Introduction to Antibiotics 1 st yr( Respiratory block) Prof. Azza Elmedany
Definition of Antibiotics Chemical substances produced by various microorganisms that have the capacity to inhibit or destroy other microorganisms Now a day they are chemically synthesized drugs. Antibiotics will not cure infections caused by viruses.
CLASSIFICATION OF ANTIBIOTICS ACCORDING TO MECHANISM OF ACTION INHIBITION OF CELL WALL SYNTHESIS e.g. Penicillins INHIBITION OF CELL WALL SYNTHESIS e.g. Penicillins INHIBITION OF PROTEIN SYNTHESIS e.g. Macrolides INHIBITION OF PROTEIN SYNTHESIS e.g. Macrolides INHIBITION OF NUCLEIC ACID SYNTHESIS e.g. Quinolones. INHIBITION OF NUCLEIC ACID SYNTHESIS e.g. Quinolones.
According to spectrum Narrow spectrum, e.g.: Narrow spectrum, e.g.: penicillin G, aminoglycosides penicillin G, aminoglycosides Broad spectrum, e.g.: Broad spectrum, e.g.: ampicillin, amoxicillin ampicillin, amoxicillin
Choice of Antibiotics A) Clinical diagnosis ( e.g. syphils) B) Microbiological information C) Pharmacological consideration
B) Bacteriological information Advantages Advantages 1) The exact antibiotic to be used 2) The most effective & reject the one with little or no activity 3) The least toxic 4) The cheapest
Disadvantages 1) Occasionally these tests do not parallel in vivo sensitivity 2) Do not take in consideration certain sites of infection 3) Some bacteria can not be cultivated or take time to grow ( M. leprae, M. tuberculosis ) 4) Bacteriological services are not available at all hospitals
C) Pharmacological consideration 1) Site of infection 2) Host factors 2) Host factors a)Immune system ( Alcoholism, diabetes, HIV) a)Immune system ( Alcoholism, diabetes, HIV) b)Genetic factors b)Genetic factors Patients with G-6-PD deficiency with sulfonamides or chloramphenicol Patients with G-6-PD deficiency with sulfonamides or chloramphenicol
Choice of Antimicrobials ( Cont.) c) Pregnancy and Lactation Aminoglycosides ( hearing loss ) Tetracyclines ( bone deformity ) d) Age of the patient e.g. Grey baby Syndrome (chloramphenicol) e) Renal function e.g. Aminoglycosides ( renal failure ) f)Liver function e.g. Erythromycin ( hepatic failure ) g) Poor perfusion ( lower limbs of diabetes)
( Cont.) ( Cont.) 3- Drug Allergy 4- Potential Side Effects (Drug safety) Chloramphenicol ( a plastic anaemia) Flouroquinolones ( cartilage damage ) 5- The cost of therapy
MISUSES OF ANTIBIOTICS T T T Treatment of untreatable infections e.g. viral infections I I I Improper dosage. T T T Therapy of fever of unknown origin. P P P Presence of pus or necrotic tissues, or blood at the surgical site E E E Excessive use of prophylactic antibiotics in travelers. L L L Lack of adequate bacteriological information.
Prevention of bacterial resistance Use antibiotic only when absolutely required Use antibiotics in adequate dosage for sufficient period of time Combination of antibiotics may be required to delay resistance
General Principles of Chemotherapy A A A Administer drug in full dose, at proper interval and by the best route W W W When apparent cure achieved-continue for about 3 days further to avoid relapse SSSSkipping doses may decrease effectiveness of antibiotics & increase the incidence of bacterial resistance
Cont. T T T Two or more antimicrobials should not be used without good reason, e.g.: Ill patient of unknown etiology To prevent emergence of resistance (e.g. TB ) To achieve synergism e.g. piperacillin+ gentamicin (p. aeruginosae)
Cont. In some infections bacteriological proof of cure is desirable Measurement of plasma conc. Of antibiotics is seldom needed, except in some conditions such as streptomycin in renal TB.
Indications for antibiotics prophylaxis Surgical prophylaxis bowel surgery, joint replacement, gynecological intervention bowel surgery, joint replacement, gynecological intervention Immunosuppressed patients very old, very young, diabetic, cancer very old, very young, diabetic, cancer Dental extraction Dental extraction patient with joint replacement or cardiac abnormalities patient with joint replacement or cardiac abnormalities