Amoxicillin is a broad-spectrum antibiotic indicated for the treatment of commonly occurring bacterial infections such as:
Upper respiratory tract infections: e.g. sinusitis, acute pharyngitis
Lower respiratory tract infections: e.g. acute exacerbation of chronic bronchitis, lobar and bronchopneumonia, uncomplicated community acquired pneumonia, H. influenzae infections
Gastrointestinal tract infections: e.g. acute gastritis, peptic ulcer disease and invasive salmonellosis
Skin and soft tissue infections: e.g. cellulitis, erysipelas, osteomyelitis.
Genito-urinary tract infections: e.g. cystitis, urethritis, pyelonephritis, bacteriuria in pregnancy, septic abortion, puerperal sepsis.
ENT infections: Cervical adenitis, otitis media
Dental infections: Dental abscess (as an adjunct to surgical management), suppurative odontogenic infections.
Amoxicillin is 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.
Amoxicillin is a semi-synthetic aminopenicillin of the beta-lactam group of antibiotics. It 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. It is rapidly bactericidal and possess the safety profile of a penicillin.
Amoxicillin is well absorbed. Oral administration, usually at convenient t.d.s. Dosage, produces high serum levels, independent of the time at which food is taken. Amoxicillin is not highly protein bound; approximately 18% of total plasma drug content is bound to protein. Amoxicillin 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 amoxicillin. The elimination half-life is approximately 1 hour. The major route of elimination for amoxicillin is via the kidneys; approximately 60-70% of amoxicillin is excreted unchanged in urine during the first 6 hours after administration of a standard dose. Amoxicillin is partly excreted in the urine as the inactive penicilloic acid in quantities equivalent to 10-25% of the initial dose.
Dosage and administration
Standard adult dosage
250mg three times daily, increasing to 500mg three times daily for more severe infections.
High dose therapy: Maximum recommended oral dosage 6gm daily in divided doses
Short course therapy
Simple acute urinary tract infection: two 3g doses with 10-12 hours between the doses
Dental abscess: two 3g doses with 8 hours between the doses
Urinary tract infections: 3g repeated after 10-12 hours
Standard children’s dosage (up to 10 years of age)
Child up to 10 years: 125mg every 8 hours doubled in severe infections
Amoxicillin is a penicillin and should not be given to penicillin hypersensitive patient. Attention should be paid to possible cross-sensitivity with other beta-lactam antibiotics e.g. cephalosporins
Special warning and precautions for use
Before initiating therapy with amoxicillin, careful inquiry should be made concerning previous hypersensitivity reactions to penicillins, cephalosporins.
Serious and occasionally fatal hypersensitivity (anaphylactoid) reactions have been reported in patients on penicillin therapy. These reactions are more likely to occur in individuals with a history of hypersensitivity to beta-lactam antibiotics Erythematous (morbilliform) rashes have been associated with glandular fever in patients receiving amoxicillin.
Prolonged use may also occasionally result in overgrowth of non-susceptible organisms.
Dosage should be adjusted in patients with renal impairment
Interaction with other medicines
In common with other broad-spectrum antibiotics, Amoxicillin may reduce the efficacy of oral contraceptives and patients should be warned accordingly. Concurrent administration of Allopurinol during treatment with amoxicillin can increase the likelihood of allergic skin reactions.
Prolongation of prothrombin time has been reported rarely in patients receiving Amoxicillin. Appropriate monitoring should be undertaken when anticoagulants are prescribed concurrently.
It is recommended that when testing for the presence of glucose in urine during amoxicillin treatment, enzymatic glucose oxidase methods should be used. Due to the high urinary concentrations of amoxicillin, false positive readings are common with chemical methods.
Probenecid decreases the renal tubular secretion of Amoxicillin. Concurrent use with amoxicillin may result in increased and prolonged blood levels of amoxicillin.
Pregnancy and lactation
Animal studies with amoxicillin have shown no teratogenic effects. However treatment with Amoxicillin may be considered appropriate when the potential benefits outweigh the potential risks associated with treatment.
Amoxicillin may be given during lactation. With the exception of the risk of sensitisation associated with the excretion of trace quantities of Amoxicillin in breast milk, there are no known detrimental effects for the breast-fed infant.
Effects on ability to drive or operate machinery
Adverse effects on the ability to drive or operate machinery have not been observed.
Side effects, as with other penicillins, are common and mainly of a mild and transitory nature.
Hypersensitivity reactions: if any hypersensitivity occurs, the treatment should be discontinued.
Skin rash, pruritis and urticaria have been reported occasionally. Rarely, skin reaction such as erythema multiforme and Steven-Johnson syndrome, toxic epidermal necrolysis and bullous and exfoliative dermatitis have been reported. As with other antibiotics, severe allergic reactions including angioneurotic oedema, anaphylaxis, serum sickness, and hypersensitivity vasculitis have been reported rarely.
Gastrointestinal reactions: effects include nausea, vomiting and diarrhea. Intestinal candidiasis and antibiotic associated colitis (including pseudo-membranous colitis and haemorrhagic colitis) have been reported rarely intestinal nephritis can occur rarely.
Hepatic effects: a moderate rise in AST and/or ALT has been occasionally noted but the significance of this is unclear. As with other beta-lactam antibiotics, hepatitis and cholestatic jaundice have been reported rarely.
Hematological effects: as with other beta-lactam antibiotics, reversible leucopenia (including severe netropenia or agranulocytosis), reversible thrombocytopenia and haemolytic anaemia have been reported rarely. Prolongation of bleeding time and prothrombin time have also been reported rarely.
CNS effects: CNS effects have been reported rarely. They include hyperkinesias, dizziness and convulsions. Convulsions may occur in patients with impaired renal function or in those receiving high doses.
Miscellaneous: Superficial tooth discoloration has been reported rarely and mostly with the suspension and chewable tablets. It can usually be removed by brushing.
Problems of overdosage with amoxicillin are unlikely to occur. If encountered, gastrointestinal effects such as nausea, vomiting and diarrhoea may be evident and should be treated symptomatically with attention to the water/electrolyte balance. During the administration of high doses of amoxicillin, adequate fluid intake and urinary output must be maintained. Amoxicillin can be removed from the circulation by haemodialysis.