Antibiotics

Prepared by

Dr Muhammad Ashiq Toor

DVM , Bs (Zoology)

from IUB BWP (2010 – 2015)

+92-344-499-7375

+92-300-364-2402

AntibioticsClass wise , Spectrum , Bacterial activity , MOA & dose rates.

The Spectrum of Antimicrobial Activity

Narrow spectrum (limited spectrum)

Antimicrobials effective against a (limited spectrum)

of microbial types.

A drug effective on G+ve or G-ve bacteria.

Broad spectrum (extended spectrum)

Antimicrobials effective against a (extended spectrum) wide

variety of microbial types .

A drug effective against both G+ve & G-ve bacteria .

Broad spectrum

Some examples of broad-spectrum antibiotics include :

Penicillin

Cephalosporin

Tetracycline

Ciprofloxacin

Levofloxacin

These drugs work on both G+ve & G-ve organisms.

Narrow Spectrum

Vancomycin

Azithromycin

Clarithromycin

Clindamycin

Clindamycin + Benzoyl Peroxide

Erythromycin

No antibiotic is effective against all

microbes

The Action of Antimicrobial Drugs

Bacteriocidal

Kill microbes directly

Bacteriostatic

Prevent microbes from growing

Bacteriostatic vs Bactericidal

Bacteriocidal antibiotics

Kill the target bacteria. These drugs include :

Penicillins

Cephalosporins

Carbapenems

Aminoglycosides

Fluoroquinolones

Nitroimidazoles

Bacteriostatic antibiotics

Slow down bacterial growth & allowing the host immune

system to fight the bacteria. These drugs include :

Macrolides

Tetracyclines

Sulfonamides

Clindamycin

Chloramphenicol

Mechanisms of Antibiotics Action

1- Inhibition of Cell Wall Synthesis

2- Injuring the Plasma Membrane

3- Inhibition of Protein Synthesis

4- Inhibition of Nucleic Acid Synthesis

5- Inhibiting the Synthesis of Essential Metabolites

The Action of Antimicrobial Drugs

Mechanisms of Antibiotics Action Dihydrofolate

Mechanisms of Action:

inhibit the last step in the peptidoglycan synthesis of the cell wall

1. inhibition of transpeptidase enzymes

2. activation of penicillin binding proteins (PBPs)

3. activation of autolysins (murein hydrolases)

Protein Synthesis

Inhibition of Protein Synthesis by antibiotics

Inhibition of Protein Synthesis by

Antibiotics

Figure 20.4

Inhibition of Cell Wall Synthesis

Transpeptidases, Carboxypeptidases & Transglycosylases

Penicillin-binding proteins (PBPs(

β-Lactam antibiotics: generally are bacteriocidal agents

1- Beta-Lactam Antibiotics :

Penicillins

Cephalosporins

2- Glycopeptides :

Vancomycin

3- Lipopeptides :

Daptomycin

4- Polypeptides :

Bacitracin

Inhibition of Cell Wall Synthesis

1- Aminopenicillins: Ampicillin, Amoxicillin

Ampicillin was limited primarily to Escherichia & Proteus species .

2- Carboxypenicillins: Carbenicillin, Ticarcillin

Are effective against a broader range of G-ve bacteria i.eKlebsiella, Enterobacter, & Pseudomonas species .

Broad-spectrum penicillins

Clavulanic acid, Sulbactam, Tazobactam

(ampicillin, amoxicillin, ticarcillin, piperacillin)

Amoxicillin/clavulanic acid (Co-amoxiclav)

Ampicillin/sulbactam (Sultamicillin)

Cephalosporins

More stable to β-lactamase hydrolysis

Antimicrobial spectrum of cephalosporins

Generation of cephalosporin

s

Active towards

Gram-positive bacteria

Gram-negative bacteria

І +++ +/-

ІІ ++ +

ІІІ + +++

ІV ++ +++

CEPHALOSPORINS

CLASSIFICATION

A. First Generation

1. Cephaloridine-Loridine, Ceporan 2. Cephalothin-Keflin 3. Cephalexin-Keflex, Ceporex 4. Cefazolin-Cefacidal 5. Cephradine-Velosef 6. Cepharpirin-Cefadyl 7. Cephadroxil-Doricef, Cefamox

Second Generation

1. Cefaclor-Ceclor

2. Cefoxitin – Mefoxin

3. Cefuroxime – Zinacef, Zinnat

4. Cefonicid – Monocid

5. Cefotetan - Cefotan

6. Cefamdandole – Mandol

7. Cefprozil – Cefzil

8. Loracarbef – Lorabid

9. Cefmetazole – Zefazone

10. Ceforanide

Third Generation

1. Cefotaxime – Claforan

2. Cefoperazone – Cefobid

3. Moxolactam – Moxam

4. Ceftizoxime – Cefizox

5. Ceftriaxone – Rocephin

6. Ceftazidime – Fortum

7. Cefotiam – Ceradolan

8. Cefixime – Suprax

9. Cefetamet – Globocef

10. Cefpodoxime – Vantin

11. Ceftibuten – Cedax

12. Cefdinir –Omnicef

13. Cefditoren

Fourth Generation

1. Cefepime – Maxipime2. Cefpirome – Cefrom

Broad-spectrum antibiotics

Active against virtually all organisms

Imipenem, Meropenem, Ertapenem

Carbapenems

Narrow-spectrum antibiotics

Are active only against aerobic & G-ve bacteria

Aztreonam

Monobactams

Damage cytoplasmic membrane and inhibit RNA transcription

The treatment of skin infections

Used in creams, ointments, sprays

Polypeptides: Bacitracin

Bactericidal

Bind irreversibly to ribosomal proteins

Misreading of the messenger RNA (mRNA)

Premature release of the ribosome from mRNA

Streptomycin, Neomycin, Kanamycin, & Tobramycin

Streptomyces species

Gentamicin & Sisomicin

Micromonospora species

Amikacin from kanamycin

Aminoglycosides

Broad-spectrum

Bacteriostatic

Tetracycline, Doxycycline, Chlorotetracycline

Binding reversibly to the 30S

Blocking the binding of aminoacyl-tRNA

Chlamydia, Mycoplasma, Rickettsia

Tetracyclines

Chloramphenicol

Broad spectrum

Bacteriostatic

Blocking peptide elongation

Typhoid fever

Broad spectrum

Bacteriostatic

Reversible binding to the 50S rRNA

Erythromycin, Azithromycin, Clarithromycin

Macrolides

Inhibition of Nucleic Acid Synthesis

1- Quinolones

2- Rifampin

3- Metronidazole

Synthetic

Inhibit bacterial DNA gyrases (II) or topoisomerases (IV)

Nalidixic acid

Fluoroquinolones:

Ciprofloxacin Levofloxacin Enrofloxacin

Quinolones

Reduction of its nitro group by bacterial nitroreductase

Producing cytotoxic compounds that disrupt the host DNA

Anaerobic bacterial infections (B. fragilis)

Metronidazole

Antimetabolites

Sulfonamides

Preventing the synthesis of the folic acid

Compete with para-amino-benzoic acid (PABA)

Trimethoprim

Blocks the conversion of dihydrofolate to tetrahydrofolate

Inhibiting dihydrofolate reductase

Trimethoprim + sulfamethoxazole: Synergistic combination

Treatment of acute and chronic urinary tract infections

Antimetabolites

S

No Group name Spectrum Activity Examples MOA

1. Beta Lectum Broad spectrum bactericidal Penicillins

Cephalosporins

Inhibit cell wall synthesis

2. Macrolids Narrow spectrum (G

+ve)

bacteriostati

cAzithromycin

Clarithromycin

Erythromycin

30s rRNA block

3. Quinolones Broad spectrum bactericidal Ciprofloxacin

Levofloxacin

Gatifloxacin

Inhibit bacterial DNA

gyrases

4. Tetracycline Broad spectrum bacteriostati

cTetracycline,

Doxycycline,

Minocycline

30s rRNA block

5. Aminoglycosides Narrow spectrum (G -

ve)

Bactericidal Streptomycin,

Neomycin,

Kanamycin, &

Tobramycin

30s rRNA block

S

No Group name Spectrum Activity Examples MOA

6. Chloramphenical

s

Broad spectrum Bacteriostatic Florphenicol

Achlor

Chloromycetin

Binding reversibly to the peptidyl

transferase (50S)

7. Cephalosporins Broad spectrum bactericidal Inhibition of cell wall synthesis

First-generation Narrow-

spectrum

(G +ve)

bactericidal Cefazolin

Cephalothin

Cephradine

Second

generation

expanded-

spectrum (G -

ve)

bactericidal Cefamandole,

Cefaclor,

Cefuroxime

Third generation broad-spectrum

Noscomial

diseases

bactericidal Cefixime,

Cefoperazone

Ceftriaxone

Fourth

generation

broad-spectrum

Covers

pseudomonal

infections

bactericidal Cefepime,

Cefpirome

Fifth generation Used to treat

MRSA

bactericidal Ceftobiprole,

Ceftaroline

Dose rates of Antibiotics

Macrolids

Erythromycin Cattle 8–15 mg/kg, IM, sid-bid

Cat 15 mg/kg, PO, tid

Foals 25 mg/kg, IM, tid

Tylosin Cattle 10–20 mg/kg, IM, sid-bid

Pigs 10 mg/kg, IM, sid-bid

7–10 mg/kg, PO, tid

Cats 10 mg/kg, IM, bid

Quinolone

Nalidixic acid Cats, dogs 3 mg/kg, PO, qid

Enrofloxacin Cats 5 mg/kg, PO, sid-bid

Dogs 5–20 mg/kg, PO, sid-bid

2.5 mg/kg, SC, once then

PO

Beef cattle (not veal or

dairy)

7.5–12.5 mg/kg, SC, once

2.5–5 mg/kg, SC, sid

Pigs 2.5–5 mg/kg, PO or IM, sid

Preruminant calves 2.5–5 mg/kg, PO or SC, sid

Marbofloxacin Cats, dogs 2.75–5.5 mg/kg, PO, sid

Difloxacin Dogs 5–10 mg/kg, PO, sid

Orbifloxacin Cats, dogs 2.5–7.5 mg/kg, PO, sid

Tetracycline

Tetracycline Cat , Dog 7 mg/kg, IM, or IV sid-bid

20 mg/kg, PO, tid

OTC Cat , Dog 7 mg/kg, IM or IV , bid

Cattle , sheep ,

pig

5-10 mg/kg, IM or IV, sid-bid

Horse 5 mg/kg, p o bid

Doxy Dog 5 - 10mg/kg, p o sid

Cats 5 mg/kg, IM, sid

Aminoglycoside

Gentamicin 6–12 mg/kg, IM or SC, sid

Kanamycin 25–30 mg/kg, IM or SC, sid

Streptomycin 15–25 mg/kg, IM or SC, sid

Amikacin 15–22 mg/kg, IM or SC, sid

Netilmicin 6–12 mg/kg, IM or SC, sid

Neomycin 15 mg/kg, PO, sid-bid

0.5–1 g/quarter,

intramammary, sid

Cephalosporin

Dosage, Route, and Frequency

Cephapirin 30 mg/kg, IM or IV, every 4–6 hr

Cefazolin 20–25 mg/kg, IM or IV, tid-qid

Cefpodoxime 8 mg/kg, SC, every 14 days

Cefovecin 5–10 mg/kg, PO sid-bid

Cephalexin 10–30 mg/kg, PO, tid-qid

Cefadroxil 22 mg/kg, PO, bid

Ceftiofur 1.1–2.2 mg/kg, IM, sid

Dosages of Sulfonamides

Sulfonamide Species Dosage, Route, and

Frequency

Sulfathiazole Horses 66 mg/kg, PO, tid

Cattle, sheep, pigs 66 mg/kg, PO, every 4 hr

Sulfamethazine Cattle 220 mg/kg, PO or IV, sid

Sulfadiazine All 50 mg/kg, PO, bid

Sulfadimethoxine All 55 mg/kg, PO,

Sulfaethoxypyridazine Cattle 55 mg/kg, PO, sid

Pigs 110 mg/kg, PO, sid

Sulfapyridine Cattle 132 mg/kg, PO, bid

Succinylsulfathiazole All 160 mg/kg, PO, bid

Examples of antibiotics available

in market

Almox-LA:

Composition:

Amoxicilline trihydrate 150mg

Company: Star

Medicine Form: Injectable

Dose Rate: 1m/ 10kg

Availability: 50 ml vial

Price: Rs. 250/=

Tylosel:

Composition:

Tylosin Tartarate 200mg

Company: Selmore


Dose Rate: 0.05ml/kg

Availability 50ml vial

Price: Rs. 221/=

Genton:

Composition:

Gentamycin Sulphate 100mg

Company: ICI


Dose Rate: 1ml/20kg

Availability 50ml vial

Price: Rs. 275/=

Diarex Forte:Composition

Sulphadiazine 35.5mg

Sulphadimidine 28.4mg

Neomycine Sulphate 1.8mg

Hyoscine Methylbromide 0.04mg

Pectin 7.1mg

Company: zakfas Pharma

Medicine Form: Oral suspension

Dose Rate: 100ml/L.A & 50ml/ S.A

Availability 100ml pack

Price: Rs. 150/=

Utinol Tabs:

Composition:

Sulphadiazol 1750mg

Pencilline G 10000i.u

Streptomycine sulphate 50mg

Etinyl estradiol 0.5mg

Company: Star

Medicine Form:Intrauterine passeries

Dose Rate: 4-8/ L.A & 2-4/S.A

Availability 20 passeries per pack

DRUGS HALF LIFE ORAL ABS

1.short actingSulfacytine

Sulfisoxazole

Sulfamethizole

Short

Short (6 h)

Short (9 h)

Prompt (peaks in

1-4h)

Prompt

Prompt

2. Medium acting

Sulfadiazine

Sulfamethoxazole

Sulfapyridine

Intermediate(10-17h)

Intermediate (10-12h)

No data

Slow (peak in 4-8h)

Slow

Slow

3.Long Acting

Sulfadoxine Long (7-9 days) Intermediate

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Antibiotics