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Antimicrobials
Abx, anti-virals, anti-protozoa, anti-fungals
| Term | Definition |
|---|---|
| What is the minimal inhibitory concentration? | Lowest [drug] preventing growth of particular bacterium |
| What is the minimal bactericidal concentration? | Lowest [drug] killing bacterium |
| Which drugs are bacteriostatic? | Protein biosynthesis, antimetabolites, anti-membrane |
| Which drugs are bactericidal? | Cell wall synthesis, DNA replication/repair |
| What is the therapeutic index? | Ratio of max non-toxic dose : minimum effective drug dose, penicillin -> high degree of selective toxicity (target PG cell wall) -> large therapeutic index, amphotericin B -> low degree of selective toxicity (create pores in CSM) -> low therapeutic index |
| What is the MoDA of cycloserine? | PG biosynthesis -> G +ve/-ve -> structural analogue of D-Ala -> inhibits L-Ala racemase (L -> D-Ala), inhibits D-Ala-D-Ala synthetase, inhibits ligase (connect D-Ala-D-Ala to UDP-NAMT) |
| What is the MoDA of fosfomycin? | PG biosynthesis -> G +ve/-ve -> inhibits pyruvyl transferase (transfers PEP to UDP NAG to form UDP-NAMT) |
| What is the MoDA of vancomycin? | PG biosynthesis -> G +ve -> binds to pentapeptidyl tails (D-Ala-D-Ala) -> reduce accessibility of D-Ala-D-Ala terminus to transpeptidase enzyme -> reduce accessibility of PG repeating unit to transglycosylase enzyme |
| How do bacteria gain resistance to vancomycin? | PG biosynthesis -> replace last D-Ala w/ D-Lac -> prevent vancomycin binding to target |
| What is the MoDA of bacitracin? | PG biosynthesis -> G +ve -> cyclic peptide forms tight complex w/ Mg2+ and bactoprenol pyrophsophate -> inhibits regeneration of lipid II carrier |
| What is the MoDA of beta-lactams? | PG biosynthesis -> G +ve/-ve -> penicillin derivatives (penams), cephalosporin/cephamycins (cephems), monobactams, carbapenems, carbacephems -> D-Ala-D-Ala analogues -> inhibit PG transpeptidase (PBPs) |
| How do bacteria gain resistance to beta-lactams? | PG biosynthesis -> develop beta-lactamases -> cleave beta-lactam ring of Abx -> some bacteria evolved extended spectrum beta-lactamases (ESBL) -> hydrolyse many oxyimino-cephalosporins -> CTX-M plasmid transfer from pre-existing ESBL genes |
| What is the MoDA of sulfamethoxazole? | Bacteria antimetabolite -> G +ve/-ve -> inhibit DHPS (converts p-aminobenzoic acid -> dihydropteroic acid) |
| How do bacteria gain resistance to sulfamethoxazole? | Bacteria antimetabolite -> mutated DHPS |
| What is the MoDA of trimethoprim? | Bacteria antimetabolite -> G +ve/-ve -> inhibit DHFR (converts dihydrofolic acid -> tetrahydrofolate) -> high selectivity for bacteria (different human DHFR) |
| What is the MoDA of co-trimoxazole? | Bacterial antimetabolite combination drug of sulfamethoxazole (inhibit DHPS) and trimethoprim (inhibit DHFR) -> just sulfamethoxazole preserves folic acid pools (slow action), adding trimethoprim traps folate coenzyme in inactive form -> rapid depletion |
| What is the MoDA of sulfadoxin? | Protozoa antimetabolite -> sulfamethoxazole analogue -> inhibit DHPS |
| What is the MoDA of pyrimethanine? | Protozoa antimetabolite -> trimethoprim analogue -> inhibit DHFR |
| What is the contraindications for antimetabolites? | Pregnant women -> baby needs folate for neural tube closure -> anencephaly/spina bifida |
| What is the MoDA of fansidar? | Protozoa antimetabolite combination drug of sulfadoxin (inhibit DHPS) and pyrimethanine (DHFR) -> treat malaria |
| What is the MoDA of valinomycin? | Bacteria anti-membrane -> G +ve -> coordinates K+ ion in hydrophilic interior of circular structure -> bound K+ gives single +ve charge -> diffuses across membrane to extracellular (K+ uniporter) -> disrupt ion gradients |
| What is the MoDA of gramicidin A? | Bacteria anti-membrane -> G +ve -> hydrophobic linear polypeptide -> dimerises in membrane -> form transmembrane ion channel -> passive diffusion of monovalent cations (H+, K+, Na+, Li+) |
| What is the MoDA of polymixin? | Bacteria anti-membrane -> G -ve -> cyclic amphipathic protein -> net charge of +5 -> binds -ve charge phosphate group on outer CSM (G -ve LTA) -> aggregates into micelle-like complexes -> affect CSM permeability |
| What is the MoDA of daptomycin? | Bacteria anti-membrane -> G +ve -> cyclic lipopeptidolactone -> inserts into CSM via phosphatidylglycerol-dependent fashion -> requires complex w/ Ca2+ -> aggregation affects CSM curvature -> ion leakage channels formed |
| What is the disadvantages of anti-membrane drugs? | Lack of selectivity -> phospholipid bilayer not restricted to bacterial cells |
| What is the MoDA of amphotericin B/nystatin? | Fungi/Leishmania anti-membrane -> bind to ergosterol in CSM -> create pore channels for ions/macromolecules -> selective for fungal ergosterol (human cholesterol) -> polyene anti-microbial |
| What is the MoDA of azoles? | Fungi anti-membrane -> inhibit 14 alpha-demethylase (CYP450) -> prevent conversion of lanosterol to ergosterol -> reduce membrane fluidity/permeability |
| What is the side effects of azoles? | Fungi anti-membrane -> fluconazole inhibits testosterone synthesis (gynaecomastia), disrupt liver function (CYP450) |
| What is the MoDA and clinical usage of terbinafine? | Fungi anti-membrane -> inhibit squalene epoxidase (ergosterol synthesis) -> treat onchomycosis (finger/toe nails) |
| What is the MoDA , side effects and clinical usage of griseofulvin? | Fungi anti-mitosis -> binds to tubulin -> inhibiting microtubule formation -> inhibit mitosis -> teratogenic -> oral treatment of dermatophytosis (ringworm) |
| What is the MoDA of caspofungin? | Fungi anti-cell wall -> inhibits 1.3 beta-D-glucan synthetase -> interrupts beta-glucan synthesis -> echinocandin anti-microbials |
| What is the MoDA and side effect of flucytosine? | Funi anti-metabolite -> converted to 5-fluorouracil by cytosine deaminase -> inhibit thymidine synthetase -> disrupt DNA/RNA synthesis -> can cause bone marrow suppression |
| What is the MoDA of tetracycline? | Bacteria anti-metabolite -> G +ve/-ve -> targets 30S subunit -> blocks rotation of aa-tRNA into A site -> prematurely released -> no peptide bond formation -> interrupt mRNA translation/protein synthesis |
| What is the MoDA, clinical usage and side effects of aminoglycosides? | Bacteria anti-metabolite -> G -ve -> targets 30S subunit -> streptomycin/gentamycin -> impair translation proofreading -> misread mRNA -> small ion leakage -> high penetrance for infective endocarditis -> can cause deafness to IHCs |
| What is the MoDA of chloramphenicol? | Bacteria anti-metabolite -> G +ve/-ve -> targets 50S subunit -> blocks aa-tRNA interaction w/ peptidyltransferase A site -> interrupt mRNA translation/protein synthesis |
| What is the MoDA of erythromycin? | Bacteria anti-metabolite -> G +ve -> targets 50S subunit -> binds at 23S rRNA entrance to E tunnel -> interrupt mRNA translation/protein synthesis ->macrolide Abx |
| What is the MoDA and clinical use of lincomycin/clindamycin? | Bacteria anti-metabolite -> G +ve/-ve -> targets 50S subunit -> peptidyltransferase inhibitors (competes w/ loaded tRNA)-> good penetrance -> effective for soft tissue diseases -> cellulitis, necrotising fasciitis (slow growth before tissue removal) |
| How do bacteria gain resistance to aminglycosides? | Bacteria anti-metabolite -> bacterial transferase adds CH3, PO43-, adenyl to 30S site -> prevents aminoglycoside binding |
| What is the MoDA of linezolid? | Bacteria anti-metabolite -> G +ve -> targets 50 S subunit -> prevents recruitment of 50S subunit to ribosomal initiation complex -> interrupt mRNA translation/protein synthesis -> oxazolidinone anti-microbials |
| How do bacteria gain resistance to linezolid? | Bacteria anti-metabolite -> rRNA point mutation -> prevents linezolid binding |
| How do bacteria gain resistance to tetracycline? | Bacteria anti-metabolite -> bacteria gain plasmid-encoded drug efflux pumps |
| How do bacteria gain resistance to chloramphenicol? | Bacteria anti-metabolite -> bacteria gain plasmid-encoded methyltransferase -> prevent chloramphenicol binding |
| How do bacteria gain resistance to macrolides? | Bacteria anti-metabolite -> methyltaion of 23S rRNA -> prevents macrolide binding |
| What is the MoDA of fusidic acid? | Bacteria anti-metabolite -> G +ve -> binds and inhibits elongation factor G -> block polypeptide translocation |
| What is the MoDA of syncercid? | Bacterial anti-metabolite -> G +ve -> quinuprist + dalfopristin -> binds to 23S rRNA 50S subunit of ribosome -> block polypeptide translocation |
| What is the MoDA of spectinomycin? | Bacterial anti-metabolite -> G +ve/-ve -> interferes w/ elongation factor G during translocation -> interrupt mRNA translation/protein synthesis |
| What is the MoDA of coumarins? | Bacterial anti-DNA -> inhibit ATPase domain of DNA Topo II gyrase -> prevent change of linking number in supercoiled DNA in replication/gene expression |
| What is the MoDA and clinical use of fluoroquinolones? | Bacterial/cancer anti-DNA -> G +ve/-ve -> ciprofloxacin/levofloxacin/gatifloxacin/etoposide -> inhibit type II topo -> treat UTI, gastroenteritis |
| What is the MoDA of rifampicin? | Bacterial anti-RNA -> G +ve/TB -> binds non-covalently to allosteric site on DdRP beta-subunit -> block elongating RNA chain -> inhibit RNA synthesis initiation |
| What is the MoDA of daunorubicin? | Cancer anti-DNA -> intercalates w/ DNA -> inhibits progression of Topo II |
| What is the MoDA of actinomycin D? | Bacterial/cancer anti-DNA -> intercalates w/ DNA -> inhibits progression of Topo II |
| What is the MoDA of bleomycins? | Bacterial anti-DNA -> G +ve -> metal-chelating glycopeptide -> interacts btwn O2/bound iron -> generates superoxide/OH radicals -> s/ds DNA breaks |
| What is the MoDA of mitomycin C? | Bacterial/cancer anti-DNA -> G +ve/-ve -> alkylates DNA G bases -> interstrand cross-linking -> prevent strand spearation during DNA replication/transcription -> cannot be accessed by machinery |
| What is the MoDA of melarsen oxide? | Protozoa anti-cellular integrity -> selective uptake for Trypanosomes -> arsenicals react readily w/ thiol groups in cofactors (lipoic acid)/enzymes (Pyr K -> ATP synthesis) |
| What is the MoDA of suramin? | Protozoa anti-cellular integrity -> inhibits G3P oxidase/NAD+ dependent G3P deHAse/NADH reoxidation -> inhibit ATP synthesis |
| What is the MoDA of chloroquine? | Plasmodium anti-cell membrane -> accumulate inside food vacuole -> block detoxification of haem into hemozoin -> haem accumulation is toxic to Plasmodia |
| What is the MoDA of artemisinin? | Plasmodium anti-cell membrane -> generates highly reactive organic ROS |
| What is the MoDA of amantadine/rimantadine? | Viral anti-influenza -> blocks M2 ion channel -> prevent acidification of nucleocapsid -> prevent genome uncoating |
| What is the MoDA of oseltamivir/zanmivir | Viral anti-influenza -> inhibit NA cleavage of sialic acid -> blocks release of virus from host cells |
| What is the MoDA of acyclovir? | Viral anti-herpes -> taken up by infected cells -> monophosphorylated by viral thymidine kinase -> competitively inhibits viral DNA Pol -> chain termination -> selective -> viral thymidine kinase/viral DNA Pol |
| What is the MoDA of ganciclovir/penciclovir? | Viral anti-herpes -> competitive inhibitor of DNA Pol -> monophosphorylated by CMV-encoded phosphotransferase -> effective against CMV-infected cells |
| What is the MoDA of cidofovir? | Viral anti-herpes -> pyrmidine (cytosine) analogue -> selectively inhibits CMV DNA Pol |
| What is the MoDA of trifluridine? | Viral anti-herpes -> cidofovir -> pyrimidine (cytosine) analogue -> doesn't need activation by viral thymidine kinase -> competitively inhibits DNA Pol |
| What is the MoDA of idoxuridine? | Viral anti-herpes -> cidofovir -> pyrimidine (cytosine) analogue -> requires activation by viral thymidine kinase -> competitively inhibits DNA Pol |
| What is the MoDA of foscarnet? | Viral anti-herpes -> organic pyrophosphate analogue -> selectively binds to CMV/HSV viral DNA Pol -> prevents chain elongation |
| What is the MoDA of nevirapine? | Viral anti-HIV -> non-nucleoside reverse transcriptase inhibitor -> binds to reverse transcriptase near catalytic site -> denature |
| What is the MoDA of azidothymidine/zidovudine? | Viral anti-HIV -> nucleoside reverse transcriptase inhibitor -> activation by host cell phosphorylation -> mimic naturally occuring nucleosides substrates -> incorporated into DNA -> terminate DNA synthesis -> reverse transcriptase only in early HIV |
| What is the MoDA of hydroxyurea? | Viral anti-HIV -> coadministered w/ AZT -> inhibit ribont reductase -> decrease intracellular pool of pyrimidine nucleotides -> slow down DNA synthesis |
| What is the MoDA of saquinivir/ritonavir? | Viral anti-HIV -> block aspartic proteases from cleaving Gag-Pol polyprotein -> prevent newly assembled virus from being infectious -> selective as host cells don't have aspartic proteases |
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vykleung
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