Anti-Infectives and Antibiotics

7/31/2019 Anti-Infectives and Antibiotics

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Antibiotics


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Anti-infective agents

Drugs that are designed to act onselectively on foreign organisms or cells


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Classifications of anti-infective agentsaccording to the organisms they are

designed to kill1. antibacterial or antibiotics2. antifungals3. antiprotozoals4. antihelmintics5. antivirals


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Classifications of anti-infective agentsaccording to their mechanism of action

1. inhibit of cell wall synthesis2. inactivate certain microbial enzymes3. inhibit protein synthesis by

destroying ribosomes4. interfere with DNA synthesis5. alter cell membrane permeability


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Anti-infective spectrum of

activityRefers to its effectiveness againstdifferent types of microorganisms

Narrow-spectrum anti-infectives areeffective against a few or specificspecies of pathogens

Broad-spectrum anti-infectives areeffective against a wide array ofmicroorganisms


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Anti-infective spectrum of

activityThe main goal of anti-infective therapyis to reduce the population of the

invading microorganisms to a level atwhich the immune system can take careof the infection

Anti-infective treatment in an immunecompromised host is useless


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Microorganisms may develop resistance in anumber of ways including the following

1.producing enzymes that can deactivate thedrug2.changing cellular permeability3.

altering binding sites on ribosomalmembranes

4. producing chemicals that can antagonize thedrug


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To prevent emergence of resistant strains ofmicroorganisms

1.drugs should be given at the recommendeddose

2.duration of therapy should be long enough toeradicate the population of invaders

3.doses should be spread at even intervals toinsure that critical concentrations aremaintained.

4. anti-infectives should only be used when

indicated


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Adverse reactions to

antibioticsMost common adverse reactions to anti-infective therapy

1.kidney damage (oliguria, anuria, edema)2.gastrointestinal toxicity (nausea andvomiting, diarrhea)

3.neurotoxicity (CN VIII damage vertigo,loss of hearing)4.hypersensitivity reactions

5. superinfections


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Antibiotics

anti-bacterial drugs

Two basic types of antibiotics according

to their effects on cells

1. bacteriostatic agents preventbacterial growth

2. bactericidal agents kill bacterial cells


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Antibiotics

Two types of bacterial cells according tocell wall composition

1.gram positives skin, respiratory tract2. gram negatives gastrointestinal (GI)

and genitourinary (GU) tract


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Antibiotics

Major groups of antibiotics according totheir chemical structure and mechanism

of action1. aminoglycoside2. cephalosporin3. fluoroquinolone4. macrolide5. lincosamide


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Antibiotics

Major groups of antibiotics according to theirchemical structure and mechanism of action

6. monobactam7. penicillin

8. penicillinase resistant

9. sulfonamide10. Tetracycline

11. anti-mycobacterial (anti-TB and anti-leprotic)


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Drugs under this class: amikacin, gentamicin,kanamycin, neomycin, streptomycin and

tobramycinMechanism of action (MOA): Bactericidal,inhibit protein synthesis

Spectrum: gram negatives (P.aeruginosa,E.coli, Proteus, Klebsiella-Enterobacter-Serratia, Citrobacter), gram positive(S.aureus)


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Pharmacodynamics: poorly absorbed via GIT,parenteral administration is preferred

Adverse effects: CNS (ototoxicity) renal,hepatic toxicity

Contraindications: known allergy to this drug,patients with documented renal or hepaticdisease, with active mycobacterial or herpeticinfection, CNS disorders like parkinsonismand myasthenia gravis


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Drug-drug interaction: toxic effects areincreased by CNS drugs, diuretics

Synergistic bactericidal effect withcephalosporins, penicillins andpenicillinase resistant pens


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4 generations of drugs under this class

1st gen: cefadroxil, cefazolin, cephalexin

largely effective against gram pos andsome gram negs

2nd gen: cefaclor, cefoxitin, cefuroxime

less effective against gram pos but withextended gram neg coverage


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4 generations of drugs under this class

3rd gen: cefoperazone, ceftazidime,

cefotaxime, ceftriaxone weak againstgram pos, potent against gram neg

4th gen: cefepime, cefixime broad

spectrum with good gram pos and negcoverage


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MOA: Bacteriostatic at low dose,Bactericidal, inhibit bacterial cell wall

synthesisPharmacodynamics: well absorbed viaGIT


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Adverse effects: relatively safe with non-specific side effects, Pseudomembranous

colitis (GI mucosal inflammation withhemorrhage) is a rare but severecomplication

Contraindications: known allergy to this drug

Drug-drug interaction: alcohol (disulfiram-likereaction), anticoagulants


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Ciprofloxacin, gatifloxacin, levofloxacin,moxifloxacin, norfloxacin, ofloxacin,

sparfloxacinMOA: inhibit DNA synthesis


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Spectrum: Broad spectrum, for

treatment of GUT and atypical RTI

Pharmacodynamics: well absorbed inGIT

Adverse effects: photosensitivity,suppression of bone marrow activity


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Contraindications: allergy, pregnant andlactating women, infants, children and

adolescentsDrug-drug interaction: potentiate theeffect of cardiac drugs and theophylline,

absorbed poorly if given with sucralfate,iron salts, mineral supplements andantacids


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Erythromycin, azithromycin,clarithromycin

MOA: Bacteriostatic, bactericidal,interferes with protein function

Spectrum: broad, treatment of RT, GUT,

GIT infections, used for patients whoare allergic to penicillin


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Contraindications: fungal and viralinfections, pregnancy and lactation

Adverse effects: non specific andrelatively rare

Drug-drug interaction: increases serumlevels of digoxin, anticoagulants andtheophylline, should be given on emptystomach


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Clindamycin, lincomycin

MOA: similar with macrolides

For treatment of severe skin, GUT, GITinfections

More toxic than macrolides

Adverse effects: Pseudomembranouscolitis, bone marrow depression


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Aztreonam

MOA: interferes with cell wall synthesis

Spectrum: mostly for gram pos but iseffective against some gram neginfections as well, used among patients

who are allergic to penicillins andcephalosporins


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Contraindications: allergies, pregnancyand lactation

Adverse effects: rare, mild and nonspecific


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Penicillinase: enzyme produced by penicillinresistant gram pos bacteria which can

inactivate the drugPenicillins G, V

Extended spectrum penicillins: Amoxicillin,ampicillin, carbenicillin, ticarcillin

Penicillinase resistant antibiotics: dicloxacillin,nafcillin and oxacillin


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MOA: interferes with cell wall synthesis

Spectrum: for treatment of most gram

pos infections


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Contraindications: allergy

Adverse effects: Hypersensitivity and

anaphylaxis, GIT symptoms


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Cotrimoxazole (trimethoprim-sulfamethoxazole), sulfadiazine,

sulfasalazineMOA: inhibit folic acid synthesis byblocking PABA

Pharmacodynamics: well absorbed inGIT


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Spectrum: for treatment of susceptible

GUT including trachoma and RTinfections

Contraindications: pregnancy and

lactation, TERATOGENIC!


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Adverse effects: GI disturbance, Renaland hepatotoxicity, Dermatological

including Stevens Johnson syndrome(SJS)

Drug-drug interaction: increases

hypoglycemic effect of antidiabeticdrugs


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Tetracycline, doxycycline, minocycline,oxytetracycline

MOA: inhibits protein synthesis

Spectrum: broad, treatment ofRicketssiae, Vibrio cholerae


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Pharmacodynamics: adequatelyabsorbed in GIT

Contraindications: children, pregnancyand lactation


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Adverse effects: direct irritation of GIT,fatal hepatotoxicity, weakening of bones

and teeth (Grey baby syndrome)Drug-drug interaction: interferes withabsorption of insulin, calcium containing

drugs/food products, bone marrowsuppression, decreases absorption oforal contraceptives

Anti-Infectives and Antibiotics

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