Antimicrobial Therapy Flashcards

Flashcards on Antimicrobial Therapy

Chemotherapy

Use of chemicals in infectious diseases.

Antibiotics

Substances produced by microorganisms which suppress the growth of or destroy other microorganisms.

Bacteriostatic

Agents that suppress bacterial growth.

Bactericidal

Agents that kill the bacteria

Resistance to Antimicrobial Agents

The unresponsive nature of a microorganism to an antimicrobial agent.

Natural resistance

Microorganisms have never responded to the antimicrobial; it is clinically not a problem.

Acquired resistance

Previously sensitive becomes resistant to antimicrobials by changing DNA via mutations/transfer of genes; it is clinically a problem.

Penicillins

β-lactum antibiotics: Penicillins, cephalosporins, monobactums, carbapenems

Penicillins: Mechanism of action

Inhibits the synthesis of peptidoglycan resulting in the lysis of bacteria; bactericidal especially for gram-positive bacteria.

Resistance to beta-lactums

Many organisms like staphylococci produce penicillinase which is beta-lactamase and thus opens the beta-lactum ring.

Natural penicillin

Penicillin G (Benzyl Penicillin)

Repository penicillin (slow release)

procaine penicillin (12-24hrly), benzathine penicillin (effective for 3-4 weeks)

Penicillin V (phenoxy-methyl penicillin)

Acid stable and can be given orally; narrow spectrum and used in mild infections like streptococcal pharyngitis, sinusitis and trench mouth

Penicillinase resistant Penicillin

Cloxacillin, dicloxacillin, oxacillin, methicillin, nafcillin; resistant to penicillinase produced by bacteria

Aminopenicillins

Extended spectrum penicillins effective against both gram-positive and negative organisms

Beta-lactamase inhibitors

Clavulanic acid, Sulbactum, Tazobactum; binds to and inhibits β-lactamases, broadening the antibacterial spectrum of penicillins

Cephalosporins

First generation effective against gram+ve organisms

Cephalosporins

Second generation effective against gram +ve, some gram –ve organism

Cephalosporins

Third generation (beta-lactamase resistant, Gram –ve org., anaerobes)

Cephalosporins

Fourth generation (beta-lactamase resistant, ( gram +ve, gram –ve organisms)

Cephalosporins: Mechanism of action

Inhibit bacterial wall synthesis- bactericidal like penicillins

Carbapenems

Imipenem, Meropenem, Ertapenem, Doripenem; wide antibacterial spectrum, highly resistant to Beta-lactamases, inhibit bacterial cell wall synthesis

Tetracyclines: Mechanism of action

Binds to 30s subunit of ribosome and prevents protein synthesis- bacteriostatic; effective against gram positive and negative bacteria, also rickettsiae, chlamydiae, mycoplasma, protozoa

Chloramphenicol: Mechanism of action

Binds to 50s subunit of ribosome and inhibits protein synthesis- bacteriostatic and bactericidal to some; broad spectrum

Aminoglycosides: Antibacterial spectrum

Narrow spectrum- mainly against aerobic gram-negative bacilli (E. coli, Proteus, Y. pestis, Nocardia, V. cholerae, Pseudomonas, Brucella, salmonella, Shigella, Klebsiella)

Aminoglycosides: Mechanism of action

Binds to 30S ribosomes and inhibit bacterial protein synthesis- bactericidal

Fluoroquinolones

Fluorinated quinolones with wider spectrum of activity, fewer side effects, less chance of resistance

Fluoroquinolones: Mechanism of action

Bactericidal; inhibit DNA replication

Sulfonamides: Mechanism of action

Inhibits folic acid synthesis- bacteriostatic; effective against many gram positive and negative bacteria- streptococci, H. influenzae, nocardia, E. coli, Salmonella, Shigella, Proteus, V. cholirae

Cotrimoxazole (septran)

Combination of trimethoprim and sulfamethoxazole (ratio of 1:5); inhibits folic acid synthesis

Macrolides

Antibiotics with a large lactone ring; erythromycin and its semisynthetic derivatives: clarithromycin, azithromycin, and roxithromycin

Macrolides: Antibacterial spectrum

Narrow: aerobic gram-positive bacteria and few gram-negative organisms

Macrolides: Mechanism of action

Binds to 50s ribosomes and inhibits bacterial protein synthesis

Lincosamides

Clindamycin, lincomycin; binds to 50s ribosome and inhibits protein synthesis

Glycopeptide antibiotics

Vancomycin, teicoplanin, and derivatives telavancin, dalbavancin, oritavancin; inhibits cell wall synthesis

Rifampicin: Mechanism of action

Inhibits RNA synthesis in the bacteria

Isoniazid (INH): Mechanism of action

Inhibits mycolic acid synthesis, an important component of mycobacterial cell wall

Pyrazinamide: Mechanism of action

Inhibits mycolic acid synthesis

Ethambutol: Mechanism of action

Inhibits incorporation of mycolic acids into mycobacterial cell wall

Antileprotic drugs

Dapsone, rifampicin, ethionamide, protionamide, clofazimine

Dapsone: MOA

Inhibits the incorporation of PABA into folic acid

Malaria

4 species of malarial parasite: P. falciparum, P. vivax, P. ovale, P. malariae, P. knowlesi

Malaria Transmission

Bite of female anopheles mosquito

Primaquine

Destroys hypnozoites and thus, prevents relapse in P. vivax and P. ovale malaria

Artemisinin and derivatives

Includes artemether, artesunate, arteether; interacts with heme producing free radicals which destroys the parasite membrane

Amoebiasis

Tropical disease caused by protozoan Entamoeba histolytica; spreads by fecal contamination of food and water

Metronidazole

Powerful amoebicide that inhibits trichomonas vaginalis, Giardia lamblia, Balantidium coli; sensitive to anaerobic bacteria

Metronidazole: Mechanism of action

Anerobic bacteria and protozoa reduce the nitro group of metronidazole by a nitroreductase and convert it to a cytotoxic derivative which binds to DNA and inhibits protein synthesis

Tinidazole

Longer Acting

Satranidazole

More potent than tinidazole; lacks disulfiram like reaction

Scabies

Caused by Sarcoptes scabiei (itch mite); transmitted by close body contact with infected person

Benzyl Benzoate

A liquid applied in the form of emulsion over the entire body below the chin after a hot scrub bath

Permethrin

An insecticide that effective against scabies and lice that paralyses insects

Pediculosis

Caused by louse Pediculus humanus; can infest scalp, body or pubic region

Disinfection

Destruction of all pathogenic organisms but not spores; used on inanimate objects

Antiseptic

Agent that destroys microorganisms and can be used on living tissues