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 (bacteriostatic ) or destroy ( bacteriocidal ) 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

Antibiotic Prescription Clinical situation Microbiological information Pharmacological consideration

Choice of Antimicrobial Drugs 1. C linical diagnosis e.g. Syphilis 2. Bacteriological identification a) infecting organism is not identified (UTIs,meningitis). b) infecting organism is identified but sensitivity to antibiotic isn’t known (T.B) 3. Site of infection

Choice of Antimicrobials ( Cont.) 4. Host factors a) Immune system e.g. diabetes, HIV, malnutrition, advanced age. b) Genetic factors e.g. Patients with G-6-PD deficiency treated with sulfonamides c) Pregnancy and Lactation Aminoglycosides- hearing loss in the child Tetracyclines- injury to the developing teeth ( child ) d) Age of the patient e.g. Grey baby Syndrome (chloramphenicol) Discoloration of teeth (tetracycline) e) Renal function e.g. Aminoglycosides in renal failure f)Liver function e.g. Erythromycin in hepatic failure

Choice of Antimicrobials ( Cont.) 5. Drug Allergy 6. Potential Side Effects (Drug safety) Chloramphenicol ( a plastic anaemia) Tetracyclines in children Flouroquinolones in children &pregnancy ( cartilage damage ) 7. 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.  R R R Reliance on chemotherapy with omission of surgical drainage ( pus or necrotic tissues ).  E E E Excessive use of prophylactic antibiotics in travelers.  L L L Lack of adequate bacteriological information.

BACTERIAL RESISTANCE Definition Concentration of antibiotic required to inhibit or kill the bacteria is greater than the concentration that can safely be achieved in the plasma.

General Principles of Chemotherapy  A A A Administer drug in full dose, at proper interval and by the best route  A A A Apparent cure achieved-continue for about 3 days further to avoid relapse  T T T Two or more antimicrobials should not be used without good reason, e.g.: Mixed bacterial infections Ill patient of unknown etiology To prevent emergence of resistance (e.g. TB ) To achieve synergism e.g. piperacillin+ gentamicin (p. aeruginosae)

Benefit of chemotherapeutic combination Broaden the spectrum of antibacterial activity Broaden the spectrum of antibacterial activity Reduce the doses Reduce the doses Reduce the side effects Reduce the side effects Overcome microbial resistance (TB ) Overcome microbial resistance (TB ) Produce a more potent compound ( co-trimoxazole) Produce a more potent compound ( co-trimoxazole) produce a synergistic effect (penicillin with gentamycin produce a synergistic effect (penicillin with gentamycin Treatment of severe infections (septicaemia ) Treatment of severe infections (septicaemia )