Antibiotics lecture notes, Lecture notes of Medicine

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ANTIBIOTICS

INTRODUCTION

MARK. V .K

Definitions/Terminologies

Antibiotic:

Natural compounds produced by microorganism which inhibit the growth of other microorganism Activity

Spectrum of

Activity

Antimicrobial agents

Chemotherapy:

Synthetic compounds

Bacterio static :

Antimicrobial agent that prevents the multiplication of bacteria. (inhibits growth)

Narrow Spectrum:

Antimicrobial agent that affects only selected organisms or group of bacteria (Gram - ve or +ve)

Broad Spectrum:

Antimicrobial agent that

affects both Gram +ve and Gram - ve bacteria.

Bacteri cidal :

Antimicrobial agent that kills

the bacteria. (better than bacteriostatic)

02 0 4^06

Selective Toxicity: (the more selective, the better)

07 The ability to kill or inhibit the growth of a microorganism without harming the host cells.

Helpful video

Antibacterials (antibiotics) Antibiotics

• A substance obtained from the living micro- organisms that can be used to kill or inhibit growth of micro-organisms. Antibacterial
• Drugs used to treat bacterial infections.
• In practice, they are called antibiotics
• Antibiotics are among the most commonly used and misused drugs.

Properties of ideal antibacterials

• Have highly selective toxicity to the pathogenic microorganisms in host body
• Have no or less adverse effects to the host.
• Low propensity for development of resistance.
• Have rapid and extensive tissue distribution
• Be free of interactions with other drugs.
• Be relatively cheap

Broad spectrum antibiotics

• These are antibiotics which are effective (kill or inhibit) a wide range of bacteria.
• Broad spectrum antibiotics are commonly used in mixed infections or empirical therapy.
• They are commonly associated with super infections as a result of disturbance of normal flora.
• Super infections such as vaginal candidiasis are common in patients using tetracyclines.

Broad spectrum- Examples

• Amoxicillin
• Ampicillin
• Doxycycline
• Tetracycline
• Ceftriaxone
• Erythromycin
• Ciprofloxacin
• Cephalexin

Mode of action of antibiotics

• Antibiotics can be classified as bacteriostatic or bactericidal.
• The choice of either bacteriostatic or bactericidal antibiotic is based on:
• The severity of the infection and status of the immune system of the patient.
• Bactericidal antibiotics are recommended for severe infections and in immunosuppressed patients.

❖ Mechanisms of Action of antimicrobials _1) Inhibition of cell wall synthesis

2. alteration of Cell membrane
3. Inhibition of protein synthesis
4. Inhibition of nucleic acid synthesis
5. Anti-metabolite OR Competitive antagonism_ (^). Beta – Lactam antimicrobial agents Vancomycin ( Teicoplanin ) o Penicillins o Cephalosporins o Cephamycin o Carbapenems (imipenem & meropenem) o Monobactams (aztreonam) o Beta-Lactamase inhibtors Polymyxin B Colistin Aminoglycosides Tetracyclines Chloramphenicol Macrolides Rifamycins Quinolones Metronidazole Inhibit folate metabolism Trimethoprim Sulfamethoxazole

Bacteriostatic antibiotics

• Bacteriostatic antibiotics stop or inhibit the growth of bacteria.
• Some bacteriostatic antibiotics maybe become bactericidal depending on the dose and type of bacteria.
• These antibiotics need the support of the immune system to clear the pathogen.

Bactericidal antibiotics

• Bactericidal antibiotics kill the bacteria immediately.
• Highly recommended in severe infections and immune suppressed patients.
• These antibiotics do not need support from the immune system.

Bactericidal antibiotics - examples

• Penicillins (amoxicillin, benzylpenicillins)
• Cephalosporins (cephalexin, ceftriaxone)
• Aminoglycosides (gentamycin, amikacin)
• Quinolones (ciprofloxacin, levofloxacin)

Natural antibiotic resistance

• This type of antibiotic resistance occurs without previous exposure to antibiotics. Example
• Ciprofloxacin is not effective to streptococcus pneumoniae naturally.
• Psuedomonas aeruginosa is resistant to penicillin G.

Acquired antibiotic resistance

• This type of resistance occurs to antibiotics which were previously effective against particular bacteria.
• Acquired resistance is caused by previous exposure to antibiotics. Example
• Ciprofloxacin was previously effective N.gonorrhoeae.
• Staph.aureus was previous sensitive to penicillin G.