Antimicrobial-Drugs ( Diploma in pharmacy)

CLASSIFICATION OF ANTIMICROBIAL DRUG
Classification based on chemical structure
1. Sulfonamide & related drug: sulfadiazine, sulfomethoxazole
2. Diaminopyrimidines: trimethoprim
3. Quinolones: norfloxacin, ciprofloxacin, levofloxacin, ofloxacin
4. Beta-Lactam antibiotics: penicillin, cephalosporins
5. Tetracyclines: tetracycline, oxytetracycline, doxycycline
6. Nitrobenzene derivatives : chloramphenicol
7. Aminoglycosides: streptomycin, gentamycin, kanamycin,
amikacin
8. Macrolides: erythromycin, clarithromycin, azithromycin.
9. Lincosamide: lincomycin, clindamycin
10.Glycopeptide antibiotics : vancomycin

11. Oxozolidiones: linezolide
12. Polypeptide,: polymcin-B, bacitracin
13. Nitrofuran derivatives: nitrofurantoin
14. Nitro-imidazoles: metronidazole, tinidazole
15. Nicotinic Acid derivatives: isoniazide
16. Polyene antibiotics; nystatin
17. Azole derivative: fluconazole, clotrimazole
18. Others including rifampin, ethambutol, griseofulvin

Classification based on spectrum of activity
1. Narrow spectrum:
 Acts only on a single or a limited group of microorganisms.
Eg isoniazid is active only against Mycobacterium.
2. Extended-spectrum antibiotics:
 antibiotics that are effective against gram+ve organisms and
also against a significant number of gram-ve bacteria eg.
ampicillin
 3. Broad spectrum:
 Drugs such as tetracycline and chloramphenicol affect a wide
variety of microbial species

Classification based on types of action
1. Bacteriosatic:
 stop the growth of microorganism.
 Eg. sulfonamides, tetracyclines, erythromycin,
chloramphenicol etc
2. Bactericidal:
 kill the microorganism, e.g. penicillins, ciprofloxacin, co-
trimoxazole etc

Classification based on types of organism
 According to types of organism by which the antimicrobial
are active are classified in to following types:
1. Antibacterial:
 Penicillin, aminoglycosides etc.
2. Antiviral:
 Acyclovir, amantadine
3. Antifungal :
 Ketoconazole, griseofulvin, terbinafine
4. Antihelmenthics:
 Albendazole, mebendazole etc.
5. Antiprotozoals:
 Metronidazole, tinidazole, chloroquine

Classification based on mechanism of action
1. Interfere with cell wall synthesis: Penicillin,
cephalosporins, vancomycin and cyclosporine
2. Damage to the cytoplasmic membrane: Polymyxins,
colistin, polyene antibiotics and detergents
3. Inhibition of protein synthesis and impairment of
function of the ribosomes: Aminoglycosides, tetracyclines,
chloramphenicol, macrolides and lincomycin
4. Interfere with transcription/translation of genetic
information: Quinolones, metronidazole and rifampicin
5. Antimetabolic action: Sulfonamide, sulfones, para amino
salicylate (PAS) and trimethoprim
6. Binding to viral enzymes essential for DNA synthesis:
Protease inhibitors and acyclovir

GENERAL PRINCIPLE OF ANTIMICROBIAL THERAPY
 1. Selection of anti-microbial agents
 The selection of an appropriate antimicrobial agent requires
knowing:
1. Identification of the infecting organism:
2. Patient factors:
3. Empiric therapy prior to identification of the organism:
4. Determining antimicrobial susceptibility of infective
organisms:
5. Safety of the agent:
6. Cost of therapy:

2. Route of administration
 The oral route of administration is appropriate for mild
infections that can be treated on an outpatient basis.
 In hospitalized patients requiring IV therapy initially, the
switch to oral agents should occur as soon as possible.
 However, some antibiotic, such as vancomycin, amphotericin
B, aminoglycoside are so poorly absorbed from the GI tract
that adequate serum levels cannot be obtained by oral
3. Determinants of rational dosing
 Rational dosing of antimicrobial agents is based
pharmacokinetic properties. Three important properties that
have a significant influence on the frequency of dosing are:
I. Concentration dependent killing
II. Time-dependent killing
III. Post-antibiotic effect (PAE).

4. Combination of anti-microbial agents
 It is advised to treat patients with a single agent that is most
specific to the infecting organism as well as it minimizes
resistant and toxicity. However, some situations require
combinations of antimicrobial drugs eg anti-TB
5. Prophylactic use of anti-microbial agents
 Pre-surgical antimicrobial prophylaxis:
 Antimicrobial prophylaxis in immunocompromise pts.
 Antimicrobial prophylaxis to prevent transmission of
communicable pathogens to susceptible contacts:
 Traumatic injuries with a high probability of infections
complications

6. Non-antimicorbial therapy for infections
 Systemic corticosteroids, used in conjunction with
antimicrobial therapy for the treatment of bacterial
meningitis, tuberculous meningitis,
7. Complication of antimicrobial therapy
i. Hypersensitivity:
ii. Direct toxicity:
iii. Super infections:
iv. Nutritional Deficiency:
8. Judicious use of antimicrobial agents
Cost considerations in antimicrobial selection:
Preventing emergence of antibiotic resistance:

MICROBIAL RESISTANCE (Drug resistance)
 The ability of microorganism to develop mechanism that
block the action of drug
 Antibiotic resistance refers to bacteria resisting antibiotics.
 Antimicrobial resistance (AMR) refers to microbs resisting
antimicrobial agent
 AMR occurs when microorganism change over time and no
longer respond to medicines, making infections harder to
treat and increasing the risk of disease spread, severe illness
and death.
 As a result of drug resistance, drug become ineffective and
infections become increasingly difficult or impossible to
treat.
 Antibiotic resistance affect people at any stage of life, as well
as the healthcare, veterinary, and agriculture industries

Causes of resistance
1. Microbial behavior
Mutation:
 When microbes reproduce, genetic mutations can occur.
Sometimes, this will create a microbe with genes that help it
survive in the face of antimicrobial agents.
Selective pressure
 Microbes that carry these resistance genes survive and replicate.
The newly generated resistant microbes eventually become the
dominant type.
Gene transfer:
 Microbes can pick up genes from other microbes. Genes
conferring drug resistance can easily transfer between microbes.
Phenotypic change:
 Microbes can change some of their characteristics to become
resistant to common antimicrobial agents

2. People’s behavior
Inexact diagnosis:
 Doctors sometimes prescribe antimicrobials “just in case,” or
they prescribe broad spectrum antimicrobials when a specific
drug would be more suitable.
Inappropriate use:
 If a person does not complete a course of antimicrobial drugs
Resistance can also develop if people use drugs for conditions
that they cannot treat. Eg. people sometimes take an antibiotic
for a viral infection.
Agricultural use:
 Using antibiotics in farm, animals can promote drug resistance.
Hospital use:
 People who are critically ill often receive high doses of
antimicrobials. This encourages the spread of AMR microbes,
particularly in an environment where various diseases are present

Mechanism of resistance
1. Drug Inactivation or Alteration
 Many bacteria produce enzymes that irreversibly modify and
inactivate the antibiotics
 One of the well-characterized enzymes is β-lactamases. They
hydrolyze the βlactam ring which is present in penicillins are
essential to their activity
2. Modification of Drug Binding Sites
 Some resistant bacteria avoid recognition by antimicrobial
agents by modifying their target sites eg. Alternation of
penicillin-binding proteins (PBPs)
3. Reduced Drug accumulation:
 By decreasing drug permeability and/ or increasing active
efflux( pumping out) of the drug across the cell surface

4. Alteration of metabolic pathway:
 Some sulfonamide-resistant bacteria don’t require para-
aminobenzoic acid(PABA) which is important precursor for
the synthesis of folic acid and nucleic acids in bacteria
inhibited by sulfonamides, instead like mammalian cell they
turn to utilized preformed folic acid
Types of resistance
1. Natural resistance :
particular microbes are inherently resistant to particular
agents eg. inability of penicillin G to penetrate Gram-
negative cell wall

2. Acquired resistance
If a microorganism is initially sensitive to an anti-
microbial agent develops resistance later.
❖Change in structure of cell wall eg. aminoglycoside
resistance to Streptococcus.
3. Cross resistance
 If the resistance of one drug causes the resistance of next
drug, the process is said to be called a cross resistance
 Eg. if one sulfonamide have resistant then all groups
develop resistance

4. Super infection
 If a person takes many antibiotics for longer period of
time, then the normal microbial flora of the canal may
decrease or loss due to decrease in immunity power of
the individuals

Antimicrobial-Drugs ( Diploma in pharmacy)

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