Antibiotics Part 3 PDF

PMP201 - Infection ISU Antibiotics - drug classes and mechanisms - Part 3 6th Nov 2024 Dr. Giulio Nannetti [email protected] Previous & complementary knowledge Health, Disease & Patient (PMP101) – 2023/24 Microbiology lectures –...

PMP201 - Infection ISU Antibiotics - drug classes and mechanisms - Part 3 6th Nov 2024 Dr. Giulio Nannetti [email protected] Previous & complementary knowledge Health, Disease & Patient (PMP101) – 2023/24 Microbiology lectures – Bacteria composition Bacterial growth Patient-Centred Learning I (PMP201) – 2024/25 Overview of antibiotics 1 – Dr Guirguis Overview of antibiotics 2 & 3 – Dr Guirguis Chemistry of antibiotic – Dr Padalino Learning Outcomes By the end of this session you will be able to: Outline the antibacterial mechanism, effect and properties of the main types of antimetabolite antibiotics Outline the antibacterial mechanism, effect and properties of inhibitors of nucleic acids synthesis Outline the antibacterial mechanism, effect and properties of antibiotics acting with an alternative mechanism of action Identify the therapeutic agents for tuberculosis Patient Centred Integration Human Biology Clinical Pharmacy Cellular & Pharmacy Molecular Practice Bioscience Pharmacology & Pharmaceutics Therapeutics Pharmaceutical Chemistry  Mechanism of actions - RECAP 5- Alternative mechanisms Generating instable and reactive free radicals 2- Inhibition of protein synthesis 1- Inhibition of cell wall synthesis 3- Acting as antimetabolites 4- Inhibition of nucleic acids synthesis  1- Inhibitors of cell wall synthesis - RECAP 1- Inhibitors of cell wall synthesis Transpeptidation reaction By bacterial transpeptidase form peptide cross-link bridges between tetrapeptide of NAMs of peptidoglycan strands β-Lactam and Non β-Lactam classes inhibiting cell wall synthesis - RECAP β-lactams – bactericidal β-lactam ring Target transpeptidase enzymes (mimicking their substrate) Structurally different chemical classes (with β-lactam ring) Non β-lactams: Glycopeptide (Vancomycin) - bactericidal No β-lactam ring Target transpeptidase’s substrate Same mechanism of action 2) Protein Synthesis Inhibitor classes - RECAP 2- Inhibitors of protein synthesis Macrolides -thromycin suffix Lincosamines Block the translocation e.g. Clindamycin Block the translocation Oxazolidinones e.g. Linezolid Block the translation initiation Large subunit Chloramphenicol Block the attachment of tRNA to the ribosome site A Small subunit Aminoglycosides -mycin suffix cause mRNA misreading (faulty/premature protein). Tetracyclines Also, they may block the -cycline suffix translation initiation Block the attachment of tRNA to the ribosome site A 3) Antibiotic classes acting as antimetabolites Inhibit bacterial metabolic pathways (distinct from those in eukaryotic cells) → selective toxicity. Primarily target key enzymes to block folic acid synthesis, essential for 3- Antimetabolites nucleotide production. Bacteriostatic effect 3a) Sulphonamides Sulfamethoxazole Sulphonamides mechanism Folic acid is essential to produce purines (nucleotides) Bacteria cannot uptake folic acid from outside Bacteria synthesise folic acid, starting from a precursor p-aminobenzoic acid (PABA) Sulphonamides act by competing with PABA to inhibit the first enzyme dihydropteroate synthase (DHPS) In Human body - Folic acid (Vitamin B9) obtained in the diet 3b) Trimethoprim Trimethoprim mechanism ▪ Trimethoprim targets dihydrofolate reductase (DHFR) ▪ DHFR is present in human cells, for the dietary folic acid activation ▪ Selective toxicity: Trimethoprim has 100,000x higher affinity for bacterial DHFR over human counterpart. From Basic medical Key 3a+b) Sulphonamides + trimethoprim (co-trimoxazole) Sulfamethoxazole + trimethoprim in combination (PABA) Sequential blocking mechanism Both drugs block the folic acid synthesis at two distinct steps of → potential synergistic effect Bacteriostatic effect Spectrum: Broad (Gram +ve and Gram –ve) From Basic medical Key 3a+b) Sulphonamides + trimethoprim (co-trimoxazole) Co-trimoxazole or trimethoprim Refer to Prof. Guirguis’s lecture Uses: UTIs, prostatitis, Pneumocystis jirovecii pneumonia in immunocompromised patients Side effects ▪ Risk of folate deficiency (during pregnancy is associated with neural tube defects- contraindicated) ▪ Hyperkalaemia (high levels of potassium - monitor renal function) ▪ Hypersensitivity; rash and anaphylaxis Contraindications: Avoid in first-trimester of pregnancy & patients with blood dyscrasias Cautions: in acute porphyria, elderly, neonates, predisposition to folate deficiency NICE - Co-trimoxazole  4) Inhibition of nucleic acids synthesis 4- Inhibitors of nucleic acids synthesis  4) Nucleic Acid Synthesis Inhibition Nucleic acid synthesis inhibitors: DNA/RNA polymerase Fluoroquinolones target topoisomerases, Fluoroquinolones essential for DNA replication. Topoisomerase Rifamycins inhibit RNA polymerase, blocking DNA transcription to mRNA Both exert a bactericidal effect Rifampycin Lower selective toxicity due to similarities between bacterial and eukaryotic mechanisms. DNA structure in bacteria (extra material) Bacterial DNA is Circular and supercoiled, making DNA more compact Add Coils Similar to the phone cord relaxation The DNA helix form is always maintained Topoisomerase Enzymes (DNA topoisomerase IV and DNA gyrase): Form and relax supercoils to prevent DNA tangling and facilitate DNA replication and transcription processes. Fluoroquinolones inhibit DNA gyrase and topoisomerases IV → making DNA inaccessible → blocking bacterial DNA replication → leading to cell death 4a) Fluoroquinolones Ciprofloxacin, levofloxacin, Moxifloxacin, Norfloxacin floxacin- suffix Mechanism: ▪ Inhibit DNA replication by interfering with the bacterial topoisomerases (2 types) ❖ DNA gyrase (not present in human) → target in Gram- ❖ topoisomerase IV (the human enzyme is inhibited at high dose) → target in Gram+ This makes DNA inaccessible → prevent DNA replication/transcription → cell death Spectrum: Broad (effective against Gram +ve and -ve like H. influenzae, P. aeruginosa). Uses – Serious RTIs (CAP), skin/soft tissue infections and UTI (E. coli) Systemic fluoroquinolones must now be prescribed when other options are inappropriate. NICE - quinolones  4a) Fluoroquinolones Refer to Prof. Guirguis’s lecture All orally active, and several are available as intravenous injections Side effects: ▪ GI distress, stimulating C.difficile overgrowth ▪ tendonitis, tendon rupture – 2% cases (discontinue at the first sign of tendinitis, painful swelling) ▪ muscle weakness, joint pain ▪ prolongs QT interval and risk of aortic aneurysm (very rare) ▪ Seizures (rare, but higher risk with NSAIDs) and peripheral neuropathy ▪ Overuse is leading to rapid development of resistance Contraindications: Patients with history of tendon damage or taking corticosteroids Cautions: Patients with QT prolongation risk factors, in epilepsy, psychiatric disorders, patients with renal impairment, exposure to sunlight. 4b) Rifamycins (Rifampicin) Rifampicin Mechanism: ▪ Inhibit the initiation of bacterial DNA transcription ▪ By blocking the activity of the bacterial RNA polymerase RNA polymerase ▪ Bactericidal effect DNA messenger RNA Rifampicin 4b) Rifamycins (Rifampicin) Refer to Prof. Guirguis’s lecture Spectrum: Broad (Gram +ve and –ve) and Mycobacterium tuberculosis Uses - To treat tuberculosis and N. meningitidis/H. influenzae meningitis (it enters the cerebrospinal fluid) Side effects ▪ GI distress rapid development of resistance ▪ Minor hepatotoxicity ▪ Discoloration of body fluids (urine and sweat turn orange - harmless) ▪ Many interactions (by inducing cytochrome P450) Contraindications: Patients with acute porphyrias NICE - Rifampicin 5) Alternative mechanisms 5- Alternative mechanisms Generating free radicals Nitroimidazoles Metronidazole Nitrofurantoin 5a) Nitroimidazoles Do not need to memorise Metronidazole -azole suffix the structure and details Anaerobes Ferredoxin - Mechanism – Generating free radicals in bacteria Red Metronidazole ▪ Once reduced, it generates an instable nitroso radical Ferredoxin -Ox Metabolite metabolites (ROS) nitroso-Red. ▪ ROS leads to DNA fragmentation Act on DNA (ROS) ▪ Bactericidal effect DNA fragmentation CELL DEATH (Bactericidal) Spectrum: Only anaerobes (including protozoa – other class of microbes) ▪ To be activated/reduced, it requires low redox potential within cells ▪ In aerobic bacteria, there is high redox potential due to O2, which cannot activate ROS Uses – Used to treat infections of anaerobic bacteria, H. pylori eradication 5a) Nitroimidazoles Refer to Prof. Guirguis’s lecture Metronidazole Rapid and effective absorption (Oral and IV) Penetrate well all tissues Side effects ▪ GI distress ▪ Taste disturbances (metallic taste), furred tongue ▪ Peripheral neuropathy (rare) ▪ Disulfiram-like adverse reactions when alcohol is consumed Cautions: Avoid exposure to sunlight with topical use. Avoid intravaginal preparations in young girls. Avoid alcohol NICE - Metronidazole 5b) Nitrofurantoin Nitrofurantoin Mechanism - generating reactive free radicals ▪ Activate pathways in bacteria to generate instable metabolites that interfere with RNA, DNA and other components synthesis. ▪ Bactericidal effect Giske, 2015; Clinical Microbiology and Infection. https://doi.org/10.1016/j.cmi.2015.05.022 Spectrum: effective against most Gram +ve and some Gram -ve (E. coli) Uses: to treat and prevent uncomplicated acute UTIs 5b) Nitrofurantoin Refer to Prof. Guirguis’s lecture Side effects ▪ Discoloration of body fluids (urine and sweat turn orange/brown - harmless) ▪ Pulmonary toxicity (fever, chills, cough, myalgia, and dyspnoea) ▪ Peripheral neuropathy (rare) ▪ blood disorders (rare, haemolytic anemia) Contraindications: Patients with Decreased renal function (eGFR < 45 mL/min), G6PD deficiency; Infants: Less than 3 months old Cautions: In anaemia, diabetes, electrolyte imbalances and folate deficiency NICE - Nitrofurantoin Treatment for tuberculosis (TB) 10.6 million people fell ill with tuberculosis (TB) caused by Mycobacterium tuberculosis worldwide in 2021 1.6 million people died worldwide from TB in 2021 Infection in the lungs (pulmonary), or spread to other organs (extrapulmonary) Latent (asymptomatic) and active tuberculosis (symptomatic) Mycobacterium tuberculosis Gram+ and aerobe (requires oxygen - lungs) Complex and unique cell wall Virulence factors – allowing the bacteria to survive after the phagocytosis of macrophages. Mycobacteria can even replicate inside a macrophage and kill it Marker for the microbiological diagnosis ▪ acid-fast staining (lipid-rich cell wall) ▪ auramine fluorescent staining (mycolic acids of the cell wall) Therapeutic target  Cell wall of Mycobacteria + free lipids UNIQUE components in bacteria Mycobacteria cell wall Not required to be memorised Mycobacterium cell wall – thick, hydrophobic, robust and waxy (variety of lipids) ▪ Hydrophobic barrier to antibiotics → difficult to treat Mycobacteria  Treatment for tuberculosis (TB) First-line drugs: RIPE → Drug combinations to prevent drug resistance R- Rifampicin (RNA polymerase inhibitor) Mycobacteria cell wall I- Isoniazid (Prodrug) - Inhibitor of mycolic acids synthesis P- Pyrazinamide (Prodrug) - interferes with fatty acid synthesis E- Ethambutol interferes with synthesis of arabinogalactans Treatment for tuberculosis (TB) NEWLY DIAGNOSED (6-months therapy) ▪ initial (RIPE):Rifampicin+ Isoniazid + Pyrazinamide + Ethambutol (2 months) ▪ continuation (RI): Rifampicin+ Isoniazid (4 months) RE-TREATMENT (7-months therapy) Treatment needs to be ▪ initial: RIPE + Streptomycin (2 months) CLICK supervised in patients at ▪ Continuation: RI + Ethambutol (5 months) risk of non-compliance Drug resistant strains Multidrug-resistant TB (MDR-TB), TB resistant to Rifampicin AND Isoniazid Extensively drug-resistant TB (XDR-TB), TB resistant to Rifampicin, Isoniazid, AND at least two types of drugs of the second line Quiz Which of the following is the target of the antibiotic trimethoprim? a) Cell wall synthesis b) Protein synthesis c) Folic acid synthesis d) RNA polymerase Quiz Which of the following is NOT a first line drug in the treatment of tuberculosis? a) Rifampicin b) Isoniazid c) Pyrazinamide d) Amoxicillin e) Ethambutol  Recommended readings BNF and BNFC - Medicines Complete Link Prescott's microbiology. 12th/11th editions 2023/2020. Chapters 9 (Relevant content) ebook Link Pharmacology for pharmacy and the health sciences:a patient-centred approach. 2nd ed., 2017. Chapter 22 (Relevant content) Foye’s Principles of Medicinal Chemistry. 7th Ed. Chapter 33 -8th Ed. Chapter 29 The lecture content is covered in other Microbiology and Pharmacology textbooks British National Formulary NICE | The National Institute for Health and Care Excellence DISCLAIMER NOTE Permission to use some images granted by the publishers W.W. Norton & Company and McGraw- NICE Hill US Higher Ed ISE. Guidelines All the other images used in this presentation are available in the Public Domain, have a Creative Commons license or prepared by the author. Please email me if you have any doubts or further queries [email protected]