Amoxicillin: This is a general "all purpose" antibiotic that is cheap and easy to come by, but it does not knock down staph infections. The oral dosage for amoxicillin is 10 mg per pound of dog, given every 8 to 12 hours, depending on the severity of the problem. The fish-version of amoxicillin (Fish-Mox) can be ordered in 250 mg capsules without a prescription from Revival Animal Health or any other online pet store. You probably have some old amoxicillin around the house from the last time you got sick. This is fine to use even if "expired" more than a year ago. Expiration dates on non-liquid antibiotics are a marketing tool (i.e. they encourage people to throw good drugs down the drain) and have no scientific basis -- a fact demonstrated by the U.S. military

Cephalexin: This is one of the best drugs for skin and wound infections and It is easy to come by without prescription, and inexpensive. Two common brand names are Keflex and Celaxin, and it is often prescribed for acne. Cephalexin only comes in oral form, and the dose is
15 mg per pound of body weight, given every 8 to 12 hours depending on the severity of the problem. If you are using a maintenance dose, give it every 12 hours. If the dog has an infection already, use it every 8 hrs.
Either Cephalexin or Clavamox  are “must have" drug for your vet kit. The fish-version of cephalexin is called cefalexin (Fish-Flex) and can be ordered in 250 mg capsules without a prescription. The 250 mg capsule
is a perfect dose for a 15 pound dog.

Penicillin: If it's the capsule form, forget it unless it's the only antibiotic you have. A lot of infections are immune to penicillin, and it generally won’t help a staph infection at all. If this is the only antibiotic you have and you are on a desert island, use it, but otherwise look for something stronger. Indictable penicillin is not worth the trouble when we have so many other readily available options, such as cephelaxin (Fish-Flex).

Clavamox: This is very similar to amoxicillin but is a bit stronger and this one will knock down a staph infection -- an important difference between the two drugs. Clavamox will also treat respiratory infections and ear infections, so it's a good all-rounder, as is cephalexin. Clavamox is only given orally. The oral dose is 6.25 mg per pound, and it comes pre-packaged in foil strips in 3 sizes. There are 62.5 mg for 10-pound puppies, 125 mg for 20 pound dogs, and 250 mg for 40-pound dogs. The most common human version of Clavamox, is called Augmentin and most parents have some old tablets around the house. Although both Clavamox and Augmentin are expensive, they are worth it because they work for a lot of different kinds of problems. Your dog may throw up on Clavamox or Augmentin – this is not terribly unusual if your dog has a weak stomach. Clavamox can be ordered from http://lambriarvetsupply.com/index.pl but you will need to fax them a prescription from your vet. Again, check around the house; you may have Clavamox in your medicine cabinet.

Baytril: This is a pretty powerful antibiotic, and should only be given when other antibiotics have failed or if the dog already has a serious infection. Baytril works very well for skin, ear, wound, urinary, and mammary infections. In tablet form the dose for Baytril is 5.7 mg per 5 pounds of weight given orally twice a day (every 12 hours). For a 20 pound dog you would give one of the 22.7 mg tablets every 12 hours, or two of the 22.7 mg tablets once a day. Baytril can be ordered from http://lambriarvetsupply.com/index.pl but you will need to fax them a prescription from your vet. It is fairly expensive -- about 62 cents a pill