2. Contents
Introduction
Classification of AMAs
Factors affecting choice
of AMAs
Combined use of antibiotics
Drug resistance
Beta lactam aantibiotics
a)Penicillins
b)Cephalosporins
Tetracyclines
Sulfonamides
a)Cotrimoxazole
b)Quinolones
Macrolides
Aminoglycosides
Antibiotic prophylaxis
Conclusion
Reference
3. INTRODUCTION
Antibiotics are substances produced by
microorganisms which are selectively supress the
growth or kill other microorganisms at low
concentrations.
Chemotherapy is the treatment of systemic infections
with specific drugs that selectively supress the infecting
microorganism without significanly affecting the host.
Appropriate choice of drugs are important in any
treatment and its prognosis.
4. Classification
1)Based on mechanism of action
a)Inhibit cell wall synthesis : Penicillins,cephalosporins
b)Inhibit protein synthesis : Tetracyclins,Chloramphynicol
c)Inhibit DNA gyrase : Fluoroquinolones
d)Interfere DNA synthesis : Acyclovir
e)Causing misreading of mRNA &
affect permiability : Aminoglycosides
2)Based on spectrum of activity
a)Narrow Spectrum : Penicillin G,Streptomycin
b)Broad spectrum : Tetracyclins,Chloramphinicol
5. 3)Based on type of action
a)Primarily bacteriostatic : Tetracyclines,Chloramphinicol
b)Primarily bacteriocidal : Penicillins,Cephalosporins
4)Based on type of organisms against which
primarily active
a)Antibacterials: Penicillins,Aminoglycocides
b)Antifungal : Ketoconazole,Amphotericin B
c)Antiviral : Acyclovir,Zidovudine
6. Factors affecting choice of AMA’s
1)Patient factors :
Age
Renal & hepatic function
Local factors like :
a)Presence of pus & secretions
b)Presence of necrotic material/foreign body
c)pH
Drug allergy
Impaired host defence
7. Pregnancy
All AMAs should be avoided due to risk of foetus.
Penicillins,cephalosporins &erythromycin are safe.
Tetracycline contraindicated-Pancreatitis & kidney damage
in mother and teeth & bone deformities in children.
Aminoglycosides causes foetal ear damage.
Genetic factors
Sulfonamides,fluoroquinolones carry risk of producing
haemolysis in G6PD deficient patient.
8. 2)Drug factors
Spectrum of activity
For definitive treatment – Narrow spectrum & for
emperical – broad spectrum
Type of activity
Acute infection resolve faster with cidal than with
static,as the cidal drug reduces the number of bacteria at
the site of infection while static only prevent the increase
in the number.
Sensitivity of organism
Relative toxicity-less toxic preferred(i.e beta lactam over
aminoglycosides)
9. Route of administration
Penicillin G have to be given by injection (20-24MU
daily)
For less severe infections, oral antibiotic is
preferrable.But for serious infection like meningitis
parenteral would be more reliable.
Cost
10. Combined use of antibiotics :
1)To achieve synergism :
Synergism(supra additive effect),additive action,
antagonism may be observed when 2 AMAs used together.
If MIC of one AMA is reduced in presence
of other– Synergism
11. 2)To reduce severity / incidence of adverse effects
Needed for AMAs with low safety margin
Amphotericin B + rifampin : the latter is not themselves
antifungal but enhance action of amphotericin B.
3)To prevent emergence of resistance
4)To broaden the spectrum of antibiotic
a)Treatment of mixed infection
b)Initial treatment of severe infections
12. Disadvantages :
Toxicity of one agent may enhanced by another.
Increased chances of super infections
High cost of therapy
Emergence of resistance
13. Drug Resistance
1)Natural resistance :
Develop due to lack of metabolic processes or the
target site which is affected by the particular drug.
Eg : gram negative bacilli are unaffected by penicillin G
2)Acquired resistance :
Arise due to use of an AMA over a period of time.
Eg : Gonococci develop resistance to penicillin.
14. Resistance may develop by :
a)Mutation
a1)Single step – E coli to rifampin
a2)Multiple step – Staphy. to rifampin
b)Gene transfer
b1)Conjugation - E coli to streptomycin
b2)Transduction – Resistance of stph.aureus
b3)Transformation – Pneumococci resistance to penicillin G
15. Beta lactam Antibiotics
Penicillins
1st antibiotic to be used clinically in 1941.
Antibiotics having a beta lactam ring.
2 major groups include penicillins & cephalosporins.
Mechanism of action :
Interfere the synthesis of bacterial cell wall.
Bacterial cell wall has crosslinked peptidoglycans, which
provide rigidity & stability to cell wall.
Beta lactam antibiotics inhibit the transpeptidase-
cross linking doesn’t take place.
16.
17. Such bacteria which divide in presence of beta lactam
antibiotic produce cell wall deficient forms.
They swell & burst –Bacterial lysis.
Preparations of Penicillin G
Duration of action of PnG increased by combining it
with poorly water soluble compounds like procaine,
benzathine..which are referred as repository penicllins.
Dose
Adult-500mg - t.i.d
Pediatric -250mg - t.i.d
18. Uses of penicillin G
Vincent angina,necrotizing gingivitis
Penumococcal infections-pnuemonia, meningitis
Diphtheria
Syphilis
Streptococcal infections-pharyngitis, rheumatic fever…
19. Adverse effects :
Local irritancy like pain at i.m injection site,nausea
on oral ingestion…
Direct toxicity to brain manifests as mental confusion,
convulsions & coma.
Hypersensitivity reactions
Jarisch – Herxheimer reaction :
Penicillin injection in syphilitic patient may produce
shivering,fever,myalgia…due to sudden release of
spirochetal lytic products.
20. Limitations of Penicillin G
1)Acid labile-orally not well effective
2)Short duration of action
3)Narrow spectrum of activity
4)Destroyed by penicillinase enzyme.
Classification of penicillins
a)Natural penicillins : Penicillin G,
Procain penicillin(0.6-1.2 MU),
benzathine penicillin(0.6-2.4 MU)
(PENIDURE).
22. B4)beta lactamase inhibitors – Clavulanic acid
It has beta lactam ring but no antibacterial activity of
its own.
Clavulanic acid combine with amoxicillin which have
similar half life (AUGMENTIN-
250mg amoxicillin+ 125 mg clavulanic acid)
Bact.fragilis not responsive to amoxicillin alone but inhibited
by combination.
Addition of Clavulanic acid re-establishes the activity of
amoxicillin against beta lactamase producing Staph.aureus.
It can be used in Skin & soft tissue infections ,Gonorrhoea
25. Uses :
1st generation – Cefazolin(ORIZOLIN) 1 g i.m / i.v ,30 min
before used for prophylaxis of bacterial endocarditis
before dental procedures & also used in odentogenic
infections.
2nd generation – Cefaclor(KEFLOR) -250mg useful in
orodental infections.
3rd generation – Used in severe gram negative
infections like community acquired pneumonia,
typhoid fever, gonorrhoea…
Adverse effects
Hypersensitivity
GIT disturbances-diarrhoea, vomiting…
Pain at site of infection.
26. Tetracyclines
Class of antibiotics having nucleus of 4 cyclic rings.
Mechanism of action
:
They are primarily
bacteriostatic
They inhibit protein
synthesis by binding to 30S
ribosome .
Thus interfere the binding
of aminoacyl tRNA to the
acceptor site of mRNA
28. Adverse effects
Irritative effects – nausea,vomiting,diarrhoea
Liver damage - In pregnant women may precipitate
acute hepatic necrosis.
All tetracyclines except doxycycline,accumulate &
enhance renal failure.
Phototoxicity – Sunburn like skin lesions on exposed parts.
Teeth & bones – Calcium-tetracycline chelate may get
deposited in teeth & bone.
If given during pregnancy,brown discoloration of
deciduous teeth,which become susceptible to caries.
Hypersensitivity reactions
Superinfection eg-pseudomonas enterocolitis
29. Chloramphenicol
Broad spectrum antibiotic but use is limited due
to its dangerous side effect – bone marrow supression
Mechanism of action
Bind reversibly to 50S ribosomal subunits-prevent
peptide bond formation-thus inhibit protein synthesis.
Uses
Never use it for minor infections or those of unknown
etiology or infections treatable by other safer AMAs
30. Daily dose not exceed 2-3 g & duration of therapy
to be <2 weeks.
Typhoid fever
Bacterial meningitis – In combination with ampicillin.
Intraocular infections
Anaerobic infections – caused by B.fragilis
Adverse effects
Bone marrow supression
1)Dose depent reversible supression-anaemia,leucocytopenia
2)Idiosyncratic nondose related aplastic anaemia-fetal.
Gray baby syndrome in neonates-Due to reduced
degradation in liver-skin appears ashengray colour.
Hypersensitivity reactions
31. Sulphonamides
1st AMAs effective against pyogenic bacterial infections.
Bacteriostatic
Classification :
1)Short acting – Sulfadiazine-0.5g tab q.i.d
2)Intermediate acting – Sulfamethoxazole-1 g BD
3)Long acting – Sulfadoxine.
Mechanism of action
PABA is a Component of folic acid,which is
produced by the bacteria & needed
for growth and multiplication of bacteria
Sulfonamides are structural analogous of PABA.
32. As the human cell not produce folic acid,but utilize it,
They are unaffected by sulfonamides.
Pus & tissue extracts contains purines & thymidine
which decrease bacterial requirement for FA & antagonize
the sulfonamide action.
Sulfonamide may itself get incorporated to
form an altered folate which is metabolically
injurious.
Thus they inhibit bacterial folate synthesis-
FA not formed-bacteriostatic effect.
33.
34. Doses
Sulfadiazine – 500mg –QID
Sulfamethoxazole – 1g- BD
Uses
Sodium salt of sulphacetamide used topically for
treatment of ophthalmic infections.
Silver sulfadiazine used topically for preventing
infection of burn wound.
Combined with trimethaprim,sulfamethoxazole is
used in many infections.
With pyrimethamine, certain sulfonamides are used for
malaria.
35. Adverse affects
Nausea,vomiting,epigastric pain
Hypersensiticity reactions
Hepatitis
Kernicterus in newborn
Cotrimoxazole is the fixed dose combination of
trimethoprim and sulfamethoxazole.
Optimum synergic effect seen at concentration ratio
20 : 1 (Sulphamethoxazole : Trimethoprim)
Used in UTI infections,Bronchitis,Typhoid fever…
Adverse effects are Skin rashes,GIT disturbances
Cotrimoxazole
36. Individually both sulfonamide & Trimethoprim are
bacteriostatic.But the combination become bactericidal
against many organisms.
37. Quinolones
1st quinolone nalidixic acid is a urinary antiseptic.
Fluoroquinolones are fluorinated analogoues of
nalidixic acid.
Classification :
1st generation fluoroquinolones – Ciprofloxacin,ofloxacin
2nd generation fluoroquinolones – Levofloxacin , moxifloxacin
Mechanism of action
They inhibit bacterial DNA synthesis – bactericidal.
They inhibit DNA gyrase thus blocking DNA replication
in gram negative bacteria.
38. Uses
Ofloxacin used in TB,leprosy
Moxifloxacin & levofloxacin are used in community
acquired pneumonia
UTI
Bacterial diarrhoea
Ciprofloxacin is the preffered drug for treatment
of typhoid fever
Chancroid
Adverse effects
Nausea,vomiting
Headache,insomnia,convulsions
Hypersensitivity reactions
39. Macrolids
Antibiotics having macrocyclic lactone ring with
attached sugers.
Erythromycin is the 1st member discovered.
Safer to use in pregnancy.
Mechanism of action
They are bacteriostatic at low and cidal at high
concentrations.
They inhibit protein synthesis by binding with 50S
subunit of ribosome.
Activity enhanced in alkaline medium.
40. Dose
Erithromycin : 250-500mg – oral – q.i.d
Clarithromycin (CLARIBID): 250 mg – b.d
Azithromycin(AZITHRAL) : 500mg - o.d
Uses
Alternative to penicillin to treat orodental infections.
Prophylaxis of dental infections –gingivitis, peridontitis…
Drug of choice in : pneumonial infections, chlamydal
Infections,diphtheria,pertussis…
42. Aminoglycosides
They have amino groups linked glycosidically to 2 or
more aminosugar residues.
Classification :
1)Systemic – Streptomycin,gentamycin,amikacin
2)Topical – Neomycin,framycetin.
Mechanism of action
They inhibit protein synthesis –bactericidal.
Streptomycin binds to 30S ribosomes but other
aminoglycosides bind to additional sites on 50S
subunit,as well as to 30S-50S interface.
43. Uses
Streptomycin is a 1st line drug in TB.
Gentamycin used in aerobic gram negative bacillary
infections.
Neomycin used only for local effect.
Adverse effects
Ototoxicity
Nephrotoxicity
Hypersensitivity reactions
Neuromuscular blocking effect
45. Conclusion
Antibiotics exert their action by various methodes
which include ; inhibition of cell wall synthesis,Inhibit
protein synthesis…
AMAs used in combinations to obtain better results.
Selection of drug,dose,freequency of taking are all
affect the net result.
GIT problems,hypersensutuvity,toxicity are most
frequently encountered adverse effects.
Accuarate drug choice is important for better
treatment and prognosis.
46. Reference
1) Essentials of medical pharmacology : 7th edition , by
K.D.TRIPATHI
2) Pharmacology for dentistry : 3rd edition ;by Tara V
Shanbhag,Smita Shenoy,Veena Nayak