1. Principles of Antimicrobial Therapy
Course Coordinator
Jamaluddin Shaikh, Ph.D.
School of Pharmacy, University of Nizwa
Lecture 1
January 28, 2013

2. Chemotherapy The chemical treatment of infection
Of course, treatment of cancer has also been included
In fact, the word ‘chemotherapy’ is increasingly restricted nowadays to the treatment of cancer
In a series of lectures, we will discuss about chemotherapeutic drugs
Infestation refers to the state of being invaded or overrun by parasites. or other pests

3. What is Antimicrobial Drugs?
Substances that kill or inhibit the growth of microorganisms (e.g., bacteria, virus, fungi, protozoa)
Antimicrobial drugs either kill microbes or prevent the growth of microbes
Disinfectants are antimicrobial substances used on non-living objects

4. Few Terminology Antibacterial
Drugs used to treat infections caused by bacteria
Classified as either Gram-positive or Gram-negative depending on whether or not stain with Gram's stain
The cell wall of Gram-positive organisms is a relatively simple structure. Whereas, the cell wall of Gram-negative organisms is much more complex
Difficulty in penetrating this complex outer layer is probably the reason why some antibiotics are less active against Gram-negative than Gram-positive bacteria
Method is named after the Danish bacteriologist Hans Christian Gram
A method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative). It is based on the chemical and physical properties of their cell walls. Primarily, it detects peptidoglycan, which is present in a thick layer in Gram positive bacteria. A Gram positive results in a purple/blue color while a Gram negative results in a pink/red color

5. Few Terminology, continued……
Antiviral
Drugs used to treat infections caused by virus
Viruses are small (usually in the range nm) infective agents
Incapable of reproduction outside their host cells
The free-living virus particle is termed as virion, and consists of either RNA or DNA

6. Few Terminology, continued……
Antifungal
Drugs used to treat infections caused by fungi
Infectious diseases caused by fungi are called mycoses, and they are often chronic in nature
Infections are superficial and only involve the skin
Some fungi may penetrate the skin, causing subcutaneous infections

7. Few Terminology, continued……
Bacteriostatic
Drugs that inhibit the growth of bacteria
Bactericidal
Drugs that kill the bacteria
A bactericidal antibiotic kills the bacteria, usually either interferes with the formation of the bacterium's cell wall or its cell contents.
A bacteriostatic stops bacteria from multiplying

8. What is Antibiotic? Definition Selective toxicity
Drugs obtained from some microorganisms which are effective against other organisms in small doses
Selective toxicity
Able to kill or stop growth of microorganisms but have no effect in host cells

9. Diagnosis of Infection
This is usually made on history and clinical examination supported by appropriate investigations, e.g. chest X-ray, bacteriological culture
The site and severity of infection are important

10. Patient Factors Age, sex Weight and height Pregnant, lactating
Immune status, renal function, hepatic function and concurrent medication that may cause drug interaction

11. Drug Factors Antimicrobial spectrum
Pharmacokinetics, i.e. availability at the site of action
Adverse effects
Drug interaction
Convenience
Cost

12. MIC and MBC Minimal inhibitory concentration (MIC):
Below this concentration microbial growth is not prevented
Minimal bactericidal concentration (MBC):
Minimum bactericidal concentration of an antibiotic that kills 99.9% of the bacteria

13. Effectiveness of Antibiotic
Microbial Resistance
Microbes are said to be resistance to an antibiotic if their growth is not prevented by the maximal level of the antibiotic that can be tolerated by the host
Effectiveness of Antibiotic
Must reach its target in an active form
Bind to the target
Interfere with its function

14. Mechanisms of Bacterial Resistance
Drug does not reach its target
Restriction of entry of the drugs into the microbe by altered permeability
Drug is not active
Inactivation of the drug either by disruption of its chemical structure or by addition of a modifying group

15. Drug Combinations Most infections can be treated with single agent
However, there are 4 main situations in which more than one antimicrobial drug is prescribed concurrently
To achieve broad antimicrobial activity in critically ill patients with an undefined infection, e.g., aminoglycoside plus penicillin to treat septicemia
To treat mixed bacterial infections (e.g., following perforation of bowel) where no single agent is effective
To prevent emergence of resistance, e.g., treating tuberculosis
To achieve an additive or synergistic effect
Septicemia is the presence of bacteria in the blood

16. Antimicrobial Spectrum
Narrow Spectrum
Antibiotic acting on a single or limited group of microorganism, e.g., isoniazide
Extended Spectrum
Antibiotics that are effective against Gram +ve and also against some Gram –ve organisms, e.g., amoxycillin
Broad Spectrum
Antibiotics acting against a wide variety of microorganisms, e.g., tetracycline