Amoxicillin

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[edit] BRAND NAMES

  • International: Amoxil
  • Palestine: Amoxitid

[edit] STRUCTURE

Amoxicillin.jpg

[edit] MECHANISM OF ACTION

Amoxicillin is a semisynthetic aminopenicillin of the beta-lactam group of antibiotics.

Amoxicillin binds to penicillin-binding protein (PBP) located inside the bacterial cell well. Penicillins acylate the penicillin-sensitive transpeptidase C-terminal domain by opening the lactam ring. This inactivation of the enzyme prevents the formation of a cross-link of two linear peptidoglycan strands, inhibiting the third and last stage of bacterial cell wall synthesis. Cell lysis is then mediated by bacterial cell wall autolytic enzymes such as autolysins.

Amoxicillin has a broad spectrum of antibacterial activity against many Gram-positive and Gram-negative microorganisms, acting through the inhibition of biosynthesis of cell wall mucopeptide. Amoxycillin is, however, susceptible to degradation by beta-lactamases and therefore the spectrum of activity does not include organisms that produce these enzymes including resistant staphylococci, and all strains of Pseudomonas, Klebsiella, and Enterobacter.

Strains of the following organisms are generally sensitive to the bactericidal action of amoxycillin in vitro:

Gram-positive
Gram-negative
Other
Streptococcus faecalis
Streptococcus pneumoniae
Streptococcus pyogenes
Streptococcus viridans
Staphylococcus aureus 
(penicillin sensitive)
Clostridium species
Corynebacterium species
Bacillus anthracis
Listeria monocytogenes
Haemophilus influenzae
Escherichia coli
Proteus mirabilis
Salmonella
 species
Shigella species
Bordetella pertussis
Brucella 
species
Neisseria gonorrhoeae
Neisseria meningitidis
Pasteurella septica
Helicobacter pylori
Leptospira spp
Fusobacterium spp
Vibrio Cholerae
Borrelia burgdorferi

[edit] INDICATIONS

Amoxicillin is used to treat infections caused by susceptible organisms, such as otitis media, bronchitis, sinusitis, Helicobacter pylori, and bacterial cystitis.

Amoxicillin may be used for the prevention of bacteraemia associated with procedures such as dental extraction in patients at risk of developing bacterial endocarditis.

[edit] DOSAGE

Amoxicillin is not affected by food and may therefore be administered without regard to meals.

With the exception of gonorrhoea, treatment with Amoxicillin should be continued for a minimum of 48-72 hours beyond the time at which the patient becomes asymptomatic or evidence of bacterial eradication has been obtained.

Upper Respiratory Tract and Chest Infections
Adults and Children over 10 Years of Age
The recommended dosage is 250-500 mg 3 times daily, every 8 hours.

Infants and Children under 10 Years of Age
In infants under 2 years of age, the dosage is 62.5 mg 3 times daily, every 8 hours.
In children 2-10 years of age, the dosage is 125 mg 3 times daily, every 8 hours. For more severe infections, the dosage may be increased to 250 mg 3 times daily.

The recommended dosage according to body weight is 20 mg/kg per day in divided doses every 8 hours. For more severe infections, the dosage may be increased to 40 mg/kg body weight per day every 8 hours.


Skin and Soft-tissue Infections
Treat as for upper respiratory tract and chest infections.


Uncomplicated Lower Urinary Tract Infections
Adults
A single dose of 3 grams may be administered.

Children
A single dose of 100 mg/kg body weight may be administered.


Gonorrhoea
A single dose of 3 grams may be administered.


Prophylaxis of Bacterial Endocarditis (in dental procedures)
Adults and Children over 10 Years of Age
A single dose of 3 grams about 1 hour prior to the procedure, to prevent bacteraemia.

Children under 10 Years of Age
Half the adult dose.

[edit] CONTRAINDICATIONS

Known hypersensitivity to a penicillin-type drug.

Amoxicillin should not be administered to babies born to mothers with a history of hypersensitivity to a penicillin type drug.

[edit] WARNINGS AND PRECAUTIONS

Serious and occasionally even fatal hypersensitivity reactions due to penicillin therapy have been reported. Although anaphylaxis is more frequent following parenteral therapy, it has occurred in patients receiving oral penicillins. Such reactions are more likely to occur in individuals with a history of hypersensitivity to penicillins and/or a history of sensitivity to multiple allergens. There have also been reports of individuals with a history of penicillin hypersensitivity experiencing severe reactions when treated with cephalosporins.

Therefore before initiating therapy with this drug, careful inquiry should be made concerning previous hypersensitivity reactions to penicillins, cephalosporins, or other allergens, because of the risk of anaphylactoid reactions.

If an allergic reaction occurs, the drug should be discontinued and appropriate therapy instituted.

Serious anaphylactoid reactions require immediate emergency treatment with adrenaline. Oxygen, intravenous steroids and airway management including intubation, should also be administered as indicated.

Amoxicillin should not be used in patients suffering from mononucleosis, since these patients run a high risk of developing a skin rash.

[edit] INTERACTIONS

[edit] PHARMACOKINETICS

  • Absorption: Amoxycillin is rapidly absorbed from the gut to an extent of 72-93%. Absorption is independent of food intake.
  • Distribution:Peak blood levels are achieved 1-2 hours after administration. After 250 and 500 mg doses of amoxycillin, average peak serum concentrations of 5.2 mcg/ml and 8.3 mcg/ml respectively have been reported.
    Amoxycillin is not highly protein bound; approx. 18% of total plasma drug content is bound to protein. Amoxycillin diffuses readily into most body tissues and fluids, with the exception of the brain and spinal fluid. Inflammation generally increases the permeability of the meninges to penicillins and this may apply to amoxycillin.
  • Excretion: The major route of elimination for amoxycillin is via the kidney. Approximately 60-70% of amoxycillin is excreted unchanged in urine during the first 6 hours after administration of a standard dose. The elimination half-life is approximately 1 hour. Amoxycillin is also partly excreted in the urine as the inactive penicilloic acid in quantities equivalent to 10-25% of the initial dose. Concurrent administration of probenecid delays amoxycillin excretion.
    Small amounts of the drug are also excreted in feces and bile.

[edit] PREGNANCY AND LACTATION

Pregnancy Category B (US). Safety for use in pregnancy has not been established.

Nursing Mothers: Since penicillins are excreted in breast milk, administration of this drug to nursing mothers may lead to sensitization of their infants. Therefore, having taken into account the importance of the drug to the mother, either discontinue nursing or discontinue the drug.

[edit] SIDE EFFECTS

As with other penicillins, it may be expected that untoward reactions will be essentially limited to sensitivity phenomena. These reactions are more likely to occur in individuals who have previously demonstrated hypersensitivity to penicillins and in those with a history of allergy, asthma, hay fever, or urticaria.

In common with other ß-lactam antibiotics, angioedema and anaphylaxis may occur.
The following adverse reactions have been reported as being associated with the use of penicillins.


Hypersensitivity
Anaphylaxis is the most serious potential adverse reaction to a penicillin drug. It is usually associated with the administration of parenteral rather than oral dosage forms. Serious anaphylactoid reactions require immediate emergency treatment with adrenaline. Oxygen, intravenous steroids and airway management including intubation, should also be administered as indicated.

Erythematous maculopapular rashes, urticaria, and occasional cases of exfoliative dermatitis, erythema multiforme and Stevens-Johnson syndrome have been reported. Laryngeal edema and serum sickness-like reactions including chills, fever, edema and arthralgia have also been reported. Such reactions may be controlled with antihistamines and, if necessary, systemic corticosteroids. Whenever such reactions occur, the drug should be discontinued unless, in the opinion of the physician, the condition being treated is life threatening andamenable only to penicillin therapy.


Gastrointestinal
Clossitis, stomtatitis, black "hairy" tongue, nausea, vomiting, enterocolitis, pseudomembranous colitis and diarrhea have been observed.


Hepatic
A moderate rise in serum glutamic oxaloacetic transaminase (SGOT) and/or serum glutamic pyruvic transaminase (SGPT) has been noted, particularly ininfants, but the significance of this finding is unknown. Rare cases of transient hepatitis and cholestatic jaundice have been reported.


Haematological
Haematological reactions including haemolytic anaemia, thrombocytopenia, thrombocytopenic purpura, eosinophilia, Leukopenia, and agranulocytosis have been observed. These are believed to be hypersensitivity phenomena and are usually reversible upon discontinuation of therapy.


Central Nervous System
Rare cases of reversible hyperactivity, agitation, anxiety, insomnia, confusion, behavioural changes, and/or dizziness have been reported.

[edit] OVERDOSAGE

Overdosage of penicillin drugs may cause neuromuscular hyperirritability or convulsive seizures.

Discontinue medication, treat symptomatically, and institute supportive measures as required. In patients with renal function impairment, the antibiotic may be removed from the circulation by haemodialysis, not by peritoneal dialysis.

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[edit] REFERENCES