Veterinary Dermatology

Cephalexin for Dog Skin Infections: Dosing, Duration, and Side Effects

Based on peer reviewed veterinary research · For educational purposes only · Updated October 2026 · 9 min read

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Key Takeaways

Cephalexin is a first-generation cephalosporin antibiotic and the first-tier empirical choice for canine superficial bacterial folliculitis under international veterinary guidelines.
Published dosing for canine pyoderma is 15 to 30 mg/kg given orally every 12 hours, with many dermatologists using the upper end of that range for skin.
Superficial pyoderma usually needs at least 21 days of therapy, continued 7 days past visible resolution. Deep pyoderma often needs 4 to 8 weeks.
Gastrointestinal upset is the most common adverse effect, and giving the dose with food reduces it without meaningfully lowering absorption.
Cephalexin has no activity against yeast, so concurrent Malassezia overgrowth will persist unless it is addressed topically.

Products for this topic

Chlorhexidine Spray

Antiseptic chlorhexidine spray for localized bacterial skin problems, scabs, hot spots and minor wounds.

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Chlorhexidine Shampoo

Medicated chlorhexidine shampoo for widespread bacterial skin problems and recurring pyoderma.

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What Is Cephalexin and What Does It Treat in Dogs?

Cephalexin is a first-generation cephalosporin antibiotic used in dogs to treat bacterial skin infections, most commonly superficial bacterial folliculitis (the clinical term for the classic pyoderma that produces papules, pustules, and epidermal collarettes). It is a beta-lactam drug, meaning it kills bacteria by binding penicillin-binding proteins and blocking cross-linking of the bacterial cell wall, which causes the organism to rupture under its own internal pressure.

The reason cephalexin sits at the top of the veterinary dermatology formulary is the organism it targets. Staphylococcus pseudintermedius is the causative agent in the large majority of canine pyoderma cases, and wild-type (non-resistant) strains of this organism remain predictably susceptible to first-generation cephalosporins. The 2014 International Society for Companion Animal Infectious Diseases (ISCAID) antimicrobial guidelines list cephalexin among the first-tier drugs that can be selected empirically, meaning without waiting on a culture, in an uncomplicated first-time infection.

Cephalexin is not a broad answer to every itchy dog. It treats bacteria. It does nothing to demodex mites, nothing to dermatophytes, nothing to allergy, and nothing to yeast. A dog placed on cephalexin who is still itching at week three usually does not need a stronger antibiotic, it needs a correct second diagnosis. Understanding that distinction is covered further in Antiseptic vs Antibiotic for Dog Skin: When to Use Each.

What Is the Correct Cephalexin Dose for a Dog?

Published veterinary dosing for canine pyoderma is 15 to 30 mg/kg administered orally every 12 hours. ISCAID guidance cites this range, and clinical dermatology practice commonly favours the upper portion of it, near 25 to 30 mg/kg twice daily, because skin and hair follicle tissue concentrations sit lower than plasma concentrations. Some protocols use 22 mg/kg every 8 hours for deep infections where penetration is the limiting factor.

Only your veterinarian can set the actual dose. Body weight, kidney function, concurrent medication, and whether the infection is superficial or deep all change the arithmetic, and cephalexin capsules are manufactured in fixed sizes that require rounding. The figures below are the published reference ranges, not a prescription.

Infection type	Typical published dose	Minimum duration	Stop rule
Superficial bacterial folliculitis	15 to 30 mg/kg q12h	21 days	7 days past clinical resolution
Deep pyoderma / furunculosis	22 to 30 mg/kg q12h	4 to 8 weeks	14 days past clinical resolution
Surface pyoderma (intertrigo, hot spot)	Often no systemic antibiotic indicated	Topical therapy preferred	Resolution of the moist lesion

Cephalexin absorption is not meaningfully impaired by food in dogs, so the dose can and generally should be given with a meal to blunt nausea.

How Long Should a Dog Stay on Cephalexin?

Duration is where most pyoderma treatment fails, and it fails in a specific direction: owners stop early. The pustules crust and fall off within 7 to 10 days, the dog looks normal, and the course is abandoned at day twelve. The follicle is still colonised. Two weeks later the rash is back, and the second course is now selecting for resistance.

The rule taught in veterinary dermatology is to treat to 7 days beyond complete clinical resolution for superficial pyoderma, which in practice means a minimum 21 day course. Deep pyoderma requires 4 to 8 weeks and is continued 14 days beyond resolution, because furunculosis involves ruptured follicles, dermal inflammation, and often tracts of scar tissue that the drug must penetrate.

Recheck matters more than the calendar. A dermatologist assessing a pyoderma case at day 21 is palpating for residual papules, examining the interfollicular skin, and deciding whether resolution is genuine or cosmetic. If lesions persist at that recheck despite correct dosing and good compliance, the next step is a bacterial culture and susceptibility test, not a longer course of the same drug. Methicillin-resistant Staphylococcus pseudintermedius (MRSP) carries the mecA gene, which confers resistance to all beta-lactam antibiotics including cephalexin, and no amount of extended dosing overcomes it. The wider problem is discussed in Antimicrobial Resistance in Dog Skin Bacteria.

What Are the Side Effects of Cephalexin in Dogs?

Gastrointestinal upset is by far the most frequently reported adverse effect, presenting as vomiting, soft stool or diarrhoea, drooling, and reduced appetite. It is dose-related and usually manageable by giving the capsule with food rather than on an empty stomach. Most dogs tolerate a full course without incident.

Less common effects include hypersensitivity reactions (facial swelling, urticaria, pruritus that is new and different from the original itch), and rarely elevated liver enzymes. Dogs with a documented penicillin allergy have a small but real risk of cross-reactivity with cephalosporins, so that history belongs on the record before the first dose. Dogs with reduced renal function may need dose interval adjustment, since cephalexin is cleared renally.

The effect owners least expect is the one on the skin microbiome itself. A three to eight week course of a systemic antibiotic does not only suppress the pathogenic staphylococci, it flattens the commensal bacterial population that competes with yeast for space on the skin surface. This is why a subset of dogs finish an antibiotic course with the bacterial rash resolved but a new greasy, musty, rust-coloured yeast problem. That trade-off is examined in How Antibiotics Disrupt Your Dog's Skin Microbiome and Restoring Your Dog's Skin Microbiome After Antibiotic Treatment.

Why Topical Therapy Belongs Alongside Cephalexin

Systemic antibiotics reach the follicle through the bloodstream. Topical antimicrobials act on the skin surface, where the organisms actually live, and they do it without applying selection pressure across the whole body. Evidence supports the pairing strongly. A randomised trial by Borio and colleagues found that topical chlorhexidine shampoo therapy alone was not inferior to systemic amoxicillin-clavulanate for canine superficial pyoderma, which is a striking result for a condition reflexively treated with oral drugs.

Topical care also addresses the gap cephalexin leaves. Cephalexin is a cell-wall inhibitor active against bacteria, and it has no antifungal activity whatsoever. Malassezia pachydermatis is a normal skin commensal that overgrows opportunistically, and concurrent bacterial and yeast overgrowth is common in allergic dogs, particularly in paws, axillae, and skin folds. When a dog completes an antibiotic course and the odour and greasiness remain, yeast is the usual explanation.

Yeast Dermatitis Shampoo contains ketoconazole, an azole antifungal that inhibits lanosterol 14-alpha-demethylase, the enzyme Malassezia requires to build ergosterol for its cell membrane. Without ergosterol the membrane loses integrity and the organism cannot maintain its population. It is a medicated product rather than a cosmetic cleanser, and it works on the fungal side of the problem that an oral cephalosporin cannot touch. Contact time matters: a medicated shampoo needs 10 minutes on the coat before rinsing.

If you are still trying to determine whether the lesions in front of you are bacterial, fungal, or both, start with the bacterial skin infections guide or work through the Dog Skin Condition Checker.

Preventing the Next Course of Antibiotics

Recurrent pyoderma is not an antibiotic problem, it is an underlying disease problem. Superficial bacterial folliculitis in an adult dog is a secondary condition in the overwhelming majority of cases, sitting on top of atopic dermatitis, flea allergy, food allergy, hypothyroidism, or hyperadrenocorticism. A dog on his third course of cephalexin in a year has a primary diagnosis that has not been made.

The practical prevention strategy has three parts. First, identify and control the primary driver, which usually means allergy workup, endocrine testing in older dogs, and year-round flea prevention. Second, maintain barrier and surface hygiene between flares with regular medicated bathing and targeted cleaning of the high-risk sites, the interdigital spaces, folds, ventral abdomen, and perineum. Third, resist the impulse to start an antibiotic at the first papule. Surface pyoderma and mild superficial cases frequently resolve on topical therapy alone, and every course avoided is selection pressure avoided.

Owner compliance is the quiet variable. Studies of antimicrobial use in companion animal practice repeatedly find that courses are stopped early, doses are missed, and leftover capsules from a previous illness are reused without veterinary direction. That last habit is the single most effective way to create a resistant infection in your own household.

>90%

of canine superficial bacterial folliculitis cases are caused by Staphylococcus pseudintermedius, the organism cephalexin is chosen to target (Hillier et al., ISCAID guidelines, Veterinary Dermatology, 2014)

Getting a Cephalexin Course Right

✓Give every dose with food to reduce nausea, and give it at consistent 12 hour intervals.
✓Finish the entire prescribed course even after the skin looks normal, a minimum of 21 days for superficial pyoderma.
✓Book the recheck appointment at the start, not after the capsules run out.
✓Report vomiting, diarrhoea, facial swelling, or hives to your veterinarian rather than stopping the drug unilaterally.
✓Ask for a bacterial culture and susceptibility test if lesions persist at the recheck despite good compliance.
✓Never reuse leftover antibiotics from a previous illness or from another pet.
✓Pair the oral course with medicated topical therapy to address surface organisms and yeast.

⚠️ Important: Cephalexin is a prescription medication. Doses in this article are published reference ranges for context only, not a recommendation. Never start, stop, adjust, or repeat an antibiotic course without your veterinarian, and never give a dog antibiotics prescribed for a person or for another animal.

Yeast Dermatitis Shampoo

Yeast Dermatitis Shampoo is a medicated ketoconazole shampoo that targets the Malassezia overgrowth an oral antibiotic like cephalexin cannot reach.

View Yeast Dermatitis Shampoo

Not sure what's affecting your dog's skin?

Use our free Dog Skin Condition Checker to identify symptoms, compare conditions, and learn when to see a vet.

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Frequently Asked Questions

How much cephalexin can I give my dog for a skin infection?

Published veterinary dosing for canine pyoderma is 15 to 30 mg/kg orally every 12 hours, with dermatology practice often using the upper end for skin infections. Cephalexin is prescription-only, and the exact dose must come from your veterinarian based on your dog's weight, kidney function, and infection depth.

How long does cephalexin take to work on a dog's skin infection?

Visible improvement in pustules and redness usually appears within 7 to 10 days. That is not the finish line. Superficial pyoderma requires a minimum 21 day course continued 7 days past complete resolution, and deep pyoderma requires 4 to 8 weeks continued 14 days past resolution.

Can I stop cephalexin early if my dog's skin looks better?

No. Lesions clear well before the follicles are free of bacteria, and stopping early is the most common cause of relapse and of resistance selection. Complete the full course and attend the recheck, even if the coat looks perfect at day twelve.

What are the most common cephalexin side effects in dogs?

Gastrointestinal signs lead the list: vomiting, soft stool or diarrhoea, drooling, and reduced appetite. Giving the dose with food usually resolves it. Less commonly dogs show hypersensitivity reactions such as facial swelling or hives, which warrant a call to your veterinarian.

Sources

Hillier A, Lloyd DH, Weese JS, et al. Guidelines for the diagnosis and antimicrobial therapy of canine superficial bacterial folliculitis (Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases). Veterinary Dermatology. 2014;25(3):163-e43.
Borio S, Colombo S, La Rosa G, et al. Effectiveness of a combined 0.5% chlorhexidine digluconate shampoo and solution protocol in the management of canine superficial bacterial pyoderma: a randomized, blinded, antibiotic-controlled study. Veterinary Dermatology. 2015;26(5):339-e72.
Loeffler A, Lloyd DH. What has changed in canine pyoderma? A narrative review. The Veterinary Journal. 2018;235:73-82.
Beco L, Guaguere E, Lorente Mendez C, et al. Suggested guidelines for using systemic antimicrobials in bacterial skin infections. Veterinary Record. 2013;172(3):72-78.
Bond R, Morris DO, Guillot J, et al. Biology, diagnosis and treatment of Malassezia dermatitis in dogs and cats. Veterinary Dermatology. 2020;31(1):27-e4.