Penicilins



BENZYLPENICILLIN
(Penicillin G, Penethamate hydriodide)
Indications. Penicillin-sensitive infections.
Contra-indications. Penicillin or cephalosporin hypersensitivity; should not be administered to gerbils, guinea pigs, hamsters, rabbits
Side-effects. Allergic reactions; diarrhoea
Warnings. Penicillins and cephalosporins may cause hypersensitivity (allergy) following self-injection, inhalation, ingestion, or skin contact. Operators with known hypersensitivity should not handle these drugs. Clinical signs of allergic reaction in operators include skin rash, swelling of the face, lips, or eyes, or difficulty breathing. Operators should seek medical advice.
Dose. Horses: by intravenous injection, 10 mg/kg twice daily for 1 day

PHENOXYMETHYLPENICILLIN
(Penicillin V)
Indications. Penicillin-sensitive infections.
Contra-indications. Penicillin or cephalosporin hypersensitivity; should not be administered to gerbils, guinea pigs, hamsters, rabbits, horses
Side-effects. Allergic reactions; diarrhoea
Warnings. Safety in pregnant pigs has not been established. Penicillins and cephalosporins may cause hypersensitivity (allergy) following self-injection, inhalation, ingestion, or skin contact; operators should wear suitable protective clothing; operators with known hypersensitivity should not handle these drugs; clinical signs of allergic reaction in operators include skin rash, swelling of the face, lips, or eyes, or difficulty breathing; operators should seek medical advice.
Dose. Pigs: by addition to feed, 200 g/tonne feed
Dogs, cats: by mouth, 10 mg/kg 3 times daily
Withdrawal Periods. Slaughter 1 day
PROCAINE BENZYLPENICILLIN
(Procaine penicillin)
Indications. Penicillin-sensitive infections
Contra-indications. Penicillin or cephalosporin hypersensitivity; should not be administered to gerbils, guinea pigs, hamsters, rabbits, horses
Side-effects. Allergic reactions; diarrhoea
Warnings. Penicillins and cephalosporins may cause hypersensitivity (allergy) following self-injection, inhalation, ingestion, or skin contact. Operators with known hypersensitivity should not handle these drugs. Clinical signs of allergic reaction in operators include skin rash, swelling of the face, lips, or eyes, or difficulty breathing. Operators should seek medical advice.
Dose. Dosages vary, for guidance.
Horses: by intramuscular injection, 10 mg/kg once daily
Cattle: by intramuscular injection, 10 mg/kg once daily
cattle, non lactating: by depot subcutaneous or intramuscular injection, 20 mg/kg. Repeat after 3 days if required
cattle, lactating: by depot intramuscular injection, 20 mg/kg. Repeat after 3 days if required.
Sheep: by intramuscular injection, 10 mg/kg once daily
Pigs: by intramuscular injection, 10 mg/kg once daily by depot intramuscular injection, 20 mg/kg. Repeat after 3 days if required
Dogs, cats: by subcutaneous injection, 30 mg/kg once daily
BENZATHINE BENZYLPENICILLIN and PROCAINE BENZYLPENICILLIN
(Benzathine Penicillin and Procaine Penicillin)
Indications. Penicillin-sensitive infections
Contra-indications. Side-effects. Warnings. See under Benzylpenicillin
Dose. Expressed for a suspension containing benzathine benzylpenicillin 112.5 mg + procaine benzylpenicillin 150 mg/mL
Horses, cattle, sheep, pigs: by intramuscular injection, 1 mL/25 kg body-weight, repeat after 3–4 days if required
Dogs, cats: by intramuscular injection, 1 mL/10 kg bodyweight, repeat after 3–4 days if required
Depot injection, benzathine benzylpenicillin 112.5 mg, procaine benzylpenicillin 150 mg/mL, for horses, cattle, sheep, pigs, dogs, cats
Withdrawal Periods. Should not be used in horses intended for human consumption.
Cattle: slaughter 60 days, milk 3 days. Sheep: slaughter 60 days, should not be used in sheep producing milk for human consumption.
Pigs: slaughter 60 days
Beta-lactamase resistant penicillins
Isoxazolylpenicillins have the antibacterial spectrum of benzylpenicillin but they are stable in the presence of staphylococcal beta-lactamases; in addition, they block the activity of these enzymes. They are effective in infections caused by penicillin-resistant staphylococci, the sole indication for their use. Cloxacillin and oxacillin are incorporated into intramammary or ophthalmic preparations. Flucloxacillin is absorbed from the gastro-intestinal tract and is available for oral administration. Its bioavailability is significantly reduced by the presence of food thus this drug should be given before feeding.
FLUCLOXACILLIN
Indications. Infections caused by beta-lactamase-producing staphylococci
Contra-indications. Penicillin or cephalosporin hypersensitivity; gerbils, guinea pigs, hamsters, rabbits; oral administration to horses or calves with a functional rumen
Side-effects. Allergic reactions; diarrhoea
Dose. Dogs, cats: by mouth, 15 mg/kg 4 times daily, given on an empty stomach
Broad-spectrum penicillins
Ampicillin and amoxicillin have slightly less activity than benzylpenicillin against Gram-positive bacteria and obligate anaerobes but considerably greater activity against Gram-negative bacteria, although their action is poor against Klebsiella, some Proteus spp., and Pseudomonas spp. In addition, they are broken down by beta-lactamases, both the staphylococcal enzymes and those produced by Gram-negative organisms such as E. coli and Haemophilus spp. Acquired resistance in such organisms has limited the usefulness of these antibiotics.
Amoxicillin is better absorbed following administration by mouth than ampicillin, giving higher plasma and tissue concentrations. Its absorption is less affected by the presence of food in the stomach. Ampicillin should be given to fasted animals and at least an hour should then elapse before food is provided. Ampicillin and amoxicillin are excreted into both bile and urine.
Depot preparations of both amoxicillin and ampicillin are available. The drug is incorporated into an oily vehicle to prolong the action of the antibacterial. Depot oil-based ampicillin preparations include aluminium monostearate in the formulation.
Pivampicillin is the pivaloyloxymethyl ester of ampicillin and as such is a prodrug. It is hydrolysed by non-specific esterases in the mucosal wall of the gastro-intestinal tract and in plasma to release ampicillin (75% by weight is converted to ampicillin).
Clavulanic acid has no significant antibacterial activity, but is a potent beta-lactamase inhibitor. Therefore, its inclusion in preparations of amoxicillin (co-amoxiclav) renders the combination active against most strains of Staph.aureus, some E. coli spp., in addition to Bacteroides and
Klebsiella spp.
AMOXICILLIN
(Amoxycillin)
Indications. Amoxicillin-sensitive infections; hepatic encephalopathy.
Contra-indications. Penicillin or cephalosporin hypersensitivity; gerbils, guinea pigs, hamsters, rabbits; oral administration to horses or calves with a functional rumen
Side-effects. Allergic reactions; diarrhoea
Warnings. Penicillins and cephalosporins may cause hypersensitivity (allergy) following self-injection, inhalation, ingestion, or skin contact; operators should wear suitable protective clothing; operators with known hypersensitivity should not handle these drugs; clinical signs of allergic reaction in operators include skin rash, swelling of the face, lips, or eyes, or difficulty breathing; operators should seek medical advice
Dose. Dosages vary. For guidance.
Cattle: by intramuscular injection, 7 mg/kg daily by depot intramuscular injection, 15 mg/kg, repeat after 2 days
calves: by mouth, 8 mg/kg twice daily
Sheep: by intramuscular injection, 7 mg/kg daily by depot intramuscular injection, 15 mg/kg, repeat after 2 days
Pigs: by addition to drinking water, 20 mg/kg daily by intramuscular injection, 7 mg/kg daily
by depot intramuscular injection, 15 mg/kg, repeat after 2 days
piglets: by addition to feed, 15 mg/kg body-weight daily for 14 days
Dogs, cats: by mouth, 10 mg/kg twice daily by subcutaneous or intramuscular injection, 7 mg/kg daily by depot subcutaneous or intramuscular injection, 15 mg/kg, repeat after 2 days
Poultry: by addition to drinking water, 15–20 mg/kg
Pigeons, ducks: by addition to drinking water, 20 mg/kg
Fish: see Prescribing for fish for preparation details and dosage
Note. Amoxicillin 1 g = amoxicillin trihydrate 1.15 g
AMOXICILLIN with CLAVULANIC ACID
(Co-amoxiclav: preparations of amoxicillin (as trihydrate or the sodium salt) and clavulanic acid (as potassium clavulanate); the proportions are expressed in the form x/y, where x and y are the strengths in milligrams of amoxicillin and clavulanic acid respectively)
Indications. Amoxicillin-sensitive infections including beta-lactamase-producing micro-organisms
Contra-indications. Penicillin or cephalosporin hypersensitivity; gerbils, guinea pigs, hamsters, rabbits; oral administration to horses or calves with a functional rumen
Side-effects. Allergic reactions; diarrhoea
Warnings. Penicillins and cephalosporins may cause hypersensitivity (allergy) following self-injection, inhalation, ingestion, or skin contact. Operators with known hypersensitivity should not handle these drugs. Clinical signs of allergic reaction in operators include skin rash, swelling of the face, lips, or eyes, or difficulty breathing. Operators should seek medical advice
Dose. Expressed as amoxicillin
Cattle: by intramuscular injection, 7 mg/kg once daily
calves: by mouth, 5–10 mg/kg twice daily
Pigs: by intramuscular injection, 7 mg/kg once daily
Dogs, cats: by mouth, 10–20 mg/kg twice daily by subcutaneous or intramuscular injection, 7 mg/kg once daily
AMPICILLIN
Indications. Ampicillin-sensitive infections
Contra-indications. Penicillin or cephalosporin hypersensitivity; gerbils, guinea pigs, hamsters, rabbits; oral administration to horses or calves with a functional rumen; severe renal impairment with anuria and oliguria in cats; presence of beta-lactamase producing bacteria
Side-effects. Allergic reactions; diarrhoea; occasional reaction at site of injection
Warnings. Penicillins and cephalosporins may cause hypersensitivity (allergy) following self-injection, inhalation, ingestion, or skin contact. Operators with known hypersensitivity should not handle these drugs. Clinical signs of allergic reaction in operators include skin rash, swelling of the face, lips, or eyes, or difficulty breathing. Operators should seek medical advice
Dose.
Horses: by intramuscular injection, 7.5 mg/kg once daily
Cattle, sheep: by intramuscular injection, 7.5 mg/kg once daily by depot intramuscular injection, 15 mg/kg, repeat after 2 days
Pigs: by intramuscular injection, 7.5 mg/kg once daily by depot intramuscular injection, 25 mg/kg, repeat after 2 days
Dogs: by mouth, 10–20 mg/kg twice daily given on an empty stomach by subcutaneous or intramuscular injection, 7.5 mg/kg once daily by depot subcutaneous injection, 15 mg/kg, repeat after 2 days
Cats: by mouth, 10–20 mg/kg twice daily given on an empty stomach by subcutaneous or intramuscular injection, 7.5 mg/kg once daily by depot subcutaneous injection, 20 mg/kg, repeat after 2 days. Accidental self-injection with oil-based formulations can cause severe pain and intense swelling, which may result in ischaemic necrosis and loss of a digit. Prompt medical attention is essential.
Antipseudomonal penicillins
The carboxypenicillin ticarcillin is principally indicated for the treatment of Pseudomonas aeruginosa infections although it is also active against a number of other Gram-negative organisms including Proteus and Bacteroides spp. Ticarcillin is broken down by the beta- lactamase produced by some strains of Pseudomonas aeruginosa and is available in preparations to which clavulanic acid has been added to inhibit beta-lactamase. The ureidopenicillin, piperacillin is broad spectrum and is more active than ticarcillin against Pseudomonas aeruginosa.
TICARCILLIN with CLAVULANIC ACID
Indications. See notes above
Contra-indications. Penicillin or cephalosporin hypersensitivity; should not be administered to gerbils, guinea pigs, hamsters, rabbits
Side-effects. Allergic reactions; diarrhoea
Dose. Expressed as ticarcillin
Foals: by intravenous injection, 50 mg/kg 4 times daily
Dogs, cats: by intravenous infusion, 30–100 mg/kg 3 times daily

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