Antibiotics Lecture Notes PDF

ANTIBIOTICS DR. KHALIFA BINKHAMIS & DR. FAWZIA ALOTAIBI DEPARTMENT OF PATHOLOGY, COLLEGE OF MEDICINE KING SAUD UNIVERSITY  Lecture Objectives.. By the end of this lecture the student should be able to: Define antibiotics, chemotherapy and selective to...

ANTIBIOTICS DR. KHALIFA BINKHAMIS & DR. FAWZIA ALOTAIBI DEPARTMENT OF PATHOLOGY, COLLEGE OF MEDICINE KING SAUD UNIVERSITY  Lecture Objectives.. By the end of this lecture the student should be able to: Define antibiotics, chemotherapy and selective toxicity Describe the difference between bactericidal and bacteriostatic antibiotics Recognize the narrow and broad spectrum antibiotics Define the therapeutic index  Lecture Objectives.. Recall the mechanism of action of antimicrobial agents. Recognize the various classes of antimicrobial agents and important agents within the classes (action, spectrum and side effects) Explain the criteria for an ideal antimicrobial  Definitions/Terminologies ANTIBIOTICS: Natural compounds produced by microorganism which inhibit the growth of other microorganism. CHEMOTHERAPY: Synthetic compounds. All together are called Antimicrobial Agents.  SELECTIVE TOXICITY Ø The ability to kill or inhibit the growth of a microorganism without harming the host cells. BACTERICIDAL : Antimicrobial agent that kills the bacteria BACTERIOSTATIC : : Antimicrobial agent that prevents multiplication of the bacteria. Spectrum of activity Broad spectrum : Antimicrobial agent that affects Gram positive & Gram negative bacteria Narrow spectrum : Antimicrobial agent that affects only selected organisms or group of bacteria ( G+VE,or G-VE). THERAPEUTIC INDEX The Ratio of Toxic dose to human / Therapeutic dose against bacteria. Examples: Penicillin: has a High therapeutic index and so is safe to human. Aminoglycosides : has a low therapeutic index. Polymyxin B : has the lowest therapeutic index and very toxic to human when given systemically.  MECHANISMS OF ACTION OF ANTIMICROBIAL AGENTS 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. Mechanisms of action of antimicrobial agents  ANTIMICROBIALS THAT INHIBIT CELL WALL SYNTHESIS Ø 1- Beta – Lactam antimicrobial agents are : Penicillins Cephalosporins Carbapenems Monobactam Beta lactamase inhibitors Ø 2- Glycopeptides : eg. Vancomycin Beta-Lactam Antibiotics b - LACTAM ANTIBIOTICS Ø Composed of : Beta- Lactam ring & Organic acid. Ø Natural & Semi-synthetic Ø Bactericidal Ø Bind to Penicillin Binding Protein (PBP)and interfere with trans- peptidation reaction that lead to cell wall destruction. Toxicity: common include : § Allergy (common) § Anaphylaxis ( serious) § Diarrhea. Penicillins Benzyl penicillin ::acts mainly on Gram positive bacteria, examples; - Penicillin V ,Procaine penicillin & Benzathine penicillin Isoxazolyl penicillins: Cloxacillin –effective for Staphylococcus aureus. Amino-penicillins: Ampicillin – effective for Enterobacteria. Acylaminopenicillins: Piperacillin- effective for Pseudomonas.  CEPHALOSPORINS First Generation:.Effective on Gram positive & some Gram negative bacteria Cefazolin, cephalexin Fourth generation:.Effective on Gram negative and some Gram positive bacteria: Second generation: Cefepime.Effective on Gram positive & some Gram negative bacteria: cefuroxime.Acts on Anaerobes: cefoxitin Fifth generation:.Effective on multi resistant Gram Third generation: positive & Gram negative bacteria:.Expanded spectrum Ceftobiprole. Effective on Gram negative & some Gram positive bacteria: ceftriaxone.Effective on Pseudomonas: ceftazidime β-Lactamase inhibitors β-Lactams with limited antibacterial activity Irreversibly bind to β-lactamase enzyme Clavulanic acid, Sulbactam, Tazobactam Effective on Staph. Penicillinases and broad spectrum β-lactamases. eg. amoxicillin/clavulanic acid, ticarcillin /clavulanic acid and piperacillin /tazobactam. Carbapenems Beta-lactams. Cover gram positive ,gram negative bacteria as well as anaerobes ( broad spectrum). Restricted to critically ill patients or patients infected with multi-resistant organisms. Given by injection. eg. Imipenem & Meropenem.  VANCOMYCIN Ø A Glycopeptide, inhibits cell wall synthesis. Ø Bactericidal. Acts on Gram positive bacteria only ( narrow spectrum). Ø Given by injection Ø Used for systemic infection by methicillin resistant Staphylococcus aureus (MRSA), empirical treatment of Gram positive infections & pseudomembranous colitis. Ø Side effects: nephrotoxicity & ototoxicity, phlebitis, Red man syndrome  ANTIBIOTICS THAT ALTER CELL MEMBRANES Polymyxin B and Colistin (polymyxin E): a Peptide, active against Gram negative bacteria only (narrow spectrum). Bactericidal. Used to treat multi-resistant infection caused by Gram negative bacteria such as Pseudomonas and Acinetobacter infections. Risk of nephrotoxicity.  ANTIBIOTICS THAT INHIBIT PROTIEN SYNTHESIS Ø AMINOGLYCOSIDES, binds 30s ribosomal subunit Ø TETRACYCLINES, binds 30s ribosomal subunit Ø CHLORAMPHENICOL, binds 50s ribosomal subunit Ø MACROLIDES/LINCOSAMIDE, binds 50s ribosomal subunit Ø OXAZOLIDONONES, binds 50s ribosomal subunit AMINOGLYCOSIDES 1. Bactericidal 2. Acts only on Gram negative bacteria ( narrow spectrum) 3. Streptococci & anaerobes are naturally resistant. 4. Examples: Gentamicin, Amikacin , Neomycin. 5. Given mainly by injection 6. Side effects : dose related Nephrotoxicity & Ototoxicity. TETRACYCLINS Ø Broad spectrum , bacteriostatic. Given by oral route. Ø Effective for Intracellular organisms eg. Mycoplasma, Chlamydia ,Brucella also effective for Nocardia and Vibrio cholerae. Classes Ø Short acting: Tetracyclin Ø Long acting: Minocycline , Doxycycline ( good CSF penetration). Ø New tetracycline : Tigycyclin ( covers multiresistant Gram positive and some Gram negative bacteria and anaerobes). Ø Side effects : Permanent teeth discoloration , GIT disturbance Ø Should NOT be used for children < 8 year old and pregnant women. CHLORAMPHENICOL ØBroad spectrum & bactericidal ØSerious side effects : it affects bone marrow cells and cause a plastic anemia. ØLimited use nowadays : only for severe infections not responding to treatment by other antimicrobials. Ø can be applied topically (locally) for eye and ear infections. MACROLIDES / LINCOSAMIDES Erythromycin ( Macrolide ) Clindamycin ( Lincosamide) Ø Both are Bacteriostatic Ø Macrolides active on: Legionella, Camylobacter, Gram negative and positive infections for patients allergic to Penicillins and Cephalosporins including oral infections. Ø Clindamycin acts on Staphylococci, Streptococci and anaerobes Ø Side effects : GIT disturbance, Pseudomembraneous colitis (mainly clindamycin). Ø New Macrolides : Azithromycin & Clarithromycin. Less side effects , better tissue penetration and longer half life. Oxazolidonones Linezolid Inhibits protein synthesis Used to treat multi-resistant gram positive bacterial infections. Common side effects: – Thrombocytopenia – Diarrhea ANTIMICROBIALS THAT ACT ON NUCLEIC ACID Ø Rifampicin Ø Quinolones Ø Metronidazole RIFAMPICIN Ø Semi-synthetic, bactericidal , acts on Gram positive bacteria and selected Gram negative bacteria. Ø Reserved for Tuberculosis Ø Resistance develops quickly. Must be used in combination with other antimicrobial agent. Ø Side effects: Causes discoloration of body fluids & hepatotoxicity. QUINOLONES Ø Synthetic, bactericidal, inhibit DNA Gyrase and /or Topoisomerase. Ø Generations: Ø first generation: Nalidexic acid –locally acting Ø Second generation: Fluoroquinolones eg. Ciprofloxacin, Norfloxacin, Ofloxacin,Levofloxacin Ø Third generation: Sparfloxacin, Gatifloxacin Ø Fourth generation: Moxifloxacin, Trovafloxacin Side effects: affects the cartilages (mainly in animals) & the heart Should be used with caution for patients under 18 year and pregnancy. Metronidazole A Nitroimidazole active on anaerobic bacteria and parasites. Causes DNA breakage. Used for the treatment of infections due to : Bacteroides fragilis ( bacteria) , Trichomonas vaginalis , amoebiasis and giardiasis (parasites).  ANTIMETABOLITES ( folate inhibitors) Ø Trimethoprim-Sulfamethoxazole ( TMP-SMX) Ø Commonly used in Combination of TMP-SMX. Ø Block sequential steps in folic acid synthesis Ø Effective of infections caused by different organisms ,eg. Nocardia, Chlamydia, Protozoa & Pneumocystis caranii infections Ø Used for the treatment of upper & lower respiratory tract infections , otitis media, sinusitis & infectious diarrhea. Ø Side effects: GIT, hepatitis , bone marrow depression & hypersensitivity  Anti-tuberculosis agents First line agents Second line agents Isoniazid (INH) Sterptomycin Rifampicin Para amino salicylic acid Ethambutol (PASA) Pyrazinamide Cycloserine A combination of 3 or 4 drugs used Capreomycin for 4-6 months. Used for resistant cases or eg. INH+ Rifampicin + Ethambutol + cases not responding to Pyrazinamide for 2 months then continue INH + Rfampicin for 4 first line drugs. months. ISONIAZIDE (INH) ØBactericidal ØInhibits mycolic acid synthesis ØAffects mycobacteria at different sites of lung tissues ØUsed for the treatment & prophylaxis of tuberculosis ØCan cause peripheral neuritis (pyridoxine (vitamin B6) added in certain patients) and hepatitis  Pyrazinamide Ethambutol § Affects cell wall synthesis § Exact mechanism § Optic neuritis unknown § Hepatitis & arthralgia  ANTIBIOTIC RESISTANCE IN BACTERIA Ø Resistance develops due indiscriminate use of antimicrobial agents. Ø This creates a selective advantage for bacteria to grow in the presence of antibiotic. Types of resistance: Primary (Innate) resistance eg. Streptococcus & anaerobes are naturally resistant to Gentamicin. Secondary (acquired) resistance due to: - Mutation -Gene transfer (e.g. plasmid mediated or through transposons)  Antimicrobial Selection of Resistance Spontaneous mutations during replication and division Bacterial Population Exposure to selecting antibiotic Susceptible population killed, mutants survive & proliferate Wild type Resistant Dead Mechanisms of Resistance to Antimicrobial Agents 1- Decreased permeability to antimicrobial agent. 2- Alteration of antibiotic binding sites. 3- Inactivation by enzymes. 4- Active transport out ( efflux pumps) of cells Mechanisms of Resistance to Antimicrobial Agents PRINCIPLES OF ANTIMICROBIAL THERAPY § INDICATION § CHOICE OF DRUG Prophylaxis ( to prevent recurrence of infection) : § ROUTE SHORT TERM PROPHYLAXIS: § DOSAGE § MENINGITIS § DURATION § DISTRIBUTION LONG TERM PROPHYLAXIS: § Tuberculosis, Recurrent urinary tract § EXCRETION infections , Rheumatic fever § TOXICITY § COMBINATION USE AS IN TUBERCULOSIS § PROPHYLAXIS. CRITERIA FOR IDEAL ANTIMICROBIAL: Ø SELECTIVE TOXICITY Ø NO HYPERSENSITIVITY Ø PENETERATE TISSUES QUICKLY Ø RESISTANCE NOT DEVELOP QUICKLY Ø NO EFFECT ON NORMAL FLORA Ø BROAD SPECTRUM  Reference book and the relevant page numbers.. Sherries Medical Microbiology, an introduction to Infectious Diseases. Latest edition, Kenneth Ryan and George Ray. Publisher: Mc Graw Hill.  Take home messages Antibiotics can do harm, resistance can develope so must be used judiciously. Antibiotics potentiate the function of human immune system to fight microbes. Physicians must know the pharmacokinetics, spectrum of activity and toxicity of antimicrobial agents to make best use antibiotics.