Antibiotics are used to fight
bacteria and fungus in and on the body. Bacteria are classified according to
their ability to cause disease. Pathogenic bacteria are capable of producing a
particular illness or infection. Nonpathogenic bacteria live on or within the
host but do not cause illness under normal conditions. These bacteria are
called normal flora. Some actually produce substances necessary to the
well-being of the host. For example, bacteria in the bowel synthesize vitamin
K, which is necessary for blood clotting. Rarely, nonpathogenic bacteria will
overgrow and cause symptoms due to their sheer numbers.
Antibiotics fall into two categories: Bacteriostatic and fungistatic drugs
inhibit the growth of microorganisms but don’t kill them; bactericidal and
fungicidal drugs destroy the microorganisms outright.
Antibiotics may not always be effective, for a number of reasons.
Inadequate Wound Care
Antibiotics enter the bloodstream and are carried to the source of the
infection. Abscesses, wounds that contain devitalized
tissue, and wounds with foreign bodies (dirt or splinters, for example) are
resistant areas. Under such circumstances, antibiotics can’t penetrate the
wound completely. Accordingly, it is essential to drain abscesses, clean dirty
wounds, and remove foreign bodies.
An antibiotic chosen to treat an infection must be effective against the
specific type of bacteria that is infecting the body. The best way to determine
susceptibility is to sample the organism, grow it on a culture plate, and
identify it by the way its colony appears and by microscopic characteristics.
Antibiotic discs are then applied to the culture plate to see which discs
inhibit the growth of bacteria colonies. The results are graded according to
whether the bacteria are sensitive, indifferent, or insensitive to the effects
of the antibiotic. Laboratory findings, however, do not always coincide with
results in the patient. Nonetheless, sensitivity testing is the best way to
select the most effective antibiotic.
Route of Administration
An important medical decision is choosing the best route for administration.
In a dog with severe infections,
antibiotics may be given intravenously or by intramuscular or subcutaneous
injection. Some oral antibiotics should be given on an empty stomach; others
with a meal. Incomplete absorption is one cause of inadequate levels of
antibiotics in the blood. If the dog is vomiting, oral medications may
not be absorbed.
Dose and Frequency of Administration
The dose is computed by weighing the dog, then dividing the total daily dose
into equal parts and giving them at prescribed intervals. Other factors that
must be accounted for when computing the daily dose are the severity of the
infection, the age of the dog, her overall health and stamina, and whether the
dog is taking another antibiotic. When the total dose is too low or the
antibiotic is not given often enough, the drug may not be effective.