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Definition of Antibiotics

Introduction to Antibiotics 1 st yr( Respiratory block) Prof. Mohammad Alhumayyd Pharmacology Department Tel.4671350. Chemical substances produced by various microorganisms that have the capacity to inhibit or destroy other microorganisms. Now aday they are chemically synthesized.

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Definition of Antibiotics

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  1. Introduction to Antibiotics1st yr( Respiratory block)Prof. Mohammad AlhumayydPharmacology DepartmentTel.4671350

  2. Chemical substances produced by various microorganisms that have the capacity to inhibit or destroy other microorganisms. Now aday they are chemically synthesized. They either kill bacteria(bactericidal) or keep more bacteria from growing(bacteriostatic). Antibiotics will not cure infections caused by viruses. Definition of Antibiotics

  3. CLASSIFICATION OF ANTIBIOTICSACCORDING TO MECHANISM OF ACTION • INHIBITION OF CELL WALLSYNTHESIS e.g. Penicillins, cephalosporins. • INHIBITION OFPROTEIN SYNTHESISe.g.Macrolides. • INHIBITION OF NUCLEIC ACIDSYNTHESIS e.g. Quinolones.

  4. According to spectrum • 1- Narrow spectrum , e.g.: penicillin G , aminoglycosides • 2- Broad spectrum , e.g.: ampicillin ,amoxicillin

  5. Antibiotic Prescription Clinical situation Microbiologicalinformation Pharmacological consideration

  6. Choice of Antimicrobial Drugs • Clinical diagnosis eg. Syphilis 2. Bacteriological identification a) infecting organism is notidentified.eg. UTIs ,meningitis. b) infecting organism is identified but sensitivity to antibiotic isn’t known e.g.T.B 3. Site of infection

  7. Choice of Antimicrobials ( Cont.) 4. Host factors a) Immune system e.g. diabetes, HIV, malnutrition, advanced age. b) Genetic factors eg. 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 eg. Grey baby Syndrome-chloramphenicol Discolouration of teeth-tetracycline e) Renal function eg. Aminoglycosides in renal failure f)Liver function eg. Erythromycin in hepatic failure

  8. Choice of Antimicrobials ( Cont.) 5. Drug Allergy 6. Potential Side Effects(Drug safety) Chloramphenicol ( a plastic anaemia) Tetracyclines in children (dental discol.) Flouroquinolone in children &pregnancy ( tendon dammage ) 7. The cost of therapy

  9. MISUSES OF ANTIBIOTICS • Treatment of untreatable infections e.g. viral infections • Improper dosage. • Therapy of fever of unknown origin. • Reliance on chemotherapy with omission of surgical drainage. • Excessive use of prophylactic antibiotics in travellers. • Lack of adequate bacteriological information.

  10. 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.

  11. Administer drug in full dose, at proper interval and by the best route Apparent cure achieved-continue for about 3 days further to avoid relapse ( exception TB and bacterial endocarditis ) Skipping doses may decrease effectiveness of treatment & increase the likelihood of bacterial resistance. Two or more antimicrobials should not be used without good reason, eg.: Mixed bacterial (polymicrobial) infections Desperately ill patient of unknown etiology To prevent emergence of resistance (eg. TB ) To achieve synergism eg. piperacillin+ gentamicin (p.aeruginosae) General Principles of Chemotherapy

  12. Aim of chemotherapeutic combination • Broaden the spectrum of antibacterial activity e.g: clindamycin+ gentamycin • Reduce the doses • Reduce the side effects • Overcome drug resistance(delay the rate of drug resistance) as in treatment of TB or pseudomonal infections. • Produce a more potent compound • produce a synergistic effect) as in co-trimoxazole combination or as in penicillin with gentamycin in treatment of bacterial endocarditis. • Treatment of severe infections of unknownetiology as in septicaemia.

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