Small Animal Clinical Pharmacology - CYF MEDICAL DISTRIBUTION

CLASSIFICATION OF ANTIBACTERIAL DRUGS
Nonetheless, in some circumstances administering a
shorter-acting glucocorticoid (such as hydrocortisone)
topically or prednisolone systemically for a few
days can help by suppressing an acute inflammatory
response that may be causing pain or discomfort and
provoking self trauma, as with skin or ear
infections.
Prophylactic antibacterial treatment
Prophylactic antibacterials in surgery
Perioperative prophylactic use of antibacterial drugs in
surgery is not indicated for routine, clean surgery where
no inflammation is present, the gastrointestinal, reproductive
or respiratory systems have not been invaded
and aseptic technique has not been broken.
Perioperative antibacterial prophylaxis is indicated
after dental procedures in which there has been bleeding
(almost all), patients with leukopenia (viral, druginduced),
contaminated surgery and surgery where the
consequences of infection would be disastrous (e.g.
orthopedic), there is major tissue trauma (e.g. major
thoracic and abdominal surgery) or the surgical time
exceeds 90 min.
If antibacterial agents are used prophylactically, they
should be administered before the procedure so that
adequate concentrations are present in blood and tissue
at the time of surgery; for maximum effect the drug must
be present in the wound when bacterial contamination
occurs. IV administration 20–30 min prior to surgery is
currently recommended as this gives the highest tissue
concentrations at the time of surgery. Timings of initial
and subsequent doses of perioperative antibiotics depend
on the pharmacokinetics of the selected drug in the
patient undergoing anesthesia and concomitant fluid
therapy. The advantages of perioperative antibacterial
prophylaxis are minimal if the drug is first administered
any later than 3–5 h after contamination.
Note that acute toxicity on cardiovascular or neuromuscular
function is most likely after IV administration
and drugs should be injected slowly. Anesthetic and
sedatives agents may interact to increase the likelihood
of adverse reactions; β-lactams are the safest drugs in
this respect.
The drug chosen should be appropriate in relation to
the likely contaminating pathogen. In small animal
practice this may include penicillinase-producing Staphylococcus
(from the patient or the surgeon), so that
nonpotentiated penicillins such as amoxicillin are not
suitable. If contamination by intestinal bacteria is suspected
or confirmed, drugs that are effective against
obligate anaerobes and Gram-negative aerobes should
be chosen (see Fig. 8.25).
Chemoprophylaxis is not usually continued for longer
than 24 h post surgery and in some institutions a postoperative
dose of antibacterial is only administered if
surgery time exceeds 90 min.
Other prophylactic uses of antibacterial agents
Prophylactic use of antibacterial agents has been important
in controlling certain infectious diseases, primarily
in intensively managed production animals. Metaphylaxis
refers to treating the whole group when only a
proportion shows clinical signs.
Potential disadvantages include:
● toxicity
● encouragement of selection of drug resistance
● residues in edible animal products
● cost.
Principles of successful prophylaxis include the
following.
● Medication should be directed against a specific
pathogen or disease condition.
● Target organism should be one that does not
readily develop drug resistance.
● Duration should be as short as possible consistent
with efficacy.
● Should only be used where efficacy is clearly
established.
● Dosage should be the same as used therapeutically.
CLASSIFICATION OF ANTIBACTERIAL
DRUGS
Bactericidal versus bacteriostatic
Antibacterial agents are often described as bacteriostatic
or bactericidal. However, this classification only really
applies under strict laboratory conditions, is inconsistent
against all bacteria and becomes more arbitrary in
clinical cases.
Bacteriostatic drugs
Bacteriostatic drugs (chloramphenicol, lincosamides,
macrolides, sulfonamides, tetracyclines, trimethoprim)
temporarily inhibit the growth of organisms but the
effect is reversible once the drug is removed. For these
drugs to be clinically effective, the drug concentration
at the site of the infection should be maintained above
the MIC throughout the dosing interval. Many bacteriostatic
drugs can be bactericidal if drug exposure is
sufficiently high or prolonged. Although traditionally
bacteriostatic drugs have been avoided in serious infections,
evidence from human studies suggests that clindamycin,
a bacteriostatic drug, might be preferred for the
treatment of staphylococcal and streptococcal infections
as it inhibits the toxic shock syndrome that can occur
when bactericidal drugs are used.
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