If you accidentally took a double dose of cephalexin, serious harm is unlikely for most adults. An upset stomach, nausea, or diarrhea is the most likely result. Two things call for a faster phone call: kidney disease and taking metformin. Do not take more, and call your pharmacist or Poison Control at 1-800-222-1222 before your next dose.
Cephalexin leaves fast through healthy kidneys. The FDA label for cephalexin capsules says over 90% of a dose is gone in the urine within 8 hours. In a 10-year review of 876 double-dose cases at the California Poison Control System, antimicrobials (the group that includes antibiotics) were "well tolerated," and there were no deaths in any case.
This article provides general information about medication management and is not a substitute for professional medical advice. Always consult your doctor or pharmacist before making changes to your medication schedule. Consult your doctor or pharmacist for advice specific to your medications.
Can I Take 2 Cephalexin 500 mg at One Time?
Check the strength first. Cephalexin capsules come in 250 mg and 500 mg and 750 mg, so two capsules can mean very different totals. If your pharmacy label says to take two capsules at a time, that was your dose, not a double dose.
Each total sits next to an amount doctors give on purpose, chosen for one person and one reason. None of them is a safe limit for you.
| What you took | Total cephalexin | Where doctors use this amount on purpose |
|---|---|---|
| Two 250 mg capsules | 500 mg | One dose in the label's every-12-hours adult schedule |
| Two 500 mg capsules | 1,000 mg | A small 2023 trial gave adults 1,000 mg four times a day for a skin infection |
| Two 750 mg capsules | 1,500 mg | The American Heart Association lists one 2 g dose before dental work for some heart patients allergic to penicillin |
The second-row trial was small: 66 adults with a skin infection were prescribed 1,000 mg or 500 mg four times a day for 7 days. Among the 62 followed up, side effects were more common at the higher dose (38.7% vs 25.8%), mostly nausea or vomiting (9.7% vs 3.2%) and diarrhea (16.1% vs 6.5%). No one stopped the antibiotic because of them. It left out people with severe kidney disease.
What Happens If You Take Cephalexin Too Close Together?
Doses a few hours apart can still overlap in your blood. The label says levels peak about 1 hour after a dose and can still be measured 6 hours later.
The US label's usual adult schedule is 250 mg every 6 hours or 500 mg every 12 hours. On the 6-hour plan, your next dose comes soon, so call before it is due. Have this ready:
- The strength on the bottle and how many capsules you took.
- The times you took them.
- Your schedule, such as every 6 hours or every 12 hours.
- Kidney problems, if you have them.
- Metformin or probenecid, if you take either. The cephalexin label flags both.
Do not skip doses on your own to "even it out." The UK's NHS says 1 extra dose of cefalexin (the UK spelling) is unlikely to harm you, and to speak to a pharmacist or doctor if you take 2 or more extra doses. For late doses, it suggests at least 4 hours between doses. See also this 4 times a day medication schedule and taking antibiotics earlier than scheduled.
How Long Does Cephalexin Stay in Your System?
Not long, if your kidneys work normally. (Other antibiotics clear at very different speeds.) In the label's studies, over 90% of the drug was gone in the urine within 8 hours.
When kidneys are slow, cephalexin can stay longer. The label tells doctors to watch those patients longer "for toxicity and drug interactions due to delayed clearance."
Can You Take Cephalexin With Kidney Disease?
Yes, at lower doses, and this is where a double dose matters most. The label sorts kidney function by creatinine clearance, a lab measure your doctor may have on file.
- With moderately reduced function (creatinine clearance 30 to 59 mL/min), the label tells prescribers to keep the whole day at or under 1 g. Two 500 mg capsules already make 1 g.
- Below 30 mL/min and not on dialysis, it tells prescribers to keep each dose at 250 mg and space doses further apart.
- Older adults are more likely to have reduced kidney function, the label notes.
The label warns that several cephalosporins, the family cephalexin belongs to, have been linked to seizures, "particularly in patients with renal impairment when the dosage was not reduced." A 2008 review found that older adults, people with kidney problems, and people with past brain or nerve conditions may be more prone to these effects, including confusion and seizures.
Poison Control adds that medicines taken at or near their maximum dose leave the least room for error. If you have kidney disease, are on dialysis, or are an older adult unsure how your kidneys are doing, call Poison Control or your pharmacist now instead of waiting to see how you feel.
Cephalexin and Metformin Taken Together
If you take metformin for diabetes, say so when you call. (Doubled your metformin instead? Read what to do after a double dose of metformin.) The cephalexin label says cephalexin raises metformin blood levels and slows how fast the kidneys clear it. It recommends careful monitoring and a metformin dose adjustment, and its summary says to monitor for low blood sugar.
In a small study of 12 healthy volunteers who took one 500 mg dose of each drug, metformin's peak level rose 34% on average. That was a normal cephalexin dose, so it does not show what a double dose does.
Cephalexin Overdose Symptoms
The label says symptoms of a cephalexin overdose may include nausea, vomiting, upper stomach discomfort, diarrhea, and blood in the urine. MedlinePlus lists "pink, red, or dark brown urine" among overdose symptoms.
| What you notice | What it may mean | What to do |
|---|---|---|
| Nausea, vomiting, stomach pain, loose stools | On the label's overdose list, and cephalexin's most common side effects | Sip fluids. Call your pharmacist if it is severe or will not settle |
| Pink, red, or dark brown urine | Blood in the urine, on the label's overdose list | Call Poison Control or your doctor today |
| Confusion, agitation, or seeing things | Listed side effects, more of a concern with kidney disease | Call Poison Control now |
| Watery or bloody diarrhea, even weeks later | A gut infection (C. difficile) the label warns can follow antibiotics | Call your prescriber |
| A seizure, collapse, trouble breathing, or a swollen face or lips | An emergency | Call 911 |
Poison Control says often no treatment is needed for an antibiotic overdose, and milder stomach cases can usually be handled at home with extra fluids. The label's overdose advice is general supportive care, and it says dialysis and similar treatments "have not been established as beneficial."
When Symptoms Are Not From the Extra Cephalexin
Not every new symptom comes from the second capsule.
Hives or swelling. The label lists allergic reactions separately from overdose symptoms. It says cross-reactions may occur in up to 10% of people with a history of penicillin allergy. For a rash, itching, or hives, MedlinePlus says to call your doctor immediately or get emergency medical treatment. Facial swelling or trouble breathing needs 911.
Pink urine from the infection. Cephalexin treats urinary tract infections, per the label, and the NIDDK lists "cloudy, bloody, or strong-smelling urine" among bladder infection symptoms. Mention it when you call anyway.
Genital itching or a yeast infection. The label lists both as cephalexin side effects, apart from its overdose list.
Confusion in an older adult. MedlinePlus notes that in older people, mental changes or confusion are often the only signs of a UTI. Confusion is also a cephalexin side effect, so call either way.
Can You Double Up on Cephalexin If You Miss a Dose?
No. MedlinePlus says to take a missed dose when you remember, or skip it if the next one is almost due: "Do not take a double dose to make up for a missed one." For missed doses in general, see the missed antibiotic dose guide.
Accidentally Gave Your Dog a Double Dose of Cephalexin?
The numbers on this page are for people. Call your veterinarian or a pet poison line:
- ASPCA Animal Poison Control: (888) 426-4435, 24 hours a day. A consultation fee may apply.
- Pet Poison Helpline: (855) 764-7661. An $89 per-incident fee applies.
Have the bottle and the dose times ready. The same goes if your dog got into your capsules.
How Pillo Helps
Cephalexin's every-6-hours schedule is one of the hardest to keep. In a review of 76 studies using electronic pill bottles, people took their prescribed doses 79% of the time on once-a-day schedules but 51% on four-times-a-day schedules. Four doses a day also means four chances to wonder, "Did I take that one?"
Pillo's persistent alarm keeps going until you respond, and confirmed doses land in your history, not your memory. Dose spacing alerts flag doses scheduled too close together. Tracking a child's or dog's antibiotic too? Dependents Management, part of Pillo's paid plan, gives each one its own schedule. Our guide to managing your pet's medications has more for pet owners.
Other antibiotics play out differently, as a double dose of amoxicillin shows, and the risk of taking medication twice changes a lot by drug type.
Frequently Asked Questions
What happens if I accidentally take a double dose of cephalexin?
For most adults, an upset stomach, nausea, or diarrhea is the most likely result, and the FDA label says over 90% of cephalexin clears healthy kidneys within 8 hours. Call your pharmacist or Poison Control at 1-800-222-1222 before your next dose, sooner with kidney disease or metformin.
Should I skip my next dose of cephalexin after taking two?
Do not decide on your own. Your pharmacist or Poison Control will tell you whether to take it on time, based on your strength, schedule, and kidneys. The label warns that skipping doses may make treatment less effective.
Can too much cephalexin kill you?
It is very unlikely. Poison Control reports over 25,000 antibiotic exposures at US poison centers in 2023, with 1 death. A review of 876 double-dose cases found no deaths. Kidney disease is a reason to call quickly, and a seizure or trouble breathing needs 911.
Is it OK to take a double first dose of cephalexin?
Only if your prescriber told you to. The label lists a usual adult schedule of 250 mg every 6 hours or 500 mg every 12 hours. Follow the directions on your pharmacy label.
I took 2 Keflex by mistake. Is that different from cephalexin?
MedlinePlus lists Keflex as a brand name for cephalexin, so the same steps apply. Check the strength on the bottle and call your pharmacist or Poison Control before your next dose.
What if it was my child's cephalexin dose?
The label doses children under 15 by weight, so adult numbers do not apply. Call Poison Control at 1-800-222-1222. For a similar mix-up with another antibiotic, see what to do after giving a child a double dose of amoxicillin.
Sources
- Cephalexin capsules 250 mg and 500 mg, FDA prescribing information on DailyMed (National Library of Medicine), Aurobindo
- Cephalexin capsules 750 mg, FDA prescribing information on DailyMed (National Library of Medicine), Aurobindo
- Yadav et al., High-dose cephalexin for cellulitis: a pilot randomized controlled trial (CJEM, 2023)
- Correia et al., A 10-year review of single medication double-dose ingestions in the nation's largest poison control system (Clinical Toxicology, 2019)
- Jayasagar et al., Effect of cephalexin on the pharmacokinetics of metformin in healthy human volunteers (Drug Metabolism and Drug Interactions, 2002)
- Grill and Maganti, Cephalosporin-induced neurotoxicity (Annals of Pharmacotherapy, 2008)
- Claxton et al., A systematic review of the associations between dose regimens and medication compliance (Clinical Therapeutics, 2001)
- American Heart Association: Prevention of Viridans Group Streptococcal Infective Endocarditis (Circulation, 2021)
- MedlinePlus: Cephalexin
- MedlinePlus: Bladder infection, adults
- NIDDK: Symptoms and causes of bladder infection in adults
- Poison Control: Antibiotics, overdose vs. misuse
- Poison Control: Double dosing, what to do if you take too much
- NHS: How and when to take cefalexin
- ASPCA Animal Poison Control
- Pet Poison Helpline
