If your dog is constantly licking a red, crusty patch on their belly or smells a bit like corn chips, you’re probably looking at a staph infection. It’s frustrating. You see them itchy and miserable, and you just want it to stop. Most vets reach for one specific tool: cephalexin. It’s a first-generation cephalosporin antibiotic that’s been around forever because, frankly, it works. But getting the cephalexin dosage for dogs by weight right isn't just about reading a label. It’s actually a bit of a balancing act between killing the bacteria and not destroying your dog’s stomach.
Veterinary medicine isn't always a "one size fits all" situation.
Standard dosing usually sits between 10 mg and 15 mg per pound of body weight. Most vets prefer the higher end of that range for stubborn skin issues. If you have a 50-pound Labrador, you're looking at roughly 500 mg to 750 mg per dose. Typically, this happens twice a day. Sometimes three. It depends on the severity. But here’s the kicker: if you stop the meds the moment the skin looks "fine," you are basically training the bacteria to survive the next round. That’s how we get superbugs.
Why weight is only half the battle
You can’t just eyeball it. Cephalexin (often sold under brand names like Keflex or Rilexine) is remarkably safe, but it’s cleared by the kidneys. If you have an older dog with renal issues, the standard cephalexin dosage for dogs by weight might actually be too much for their system to process. Dr. Marty Greer, a well-known DVM, often emphasizes that we treat the patient, not the paperwork.
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Small dogs are particularly tricky. A 5-pound Chihuahua needs a tiny amount, often requiring the liquid oral suspension because trying to quarter a 250 mg capsule is a nightmare and wildly inaccurate.
The math usually works like this:
For a tiny 10-pound dog, a 150 mg dose twice daily is common.
A medium 40-pound dog might take 500 mg twice daily.
For the giants, like a 100-pound Great Dane, you might be looking at 1000 mg to 1500 mg per dose.
It sounds like a lot. It is. But skin is a tough place for antibiotics to reach. The blood supply to the outer layers of the dermis isn't as robust as the supply to, say, the lungs or the liver. Because of this "delivery" problem, vets have to use higher dosages for skin infections than they might for a urinary tract infection (UTI).
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Common mistakes and the "hidden" side effects
Most people think the biggest risk is an allergic reaction. While hives or difficulty breathing can happen, it’s actually pretty rare. The real enemy? The "puke factor." Cephalexin is notorious for causing nausea. Honestly, if you give this stuff on an empty stomach, there’s a 50/50 chance your dog is going to lose their breakfast on your rug. Always, always give it with a meal. A little bit of wet food or a spoonful of plain Greek yogurt can act as a buffer.
Speaking of yogurt, let's talk about the gut. Antibiotics are tactical nukes. They don't just kill the "bad" Staphylococcus pseudintermedius; they wipe out the "good" bacteria that help your dog digest food. This is why many dogs get diarrhea about three days into the cycle.
You’ve probably heard of "probiotic loading." It’s a smart move. Just don't give the probiotic at the same exact time as the cephalexin. If you do, the antibiotic will just kill the probiotics you just paid $30 for. Space them out by at least two hours. It makes a huge difference in stool consistency, trust me.
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The timeline: why 7 days is never enough
I see this all the time on forums. An owner gives the meds for five days, the redness goes away, and they stop. That is a recipe for disaster. Deep pyodermas (skin infections) often require 21 days or even a full month of treatment. You have to treat for at least seven to ten days past the point of clinical resolution. That means if the skin looks perfect on day 14, you keep going until day 21.
What if you miss a dose?
Don't panic. You don't need to double up. If you remember four hours late, just give it then and shift the next dose back a little. If it's almost time for the next one, just skip the missed one. Doubling the cephalexin dosage for dogs by weight in a single sitting is a fast track to a very upset stomach and potential toxicity, though cephalexin has a wide margin of safety.
It’s also worth noting that some dogs are just "non-responders." If you’ve been doing the 15 mg/lb dose for a week and see zero improvement, it might not be a staph infection. It could be fungal (yeast) or a resistant strain of bacteria. This is when a vet will suggest a culture and sensitivity test. It’s more expensive upfront, but it beats buying three rounds of the wrong antibiotic.
Actionable steps for the next 24 hours
If your vet just prescribed this, or you’re checking the math on an old bottle, here is how you handle it like a pro.
- Get a precise weight. Don't guess what your dog weighed last summer. Use a scale. Five pounds of difference can change the dosage tier.
- Prepare the "delivery vehicle." Get some low-sodium peanut butter or plain canned pumpkin. This isn't just for taste; the fat and fiber help coat the stomach lining against the acidity of the medication.
- Set a phone alarm. Consistency matters. Antibiotics work by maintaining a "minimum inhibitory concentration" (MIC) in the bloodstream. If you let the levels drop too low by skipping doses, the bacteria get a chance to regroup.
- Watch the water bowl. Cephalexin can make some dogs extra thirsty. Ensure they have constant access to fresh water to help the kidneys flush the metabolic byproducts.
- Check the paws. If your dog is on cephalexin for a skin infection but is still obsessively chewing their paws, there is likely an underlying allergy (food or environmental) that the antibiotic won't fix. The meds kill the infection, but they don't stop the itch that caused the scratching in the first place. Consider an Apoquel or Cytopoint discussion with your vet to break the itch-scratch cycle while the cephalexin does the heavy lifting.
The goal is a healed dog and a healthy gut. Stick to the weight-based math, never skip the meal, and finish the entire bottle regardless of how good the skin looks.