Cephalexin 500 mg is typically taken every 6 or every 12 hours, depending on your prescription. The most common schedule for 500 mg tablets is every 12 hours (twice a day), while a 250 mg dose is usually taken every 6 hours (four times a day). Your specific interval depends on the infection being treated and its severity, so the number on your prescription label is the one to follow.
Common Dosing Schedules
The FDA-approved prescribing information for cephalexin lists two standard approaches: 250 mg every 6 hours, or 500 mg every 12 hours. Both deliver roughly the same total amount of medication per day (about 1,000 mg). For more severe infections, doses can go higher, up to 4,000 mg daily split into two to four evenly spaced doses.
In practice, this means your schedule will look like one of these:
- Every 12 hours (twice daily): Take one dose in the morning and one in the evening, about 12 hours apart. For example, 8 a.m. and 8 p.m.
- Every 8 hours (three times daily): Space doses across the day, such as 7 a.m., 3 p.m., and 11 p.m.
- Every 6 hours (four times daily): Take a dose roughly four times throughout the day and night, such as 6 a.m., noon, 6 p.m., and midnight.
You don’t need to wake up in the middle of the night for most twice-daily prescriptions. But if you’ve been prescribed a dose every 6 hours, spacing them as evenly as possible through waking hours is a reasonable approach.
Why Even Spacing Matters
Cephalexin works by killing bacteria while it’s active in your bloodstream. In a person with normal kidney function, the drug’s half-life is about one hour, meaning your body clears it relatively quickly. That’s why consistent spacing is important: each dose needs to arrive before the previous one has worn off, keeping drug levels high enough to fight the infection throughout the day.
When doses are bunched too close together, you get a spike that’s higher than necessary followed by a long gap where levels drop too low. Bacteria can recover and multiply during those gaps, which makes the antibiotic less effective and can contribute to resistance. Evenly spaced doses maintain steadier levels in your system.
What to Do if You Miss a Dose
If you realize you’ve missed a dose, take it as soon as you remember. The exception is when your next scheduled dose is coming up soon. In that case, skip the missed dose entirely and continue with your regular schedule. Never double up to compensate for the one you missed.
A practical way to think about it: if you’re on a 12-hour schedule and you remember the missed dose 3 or 4 hours late, go ahead and take it, then adjust your next dose so you’re back to roughly 12 hours apart. If it’s already 10 hours since you should have taken it and your next dose is only 2 hours away, just skip ahead to the next one.
Taking It With or Without Food
Cephalexin can be taken with or without food. Food does not significantly reduce the total amount of the drug your body absorbs, though it may slightly delay how quickly it reaches peak levels in your blood. If cephalexin upsets your stomach, taking it with a small meal or snack often helps without affecting how well it works.
Kidney Function Can Change the Interval
Your kidneys are responsible for clearing cephalexin from your body. When kidney function is reduced, the drug stays in your system longer, and the half-life increases dramatically. In someone with severely impaired kidneys, the half-life can stretch from about one hour to over 15 hours.
Doctors adjust the dosing interval based on how well your kidneys filter. For people with moderately reduced kidney function, the interval typically extends to every 8 hours. With more significant impairment, it stretches to every 8 to 12 hours, and with severe impairment, every 12 to 24 hours. If you have known kidney problems, your prescriber has likely already accounted for this. The interval on your prescription label reflects these adjustments.
Finishing the Full Course
However many hours apart you’re taking your doses, the most important thing is to finish the entire prescribed course, even after you start feeling better. Stopping early leaves surviving bacteria behind, which can regrow and cause a relapse. Most cephalexin courses run 7 to 14 days depending on the type and severity of infection, though some are shorter. Stick with the schedule until every pill is gone.