Amoxicillin 250mg Capsules
Amoxicillin is a broad-spectrum antibiotic which provides bactericidal activity against a wide range of common gram-positive and gram-negative pathogens. Amoxicillin has bactericidal activity against susceptible organisms similar to that of ampicillin. It acts by inhibiting the biosynthesis of bacterial cell wall mucopeptides. Most strains of the following gram-positive and gram-negative bacteria have demonstrated susceptibility to amoxicillin, nonpenicillinase-producing staphylococci, alpha- and beta-hemolytic streptococci, Streptococcus faecalis, Escherichia coli and Proteus mirabilis. Amoxicillin does not resist destruction by penicillinase; therefore, it is not effective against penicillinase-producing bacteria, particularly resistant staphylococci. Most strains of Enterobacter and Klebsiella and all strains of Pseudomonas are resistant.
Amoxicillin may be given without regard to meals because it is stable in gastric acid. It is rapidly absorbed following oral administration and diffuses readily into most body fluids and tissues. It diffuses poorly into the brain and spinal fluid except when the meninges are inflamed. Most of amoxicillin is excreted in the urine unchanged.
Pharmacology/Uses/Indications
Although there may be some slight differences in
activity against certain organisms, amoxicillin generally shares the same
spectrum of activity and uses as ampicillin. Because it is better absorbed
orally (in non-ruminants), higher serum levels may be attained than with
ampicillin.
Penicillins are usually bactericidal against susceptible
bacteria and act by inhibiting mucopeptide synthesis in the cell wall resulting
in a defective barrier and an osmotically unstable spheroplast. The exact
mechanism for this effect has not been definitively determined, but beta-lactam
antibiotics have been shown to bind to several enzymes (carboxypeptidases,
transpeptidases, endopeptidases) within the bacterial cytoplasmic membrane that
are involved with cell wall synthesis. The different affinities that various
beta-lactam antibiotics have for these enzymes (also known as penicillin-binding
proteins; PBPs) help explain the differences in spectrums of activity the drugs
have that are not explained by the influence of beta-lactamases. Like other
beta-lactam antibiotics, penicillins are generally considered more effective
against actively growing bacteria.
Contraindications/Precautions
Penicillins are contraindicated in patients who have a
history of hypersensitivity to them. Because there may be cross-reactivity, use
penicillins cautiously in patients who are documented hypersensitive to other
beta-lactam antibiotics (e.g., cephalosporins, cefamycins, carbapenems).
Do not administer systemic antibiotics orally in patients
with septicemia, shock, or other grave illnesses as absorption of the medication
from the GI tract may be significantly delayed or diminished. Parenteral
(preferably IV) routes should be used for these cases.
Reproductive/Nursing Safety
Penicillins have been shown to cross the placenta and
safe use of them during pregnancy has not been firmly established, but neither
have there been any documented teratogenic problems associated with these drugs.
However, use only when the potential benefits outweigh the risks. In humans, the
FDA categorizes this drug as category B for use during pregnancy
(Animal studies have not yet demonstrated risk to the fetus, but there are no
adequate studies in pregnant women; or animal studies have shown an adverse
effect, but adequate studies in pregnant women have not demonstrated a risk to
the fetus in the first trimester of pregnancy, and there is no evidence of risk
in later trimesters.) In a separate system evaluating the safety of drugs in
canine and feline pregnancy, this drug is categorized as in class: A
(Probably safe. Although specific studies may not have proved the safety of all
drugs in dogs and cats, there are no reports of adverse effects in laboratory
animals or women.)
Adverse Effects/Warnings
Adverse effects with the penicillins are usually not
serious and have a relatively low frequency of occurrence.
Hypersensitivity reactions unrelated to dose can occur
with these agents and can be manifested as rashes, fever, eosinophilia,
neutropenia, agranulocytosis, thrombocytopenia, leukopenia, anemias,
lymphadenopathy, or full-blown anaphylaxis. In humans, it is estimated that up
to 15% of patients hypersensitive to cephalosporins will also be hypersensitive
to penicillins. The incidence of cross-reactivity in veterinary patients is
unknown.
When given orally, penicillins may cause GI effects
(anorexia, vomiting, diarrhea). Because the penicillins may also alter gut
flora, antibiotic-associated diarrhea can occur, as well as selecting out
resistant bacteria maintaining residence in the colon of the animal (superinfections).
High doses or very prolonged use has been associated with
neurotoxicity (e.g.,ataxia in dogs). Although the penicillins are not considered
hepatotoxic, elevated liver enzymes have been reported. Other effects reported
in dogs include tachypnea, dyspnea, edema and tachycardia.
Overdosage/Acute Toxicity
Acute oral penicillin overdoses are unlikely to cause
significant problems other than GI distress, but other effects are possible (see
Adverse Effects). In humans, very high dosages of parenteral penicillins,
especially in patients with renal disease, have induced CNS effects.
Drug Interactions
In vitro studies have demonstrated that
penicillins can have synergistic or additive activity against certain bacteria
when used with aminoglycosides or cephalosporins.
Use of bacteriostatic antibiotics (e.g.,chloramphenicol,
erythromycin, tetracyclines) with penicillins is generally not recommended,
particularly in acute infections where the organism is proliferating rapidly as
penicillins tend to perform better on actively growing bacteria. In low
concentrations, certain penicillins (e.g.,ampicillin, oxacillin or nafcillin)
may have additive or synergistic effects against certain bacteria when used with
rifampin, but there is apparent antagonism when the penicillin is present
in high concentrations.
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