cephalexin (often recognized by the brand name Keflex) is a commonly prescribed antibiotic used to treat bacterial infections, including uncomplicated urinary tract infections (UTIs). As a first-generation cephalosporin, the medication works by interfering with the bacteria’s ability to build and maintain its cell wall. This structural inhibition ultimately stops the bacteria from growing and helps the body clear the infection. Cephalexin is effective for UTIs because a large percentage of the drug is excreted unchanged directly into the urine, where it concentrates its effects against the invading bacteria.
The Expected Timeline for Symptom Relief
Patients typically begin to experience relief from uncomfortable UTI symptoms within one to three days of starting cephalexin. The drug is quickly absorbed after being taken orally, often reaching peak concentration in the bloodstream within about an hour. This rapid absorption means the antibiotic begins working on the bacteria in the urinary tract shortly after the first dose.
Symptom relief is usually gradual, not an immediate halt to all discomfort. The first symptom to show improvement is often the burning sensation or pain associated with urination. As the bacterial load decreases, the inflammation in the bladder and urethra begins to subside.
Symptoms related to urinary frequency and urgency, which are caused by bladder irritation, may take slightly longer to fully resolve. The residual inflammation can continue to cause a frequent feeling of needing to urinate for a few days. If the UTI is more complex or severe, the timeline for noticeable relief might extend past the initial 72-hour window.
What To Look For When Assessing Effectiveness
A reduction in the intensity of the urge to urinate confirms that cephalexin is working effectively against the infection. This change indicates that the lining of the bladder is becoming less irritated by the presence of bacteria.
Changes in the appearance and smell of urine are also indicators to monitor. As the infection clears, urine that was previously cloudy or had a foul odor should begin to return to its typical color and scent. This visual change reflects the reduction of white blood cells and bacteria in the urinary tract.
The reduction in pain should include not only the burning sensation but also any lower abdominal pressure or cramping that was present. Tracking the frequency of bathroom visits, especially at night, provides objective evidence of improvement. A gradual return to a normal urination pattern over the first few days suggests the antibiotic is successfully eradicating the bacteria.
Understanding the Full Treatment Course
Even if symptoms disappear completely within the first few days, it is necessary to complete the entire prescribed course of cephalexin. A typical course for an uncomplicated UTI often lasts between five and seven days, though some prescriptions may extend to 14 days. Stopping the medication early is a significant factor in the development of antibiotic resistance.
If the full course is not completed, a small number of resilient bacteria may survive the initial treatment. These surviving bacteria can then multiply, leading to a recurrence of the infection. This recurrence often involves a strain that is now partially resistant to cephalexin, making future infections much more difficult to treat.
If a dose is missed, take it as soon as it is remembered unless it is nearly time for the next scheduled dose. In that case, skip the missed dose to avoid taking two doses too close together. Compliance with the dosing schedule ensures a continuous therapeutic level of the antibiotic necessary for complete bacterial eradication.
When to Seek Urgent Medical Advice
Certain symptoms indicate that the infection is not responding to cephalexin or has spread beyond the bladder, requiring immediate medical attention. If symptoms worsen significantly or do not show any improvement after 72 hours of treatment, contact a healthcare provider promptly. This lack of response could signal that the bacteria are resistant to cephalexin or that the infection is more complex than initially thought.
Signs that the infection may have spread to the kidneys (pyelonephritis) include a persistent fever or chills. Severe pain in the back or flank area, just below the ribs, is another serious indicator. Nausea and vomiting, particularly if severe enough to prevent keeping down liquids, also warrant urgent medical evaluation.