Cephalexin Pediatric Dose Calculator (Keflex)
Use this cephalexin pediatric dose calculator to convert mg/kg targets into exact mL for common Keflex liquid strengths like 125 mg/5 mL and 250 mg/5 mL, then match the plan to strep, skin, or urinary infection dosing.
Cephalexin (Keflex) dosage chart by weight for children (250 mg/5 mL)
For children 1 year and older: cephalexin doses with 250 mg/5 mL suspension for strep throat and skin infections, given twice a day. Use the column that matches the dose your child's prescriber ordered, and the calculator above for ear or bladder infections, other schedules or 125 mg/5 mL.
- Give the mL on your pharmacy label. Differences of up to about 0.5 mL are just rounding; if it differs by more, call the pharmacist. Don't change the dose yourself.
- This chart is only for 250 mg/5 mL. 125 mg/5 mL needs twice the mL: use the calculator above for any other bottle.
- Ear infections, bladder infections and some skin infections use 3 or 4 doses a day: use the calculator above, not this chart.
| Weight (lb) | Weight (kg) | Strep throat: 20 mg/kg twice a daymL of 250 mg/5 mL suspension per dose (mg it contains) | Skin infection: 25 mg/kg twice a day (50 mg/kg/day)mL of 250 mg/5 mL suspension per dose (mg it contains) |
|---|---|---|---|
| 20check age: 1 year and older | 9.1 | 3.6 mL (180 mg) | 4.5 mL (225 mg) |
| 25check age: 1 year and older | 11.3 | 4.5 mL (225 mg) | 5.5 mL (275 mg) |
| 30 | 13.6 | 5.5 mL (275 mg) | 7 mL (350 mg) |
| 35 | 15.9 | 6.5 mL (325 mg) | 8 mL (400 mg) |
| 40 | 18.1 | 7.5 mL (375 mg) | 9 mL (450 mg) |
| 45 | 20.4 | 8 mL (400 mg) | 10 mL (500 mg) |
| 50 | 22.7 | 9 mL (450 mg) | 11.5 mL (575 mg) |
| 55 | 24.9 | 10 mL (500 mg) | 12.5 mL (625 mg) |
| 60 | 27.2 | 10 mL (500 mg) max dose | 13.5 mL (675 mg) |
| 65 | 29.5 | 10 mL (500 mg) max dose | 14.5 mL (725 mg) |
| 70 | 31.8 | 10 mL (500 mg) max dose | 16 mL (800 mg) |
| 75 | 34 | 10 mL (500 mg) max dose | 17 mL (850 mg) |
| 80 | 36.3 | 10 mL (500 mg) max dose | 18 mL (900 mg) |
- Strep throat: 20 mg/kg per dose twice a day for 10 days, max 500 mg per dose (IDSA).
- Skin infection: 25-50 mg/kg/day, split twice a day (label); the chart shows the upper end, 25 mg/kg per dose. Many prescribers use less.
- Under 1 year: the label's pediatric dosing is for children over 1 year; use only as a clinician directs.
- Bigger children are often prescribed less than the skin column (for example 500 mg every 12 hours, the usual adult dose); the prescription wins.
- Kidney disease: the dose is often lower; follow the prescription. Tell the prescriber about a penicillin or cephalosporin allergy.
- mL is rounded to 0.1 mL under 5 mL and to 0.5 mL from 5 mL (AAP metric dosing), never above the maximum; use an oral syringe. For doses over 10 mL, fill a 10 mL syringe more than once.
dose calculator basics
Keflex pediatric dose calculator details
Use this Keflex calculator as the fast parent page for weight-based dose checks, mL conversion, common strengths, and the practical safety steps that generic calculator sites often skip.
Formula
mL per dose = (child weight in kg x prescribed mg/kg/day / doses per day) / medication concentration in mg per mL.
Worked example
For a 20 kg child using 50 mg/kg/day divided 2 times daily with 125 mg/5 mL, calculate the daily mg target, divide by the schedule, then convert that mg amount into mL for the selected product.
Safety checks before using the result
- Use the exact product strength in hand before measuring the dose.
- Confirm maximum dose, age limits, and indication-specific cautions when they apply.
- Escalate urgent symptoms or medication reactions instead of repeating doses from calculator output alone.
Specific dosing support
Common formulation searches for Keflex
Practical dosing guide
Before you measure the dose
Use this page to match a cephalexin prescription to the exact liquid or capsule strength before the first dose. Keflex is the brand name for cephalexin.
- Cephalexin dose check
- Use the prescribed mg/kg target, then match it to the exact liquid strength in hand because 125 mg/5 mL and 250 mg/5 mL suspensions turn the same mg dose into different mL amounts.
- Skin and soft-tissue infections
- Cephalexin is commonly used when a child needs an oral regimen for uncomplicated skin or soft-tissue infections and can take several scheduled doses per day.
- Strep throat
- Cephalexin is also used for strep in some children, but the final schedule can look different from a skin-infection plan, so match the prescription to the indication and interval.
Keflex pediatric medication summary
Cephalexin (Keflex) treats common pediatric skin, urinary, and strep infections. The pediatric dose calculator translates mg/kg dosing into exact mL or tablet schedules for the product in hand.
Reserve for nonpurulent cellulitis, impetigo, and mild osteomyelitis step-down when cultures confirm MSSA; add MRSA coverage when purulence or risk factors are present.
Frequent dosing (every 6–8 hours) and renal adjustment in severe impairment are required to maintain time-dependent killing; counsel families about adherence before discharge.
Keflex indications and common pediatric uses
Keflex (cephalexin) is a first-generation cephalosporin used for selected pediatric infections when organism susceptibility and clinical context support narrower beta-lactam coverage.
Uncomplicated skin and soft tissue infections (impetigo, cellulitis)
Group A streptococcal pharyngitis
Uncomplicated urinary tract infection (cystitis)
Acute hematogenous osteomyelitis or septic arthritis (step-down therapy)
How to give Keflex
- Keflex is a practical first-generation cephalosporin for many pediatric bacterial infections, particularly skin and soft-tissue disease, when dosing and adherence are executed well.
- Reconstitute the suspension with the exact amount of water, shake for 10–15 seconds before each dose, and measure with a calibrated oral syringe or dosing cup. Give doses at evenly spaced intervals (BID, TID, or QID) based on the prescription, and store the suspension in the refrigerator for up to 14 days. Encourage families to complete the full course even if the child feels better to prevent recurrence and resistance.
Keflex side effects, contraindications, and interactions
Keflex (cephalexin) is usually well tolerated in children when dosed and monitored appropriately. The most common adverse effects are gastrointestinal, especially loose stools, while severe allergic and severe cutaneous reactions are rare but high-risk events that require immediate discontinuation and evaluation.
Common side effects
- Gastrointestinal Effects: Loose stools, nausea, and abdominal discomfort are the most frequent complaints and are often mild. Support with hydration and food-with-dose strategies when needed. Escalate rapidly for bloody stool, persistent watery diarrhea, fever, or significant abdominal cramping because these patterns raise concern for C. difficile-associated colitis.
- Allergic and Skin Reactions: Mild rash can occur, but clinicians should actively screen for high-risk features (widespread rash, mucosal involvement, blistering, facial swelling, breathing symptoms). Prior immediate beta-lactam reactions require careful risk review before treatment. Stop cephalexin and seek urgent care for severe or progressive skin findings.
- Central Nervous System Effects: Headache, dizziness, or fatigue may occur and are usually transient. If symptoms persist, worsen, or affect school/safety, reassess hydration, illness progression, and alternative causes rather than assuming expected drug effect.
Safety checks
- History of anaphylaxis, angioedema, or severe skin reaction to cephalexin or any cephalosporin
- Severe immediate penicillin allergy with anaphylaxis when alternative antibiotics are available
- Renal impairment requiring dose adjustment
- History of severe C. difficile colitis
- Concurrent anticoagulation/bleeding disorders
- Phenylketonuria when using suspensions containing aspartame
Drug interactions
- Review the full medication list with a clinician or pharmacist before combining therapies.
Keflex mechanism and clinical pearls
Keflex (cephalexin) works by targeting the bacterial cell wall, which is the protective outer layer that gives bacteria their shape and structural integrity. As a first-generation cephalosporin, Keflex belongs to the beta-lactam family of antibiotics, which means it has a special chemical structure that allows it to interfere with bacterial cell wall construction. Think of bacterial cell walls like the framework of a house - they're essential for keeping the bacteria intact and functioning properly. Keflex works by binding to specific proteins called penicillin-binding proteins (PBPs) that bacteria use like construction workers to build and maintain their cell walls. When Keflex attaches to these proteins, it's like removing the construction crew from a building site, making it impossible for bacteria to repair or build proper cell walls. Without functional cell walls, bacteria become weak and eventually burst due to the pressure from their internal contents, much like a balloon that loses its structural integrity. What makes Keflex particularly effective is its strong activity against gram-positive bacteria, especially Staphylococcus aureus and Streptococcus pyogenes, which are the most common causes of skin and soft tissue infections in children. Unlike some newer antibiotics that try to cover many different types of bacteria, Keflex is specifically optimized to work very well against these common pediatric pathogens. The drug has excellent penetration into skin and soft tissues, which is why it's so effective for treating conditions like cellulitis, impetigo, and wound infections. Once Keflex reaches the infection site, it maintains effective concentrations for several hours, which is why it can be dosed two to four times daily depending on the severity of the infection.
Keflex’s narrow coverage can work well for MSSA and strep skin infections, sparing gut flora and reducing diarrhea/C. diff risk.
Bubblegum/strawberry suspension means fewer battles—kids finish courses, leading to higher cure rates.
BID–QID options let you tailor regimens to daycare, school, and caregiver availability without sacrificing efficacy.
Focused spectrum provides superior outcomes for intended infections
Palatability dramatically affects treatment success
Frequently asked questions about Keflex
Use the mg/kg target from your clinician, enter your child's weight, and match it to the exact suspension strength in hand. Cephalexin liquids such as 125 mg/5 mL and 250 mg/5 mL turn the same mg dose into different mL amounts, so the strength matters before you measure the dose.
Yes. Keflex is a brand name for cephalexin, and dosing is based on the same mg/kg targets prescribed by your clinician.
Keflex (cephalexin) is used to treat bacterial infections in children such as skin infections (like impetigo and cellulitis), urinary tract infections, and strep throat in those with penicillin allergy. It’s effective against many gram-positive bacteria, including Streptococcus and Methicillin-sensitive Staphylococcus aureus (MSSA). It is not typically used for respiratory tract infections unless guided by susceptibility testing or allergy considerations. It will not treat viral infections like colds or the flu.
The prescribed cephalexin dose in milligrams stays the same, but the mL volume changes because the liquid strengths are different. Always check the label before measuring because 125 mg/5 mL requires twice as much liquid as 250 mg/5 mL for the same mg dose.
Most children start to improve within 2 to 3 days of starting Keflex. Symptoms like fever, redness, or pain should begin resolving by the third day. If your child is not improving or seems worse after 72 hours, contact the pediatrician for re-evaluation. It may mean the infection is resistant or a different diagnosis is needed. Always complete the prescribed course, even if your child feels better early.
If you miss a dose, give it as soon as you remember. If it’s close to the next dose, skip the missed one and resume the regular schedule. Never double up on doses. If your child vomits within 15 minutes of taking a dose, you may repeat it. If unsure, consult your pediatrician. To reduce vomiting, try giving the medication with a light snack and administer it slowly with an oral syringe aimed inside the cheek.
The most common side effects are mild stomach upset (such as diarrhea or nausea), and skin rash. Most of these do not require stopping the medication. Encourage fluids, and consider probiotics if approved by your provider. If the rash appears as hives or is accompanied by swelling or breathing difficulty, stop the medication and seek medical care. Any new symptoms should be discussed with your child’s doctor.
It depends on the type of allergy. If your child has had a mild, non-severe reaction (like a rash without other symptoms), Keflex may still be considered with caution. However, if your child had a serious reaction to penicillin (like anaphylaxis), cephalexin should usually be avoided due to the risk of cross-reactivity. Always consult your child’s pediatrician, who may refer to an allergist for further evaluation.
Use the mg/kg/day target from your clinician, enter your child's weight, and select the 250 mg/5 mL strength. The calculator converts that into mL per dose and the correct split schedule.
Sources reviewed for Keflex
idsa-ssti-2014
dailymed-cephalexin-2024
cdc-gas-pharyngitis-2024
aap-uti-2011
pids-osteomyelitis-2021
Cephalexin - DailyMed
U.S. National Library of Medicine
Source