Amoxicillin is stable in the presence of gastric acid and may be given without regard to meals. It is rapidly absorbed after oral administration. It diffuses readily into most body tissues and fluids, with the exception of brain and spinal fluid, except when meninges are inflamed. The half-life of Amoxicillin is 61.3 minutes. Most of the Amoxicillin is excreted unchanged in the urine; its excretion can be delayed by concurrent administration of Probenecid. Amoxicillin is not as highly protein-bound as compared to 60% for Penicillin G. Orally administered doses of 250mg and 500mg Amoxicillin result in average peak blood levels one to two hours after administration in the range of 3.5 mcg/ml to 5.0 mcg/ml and 5.5 mcg/ml to 7.5 mcg/ml respectively. Detectable serum levels are observed up to 8 hours after an orally administered dose of Amoxicillin.
Following a 1g dose and utilizing a special skin-window technique to determine levels of the antibiotic, it was noted that therapeutic levels were found in the interstitial fluid. Approximately 60% of an orally administered dose of Amoxicillin is excreted in the urine within six to eight hours. Amoxicillin exerts bactericidal action against susceptible organisms during the stage of active multiplication.
It acts through the inhibitions of biosynthesis of cell-wall mucopeptides. In vitro studies have demonstrated the susceptibility of most strains of the following gram-positive bacteria alpha- and beta-hemolytic Streptococci. Diplococcus pneumonia nonpenicillinase-producing Staphylococci, and Streptococcus faecalis.
It is active in vitro against many strains of Haemophilus influenzae, Neisseria gonorrhoeae, Escherichia coli and Proteus mirabilis. Because it does not resist destruction by Penicillinase, it is not effective against penicillinase-producing bacteria particularly resistant Staphylococci. All strains of Pseudomonas and most strains of Klebsiella and Enterobacter are resistant.
1. Infections of the ear, nose and throat due to Streptococci, Pneumococci, non-penicillinase-producing Staphylococci and H.influenzae.
2. Infections of the genitourinary tract due to E.coli. Proteus mirabilis and streptococcus faecalis.
3. Infections of the skin and soft tissues due to Streptococci, susceptible Staphylococci and E.coli.
4. Infections of the lower respiratory tract due to Streptococci. Pneumococci, non-penicillinase producing Staphylococci and H.influenzae.
5. Gonorrhoea and acute uncomplicated anogenital and urethral infections due to gonorrhea(males and females).
A history of allergic reaction to any of the penicillins is a contraindication.
Serious and occasionally fatal hypersensitivity (anaphylactoid) reactions have been reported in patients on parenteral Penicillin therapy. These reactions may occur with oral Penicillins particularly in individuals with a history of sensitivity to multiple allergens. There have been reports of individuals with a history of Penicillin hyper-sensitivity who have experienced severe reactions when treated with Cephalosporins. Before therapy with any Penicillin, careful inquiry should be made concerning previous hypersensitivity reactions to Penicillins, Cephalosporins, or other allergens. If an allergic reaction occurs, appropriate therapy should be instituted and discontinuance of Amoxicillin therapy considered.
Serious anaphylactoid reactions require immediate emergency treatment with Epinephrine, oxygen, intravenous steroids, and airway management, including intubation, should also be administered as indicated.
USAGE IN PREGNANCY
Safety for use in pregnancy has not been established.
As with any potent drug, periodic assessment of renal, hepatic and hematopoietic function should be made during prolonged therapy. The possibility of superinfections with mycotic or bacterial pathogens should be kept in mind during therapy. If superinfections occur (usually involving Enterobacter, Pseudomonas or Candida), the drug should be discontinued and/or appropriate therapy instituted.
As with other Penicillins, it may be expected that untoward reactions will be essentially limited to sensitivity phenomena. They 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. The following adverse reactions have been reported as associated with the use of Penicillin:
Gastrointestinal: Nausea, vomiting and diarrhea.
Hypersensitivity Reactions: Erythematous maculopapular rashes and uiticaria have been reported.
Note: Urticaraia, other skin rashes and serum sickness-like reactions may be controlled with antihistamines and, if necessary, systemic corticosteroids. Whenever such reactions occur, Amoxicillin should be discontinued unless, in the opinion of the physician, the condition being treated is life-threatening and amenable only to Amoxicillin therapy.
Liver: A moderate use in serum glutamic oxaloacetic transaminase (SGOT) has been noted but the significance of this finding is unknown.
Central Nervous System: Reversible hyperactivity, agitation, anxiety, insomnia, confusion behavioral changes, and/or dizziness have been reported rarely.
Hemic and Lymphatic Systems: Anemia, thrombocytopenia, thrombocytopenci purpura, eosinophilia, leukopenia and agranulocytosis have been reported during therapy with the penicillins. These reactions are usually reversible on discontinuation of therapy and are believed to be hypersensitivity phenomena.
The usual dosage regimen of Amoxicillin is 250-500mg three times a day.
In children, half of the adult dose may be used. Amoxicillin suspension may be used in children who find it difficult to swallow the capsules. Some infections may be treated with special dosage regimens given below:
a) Respiratory tract infections: 3g twice a day.
b) Acute urinary tract infection: 3g repeated once 12 hours later.
c) Gonorrhoea: 3g single dose.
d) Dental abscess: 3g repeated once 8 hours later.
e) Prophylaxis of endocarditis: Single 3g dose one hour before dental procedure from which bacteraemia may arise. Repeat 6 hours later if necessary.