Antimicrobials Flashcards
Amoxicillin
Beta lactam
Active against a wide range of gram positive, and a limited range of gram negative bacteria
Binds to penicillin binding protein 1A (PBP-1A) in bacterial cell wall. Inactivation of PBP-1A prevents cross- linking of 2 linear peptidoglycan strands, inhibiting bacterial cell wall synthesis. Cell lysis is mediated by bacterial cell wall autolytic enzymes such as autolysins
Can be combined with coagulants acid (beta lactamase inhibitor to overcome bacterial antibiotic resistance mediated through beta lactamase production
Methicillin
Transpeptidase inhibitor
Narrow spectrum beta-lactam antibiotic
Inhibits bacterial cell wall synthesis via inhibition of transpeptidase enzyme used by bacteria to cross-link the peptide (D-alanyl-alanine) used in peptidoglycan synthesis in the cell wall of gram positive bacteria
Largely replaced by flucloxacillin and dicloxacillin
Cefuroxime
Transpeptidase inhibitor
Similar to penicillin
Inhibits cell wall synthesis leading to bacterial lysis Can cross the blood brain barrier
Highly active against gram-negative cocci, gram negative bacilli, anaerobes than gram positive cocci
Benzylpenicillin
Transpeptidase inhibitor
Penicillin G. beta lactam.
Binds to penicillin binding proteins that cause inhibition of cell wall synthesis. May inhibit action of bacterial autolysin inhibitor. Stable against hydrolysis by a variety of beta-lactamases, including penicilinases and cephalosporinases and extended spectrum beta lactamases
Targets gram positive organism. (shown in vitro to
target gram negative aerobic and anaerobic bacteria)
Oxytetracycline
30s inhibitor
Inhibits bacterial cell growth by binding to 30S ribosomal subunit
This prevents the amino-acyl tRNA from binding to the A site of the ribosome causing inhibition of translation. It is lipophilic and therefore can pass through the cell membrane or passively diffuse through porin channels in the bacterial membrane
Broad spectrum antibiotic. Used for infections and acne
Erythromycin
50s inhibitor
Macrolide
Reversibly binds to 50S subunit of bacterial ribosomes, at the donor site. Binding blocks the translocation of peptides from the acceptor site to the donor site, inhibiting protein synthesis. After absorption it will diffuse readily into most body fluids and will pass into both breast milk and across the placental barrier
Treats multiple infections, including respiratory infections, syphilis, skin infections and chronic prostatitis. Effective against actively dividing organism
Erythromycin
50s inhibitor
Macrolide
Reversibly binds to 50S subunit of bacterial ribosomes, at the donor site. Binding blocks the translocation of peptides from the acceptor site to the donor site, inhibiting protein synthesis. After absorption it will diffuse readily into most body fluids and will pass into both breast milk and across the placental barrier
Treats multiple infections, including respiratory infections, syphilis, skin infections and chronic prostatitis. Effective against actively dividing organisms
Gentamicin
302/50s inhibitor
Aminoglycosides bind to bacterial 30s ribosomal subunit
to inhibit protein synthesis
Ear and kidney damage
Rifampicin
RNA/ DNA polymerase inhibitor
Easily absorbed and distributed round the body. Inhibits DNA-dependent RNA polymerase leading to suppression of RNA synthesis and cell death
Can target bacterial but not mammalian versions of the enzyme. Metabolised in liver and eliminated in bile and to a limited extent in the urine.
Broad spectrum antibiotic (targets gram positive and gram negative). Emergence of resistance so its use is restricted to mycobacterial infections
Trimethoprim
Folate antagonist
Binds to dihydrofolate reductase inhibiting reduction of dihydrofolic acid to tetrahydrofolic acid (THF). THF is an essential precursor in thymidine synthesis pathway and interference with this pathway inhibiting bacterial DNA synthesis.
Urinary tract infections, acute and chronic bronchitis
Sulfamehoxazole
Sulphonamide drug (PABA analogue)
Competes with para-aminobenzoic acid (PABA) in binding
to dihydrofolate synthesase,. It can therefore cause the inhibition of dihydrofolate synthetase, inhibiting the synthesis of tetrahydrofolic acid (THF syntheisis. THF is required for the synthesis of purines and dTMP and inhibition of its synthesis inhibits bacterial growth
Bronchitis, prostatitis and urinary tract infections.
Trimethoprim and sulfamethoxazole are commonly used in combination as they target the same pathway and reduces development of bacterial resistance
Vancomycin
Peptidoglycan inhibitor
Inhibition of incorporation of N-acetylmuramic acid (NAM) and N-acetlyglucosamine (NAG)-peptide subunits into the peptidoglycan matrix which forms the major component of gram positive cell walls
Alters bacterial cell membrane permeability and RNA synthesis (no cross resistance between vancomycin and other antibiotics)
drug of last resort’ only used after other antibiotics have failed. Active against listeria monocytogenes, Streptococcus pyogenes, Streptococcus pneumoniae (including penicillin-resistant strains), Streptococcus agalactiae, Actinomyces species, and Lactobacillus species. Vancomycin is not active in vitro against gram- negative bacilli, mycobacteria, or fungi.
Colistin
Polymyxin antibiotic agent
Disrupts bacterial cell membrane, changing its permeability Can enter the bacteria and precipitate cytoplasmic components mainly ribosomes.
Acute or chronic infections due to sensitive strains of certain gram negative bacilli, particularly pseudomonas aeruginosa. Use of polymyxins were superceded by extended spectrum penicilins and cephalosporins however resistance have led to revived use of polymyxins
Ciprofloxacin
Broad spectrum antibiotic (topoisomerase II inhibitor)
Quinolones have a different mechanism to other antimicrobials so ciprofloxacin can be used in cases of resistance to these
Inhibition of topoisomerase II (DNA gyrase) and topoisomerase IV which are required for bacterial DNA replication, transcription, repair, supercoiling repair and recombination
Broad spectrum antibiotic used against a wide range of gram negative and gram positive microorganisms Quinolones have a different mechanism to other antimicrobials so ciprofloxacin can be used in cases of resistance to these
Fusidic acid
Translocation inhibitor
Bacteriostatic antibiotic. Inhibition of trnslocation of the elongation factor G (EF-G) from the ribosome, leading to inhibition of protein synthesis
It can also inhibit chloramphenicol acetyltransferase enzymes
Creams and eyedrops
