Narrow-spectrum penicillins

Benzylpenicillin, also known as penicillin G, was the first of the penicillins, and remains an important and useful antibacterial. It is particularly active against Gram-positive bacteria. Sensitive micro-organisms include Gram-positive aerobes such as Staphylococcus aureus, streptococci, most Actinomyces spp., Erysipelothrix, and Bacillus spp. Most anaerobic bacteria including Clostridium and some Bacteroides spp. (not B.fragilis) are also sensitive. Benzylpenicillin has activity against the more fastidious Gram-negative aerobes such as Haemophilus, Pasteurella, Leptospira, and some Actinobacillus spp. Benzylpenicillin is broken down by the beta-lactamase enzymes produced by staphylococci and Bacteroides spp. A high proportion of strains of these micro-organisms are now resistant to benzylpenicillin. Other organisms mentioned retain their sensitivity to benzylpenicillin because of their inability to produce beta-lactamase.

Benzylpenicillin is inactivated by gastric acid and so is not administered by mouth. It is available as a range of salts that differ in their solubility and hence their duration of action. The sodium salt is very soluble and rapidly absorbed following injection, but gives effective concentrations for no more than 4 hours, unless the organisms involved are highly sensitive.

Procaine benzylpenicillin is slightly soluble. Following parenteral administration, it forms a ‘depot’ which slowly releases free benzylpenicillin into the circulation, maintaining effective concentrations against the more susceptible micro-organisms for up to 24 hours. It is thought that the procaine component of procaine benzylpenicillin may give rise to a febrile reaction and abortions in sows infected with Erysipelothrix. Benzathine benzylpenicillin, an almost insoluble ester, is no longer authorised for use in food-producing animals within the EU because products containing it showed prolonged persistence of injection site residues. Phenoxymethylpenicillin, or penicillin V, has a similar antibacterial spectrum to benzylpenicillin but is less active. It is gastric acid-stable and thus suitable for oral administration (not to horses). It should not be used for severe infections because absorption is unpredictable and plasma-drug concentrations are variable.

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

Prescription-only medicine: Crystapen 5 Mega for Injection (Veterinary) (Schering-Plough) UK

Injection, powder for reconstitution, benzylpenicillin (as sodium salt) 3 g, for horses

Withdrawal Periods. Should not be used in horses intended for human consumption

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

Prescription-only medicine: Phenoxymethylpenicillin (Non-proprietary) UK

Tablets, phenoxymethylpenicillin (as potassium salt) 250 mg

Oral solution, powder for reconstitution, phenoxymethylpenicillin (as potassium salt) 25 mg/mL, 50 mg/mL

Medicated feedingstuff prescription: Potencil (Novartis) UK

Oral powder, for addition to feed, phenoxymethylpenicillin potassium 100 g/kg, for pigs

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

Prescription-only medicine: Depocillin (Intervet) UK

Injection, procaine benzylpenicillin 300 mg/mL, for horses, cattle, sheep, pigs, dogs, cats

Withdrawal Periods. Should not be used in horses intended for human consumption.

Cattle: slaughter 4 days, milk 3 days.

Sheep: slaughter 4 days, should not be used in sheep producing milk for human consumption.

Pigs: slaughter 5 days

Prescription-only medicine: Duphapen (Fort Dodge) UK

Injection, procaine benzylpenicillin 300 mg/mL, for cattle, sheep, pigs

Withdrawal Periods.

Cattle: slaughter 5 days, milk 2 days.

Sheep: slaughter 5 days, should not be used in sheep producing milk for human consumption.

Pigs: slaughter 5 days

Prescription-only medicine: Duphapen Fort (Fort Dodge) UK

Depot injection, procaine benzylpenicillin 300 mg/mL, for cattle, pigs

Withdrawal Periods.

Cattle: slaughter 10 days (subcutaneous injection), 21 days (intramuscular injection), milk 5 days (intramuscular injection), should not be used by subcutaneous injection in cattle producing milk for human consumption.

Pigs: slaughter 7 days

Prescription-only medicine: Norocillin (Norbrook) UK

Injection, procaine benzylpenicillin 300 mg/mL, for cattle, sheep, pigs

Withdrawal Periods.

Cattle: slaughter 5 days, milk 2.5 days.

Sheep: slaughter 5 days, should not be used in sheep producing milk for human consumption.

Pigs: slaughter 5 days

Prescription-only medicine: Penacare (Animalcare) UK

Injection, procaine benzylpenicillin 300 mg/mL, for cattle, sheep, pigs

Withdrawal Periods.

Cattle: slaughter 5 days, milk 2.5 days.

Sheep: slaughter 5 days, should not be used in sheep producing milk for human consumption.

Pigs: slaughter 5 days

Prescription-only medicine: Ultrapen LA (Norbook) UK

Depot injection, procaine benzylpenicillin 300 mg/mL, for cattle, pigs

Withdrawal Periods.

Cattle: slaughter 10 days (subcutaneous injection), 21 days (intramuscular injection), milk 5 days (intramuscular injection), should not be used by subcutaneous injection in cattle producing milk for human consumption.

Pigs: slaughter 7 days

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 body-weight, repeat after 3-4 days if required

Prescription-only medicine: Duplocillin LA (Intervet) UK

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