Cephalexin is typically taken as 250 mg every 6 hours or 500 mg every 12 hours, with or without food, for 7 to 14 days depending on the infection. It comes in capsules, tablets, and a liquid suspension, and the most important thing you can do is space your doses evenly and finish the entire course, even after you start feeling better.
Standard Dosing for Adults
The usual adult dose is 250 mg taken four times a day (every 6 hours), but many prescribers simplify this to 500 mg twice a day (every 12 hours). For most common infections like skin infections, urinary tract infections, and strep throat, treatment runs 7 to 14 days. Strep throat specifically requires at least 10 days to fully clear the bacteria and prevent complications.
For more severe infections, your doctor may increase the total daily dose up to 4,000 mg, split into two to four doses throughout the day. The key principle is that cephalexin works best when its levels stay consistently above a certain threshold in your body, so evenly spacing your doses matters more than hitting exact clock times.
Twice Daily vs. Four Times Daily
If you’ve been prescribed cephalexin twice a day and wondered whether that’s enough, the pharmacology backs it up. A single 500 mg dose produces concentrations in the urinary tract roughly 150 times higher than what’s needed to kill susceptible bacteria, and those levels remain effective for the full 12 hours between doses. A study comparing twice-daily dosing to four-times-daily dosing for uncomplicated urinary tract infections in women found no difference in treatment failure rates: about 12.7% for twice daily versus 17% for four times daily, a gap that was not statistically significant.
Four-times-daily dosing may still be preferred for certain infections where drug levels in blood (rather than urine) matter more, since blood concentrations don’t stay elevated as long. Follow whatever schedule your prescription specifies.
Dosing for Children
Children’s doses are calculated by body weight, typically 25 to 50 mg per kilogram per day, divided into equal doses spread throughout the day. For ear infections, the dose goes higher: 75 to 100 mg per kg per day. Severe infections may also call for the higher range of 50 to 100 mg per kg daily. The maximum for any child is 4,000 mg per day. Children usually take the liquid suspension form, which your pharmacist will mix before dispensing.
Taking It With or Without Food
Cephalexin can be taken with or without food. Food does not significantly reduce the drug’s effectiveness. If the medication upsets your stomach, taking it with a meal or snack can help ease nausea or digestive discomfort, which are among the more common side effects. There’s no need to take it on an empty stomach for better absorption.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. If it’s almost time for your next scheduled dose, skip the missed one and continue with your regular schedule. Don’t double up to make up for a missed dose. Skipping doses or stopping early increases the risk that the infection won’t fully clear and that the remaining bacteria develop resistance to the antibiotic.
Why Finishing the Full Course Matters
It’s common to feel noticeably better within two or three days, but the bacteria causing your infection aren’t necessarily gone at that point. Stopping early can leave behind the hardiest organisms, which can regrow and become more difficult to treat. Finish every pill or dose of liquid in your prescription, even if your symptoms have completely resolved.
Alcohol and Cephalexin
Unlike some antibiotics that cause severe reactions with alcohol, cephalexin does not have a dangerous pharmacological interaction with drinking. The cephalosporins that cause problems with alcohol share a specific chemical structure that cephalexin lacks. Major pharmacies do not issue alcohol warnings for cephalexin. That said, alcohol can dehydrate you and strain your immune system while you’re fighting an infection, so moderation is reasonable even without a formal interaction risk.
Interactions With Other Medications
If you take metformin for diabetes, cephalexin can increase the amount of metformin circulating in your blood by about 24% and raise peak levels by roughly 34%. It does this by competing with metformin for the same pathway the kidneys use to clear both drugs. This doesn’t mean you can’t take them together, but your blood sugar may run lower than usual during your antibiotic course. Watch for symptoms of low blood sugar like shakiness, sweating, or dizziness, and let your prescriber know you’re on metformin.
Probenecid, a medication sometimes used for gout, slows the kidney’s ability to clear cephalexin. This raises cephalexin blood levels and keeps them elevated longer. Your doctor will account for this if both medications are necessary.
Safety During Pregnancy and Breastfeeding
Cephalexin is one of the antibiotics commonly prescribed during pregnancy and is considered acceptable during breastfeeding. Only small amounts pass into breast milk. After a 500 mg dose, milk levels peak around 0.7 mg/L about four hours later. An exclusively breastfed infant would receive roughly 112 micrograms per kilogram daily through milk, which is a tiny fraction (about 0.5%) of the weight-adjusted dose the mother takes, and far below the therapeutic dose used to treat infants directly.
Storing the Liquid Suspension
Capsules and tablets can be stored at room temperature. The liquid suspension, however, needs refrigeration after your pharmacist mixes it. Refrigerated suspension typically stays stable for 14 days, which lines up with the maximum treatment duration. Shake the bottle well before each dose to ensure the medication is evenly distributed. Discard any leftover liquid after you finish your course or after 14 days, whichever comes first.