Amoxicillin: A Broad Spectrum Antibiotic
Amoxicillin though originally introduced in the early 1970’s for oral use in U.K., has found a gradually regular place as broad spectrum antibacterial to treat the infections of various diseases.
Amoxicillin has been found to be more effective against gram positive than gram negative microorganisms and demonstrated greater efficacy to penicillin and penicillin V. Moreover, it has been found comparable to other antibiotics, e.g. ampicillin, azithromycin, clarithromycin, cefuroxime and doxycycline in treatment of various infections / diseases.
In the past decade, amoxicillin has been reported to be useful in the management of many indications and is used to treat infections of the middle ear (otitis media) , tonsils (tonsillitis & tonsillopharyngitis), throat, larynx (laryngitis) , pharynx (pharyngitis), bronchi (bronchitis), lungs (pneumonia), urinary tract (UTI), skin and to treat gonorrhoea.
Recent studies suggested that it can be used as prophylaxis against bacterial endocarditis, in patients with prosthetic joint replacements and in dentistry.
The renewed interest of the molecule has prompted a review of the salient facets of the drug.
Amoxicillin, an acid stable, semi-synthetic drug belongs to a class of antibiotics called the Penicillins (beta-lactam antibiotics). It is shown to be effective against a wide range of infections caused by wide range of Gram-positive and Gram-negative bacteria in both human and animals. It is a congener of ampicillin (a semi-synthetic amino-penicillin) differing from the parent drug only by hydroxylation of the phenyl side chain. It has found a niche in the treatment of ampicillin-responsive infections after oral administration. Amoxicillin monograph is available in United States, British and Indian pharmacopoeias.
History and Challenges in Development
Historically, infectious diseases have been the most important contributor to human morbidity and mortality until recent times, when non-communicable diseases begin to rival, and sometimes exceed, infections.
Today, infectious diseases still account for a large proportion of death and disability worldwide and in certain regions remain the most important cause of ill health. infectious diseases are major public health issues for both developed and developing countries.
Africa and India both suffer significant population losses each year from infectious and parasitic diseases.
Approximately 5 million people in Africa and 2 million people in India ― mostly children and young adults die each year because of these diseases. Africa and India’s 7 million infectious disease deaths account for 70% of infectious disease deaths worldwide and 13% of all deaths worldwide. The World Health Organisation (WHO) in 2005 ranked infections as the leading global burden of disease and the leading cause of mortality in children.
Acute respiratory infections are the leading infectious cause of death in all ages, worldwide. Current key community and hospital bacterial disease burdens include paediatric infections and multiple drug resistance in both Gram-positive and Gram-negative organisms.
An increasing prevalence of antibiotic resistance has led to the progressive decrease in the effectiveness of narrow-spectrum agents and to an increase in difficult-to-treat infections.
More than ever, selection of the most appropriate antibiotic therapy has become a challenge for clinicians. In the 1960s, a limited range of non beta-lactam antibacterials was available; most had certain limitations in terms of toxicity e.g. sulphonamides (rashes and renal toxicity); streptomycin and kanamycin (ototoxicity and nephrotoxicity); chloramphenicol (bone marrow aplasia); erythromycin (gastrointestinal side effects); tetracyclines (concentrate in developing bones and teeth) and colistin (neuro and nephrotoxicity).
A number of beta-lactams, penicillins: penicillin G and V (gastric acid labile), ampicillin, methicillin (nephrotoxicity) and also cephalosporins: cephaloridine and cephalothin (nephrotoxicity) were reported. All of these agents were generally given as a four times daily dose and were associated with rashes and, rarely, anaphylaxis14.
At the end of the 1960s, challenging infections requiring treatment in hospitals included meningitis, endocarditis, neonatal infections, penicillin-resistant staphylococcal infections and infections caused by Gram-negative organisms. In primary care, infections of the urinary tract, respiratory tract and skin and soft tissues were a common cause of morbidity and sometimes mortality.
Further problem areas emerging in the 1970s included mixed infections, antibiotic-resistant bacteria, new pathogens and infections in immunocompromised patients, those undergoing surgery, and infections in haemodialysis patients.
There was a requirement for broad-spectrum antibiotics active against resistant organisms and in mixed infections. The 1970s saw the introduction of a number of important new antimicrobial agents, some of which were still associated with adverse events, such as co-trimoxazole (rashes and sulphonamide toxicity), tobramycin and amikacin (aminoglycoside toxicity) and metronidazole (neuropathy).
Certain new beta-lactam antibiotics were also introduced including the cephalosporins ― cefamandole, cefuroxime; the cephamycin, cefoxitin; and the penicillins -amoxicillin, flucloxacillin, mezlocillin, azlocillin and ticarcillin. All could be associated with rashes and, rarely, anaphylaxis. In 1972, amoxicillin was introduced in the UK, which maintained the broad-spectrum activity of ampicillin, but with increased bioavailability. As beta-lactamase production by both gram-positive and gram-negative pathogens became a clinically relevant issue, efforts were made to develop an orally bioavailable, broad-spectrum penicillin that was also effective against these strains, resulting in the combination of amoxicillin and clavulanic acid (amoxicillin / clavulanate). In 1981, SmithKline Beecham patented amoxicillin or amoxicillin / clavulanate potassium tablets, and first sold the antibiotic in 1998 under the trade names of amoxicillin, amoxil, and trimox. At the close of the decade, a range of requirements for a new antibacterial still remained.
These included activity against penicillinase-producing gram-positive and gram-negative organisms (including anaerobes), a broad spectrum of activity and good tolerability, including in children, availability as both an oral and injectable formulation, and activity in a range of indications including urinary tract infections (UTIs), respiratory tract infections (RTIs), skin and soft tissue infections (SSTIs), intra-abdominal infections and septicaemia.
This set the scene for the development of an antibacterial agent that would fulfil these requirements. Although there are currently new antibacterial compounds in development, most are at a pre-clinical stage. It is necessary, therefore, to make the best use of currently available agents. The development of higher dosing regimens and pharmacokinetically enhanced formulations have allowed amoxicillin (alone and in combination) to continue to play an important role in the treatment of a range of infections, particularly those of the respiratory tract in both adults and children worldwide.
Amoxicillin Dosage Forms and Regimen
Amoxicillin available in the dosage form of tablets (200mg-875mg), chewable tablets (125-500mg), dispersible tablets (750mg), capsules (250mg-500mg), oral suspension and dry powder for oral suspension / drops (50mg/ml-400 mg/ml) strengths for oral administration and injection & dry powder for injection (250mg-1000mg) strengths for intramuscular and intravenous injection / infusion, for treatments of infections and for prophylaxis use. Dosage regimen for various disease conditions, given in table Shows Dosage regimen of amoxicillin for various disease conditions.
Shows Dosage regimen of amoxicillin for various disease conditions
| Adults and Pediatric Patients > 3 Months | |||
| Infections / Disease | Severity * | Usual adult dose | Usual Dose for Children > 3 Months ** |
| Ear / Nose / Throat | Mild / Moderate | 500 mg every 12 hours or 250 mg every 8 hours | 25 mg / kg / day in divided doses every 12 hours or 20 mg / kg / day in divided doses every 8 hours |
| Severe | 875 mg every 12 hours or 500 mg every 8 hours | 45 mg / kg / day in divided doses every 12 hours or 40 mg / kg / day in divided doses every 8 hours | |
| Lower Respiratory Tract | Mild / Moderate or Severe | 875 mg every 12 hours or 500 mg every 8 hours | 45 mg / kg / day in divided doses every 12 hours or 40 mg / kg / day in divided doses every 8 hours |
| Skin / Skin Structure | Mild / Moderate | 500 mg every 12 hours or 250 mg every 8 hours | 25 mg / kg / day in divided doses every 12 hours or 20 mg / kg / day in divided doses every 8 hours |
| Severe | 875 mg every 12 hours or 500 mg every 8 hours | 45 mg / kg / day in divided doses every 12 hours or 40 mg / kg / day in divided doses every 8 hours | |
| Genitourinary Tract | Mild / Moderate | 500 mg every 12 hours or 250 mg every 8 hours | 25 mg / kg / day in divided doses every 12 hours or 20 mg / kg / day in divided doses every 8 hours |
| Severe | 875 mg every 12 hours or 500 mg every 8 hours | 45 mg / kg / day in divided doses every 12 hours or 40 mg / kg / day in divided doses every 8 hours | |
| Gonorrhea | 3 grams as single oral dose | Pre-pubertal children: | |
| Acute, uncomplicated ano-genital & urethral infections in males & females | 50 mg / kg, combined with 25 mg / kg probenecid as a single dose. Note: since probenecid is contraindicated in children under 2 years, do not use this regimen in these cases | ||
| Duodenal ulcer, (H. pylori ― associated) | ― Triple antibiotic therapy: 1000 mg amoxicillin with 500 mg clarithromycin and 30 mg lansoprazole two times a day at twelve-hour intervals for 14 days ― Dual antibiotic therapy: 1000 mg amoxicillin with 30 mg lansoprazole three times a day at 8-hour intervals for 14 days | ||
| Bacterial endocarditis (prophylaxis) | ― 3 grams 1 hour before the procedure, then 1.5 grams 6 hours after the initial dose | ||
* Dosing for infections caused by less susceptible organisms should follow the recommendations for severe infections.
** The children’s dosage is intended for individuals whose weight is less than 40 kg. Children weighing 40 kg or more should be dosed according to the adult recommendations.
Amoxicillin: Conclusion
Amoxicillin with its comparable clinical efficacy to other antibacterials and favourable dosage, pharmacokinetic profile and tolerability is an excellent candidate to treat various infectious diseases. As it is less effective against gram negative organisms and bacterial resistance develop to the drug candidate, it is the one area where major development is required. Progression in work is also required to investigate new routes of administration and dosage forms with more efficacies to reduce the dose and associated side effects. International Journal of Pharmacy and Pharmaceutical Sciences (Vol 3. Issue 3.2011) http://www.ijppsjournal.com