Antibiotics

29.1.1 Antibiotics  The function of antibiotics is to kill, or prevent the growth of, the bacteria that cause various diseases. However, antibiotics work effectively against only certain types of bacteria. It is the AHA’s responsibility to select the correct antibiotic for a certain disease problem.

 If antibiotics are not used properly, then the bacteria get stronger and stronger until the antibiotic no longer works against that particular bacteria. This is called, “antibiotic resistance, ” and is a growing problem in the world. Some antibiotics which used to work very well against certain diseases are no longer effective.

 In general, do not feed antibiotics to adult grass-eating animals because antibiotics also kill the beneficial microorganisms located in the stomach. Instead use injectable antibiotics. However, if no one is available to give an injection, it may be necessary to feed antibiotics to an adult grass-eating animal (like cattle, buffalo, etc.).

 Do not use antibiotics to fight against diseases that are caused by viruses. An exception to this is when a disease starts out with a virus and then a bacteria causes problems. For instance an animal may get wounds on its feet from Foot and Mouth Disease (a virus). Later, these wounds become infected (a bacteria). Penicillin does nothing against the FMD virus but will help to kill the bacteria that caused the wound to become infected.

 There are 6 different groups of antibiotics in this book. Each group works differently in the body and each works differently against various microorganisms. Each type of antibiotic remains in the body for a different length of time. The correct “withdrawal” time must be observed, or the antibiotics may be harmful to any people that may eat the meat or drink the milk from animals that have been treated with antibiotics. See page 348. The five groups of antibiotics are - The penicillin and cephalosporin group, The tetracycline group, The aminoglycoside group, The sulfa group, and The chloramphenicol and miscellaneous group.

Penicillin and Cephalosporin Group This group includes penicillin , amoxicillin, ampicillin, cephalexin, ceftiofur and others. Penicillin is still a very useful antibiotic for many infections in livestock. It is especially good for the types of infections that produce pus. Penicillin is also very safe. Too much will not kill an animal, but if too little is used, it causes antibiotic resistance.

Some animals have an allergy to penicillin and may develop red, itchy skin. Other animals may develop an allergic reaction that interferes with normal breathing. Such animals can die very quickly. See Page 85. Such a reaction can be treated with epinephrine. If an animal has ever had an allergic reaction to penicillin, that animal should never be given any type of penicillin again. (The same is true for any medicine that has produced an allergic reaction - that particular animal should never receive any form of that medicine again or it may die.)

As the following tables show, penicillin is very effective different types of infections in livestock, especially for preventing tetanus when an animal has a deep wound. Penicillins and cephalosporins are often the first antibiotics used if the type of bacteria is unknown. They work especially well when combined with aminoglycoside antibiotic drugs. They should not be combined with tetracyclines, sulfas or chloramphenicol. Penicillins are rather inexpensive but cephalosporins can be quite expensive.

Aminoglycoside Group This group includes streptomycin, gentamicin, kanamycin, neomycin and others. Aminoglycosides kill bacteria by disturbing the chemical machinery inside the bacteria. They are very effective against some common bacteria but they must be used with caution because of toxic side effects to the hearing and kidneys. In general, if they are given in the gut, they stay in the gut; if injected, they stay in the internal tissues. They often work well for treating diarrhea in baby animals. Injectable aminoglycosides have very long withdrawal periods. Aminoglycosides should not be combined with tetracyclines, sulfas, or chloramphenicol.

Tetracycline Group This group includes tetracycline, oxytetracycline, chlortetracycline and others. They inhibit bacteria so the bacteria can’t grow properly. They work well in the liver, respiratory tract and skin. Tetracyclines can be given by mouth, injection or externally (topically) to the eye. Do not give them to horses because horses can die from a strange reaction to tetracyclines. They are inexpensive and easily available. Do not combine with any other antibiotics.

Sulfa Group This group includes many antibiotics that start with the name “sulfa” like sulfamethazine and sulfadimidine. This class of antibiotics has been around since the 1930s. Sulfas can be given by mouth, injection, or externally when treating wounds. Do not give sulfas with any other antibiotics.

Deciding Which Antibiotic to Use – Some Practical Tables  The large number of diseases, and the problem of antibiotic resistance, make the selection of the right antibiotic a difficult decision. However, the following rules should help to select an effective antibiotic. If the first choice does not seem to work after 3-5 days, then move to another in the list. When switching to another antibiotic, it is probably better to choose an antibiotic from a different group. For example if the penicillin is not working, it is probably better to try an antibiotic from another group. (Drugs and Their Usage, CVM Publications)

(Note: Pen = penicillin and cephalosporin group, Tet = tetracycline group, Amin = aminoglycoside group, Sulf – sulfa group, Chlor = chloramphenicol Genitourinary = condition affecting the reproductive or urinary system)

Table of Antibiotics for Horses and Donkeys Condition (Problem) First Choice Second Choice Pneumonia Pen, Amin Sulfa Diarrhea Pen, Amin (oral) Sulfa Genitourinary Pen Amino Other Soft Tissues Pen Sulfa Table of Antibiotics for Cattle and Buffalo Condition (Problem) First Choice Second Choice Pneumonia Pen, Tet Sulfa, Amin Diarrhea Amin (oral) Sulfa Genitourinary Pen Amin, Sulfa Mastitis Pen Tet, Sulfa Other Soft Tissues Pen Tet Table of Antibiotics for Swine Condition (Problem) First Choice Second Choice Pneumonia Pen Tet Diarrhea Amin (oral) Sulfa, Tylosin Genitourinary Pen Tet Skin Pen Amin Table of Antibiotics for Sheep and Goats Condition (Problem) First Choice Second Choice Pneumonia Tet Sulfa, Tylosin Diarrhea Amin Sulfa Genitourinary Tet Pen, Amin, Sulfa Mastitis Pen Amin Other Soft Tissues Pen Tet Table of Antibiotics for Dogs and Cats Condition (Problem) First Choice Second Choice Pneumonia Pen, Sulfa Amin, Tet Diarrhea Pen, Amin (oral) Sulfa, Chlor Genitourinary Pen Sulfa Other Soft Tissues Pen Sulfa Skin Chlor Erythro, Sulfa Using Penicillins and Cephalosporins Different Kinds of Penicillin Injections: Some kinds of penicillin start to work quickly but then are able to kill bacteria for only a short period of time. These are called short-acting or intermediate-acting penicillin. Other types of penicillin take longer to start working (almost a whole day) but then they work for several days. These are called long-acting penicillin.

Summary: Penicillin is the drug of choice for most infections of the skin, muscle and uterus. It especially works well for tetanus. Never give procaine or benzathine penicillin IV. Always give it IM or SC. Penicillin may be found in powder form in a vial (glass bottle) and should be mixed with distilled water or with boiled (and cooled) water. Or it may be pre-mixed and available as a liquid. After mixing the powder with water, it loses its strength in 7 days and should be thrown away.

PENICILLIN G (benzathine)

Indications: See “penicillin and cephalosporin group” above.

Dosage and Route:

Horses- 10,000-40,000 IU/kg, IM, every 2-3 days Cattle- 40,000 IU/kg, IM, every 2-3 days Swine- 40,000 IU/kg, IM, every 2-3 days Sheep- 15,000 IU/kg, IM, every 4-5 days Dogs- 40,000 IU/kg, IM, every 5 days Cats- 40,000 IU/kg, IM, every 5 days Rabbit- 40,000 IU/kg, IM, every other day Withdrawal Period: Note: effective doses greatly exceed the labeled dose, therefore the label withdrawal period must be longer than the label requires.

Cattle- IM dosing, meat 21 days, milk 13 days, SC dosing, meat 42 days Precautions: This is a long acting penicillin preparation, take special note of the long time between doses.

PENICILLIN G (procaine)

Indications: See “penicillin and cephalosporin group” above.

Dosage and Route:

Horses- 20,000-50,000 IU/kg, IM, 2-3 times daily Cattle- 20,000-54,000 IU/kg, IM, SC 1-2 times daily Swine- 20,000-54,000 IU/kg, IM, SC 1-2 times daily Sheep- 6-16 mg/kg, IM, 1-2 times daily Llama- 40,000 IU/kg, SC, daily Dogs- 20,000 IU/kg, IM, SC 1-2 times daily Cats- 20,000 IU/kg, IM, SC 1-2 times daily Rabbit- 50,000-100,000 IU/kg, IM, 2 times daily Withdrawal Period: Note: effective doses greatly exceed the label dose, therefore the withdrawal period must be longer than the label specifies.

Cattle- IM dosing, meat 21 days SC dosing, meat 42 days AMPICILLIN (Polyflex, Albipen)

Indications: See “penicillin and cephalosporin group” above.

Dosage and Route:

Horses- 11-22 mg/kg, IM, IV, 2-3 times daily Cattle- 5-12 mg/kg IM once daily Swine- 5-12 mg/kg IM once daily Llama- 11 mg/kg IV, 3 times daily Dogs- 22 mg/kg, by mouth, 3 times daily; or 11-22 mg/kg, SC, IM, 3-4 times daily Cats- 22 mg/kg, by mouth, 3 times daily; or 11-22 mg/kg, SC, IM, 3-4 times daily Ferret- 10 mg/kg IM, 2 times daily, or 20 mg/kg SC, 2 times daily, or 20 mg/kg by mouth, 2 times daily Withdrawal Period: Cattle- meat 6 days, milk 2 days CEPHALEXIN (Keflex)

Indications: See “penicillin and cephalosporin group” above.

Dosage and Route:

Horses- 10-30 mg/kg by mouth, 3-4 times daily Goats- 30 mg/kg. SC Dogs- 10-30 mg/kg by mouth, 2-4 times daily Cats- 10-30 mg/kg by mouth, 2-4 times daily Rabbit- 15 mg/kg, SC, 2 times daily Guinea Pig- 15 mg/kg, IM, 2 times daily Chicken- 55-110 mg/kg by mouth, 2 times daily CLOXACILLIN (Orbenin, Dariclox, Dri-clox)

Indications: See “penicillin and cephalosporin group” above.

Dosage and Route:

Cattle-500 mg of cephapirin benzathine; or 200 mg of cephapirin sodium by intramammary infusion into each quarter Dogs- 10-40 mg/kg by mouth or IM 3-4 times daily Cats- 10-40 mg/kg by mouth or IM 3-4 times daily Withdrawal Period:

Cattle- Cephapirin benzathine; meat & milk 30 days, Cephapirin sodium; meat 10 days, milk discarded for 2 days (2.5 days Canada).

Precautions: The benzathine infusion should only be used in dry cows.

PEN/STREP (Penicillin G Procaine + Dihydrostreptomycin)

Indications: See “penicillin and cephalosporin group” above.

Usually formulated to give 400,000 IU of Pen G Procaine + 0.5 g Dihydrostreptomycin per 2 ml.

Dosage and Route:

Horses- 10-12 ml IM, 1-2 times daily Foals- 1 ml/22 kg, 1-3 times daily Cattle- 10-12 ml IM, 1-2 times daily Calves- 1 ml/22 kg, 1-3 times daily Swine- 1 ml/22 kg, 1-3 times daily Sheep- 1 ml/22 kg, 1-3 times daily Withdrawal Period: Food animals - meat 30 days, milk 3 days Using Aminoglycosides GENTAMYCIN (Gentocin, Garamycin)

Indications: See “ aminoglycoside group” above. Gentamicin is a readily available and affordable aminoglycide which is commonly given by mouth for scours (diarrhea), by injection for generalized infections, in ophthalmic preparations for treatment of eye infections, and in otic preparations for treatment of ear infections in dogs and cats. Note the long withdrawal periods when injected in cattle and pigs. It is not absorbed from the gut when given orally.

Dosage and Route:

Horses- 2-4 mg/kg, IM, SC, IV, 1 time daily Cattle- 2.2 mg/kg, IM, IV, 3 times daily Swine- 5 mg, IM in 1-3 day old piglets, or 5 mg by mouth in 1-3 day old piglets; or 25 g/gallon of drinking water for 3 days Llama- 2 mg/kg IM, 3 times daily Dogs- 2 mg/kg, SC, IM, 3 times daily Cats- 2 mg/kg, SC, IM, 3 times daily Chicken- 0.2-1 mg total dose, SC, 1 time daily Rabbit- 4 mg/kg, IM, 1 time daily Ferret- 5 mg/kg, IM, 1 time daily Gerbil- 5 mg/kg, IM, 1 time daily Guinea Pig- 5 mg/kg, IM, 1 time daily Hamster- 5 mg/kg, IM, 1 time daily Withdrawal:

Cattle-meat 180-360 days, milk 5 days Swine-if injected, meat 40 days; if oral, meat 3-14 days Precautions: Possible kidney damage with high doses for prolonged periods. Do not use in combination with other drugs in the aminoglycoside group.

Using Tetracyclines These also are broad-spectrum antibiotics because they kill many different kinds of bacteria. They are found in the market with many different names such as Terramcycin, Oxysteclin, Hostacycline, etc. In the market, they come in different strengths such as 50mg/ml or 100mg/ml. Most commonly they start to work quickly but need to be given every day (daily). There is a long-acting tetracycline that is available sometimes. Some kinds can be given IV, others cannot. Therefore, read the label carefully!

Precautions: Never use in horses, donkeys, or mules because it damages the microorganisms of the cecum. Do not use orally in ruminants if possible. It is found in the form of tablets, powder, liquid, injection, bolus, etc. Oral tetracycline can be used in dogs and cats with no problems. However it should not be used in ruminants unless there is no one available to give an injection.

OXYTETRACYCLINE )

Indications: See “tetracycline group” above.

Dosage and Route:

Cattle- 4-11 mg/kg IM, IV daily; or 10-20 mg/kg by mouth, 4 times daily Cattle- Long acting injection (LA-200)

20 mg/kg IM once Swine- 6-11 mg/kg IM, IV daily; or 10-20 mg/kg by mouth, 4 times daily Swine-Long acting injection (LA-200)

20 mg/kg every 2 days Sheep- 10-20 mg/kg by mouth, 4 times daily; or 6-11 mg/kg IM, IV, 1 time daily Sheep-Long acting injection (LA-200)

20 mg/kg every 3 days Goats- 10-20 mg/kg by mouth, 4 times daily; or 6-11 mg/kg IM, IV, 1 time daily Goats- Long acting injection (LA-200)

20 mg/kg every 3 days Llamas- 11 mg/kg IV, once daily Llamas-Long acting injection (LA-200)

20 mg/kg every 3 days Dogs- 7-12 mg/kg IM, IV 2 times daily; or 22 mg/kg by mouth, 3 times daily Cats- 7-12 mg/kg IM, IV 2 times daily; or 22 mg/kg by mouth, 3 times daily Withdrawal Period: Cattle by mouth- meat 5 days, milk 4 days Cattle IM, IV- meat 18 days, milk 3 days Cattle Long Acting IM- meat 28 days Swine- Meat 21 days Sheep-meat 21 days Precautions: Do not use in horses. Do not give with milk, or any other antibiotics. It may cause stomach upset. If the injection is a large volume divide it into several sites.

Using Sulfas These drugs are usually sold as oral medicines but occasionally they are available as injections. Even though they work similarly to antibiotics, they seem to have fewer bad effects on the beneficial microorganisms in the rumen. Therefore these drugs are often used as oral medicines to treat infections in ruminants. They are commonly used to treat diarrhea, urinary infections and some kinds of wound and hoof infections.

These drugs must be given with lots of water. If the animal is not drinking water, then do not give these drugs or they may damage the kidney.

SULFADIAZINE + TRIMETHOPRIM (Tribrissen)

Indications: See “sulfa group” above. This medicine is a combination of sulfamethoxazole and trimethoprim. It works like a broad-spectrum antibiotic and is less expensive than ampicillin.

Dosage and Route:

Horses-30 mg/kg by mouth, 2-3 times daily; or 15 mg/kg IV, 2 times daily Cattle- 30 mg/kg by mouth, one time daily Swine- 48 mg/kg IM daily Sheep - 75 mg/kg by mouth daily; or 13-20 mg/kg IM, SC, IV daily Dogs- 15-30 mg/kg by mouth 1-2 times daily Cats- 30 mg/kg by mouth 2 times daily Withdrawal Period: Cattle-meat 3 days, milk 7 days Swine-meat 10 days Sheep-meat 14 days SULFADIMIDINE (Sulfamez)

Indications: See “sulfa group” above.

Dosage and Route:

Cattle- 110 mg/kg by mouth daily; or 150 mg/kg SC daily Swine- 110 mg/kg by mouth daily 150 mg/kg SC daily Sheep- 110 mg/kg by mouth daily 215 mg/kg SC daily Goats- 110 mg/kg by mouth daily 215 mg/kg SC daily Withdrawal Period: Cattle- meat 15 days, milk 3 days Swine-meat 15 days Sheep-meat 15 days Goats-meat 15 days, milk 3 days SULFAMETHAZINE Indications: See “sulfa group” above.

Dosage and Route:

Cattle- 200 mg/kg by mouth for one day, then 100 mg/kg one time daily Swine- 200 mg/kg by mouth for one day, then 100 mg/kg one time daily Sheep- 30 ml of 12.5% solution by mouth for one day, then 15 ml daily Dogs- 50 mg/kg by mouth 2 times daily Cats- 50 mg/kg by mouth 2 times daily Rabbit - 2 g/L drinking water Chicken- 1 g/L drinking water Withdrawal Period: Cattle- meat 10 days, milk 4 days Swine-meat 14 days