broad spectrum antibiotics - Dr Sanjana Ravindra

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antibioticsBroad spectrum antibiotics

Dr Sanjana Ravindra1st year PGDept. of OMR


definitionsDRUG is any substance or product that is used or intended to be used to modify or explore physiological systems or pathological states for the benefit of the reciepientPHARMACOKINETICS is the study of absorption, distribution, metabolism and excretion of drugs ie what the body does to the drugPHARMACODYNAMICS is the study of effects of the drugs on the body and their mechanism of action ie what the drug does to the bodyTHERAPEUTICS deals with the use of drugs in prevention and treatment of diseases

ANTIBIOTIC AGENT Against life (Greek-anti means against and biosis means life). Chemical substances produced by microorganisms that have the capacity in dilute solutions, to produce antimicrobial actionANTIMICROBIAL AGENT Substances that will suppress the growth / multiplication of microorganisms. antimicrobial agents may be antibacterial, antiviral / antifungalANTIBACTERIAL AGENT substances that destroy or suppress the growth / multiplication of bacteria. They are classified as antibiotic or synthetic agents



The term 'antibiosis', meaning "against life", was introduced by the french bacteriologistJean Paul Vuillemin

Antibiosis was first described in 1877 in bacteria when Louis Pasteur andRobert Koch observed that an airborne bacillus could inhibit the growth ofbacillus anthracis


The termantibioticwas first used in 1942 bySelman Waksmanand his collaborators in journal articles to describe any substance produced by a microorganism that is antagonisticto the growth of other microorganisms in high dilution.

The term "antibiotic" derives fromanti+ (bitikos), "fit for life, lively,which comes from (bisis), "way of life,and that from (bios), "life

HISTORY History of chemotherapy is divided into two phases.

(A) the period of empirical use (B) modern era.

Chinese mouldy curd on boilsHindus chaulmoogra oil in leprosyAztecs chenopodium for intestinal wormsParacelsus mercury for syphilis and cinchona bark for fever


1871 Joseph Lister experimented with the antibacterial action on human tissue on what he called penicillium glaucium

1877 Louis Pasteur postulated that bacteria could kill other bacteria ( anthrax bacilli)

1928 Sir Alexander Fleming discovered enzyme lysozyme and the antibiotic substance penicillin from the fungus Penicillium notatum

During 1940 and 50s streptomycin, chloramphenicol and tetracyclin were discovered

1942 Selman Waksman used the term antibiotics


BROAD SPECTRUMTetracyclineChloramphenicolSulfonamidesTrimethoprimNARROW SPECTRUMBacitracinClindamycinMacrolidesMetronidazolePenicillin G,VPenicillinase resistant penicillinPolymixinVancomycinBASED ON SPECTRUM OF ACTIVITY

Neidle E A, Pharmacology and therapeutics for Dentistry, 4th edition. Pg 486EXTENDED SPECTRUMAminoglycosidesCarbacephemsCephalosporinsExtended spectrum of penicillinsFluoroquinolonesMonobactams classification


Neidle E A, Pharmacology and therapeutics for Dentistry, 4th edition. Pg 486

Bactericidal agents should be selected over bacteriostatic ones in circumstances in which local or systemic host defenses are impaired.



BACTERIAFUNGINeidle E A, Pharmacology and therapeutics for Dentistry, 4th edition. Pg 486


PRINICIPLES OF ANTIBIOTIC THERAPYSelection of antibacterial agentAntibacterial combinationsAntibacterial prophylaxisMicrobial drug resistanceDangers of antibacterial therapyMisuse of antibacterial agents


SELECTION OF ANTIBIOTIC AGENT1)HOST RELATED FACTORS Age of the patientPregnancy and neonatal periodImmunocompetency status of the patientSeverity of the infectionAllergic reaction and intoleranceGenetic factorsRenal and hepatic function

2)PATHOGEN RELATED FACTORSEvaluation of the probable microbial etiology and expected clinical course of the infectionIdentification of the causative microorganism and its sensitivity to antibiotic drugsPossibility of drug resistance

3)DRUG RELATED FACTORSNature of the drugRisk of drug toxicityThe cost of therapyPharmacokinetic properties of the drugProbability of drug compliance by the patient

ANTIBACTERIAL COMBINATIONS1) Simultaneous use of two or more antibiotics is not routinely recommmended. These drugs can be combined under following reasonsTo achieve an additive or synergistic effect against a single organismIn mixed infections with bacteria sensitive to different drugsTo delay the development of or to overcome the drug resistanceTo decrease the adverse reactions to an individual drugWhen etiological diagnosis is difficult, the infection is severe and body defense is poorFor reducing chances of superinfections

2) If a bacteriostatic drug is combined with bacteriocidal agent following things may be happenDrug antagonismAdditive effect oftenly synergestic rarely

3) Combined antibiotic therapy involves certain risksEmergence of organism resistant to the multiple drugs usedIncreased risk of adverse reactions Increased risk of superinfection by resistant organismsSense of false securityIncrease in cost of therapy

ANTIBACTERIAL PROPHYLAXISFor prevention of meningococcal infections in healthy children during an epidemic, for prevention of diseases like syphilis, gonorrhea, malaria.

For preventing endocarditis following minor surgical procedures like tonsillectomy or tooth extraction in patients with cardiac lesions.

For preventing invasion of blood stream by pathogens during certain surgical manipulations.

In patients with compound musculoskeletal injury, penetrating wounds and skull injuries.

For those puncture wounds that are at high risk of infection.

Animal bite as they are at high risk of infection by oral flora.

To prevent microbial complications like bronchopnemonia e.g. Cases of measles and tetanus.

In paralytic states to prevent aspiration bronchopnemonia

DANGERS OF ANTIBACTERIAL THERAPYDevelopment of allergic and anaphylactic reactions e.g. PennicillinSelective toxicityDevelopment of superinfectionDevelopment of multiple drug resistant organismsDeficiency of certain vitaminsFetal damage A false sense of security in the patient as well as in physicianFailure to respond to antibiotic therapy

MISUSE OF ANTIBIOTIC THERAPY Antibiotic misuse, sometimes called antibiotic abuse or antibiotic overuse.

Produce serious effects on health.

From antibiotics now available , one needs to know the important representatives of each class and know them well e.g. Action , dosage .

It is a contributing factor to the creation of multidrug-resistant bacteria, informally called "super bugs" relatively harmless bacteria can develop resistance to multiple antibiotics and cause life-threatening infections.

MICROBIAL DRUG RESISTANCEThe recent emergence of antibiotic resistance in bacterial pathogens, both nosocomialy and in the community, is a very serious development that threatens the end of the antibiotic era.

Drug resistance is not a characteristic of all bacteria and many strains responsible for common infections have largely remained susceptible to antibiotics e.G. Pneumococci, streptococcus pyogenes, meningococci, and treponema pallidum.

Bacterial resistance is often quantitative and not qualitative. Thus an antibacterial substance which is not effective in small doses may inhibit the bacteria in vitro in large concentrations.

For an antibiotic to be effective, it must reach its target in an active form, bind to the target, and interfere with its function.

Accordingly, bacterial resistance to an antimicrobial agent is attributable to three general mechanisms: (1) the drug does not reach its target, (2) the drug is not active, or (3) the target is altered .

Natural resistance

In organisms which are naturally resistant, the drug sensitive enzyme reactions may be absent .

some naturally resistant organisms may elaborate a substance which destroys the antibiotic e.G. E coli produce pencillinase which destroys penicillin .

Following the use of an antibiotic agent which destroys the sensitive strain , these naturally resistant variants multiply and become dominant.

Some microbes have always been resistant to certain antibacterial agents.

They lack the metabolic process or the target site which is affected by the particular drug.

This is generally a group or species charateristic e .G. Gm-ive bacilli are normally unaffected by penicillin G or M. Tuberculosis is insensitive to tetracyclines.

Acquired microbial resistance

It is the development of resistance by an organism (which was sensitive before) due to the use of an AMA over a period of time.

This can happen with any microbe and is a major clinical problem.

However, development of resistance is dependent on the microorganism as well as the drug.