Antimicrobial Pharmacology I PDF

antimicrobial pharmacology i Altaf Darvesh, M. Pharm., Ph.D. 11-12-2024  Recommended Reading Katzung’s Basic and Clinical Pharmacology 16th edition, Vanderah, McGraw Hill Goodman and Gilman’s The Pharmacologic Basis of Therapeutics 14th edition, Brunton, Knollma...

antimicrobial pharmacology i Altaf Darvesh, M. Pharm., Ph.D. 11-12-2024  Recommended Reading Katzung’s Basic and Clinical Pharmacology 16th edition, Vanderah, McGraw Hill Goodman and Gilman’s The Pharmacologic Basis of Therapeutics 14th edition, Brunton, Knollman, McGraw Hill (Available online on Access Medicine & Access Pharmacy)  Objectives ▪ Identify the targets of anti-microbial pharmacotherapy ▪ Distinguish between bacteriostatic and bactericidal agents ▪ Describe general mechanisms of antimicrobial resistance ▪ Describe the structure of the bacterial cell wall ▪ Distinguish between Gram-positive and Gram-negative bacteria ▪ Classify beta-lactam antibiotics ▪ Describe the mechanism of action of beta-lactams ▪ Describe the mechanism of resistance of beta-lactams ▪ Describe the adverse effects of beta-lactams ▪ Discuss beta-lactamase inhibitors  Targets of antimicrobial pharmacotherapy ▪ Antibiotics target microbial proteins are essential components of biochemical reactions in the microbes. ▪ Antibiotics interfere with biochemical pathways and inhibit the replication of or directly kills the microorganisms. ▪ The biochemical processes commonly inhibited include: Cell wall synthesis Cell membrane synthesis and function http://www.krider.com/MPj03211260000%5b1%5d.jpg Ribosomal translation http://apartmentsurvivalist.com/wp-content/uploads/2012/02/Antibiotics.jpg Nucleic acid metabolism D > - TB D D  Bacteriostatic and Bactericidal Bacteriostatic agents ▪ Antimicrobial agents that reversibly inhibit growth of bacteria. Minimum Inhibitory Concentration (MIC) ▪ The lowest concentration of drug required to inhibit growth of the organism. Bactericidal agents ▪ Antimicrobial agents with an irreversible lethal action on bacteria. Minimum Bactericidal Concentration (MBC) ▪ The lowest concentration of drug required to kill the organism. Only MICs are routinely measured in most infections, whereas in infections in which bactericidal therapy is required for eradication of infection (eg, meningitis, endocarditis, sepsis in the granulocytopenic host), MBC measurements occasionally may be useful.  Bacteriostatic and Bactericidal ▪ Antibacterial agents may be classified as bacteriostatic or bactericidal. ▪ For agents that are primarily bacteriostatic, inhibitory drug concentrations are much lower than bactericidal drug concentrations. ▪ In general, cell wall-active agents are bactericidal, and drugs that inhibit protein synthesis are bacteriostatic. ▪ Bacteriostatic antibiotics prevent bacterial growth and reproduction by interfering with bacterial protein production, DNA replication, or other aspects of bacterial cellular metabolism. This allows the body's immune system to eliminate the bacteria. ▪ Bactericidal antibiotics kill bacteria by disrupting essential parts of the bacterial cell, such as the cell wall or DN ▪ Bacteriostatic and bactericidal agents are equivalent for the treatment of most infectious diseases in immunocompetent hosts.  Bacteriostatic and Bactericidal Bactericidal agents can be divided into two groups: ▪ Agents that exhibit concentration-dependent killing (eg, aminoglycosides and quinolones) ▪ Agents that exhibit time-dependent killing (eg, β-lactams) ▪ For drugs whose killing action is concentration-dependent, the rate and extent of killing increase with increasing drug concentrations. ▪ For drugs whose killing action is time-dependent, bactericidal activity continues as long as serum concentrations are greater than the MBC. BACTERIOSTATIC ▪ Inhibits growth ▪ Non-lethal ▪ Reversible BACTERICIDAL ▪ Kills ▪ Irreversible BACTERIOLYTIC ▪ Kills ▪ Cell lysis ▪ Irreversible  time-dep. > - time of exposure of Bacteria to antibiotic Alle amount for which the bacteria has been exposed to the antibiotic ▪ Effect of different dose schedules on shape of the concentration-time curve. ▪ The same total dose of a drug was administered as a: single dose (panel A) three equal portions every 8 h (panel B) D Bacteriostatic and Bactericidal BACTERIOSTATIC AGENTS BACTERICIDAL AGENTS Chloramphenicol Aminoglycosides Clindamycin Bacitracin Macrolides Beta-lactam antibiotics Sulfonamides Fluoroquinolones Tetracyclines Daptomycin Trimethoprim Fosfomycin Glycopeptide, lipoglycopeptide antibiotics Metronidazole BACTERIOSTATIC / BACTERCIDAL Linezolid Nitrofurantoin INDIVIDUALLY BACTERIOSTATIC – COMBINATION BACTERCIDAL Trimethoprim-Sulfamethoxazole  General mechanisms of antimicrobial resistance > - cannot stop growth or kIII bug Antimicrobial resistance can develop at any one or more of steps in the processes by which a drug reaches and combines with its target. Major mechanisms of antibiotic resistance include: Reduced concentration of the antibiotic at its target site ▪ Antibiotic concentration may be reduced below the effective concentration through the action of efflux pumps, energy-dependent transporters that expel antibiotics. Production of microbial enzymes that alter or destroy the antibiotic ▪ Inactivation of antibiotics through the function of microbial enzymes is a common mechanism of drug resistance. Alteration of antibiotic targets in ways that reduce antibiotic affinity ▪ Single or multiple point mutations can change amino acid composition and conformation of an antimicrobial’s target protein which can lead to reduced affinity of drug for its target,  General mechanisms of antimicrobial resistance Less-common mechanisms that have been discovered include: ▪ Bypass of inhibited metabolic pathways ▪ Excision of antibiotic-target complexes - > drug binas to target bug damages , ▪ Overproduction of target enzymes complex - by bug ; dose isn't sufecient enough Development of Resistance via Mutation Selection ▪ Acquisition of genetic elements that code for the resistant mechanism ▪ Mutations that develop under antibiotic pressure ▪ Constitutive induction ispontaneous Resistance by External Acquisition of Genetic Elements ▪ Drug resistance may also be acquired by horizontal transfer of resistance determinants from a donor cell, often of another bacterial species. More than one mechanism may work in concert to confer resistance to an individual antibiotic.  Structure of bacterial cell wall ▪ The cell wall is a rigid outer layer that completely surrounds the cytoplasmic membrane which: provides rigid mechanical stability maintains cell integrity prevents cell lysis from high osmotic pressure. ▪ The cell wall is composed of layers of a complex, cross-linked polymer of polysaccharides and peptides known as peptidoglycan. ▪ The polysaccharide contains alternating amino sugars N-acetylglucosamine (NAG) (G) and N-acetylmuramic acid (NAM) (M) ▪ A five-amino-acid peptide is linked to the N-acetylmuramic acid sugar which terminates in D-alanyl-D-alanine. * ▪ Transpeptidase enzyme [Penicillin-binding protein (PBP)] removes the terminal alanine in the process of forming a cross-link with a nearby peptide – transpeptidation reaction. and D-ala via * 5 glycine transpeptidase > - ridid Cel wall ▪ Cross-links give the cell wall its rigidity.  "D" in bacteria amino ands are Structure of bacterial cell wall N-acetylglucosamine = G N-acetylmuramic acid = M > - peptide side chain transpeptidase Floppy Rigid * penicillin prevents crosslink formation does NOT destroy already linked chain!  http://25.media.tumblr.com/tumblr_m3kj8snEgz1qdmutfo1_400.jpg Gram staining Hans Christian Gram – Danish scientist (1884) Method Heat fix a smear of bacterial culture Apply crystal violet – primary stain It charge Apply mordant – Gram’s iodine 1- charge ↳ fixes the color Rapid decolorization – alcohol or acetone (timing is critical) Apply counterstain – safranin or carbol fuschin Gram positive – thick peptidoglycan layer – retain the violet stain - VIOLET Gram negative – lipid layer and thin peptidoglycan layer – retain counterstain - RED Gram variable and Gram indeterminate  Gram positive and gram negative bacteria ▪ Cell wall of gram positive bacteria has 20-80 layers of peptidoglycan ▪ Cell wall of gram negative bacteria has 2-3 layers of peptidoglycan  Beta-lactam antibiotics ▪ Share common four-membered beta-lactam ring ▪ Share common mechanism of action > - PBP in cell wall Beta-lactam antibiotics  Mechanism of action ▪ β-lactam antibiotics, inhibit bacterial growth by interfering with the transpeptidation reaction of bacterial cell wall synthesis. ▪ β-lactam antibiotics are TIME-DEPENDENT BACTERICIDAL  Mechanism of action ▪ Stereomodels reveal that the conformation of a typical penicillin is very similar to that of D-alanyl-D-alanine. ▪ The structural similarity between penicillins and D-alanyl-D-alanine allows the antibiotics to act as inhibitory substrates for the transpeptidase (PBP) enzyme. D ▪ Transpeptidase is acylated, and inhibited, by penicillin (penicilloyl enzyme formed) after cleavage of the —CO—N— bond of the β-lactam ring. PBP Is Dala natural substrate for  Mechanisms of Resistance 1. Inactivation by β-lactamase (penicillinase) – most common! 2. Modification of target PBPs 3. Impaired penetration of drug to target PBPs 4. Efflux Pumps  Mechanisms of Resistance D Inactivation by β-lactamase (penicillinase) ▪ Bacteria produce β-lactamase as a defense mechanism to inactivate β- lactam antibiotics, essentially rendering them ineffective and allowing the bacteria to survive in the presence of the antibiotic. ▪ Enzymatic hydrolysis (breakdown) of the β-lactam ring by bacterial β- lactamases yields penicilloic acid, which lacks antibacterial activity. ▪ Beta-lactamase production is the most common mechanism of resistance. ▪ Hundreds of different β-lactamases have been identified. β-lactamase  Penicillins Classification Natural Penicillins ▪ Penicillin G ▪ Penicillin V Antistaphylococcal penicillins D β-lactamase resistant penicillins > - resistent to penicillinates ▪ Oxacillin bacteria ▪ Dicloxacillin produce ▪ Nafcillin Aminopenicillins - have an amino group ▪ Ampicillin ▪ Amoxicillin Ureidopenicillin ▪ Piperacillin  Penicillins Penicillin Pharmacokinetics Resistance to β-lactamase (Oral Absorption) Natural Penicillins Penicillin G Variable (Poor) NO (Used IV) Penicillin V Moderate NO Antistaphylococcal penicillins β-lactamase resistant penicillinsD Oxacillin Good YES Dicloxacillin Good YES Nafcillin Variable YES (Hepatic metabolism) Aminopenicillins Ampicillin Good NO Amoxicillin Good NO Ureidopenicillin Piperacillin Poor (Used IV) NO  Penicillins Adverse effects Hypersensitivity ** ▪ Due to degradation products of penicillins such as penicilloic acid ▪ Most common cause of drug allergy Symptoms include: ▪ Rash ▪ Fever ▪ Bronchospasm ▪ Serum sickness ▪ Anaphylactic shock (0.05%) Jarisch-Herxheimer reaction - associated with penicillin treatment of syphilis In patients with renal failure high doses can cause seizures Cross-sensitivity and cross-reactivity Cephalosporins a & resisten * know generations & Cephalosporins First generation - > gram positive Cefadroxil, Cefazolin, Cephalexin Second generation - > equal gram +- Cefaclor, Cefprozil, Cefuroxime Third generation - > gram negutive Cefdinir, Cefpodoxime, Ceftriaxone Fourth generation Cefepime Fifth generation Ceftaroline * gram negative coverage and Deta-lactamase stability Increases  Cephalosporins ▪ Cephalosporins have similar mechanism of action to penicillins. ▪ They are more stable to many bacterial beta lactamases. ▪ They have a broader spectrum of activity. ▪ Generational classification is based on antimicrobial spectrum and activity. ▪ Each newer generation has significantly greater Gram-negative antimicrobial properties than the preceding generation.  Cephalosporins Cephamycins Cefoxitin, Cefotetan ▪ Sub-class of second generation cephalosporins ▪ Possess a methoxy group at the 7-alpha position ▪ Have activity against anaerobes D ▪ More resistant to beta-lactamases commonly produced by anaerobic bacteria Core structure of the cephalosporins Core structure of the cephamycins.  Cephalosporins Ceftaroline fosamil– prodrug of Ceftaroline (fifth generation) ▪ Cephalosporin active against Methicillin-resistant Staphylococci (MRSA) * ▪ Ceftaroline has increased binding to penicillin-binding protein 2a, which mediates methicillin resistance in staphylococci, resulting in bactericidal activity against these strains. of dala-d-ala In MRSA binding pocket does not pick up antibiotic  Cephalosporins Cefiderocol "trojan horse" - exist in nature ▪ Siderophore – iron chelating compound ▪ Binds to extracellular iron and enters bacteria through active iron transporters. ▪ Resistant to most β-lactamases D A ▪ Activity against multi-drug-resistant gram-negative bacteria Cefiderocol  Allergies and cross-reactivity ▪ Like penicillins, cephalosporins may elicit a variety of hypersensitivity reactions, including anaphylaxis, fever, skin rashes, nephritis, granulocytopenia, and hemolytic anemia. ▪ Patients with documented penicillin anaphylaxis have an increased risk of reacting to cephalosporins compared with patients without a history of penicillin allergy. ▪ However, the chemical nucleus of cephalosporins is sufficiently different from that of penicillins such that many individuals with a history of penicillin allergy tolerate cephalosporins. ▪ Overall, the frequency of cross-allergenicity between the two groups of drugs is low (~1%). ▪ Cross-allergenicity appears to be most common among penicillin, aminopenicillins, and early-generation cephalosporins, which share similar R-1 side chains. * ▪ Patients with a history of anaphylaxis to penicillins should not receive first- or second- generation cephalosporins, while third- and fourth-generation cephalosporins should be administered with caution, preferably in a monitored setting.  Allergies and cross-reactivity Cross-reactivity is most likely determined by side chain similarity (rather than beta-lactam structure) R1 side chain is most important allergenic component  Monobactams Aztreonam ▪ Monocyclic beta-lactam ring ▪ Activity only against aerobic gram-negative bacteria ▪ No activity against gram-positive bacteria or anaerobes ▪ Lack of allergic cross-reactivity with other β-lactam antibiotics, with the possibleDexception of ceftazidime, ceftolozane, and cefiderocolD with which it shares similar or identical side chains ▪ Resistant to most β-lactamases ▪ Skin rash  Carbapenems Imipenem, Meropenem, Ertapenem ▪ Broad spectrum – activity against both gram-positive and gram-negative bacteria ▪ Renal clearance ▪ IV administration ▪ Seizures Imipenem / Cilastatin ▪ Imipenem is hydrolyzed rapidly by a renal dehydropeptidase found in the brush border of the proximal tubule. ▪ Consequently, it is administered together with an inhibitor of renal dehydropeptidase, cilastatin. > renal dehudropeptidase Inhibitor - ▪ Both imipenem and cilastatin have a t1/2 of about 1 h. ▪ When administered concurrently with cilastatin, about 70% of administered imipenem is recovered in the urine. use on drug that are beta-lactamase sensitive ! β-Lactamase Inhibitors ▪ β-lactamase inhibitors bind to β-lactamases and prevent the enzymes from hydrolyzing β-lactam agents in the vicinity. ▪ A β-lactamase inhibitor ▪ A β-lactamase inhibitor extends the spectrum of a β-lactam provided that the inactivity of the β-lactam is due to destruction by β-lactamase, and that the inhibitor is active against the β-lactamase that is produced. ▪ First generation inhibitors possess the β-lactam ring beta > - affinityto D ▪ Weak antibacterial actionD lactamase ; so of Clavulanic acid beta-lactam ring is the Inhibitor Sulbactam not the Tazobactam damaged drug ▪ Second generation inhibitors do not possess the β-lactam ring Avibactam Durlobactam Relebactam Vaborbactam FVl β-Lactamase Inhibitors Some available combinations ▪ Amoxicillin / Clavulanic acid ▪ Ampicillin / Sulbactam ▪ Piperacillin / Tazobactam ▪ Meropenem / Vaborbactam Cephalosporin + β-lactamase inhibitor combination ▪ Ceftolozane / Tazobactam (Zerbaxa) (IV infusion) Ceftolozane alone is not available – only in combination ▪ Ceftazidime / Avibactam (Avycaz) (IV infusion) β-lactamase inhibitor combination ▪ Sulbactam / Durlobactam (Xacduro) (IV infusion) Durlobactam alone is not available – only in combination  PRACTICE QUESTIONS 1. Which antimicrobial medication is β-lactamase-sensitive? A. Amoxicillin B. Dicloxacillin C. Nafcillin D. Oxacillin 2. Which antimicrobial medication is a first-generation cephalosporin? A. Cefazolin B. Cefprozil > - and gen C. Cefdinir > - zra yen D. Cefepime uiu - gen  PRACTICE QUESTIONS 3. Which medication is a β-lactamase inhibitor? A. Aztreonam > - monobactam B. Ceftibuten > - cephalosporin C. Imipenem > - carbapenem D. Sulbactam 4. Which medication is a renal dehydropeptidase inhibitor? A. Cilastatin B. Cefiderocol > - Cephalosporin ; iron transporter C. Clavulanic acid > - beta-lactamase inhibitor D. Ceftaroline fosamil > - Cephalosporin ; stugen-MRSA coverage  Vancomycin > - does not get absorbed viaGl given IV Dis its too heavy ; orally for Cauf infection (don't need it to be absorbed in this case)  Objectives ▪ Describe the mechanism of action of vancomycin ▪ Describe the mechanism of resistance of vancomycin ▪ Describe the pharmacokinetics of vancomycin ▪ Describe the adverse effects of vancomycin ▪ Discuss vancomycin infusion reaction ▪ Highlight the indications and uses of vancomycin ▪ Describe lipoglycopeptide agents new antiplonic agents are lipoglycopeptides ! Vancomycin in soil at > found - riverbanks ▪ Glycopeptide antibiotic isolated from the bacterium Amycolatopsis orientalis ▪ Large molecular weight – 1,449.3 ▪ Active against gram positive bacteria ▪ Lack of penetration through gram negative cell membranes ▪* Poorly absorbed from the gastrointestinal tract ▪ Vancomycin hydrochloride is water soluble > - given IV  Structure of bacterial cell wall N-acetylglucosamine = G N-acetylmuramic acid = M transpeptidase ↑ Floppy Rigid anchors on d-ald-d-ald so enzyme cannot bina Mechanism of action > - forms steric shield on L-lyS-D-ala-D-ald by Inhibiting the transaucosulases NAG and NAM Vla LCP transglycosylases -> connects a * willalsopreventppinadverten Mechanism of action Mechanism of action  Mechanism of action ▪ Polymerization / elongation of the NAG-NAM units to form peptidoglycan chains is done by the enzyme transglycosylase (glycosyltransferase) (peptidoglycan synthase). ▪ Although transglycosylase does not require D-alanine-D-alanine (D-ala-D- ala) dipeptide for its catalytic activity – the enzyme needs to anchor on D- ala-D-ala terminus attached to the lipid carrier to access the glycosylation site and link the amino sugar units. ▪ Vancomycin binds to the D-ala-D-ala terminus. ▪ Vancomycin inhibits transglycosylase from polymerizing the NAG-NAM units thus preventing elongation of peptidoglycan layers. ▪ Vancomycin also inhibits crosslinking of D-alanine to glycine. > there is - not D a glu5 * ▪ This causes formation of a weak cell wall – cell becomes susceptible to lysis. ▪ BACTERICIDAL (AUC/MIC) D D  It ponding is necessary for dimerization and activity of vancomycin Mechanisms of resistance ▪ The D-alanine terminus is crucial because it forms critical hydrogen bond with vancomycin which is required for its binding. D ▪ Resistance to vancomycin is the result of alteration of the D-alanyl-D-alanine target to D-alanyl-D-lactate or D-alanyl-D-serine. D-ala-D-ala - > d-ala-d-lactate (or -serine( ▪ This results in loss of a critical hydrogen bond that facilitates high-affinity binding of vancomycin to its target and loss of activity. fase [ ▪ Altered cell wall metabolism results in a thickened cell wall with increased D- Ala-D-Ala residues, which serve as dead end binding sites for vancomycin. D D ▪ Vancomycin is sequestered within the cell wall by these false targets and may be unable to reach its site of action.  Pharmacokinetics ▪ Poor absorption after oral administration. ▪ Approximately 30% bound to plasma protein ▪ Widely distributed in the body, including adipose tissue ▪ Appears in various body fluids, such as cerebrospinal, pleural, pericardial, and synovial fluids. ▪ Ninety percent of the drug is excreted by glomerular filtration. ▪ Elimination half-life is about 6 h in normal renal function. ▪ Drug accumulates if renal function is impaired. ** Monitor trough serum concentrations Adjust dose for renal impairment  Adverse effects ▪ Ototoxicity – rare ▪ Nephrotoxicity – high trough levels ▪ Administration with another ototoxic or nephrotoxic drug, such as an aminoglycoside, increases the risk of both these toxicities. ▪ Macular skin rashes ▪ Anaphylaxis > - Inflammation of the walls of a vein ▪ Phlebitis & pain at the site of injection ▪ Chills, rash, and fever ▪ Infusion reaction  previously called Vancomycin infusion reaction "Red Mansund. " ▪ Rapid intravenous infusion may cause erythematous or urticarial reactions, flushing, itching, tachycardia, and rarely hypotension. ▪ The extreme flushing that can occur is not an allergic reaction but a direct effect of vancomycin on mast cells, causing them to release histamine. ▪ Typically, this reaction can be ameliorated by slowing the infusion rate. ▪ Premedication with antihistaminics such as diphenhydramine. * ▪ Individuals most at risk are younger patients, particularly those under the age of 40, especially children.  Indications Oral administration ▪ Pseudomembranous colitis – Clostridium difficile (C. diff) Intravenous infusion ▪ Methicillin-resistant Staphylococcal (MRSA) infections Blood stream infections, endocarditis Vancomycin is not as effective as penicillin for serious infections such as endocarditis caused by methicillin-susceptible strains. ▪ Gram-positive infections in patients with penicillin allergy Vancomycin in combination with gentamicin is an alternative regimen to treatment of endocarditis in patients with penicillin allergy.  Lipoglycopeptides Telavancin, Dalbavancin, Oritavancin ▪ Mechanism of action and mechanisms of resistance are similar to vancomycin ▪ Intravenous administration ▪ Indicated for complicated skin and skin structure Infections (cSSSI) Telavancin Semisynthetic lipoglycopeptide derived from vancomycin Additional mechanism of action - it increases membrane permeability and disrupts the bacterial cell membrane potential. Nephrotoxicity Teratogenic potential Dalbavancin, Oritavancin  Lipoglycopeptides Dalbavancin Semisynthetic lipoglycopeptide derived from teicoplanin, an analogue of vancomycin. Extremely long half-life of greater than 10 days Single dose or two dose regimen – day 1, day 8 Oritavancin Semisynthetic lipoglycopeptide derived from chloroeremomycin, an analogue of vancomycin. Additional mechanism of action - disruption of cell membrane permeability and inhibition of RNA synthesis. Extremely long half-life of greater than 10 days Single dose only Weak inhibitor of CYP2C9 and CYP2C19, inducer of CYP3A4 and CYP2D6 D D  PRACTICE QUESTIONS 1. Which enzyme is inhibited by vancomycin? A. Penicillinase B. Transpeptidase C. Transglycosylase D. Dehydropeptidase 1. Which of the following is the mechanism of action of dalbavancin? A. Hydrolysis of the β -lactam ring B. Inhibition of the transpeptidase enzyme C. Binding to the D-alanyl-D-alanine terminus D. Replacement of the terminal D-alanine by D-lactate