SYSTEMS PHARMACOLOGY Chemotherapy of Infection: Part I

1. SYSTEMS PHARMACOLOGY Chemotherapy of Infection: Part I Dr Dhaya Perumal London Metropolitan University Dept. Health & Human Sciences Tower Building: Room T13-10 Telephone: 020 7133 4195 d.perumal@londonmet.ac.uk

2. Pathogenic (Infectious) Organisms • Are those organisms that cause diseases in human beings/ animals • Types of pathogenic organisms: 1. Microbes Bacteria, fungi and viruses 2. Parasites Protozoa and helminthes (worms)

3. Chemotherapeutic agents • Are naturally occurring or chemically synthesized substances intended to be toxic for the pathogenic organisms but innocuous to the host • Aim- To treat acute, severe, persistent or progressive infectious disease

4. Factors contributing to microbial threats to health • Microbial adaptation and change • Human susceptibility to infection • Climate and weather • Changing ecosystem • Human demographics and behaviour • Economic development and land use • International travel and commerce

5. Factors contributing to microbial threats to health (Contd.) • Technology and Industry • Breakdown of Public Health Measures • Poverty and Social Inequality • War and famine • Lack of Political will • Intent to harm (e.g. weapons of mass destruction)

6. Classic Definition: Antibiotic • (from Greek, anti – against, bios – life) • A natural substance, or derivative of a natural substance, which when taken in small doses will either kill or prevent the growth of a microorganism, but will not seriously harm the person taking it

7. Antibiotic-producing microorganisms • Penicillium and Cephalosporium Beta-lactam antibiotics: penicillin and cephalosporin • Actinomycetes, Streptomyces species Tetracyclines Aminoglycosides Macrolides Chloramphenicol • Bacillus species Polypeptide antibiotics: polymyxin and bacitracin

8. Definition (Modified):Antibiotics/Antibacterials/Antimicrobials • Any chemical compound used to kill or inhibit the growth of infectious organisms, particularly bacteria and fungi • All antibiotics share the property of selective toxicity: they are more toxic to an invading microorganism than to the animal/human host

9. Choice of suitable drug • Two considerations: 1. Patient - history of allergy - renal/hepatic function - susceptibilty to infection - ability to tolerate by mouth - severity of illness - ethnic origin - age - other medication - pregnancy, breast-feeding, OC use

10. Choice of suitable drug contd. 2. Known or likely causative organism - antibacterial sensitivity Final choice depends on microbiological, pharmacological and toxicological properties

11. Rational approach to selecting drug • Example: to treat UTI in a pregnant patient who has nausea. The organism found to be resistant to ampicillin but - sensitive to nitrofurantoin (can cause nausea) - gentamycin (only by injection and avoided in pregnancy) - tetracycline (dental discolouration) - trimethoprim (teratogenic) and - cefalexin • Safest in pregnancy is penicillins and cephalosporins • Therefore cefalexin indicated for this patient

12. Spectrum of Activity A.Broad spectrum of activity An antimicrobial drug that is effective against a large variety of microorganisms ADVANTAGES: A high degree of efficacy against an unidentified pathogen DISADVANTAGES: A high likelihood of the drug also destroying the friendly/helpful bacteria making up an individual’s normal microbial flora

13. Spectrum of Activity (Contd.) B. Narrow spectrum of activity An antimicrobial drug that is effective against only a relatively small subset of bacteria

14. Effects of Antimicrobials A. Bactericidal (kill) Interaction results in an irreversible disruption or binding  cell death B. Bacteriostatic (inhibit growth) Interaction effect involves lower affinity binding and is reversible when the antibacterial is removed from the environment

15. Safranin Crystal violet Iodine Alcohol wash DIAGNOSTIC STAINING TECHNIQUE Gram – Positive Bacteria : BLUE Gram – Negative Bacteria : RED

17. DIAGNOSTIC STAINING TECHNIQUE (Contd.) Ziehl-Neelsen Stain (Acid-fast bacteria) • Bacteria + Carbofuchsin (bring to boil 3 times) • HCl + Alcohol (1-2 min) • Alkaline methylene blue (3 min) RESULT: - Acid-fast bacilli: RED - Other bacteria: BLUE

18. Spectrum of Antibacterials • Gram Negative Bacteria • Acid fast Bacteria • Aerobic – requires oxygen • Anaerobic – does not require oxygen

19. Sensitivity Test Antibiotic sensitivity determined by size of inhibition zone

20. Mode of action of antibacterials

21. Bacterial cell wall structure Gram Negative Gram positive

22. Mode of action of antibacterials • Inhibition of cell wall synthesis • Disruption of cell membrane function • Inhibition of protein synthesis • Inhibition of nucleic acid synthesis • Action as antimetabolites

23. Major modes of action of drugs

24. A. Inhibition of cell wall synthesis • Most bacteria have peptidoglycan-based cell walls (mammals do not) • Successful cell wall synthesis by these bacteria is impossible in the absence of peptidoglycan synthesis • In the absence of cell wall integrity, most bacteria are susceptible to osmotic lysis

27. Beta-lactam antibiotics: Penicillins and Cephalosporins • Stereochemically related to D-alanyl-D-alanine, which is a substrate for the last step in peptidoglycan synthesis • Block the final transpeptidation (cross-linkage of pentapeptide side chains)

30. Glycopeptides: Vancomycin • covalently bind to the terminal two D-alanine residues at the free carboxyl end of the pentapeptide • Sterically hinder the elongation of the peptidoglycan backbone

31. Polypeptide: Bacitracin Blocks the dephosphorylation of the lipid carrier Cycloserineby competitive inhibition, the drug prevents the addition of the two terminal alanines to the initial tripeptide side-chain on N-acetylmuramic acid

32. B. Disruption of cell membrane function • Damage to cytoplasmic membrane – Increase permeability by disorganizing the structure or inhibiting the function of bacterial membranes - Polymyxins - Nystatin - Amphotericin B - Imidazoles

33. C. Inhibition of protein synthesis • The bacterial ribosome and the animal ribosome differ structurally • Inhibition of some step in the complex process of protein synthesis • Attack on specific ribosomes Tetracyclines Interferes with the attachment of t-RNA to m-RNA-ribosome complex preventing the addition of new amino acids to the growing peptide chain

34. Protein synthesis

35. C. Inhibition of protein synthesis (Contd) Chloramphenicol - Binds to the 50S portion and inhibits formation of peptide bonds Macrolides, Fusidic Acid - Binds to the 50S portion and prevents the translocation of ribosome along mRNA Aminoglycosides - Changes the shape of the 30S portion causing the misreading of code on mRNA

37. D. Inhibition of nucleic acid synthesis Quinolones - Inhibit DNA gyrase activity (DNA gyrase – topoisomerase II- is essential for DNA replication and allows supercoils to be relaxed and reformed) Rifampicin • Inhibit RNA synthesis by inhibiting DNA-dependent RNA polymerase

38. E. Action as antimetabolites Inhibit the bacterial enzymes required for the synthesis of folic acid (tetrahydrofolic acid, THF) Sulfonamides:structurally similar to para aminobenzoic acid (PABA), the substrate for the first enzyme in the THF pathway Trimethoprim:structurally similar to dihydrofolate (DHF) and competitively inhibits the second step in THF synthesis mediated by the DHF reductase

39. SIDE-EFFECTS • Toxicities: inability of drug to completely distinguish host physiology from pathogen physiology • Allergies • Normal flora disruptions

40. Antibiotic Resistance 1. Evasion - The organism may enter or be present in an antimicrobial-resistant state such that all members of a population are destroyed by the antimicrobial except those that happen to be in the resistant state (e.g. endospores)

41. Antibiotic Resistance Contd.) 2. organism may become mutated such that the site of action of the antimicrobial is no longer affected by it (a mutation affecting ribosome structure) typically resistant to only a single type of antibiotic

42. Antibiotic Resistance (Contd.) 3.Extrachromosomal antibiotic resistance (acquired antibiotic resistance) • Is associated with resistance (R) plasmids • Does not involve the mutation within a given bacteria to antibiotic resistance but instead the acquisition of resistance plasmids from other bacteria • Involves an inactivation of the antibiotic or a prevention of entry rather than a change in the structure of the antibiotic target

43. The “Super Bug” Issue • MRSA (methicillin-resistant Staphylococcus aureus) • Resistance developed against - Beta-lactam antibiotics - Aminoglycosides (Streptomycin) - Macrolides - Chloramphenicol - Sulphonamides (Sulpamethoxazole + Trimethoprim) - Rifampicin - Fusidic Acid - Quinolones • Vancomycin was the last resort against it but resistance has also developed

44. Limiting Antibiotic Resistance • Should be employed only when necessary (now often used indiscriminately and to excess) • High concentrations of drug should be maintained over long periods (i.e. taking all of one’s pills over prescribed duration of treatment) • Two antibiotics administered simultaneously may be capable of synergism when necessary

45. Combinations of antimicrobial agents • Necessary when: - Treating a life-threatening infection - Preventing the emergence of resistance - Treating a mixed infection - Enhancing antibacterial activity - Using lower concentrations of a toxic drug

46. Common Uses of Antibiotics a. Gastro-intestinal system (Invasive salmonellosis, Typhoid fever, Biliary tract, Peritonitis) b. Cardiovascular system (Endocarditis) c. Respiratory system (Chronic bronchitis, Pneumonia) d. Central nervous system (Meningitis caused by Meningococci, Pneumococci, Haemophilus influenzae, Listeria) e. Urinary tract (Acute pyelonephritis or prostatitis, Lower urinary tract infection)

47. Common Uses of Antibiotics (Contd.) f. Genital system (Syphilis, Gonorrhoea, Uncomplicated genital chlamydial infection, Urethritis or pelvic inflammatory disease) g. Blood (Septicaemia, Meningococcal septicaemia) h. Musculoskeletal system (Septic arthritis, Osteomyelitis) i. Eye, ear, nose and oropharynx (Conjunctivitis, Sinusitis, Otitis media, Throat, Dental infection) j. Skin (Acne, Cellulitis, animal/insect bite)

48. Common antibacterials • Beta-lactam Antibiotics • A.Penicillins • Natural penicillins • Penicillinase-resistant penicillin • Amino Penicillin • Antipseudomonal Penicillin

49. 1. Natural Penicillins • Penicillin G (Benzyl) • Penicillin G sodium/potassium • Penicillin G procaine • Penicillin G benzathine • Penicillin V (Phenoxymethyl-)

50. 2. Penicillinase-Resistant Penicillins • Cloxacillin Orbenin • Dicloxacillin Diclocil • Methicillin Pyopen • Nafcillin • Oxacillin