The word antibiotic is derived from two Greek words anti meaning against and bios meaning life. Antibiotics may be defined as the compounds produced synthetically, semi-synthetically or by various species of microorganism that have the capability to kill or inhibit the growth of other microorganism.
The term antibiotic and antibacterial are used synonymously. Generally antibiotics or antibacterials are the drugs used to treat infections caused by bacteria. Bacteria (singular = bacterium) are the simplest and smallest tiny organisms possessing cellular organization that can sometimes cause illness to animals and human beings, such as meningitis, syphilis, anthrax, tuberculosis, pneumonia etc. Not all bacteria are harmful but even some are good for us. When harmful bacteria attack our body, our immune system become active and destroy them before they multiply and cause symptoms of the infection. Mild infections are also eradicated by immune system, but in case it fails to fight off infection we need some help from outside the body. Antibiotics provide this aid to destroy invading microorganisms and eradicate infections.

How do antibiotics work?

All antibiotic drugs are effective in the treatment of infectious diseases because of their selective toxicity. It means that the drug is harmful to an invading microorganism without harming the cells of the host .Selective toxicity is due to biochemical differences that exist between microorganisms and the host .Concentration of the drug should be carefully controlled to attack the microorganism while still being tolerated by the host. All antibiotics work either as bacteriostatic or bactericidal.

What are bacteriostatic drugs?

Bacteriostatic drugs stop bacteria from multiplying. They inhibit the growth of microorganisms temporarily . The therapeutic success of these agents depends upon the participation of defence mechanism of the host . The effect may be reversible i.e. when the drug used is stopped , the organisms will resume growth and infection or disease will reoccur in immunocompromised patient.

These drugs kill the microorganisms . The treatment with bactericidal drugs becomes mendatory in case of those infections that cannot be controlled or eradicated by defence mechanism of host. Examples are, beta-lactam antibiotics, cephalosporins, penicillines and aminoglycosides.
However the term bactericidal and bacteriostatic are relative and not absolute. As some times prolong treatment, higher dose of bacteriostatic agents can cause death of microorganism (chlormphenicol and maningococci) while bacctericidal drugs may fail to kill the microbes e.g penicillin and enterococci.
Bactericidal drugs can be divided into two subgroups,
1- Drugs that exhibit concentration dependent killing. For these drugs, the rate and extent of killing increases with increase in concentration above MBC (minimal bactericidal concentration). Maximum peak concentration of these drugs results in increased efficacy and decreased resistance.
2- Drugs that exhibit time dependent killing. Increase in concentration of these drugs does not result in increased killing of susceptible microorganisms. Bactericidal activity is directly related to time above MBC (minimal bactericidal concentration) and not the concentration of the drug.

Amoxicillin: What Is It?


It is a broad spectrum penicillin that inhibits the growth of bacteria by inhibiting bacterial cell wall synthesis. It is usually the drug of choice within the class because it is better absorbed, following oral administration, than other β-lactam antibiotics.

Spectrum of activity

It is active against gram positive and gram negative organism is such as,

  • Streptococcus
  • Bacillus subtilis
  • Enterococci
  • Haemophilus influenzae
  • Helicobacter
  • Moraxella
  • Pneumococci
  • Gonococci


Following organisms have developed resistant to amoxicillin;

  • Citrobacter
  • Pseudomonas aeruginosa
  • E.coli
  • Staphylococcus aureus
  • Salmonella
  • Proteus
  • Shigella

Pharmacokinetics of Amoxicillin

  • It is well absorbed after oral administration.
  • Presence of food in the gut does not interfere with the absorption of amoxicillin.
  • Peale plasma concentration is achieved within 1-2 hrs.
  • It is partially metabolized to inactive metabolites.
  • Inactive metabolites and unchanged drug is excreted in urine.

Dosages forms available

It is available in the forms of;

  • Capsules
  • Oral liquids
  • Sachets
  • Injections

Therapeutic uses of amoxicillin

It is used in the treatment of;

  • Urinary tract infection
  • Otitis media
  • Streptococcal pharyngitis
  • Pneumonia
  • Sinusitis
  • Chlamydia infections
  • Gonorrhoea
  • Lyme disease
  • Endocarditis prophylaxis
  • Dental abscesses
  • Anthrax
  • Acne vulgaris

Adverse effects of amoxicillin

Most common adverse effects are;

  • Diarrhea
  • Nausea
  • Vomiting
  • Rashes
  • Confusion
  • Anxiety
  • Insomnia
  • Lethargy
  • Renal dysfunction
  • Jaundice
  • Convulsion
  • Dizziness
  • Behavioral changes sore in mouth
  • Stomach pain
  • Swollen tongue
  • Dark urine
  • Blistering
  • Oedema
  • Dyspnea
  • Hypotension
  • Leukopenia
  • Thrombocytopenia
  • Hemolytic anemia
  • Cough
  • Asthma
  • Hives
  • Abdominal pain

Drug interactions of amoxicillin

  • Sulfonamide may diminish the bactericidal effects of amoxicillin, when administered together.
  • Use of amoxicillin with allopurinol may increases the incident of rashes.
  • Methotrexate may interfere with the effects of amoxicillin when given together.

Contraindications of amoxicillin

Amoxicillin is contraindicated in the individuals with the history of;

  • Asthma
  • Diarrhea
  • Allergic to amoxicillin
  • Liver disease
  • Kidney disease
  • Oedema
  • Pregnancy
  • Lactation

Storage of amoxicillin

  • Keep this medicine out of the reach of children.
  • It should be stored in a cool, dry place and away from sunlight.
  • Liquid form of this medicine should be stored in a refrigerator.