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WEEK 18:
Pharmacology of antibiotics:
| Question | Answer |
|---|---|
| gram positive | highly charged and has a cell wall but no outer membrane. Made of peptidoglycan and acid polymer |
| gram negative | complex lipopolysaccharide outer membrane (more resistant to antibiotics) and thinner cell wall |
| classes of bacteria (4) | gram positive, gram negative, aerobic, and anaerobic |
| B-lactam antibiotics (inhibit cell wall synthesis) examples (3) | penicillins, cephalosporins and glycopeptides |
| bacterial cell walls are made of | alternating amino sugar units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAMA) where NAMA has short peptide side chains that cross link to form polymeric lattice |
| suffix for penicillins | cillin |
| penicillin is a type of what | bactericidal B-lactam antibiotic |
| how does penicillin work | target bacterial cell wall synthesis by irreversibly binding to transpeptidase (transpeptidase cross links peptidoglycans in bacterial cell wall) |
| what is penicillin effective against | only dividing organisms |
| penicillin allergy | hypersensitivity reactions (skin rashes), anaphylactic shock (rare but fatal), and broad spectrum causes GI disturbances |
| describe penicillin resistance | resistant bacteria secrete B-lactamases which inactivate penicillin |
| how do you overcome penicillin resistance | inhibit B-lactamases by using clavulanic acid and amoxicillin (co-amoxiclav) |
| cephalosporins | B-lactam antibiotic with a similar mechanism to penicillin but around 10% of those who are allergic to penicillin will have reactions to this |
| glycopeptides | inhibits peptidoglycan biosynthesis by binding to D-Ala-D-Ala at terminal of growing peptide chain during cell wall synthesis so transpeptidase is inhibited and cell wall cannot be made |
| examples of glycopeptides | teicoplanin and vancomycin |
| vancomycin | bactericidal given IV for multiresistant staphylococcal infections (MRSA) and orally for pseudomembranous colitis |
| side effects of glycopeptides and gentamicin | ototoxicity and nephrotoxicity |
| fosfomycin | used in urinary tract infections caused by ESBL (which produce enterobacteriaceae) to inhibit cell wall synthesis |
| bacitracin (polyfax) | given topically to disrupt cell wall syntehsis |
| examples of drugs against mycobacteria (TB) | isoniazid and ethambutol |
| drugs which inhibit ribosome synthesis (3) | tetracyclines, macrolides, aminoglycosides |
| why are macrolides a good alternative for those allergic to penicillin | macrolides are bactericidal and have a similar antimicrobial spectrum to penicillins |
| macrolides | cytochrome P450 inhibitors with a range of drug interactions |
| macrolides suffix | mycin |
| aminoglycosides mechanism of action | binding to aminoacyl site of 16S ribosomal RNA within 30S ribosomal subunit leading to misreading of genetic code and inhibition of translocation |
| half life of gentamicin | 2-3 hours |
| interaction (synergy) of aminoglycosides and penicillins leads to | breakdown of cell wall which increases uptake of aminoglycosides |
| gentamicin | type of aminoglycoside widely used against gram negative bacteria alongside penicillins to treat sepsis, infective endocarditis and pseudonomas aeruginosa infections via injection |
| therapeutic range of gentamicin | narrow therapeutic range and drug monitoring needed |
| drugs acting on bacterial DNA (3) | quinolones, sulphonamides, and trimethoprim |
| quinolones mechanism of function | bactericidal inhibiting activity of type II topoisomerases, DNA gyrase and topoisomerase IV which are needed for modulation of chromosomal supercoiling for DNA synthesis |
| quinolones suffix | floxacin |
| fluroquinolone treatment | disabling, long lasting or potentially irreversible adverse reactions affecting musculoskeletal and nervous systems rarely so treatment discontinued at first signs of tendon pain/ inflammation |
| metronidazole | prodrug (inactive) needed to be activated to do antibacterial/ antiprotozoal function |
| mechanism of action of metronidazole | activated by anaerobic bacteria to cytotoxic products which damage helix structure of DNA |
| clinical use of metronidazole | used against anaerobic bacteria + protozoa, for surgical prophylaxis (high risk procedures), and alcohol interaction |
| sulfonamides | inhibit growth of bacteria by competitively inhibiting enzyme dihydropteroate synthetase which is needed in the synthesis of folate and PABA so DNA needed to grow is reduced but high degree of resistance |
| sulfonamides examples | sulfasalazine (sulfapyridine-aminosalicylate) which is widely used in IBD and rheumatoid arthiritis |
| side effects of sulfonamides (4) | skin rash, nausea, headache, and very rarely Stevens-Johnson syndrome |
| what type of sulfonamide is used to treat infected burns | silver sulfadiazine |
| trimethoprim | bacteriostatic and structurally related to folate used on its own to treat simple urinary tract infections eg cystitis |
| mechanism of action of trimethoprim | folate antagonist which inhibits bacterial dihydrofolate reductase (which converts folate to tetrahydrofolate) |
| clinical use of trimethoprim | treat simple UTIs eg cystitis |
| when should trimethoprim NOT be taken | first 3 months of pregnancy |
| co-trimoxazole is made of | trimethoprim + sulfamethoxazole |
| clinical use of co-trimoxazole | limited but used in treatment of pneumonia caused by yeast in immunocompromised patients |
| clinical uses of sulfonamides | IBD and rheumatoid arthiritis and sulfamethoxazole |
| resistance in sulfonamides | high degree of bacterial resistance so limited use |
| prefix for cephalosporins | ce |
| tetracyclines mechanism of action | bind reversibly to 30s ribosomal subunit to block binding of aminoacyl-tRNA to mRNA so protein synthesis is inhibited |
| macrolides mechanism of action | bind to 50s ribosomal subunit to block binding of aminoacyl-tRNA to mRNA so protein synthesis is inhibited |
| side effects of macrolides (2) | nausea (especially with erythromycin) and QT prolongation |
| suffix for aminoglycosides | cin |
| trimethoprim therapeutic range | narrow spectrum with high degree of resistance but limited side effects and should be avoided first 3 months of pregnancy |
| drugs that are bactericidal (4) | beta-lactam antibiotics, macrolides, quinolones, and aminoglycosides |
| drugs that are bacteriostatic (3) | macrolides, tetracyclines, and folate inhibitors |
Created by:
kablooey
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