Infection

Caused by microorganisms
- Bacteria
- Viruses
- Fungi
- Protozoa
- Others

 

Mode Of Transmission

* Direct Contact : eg. Venereal, Skin infections
* Air-borne : eg. RTI, Tuberculosis
* Faeco-Oral : eg. Diarrhoea, Typhoid
* Vectors : eg. Malaria

 

Incubation Period

Time elapsing between entry of organisms into the body and onset of clinical symptoms

 

Susceptibility

Factors :
- Racial
- Alcoholism
- Diabetes
- Immunoglobulin deficiency
- Malnutrition
- Agranulocytosis
- Steroid administration
- Foreign body
- Immunization

 

Immunity

* Natural
* Acquired

Common Bacteria

Gram Positive
Cocci : Streptococcus, Staphylococci
Bacilli : Corynebacterium, Bacillus, Clostridium

Gram Negative
Cocci : Neisseria
Bacilli : Escherichia, Salmonella, Shigella, Haemophilus, Klebsiella,
Proteus, Pseudomonas

 

 

Laboratory Diagnosis Of Infection

1) Direct microscopic examination
2) Culture
3) Immunologic methods

 

Antibacterial Agents

Substances which interfere with bacterial growth

 

Selection Of An Antibacterial Agent

Based on :
1) Evaluation of probable etiology of infection and likelihood of susceptibility to the drug
2) Identification of causative organism and the degree of sensitivity
3) Nature of the drug - bactericidal / bacteriostatic
4) Severity of infection and general condition of patient

 

Selection OfAn Antibacterial Agent (Contd…)

5) Site of infection
6) Possibility of drug resistance
7) Risk of drug toxicity
8) History of previous allergy to the drug
9) Special situations eg., pregnancy
10) Cost of Therapy

 

Bactericidal/ Bacteriostatic

Penicillins
eg., Benzyl penicillin, Phenoxymethyl penicillin, Cloxacillin, Ampicillin, Carbenicillin, Ticarcillin

* Penicillin is derived from Penicillium notatum, others are semisynthetic derivatives
* Penicillins are known for efficacy and safety
* Possess beta-lactam ring and thiazolidine ring in nucleus (beta-lactam antibiotics)
* Penicillins may be inactivated by variousbeta-lactamases

Cephalosporins

* Derived from Cephalosporium acremonium
* Possess beta lactam ring and dihydrothiazine ring in nucleus (beta-lactam antibiotics)
* Stability / inactivation by various beta-lactamases

Cephalosporins

 

Macrolides
eg., Erythromycin, Roxithromycin, Azithromycin, Clarithromycin

* Orally administered antibacterials, with good efficacy against gram positive bacteria and some gram negative bacteria
* Particularly useful in RTI / ENT infections, skin & soft tissue infections
* Bacteriostatic agents

 

Tetracyclines
eg., Tetracycline, Oxytetracycline, Doxycycline

* Bacteriostatic agents
* Broad system coverage against gram positive & gram negative bacteria and Chlamydia

Chloramphenicol

* Bacteriostatic agent
* Broad spectrum
* Particularly useful in typhoid, but resistance and toxicity limits its use today

Aminoglycosides
eg., Streptomycin, Kanamycin, Gentamicin, Tobramycin, Neomycin

* Broad spectrum including Pseudomonas aeruginosa
* Bactericidal
* Used in hospital acquired infections
* Parenterally administered (except neomycin) systemic infections, also used topically
* Streptomycin used in tuberculosis

 

Sulphonamides
eg., Sulphamethoxazole, Sulphaxazole, Sulphacetamide

* Inhibit conversion of PABA to folic acid
* Bactericidal
* Sulphamethoxazole in combination with trimethoprim for synergistic bactericidal effects

 

Fluoroquinolones
eg., Ciprofloxacin, Norfloxacin, Ofloxacin, Sparfloxacin

* Structurally related to nalidixic acid with broader spectrum and less resistance
* Broad spectrum, bactericidal
* Orally efficacy against Pseudomonas aeruginosa

Nitroimidazoles
eg., Metronidazole, Tinidazole, Secnidazole

* Antiprotozoal agents
* Effective against anaerobic bacteria

 

Drug Combinations

* As a temporary expedient during investigation of an obscure illness
* To prevent bacterial resistance
* For synergistic effect
* Mixed infections
* Permit reduction dose of a potentiallytoxic drug