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Anti-microbial
| Term | Definition |
|---|---|
| Antimicrobial agents: | used for the treatment of infectious diseases caused by infective organisms |
| Antibiotics : | Are substances produced by MO or obtained from chemicals → which kill/destroy OR suppress the growth of other microorganisms |
| Minimum inhibitory concentration (MIC): | The lowest concentration of AMAs to inhibit/prevents the multiplication of MO -no visible growth of MO after 24-48 hrs of incubation |
| Concentration-dependent antibiotics : | thier optimum activity associated with peak concentrations → kill bacteria at a greater rate & to a greater extent with ↑ antibiotic concentrations |
| Time-dependent antibiotics: | with optimum activity associated with time of drug concentration above the MIC → kill bacteria at the same rate & to the same extent once an appropriate threshold concentration has been achieved |
| Post-antibiotic effect: | the period of time that bacterial growth remain inhibited after exposure to AB & removal of AB -even after their plasma concentration falls below MIC → Aminoglycosides & Quinolones |
| Selective toxicity | Deleterious actions possessed by a drug effects directed against the target pathogenic cells without comparable effects on the host healthy tissues → most antiviral & anti-neoplastic drug & anti-metabolite drugs |
| AMA inhibit protein synthesis by | - misreading of m-RNA code - insertion of incorrect amino-acid, - inhibit tRNA attachment to the ‘A’ site, - interferes with peptide-bond formation - inhibit translocation of the elongated peptide-chain from ‘A’ site to ‘P’ site |
| the range of their antimicrobial activity | Narrow-spectrum →as Penicillin G Extended-spectrum→as Ampicillin Broad-spectrum →Carbapenem |
| Superinfections: (secondary infection) | appearance of new infection during therapy of the primary infection |
| -Superinfection can be minimized by : | -Using specific/narrow-spectrum AMA -Avoiding unnecessary use of AMA -Oral supplement use of probiotics e.g Lactobacillus ---- to restore ecological order in the gut |
| Drug resistance: | -the unresponsiveness of MO to AMA -This resistance may be natural or acquired |
| Natural / intrinsic/inherent resistance: | --genetically the organisms have never responded to the antimicrobial therapy. -always been resistant due to- absence of the particular enzyme -absence of the target site affected by the drug |
| Acquired resistance: | -organisms that are initially sensitive or respond to AMA at the beginning later → become resistant -may be developed by mutation or gene transfer -is a major clinical problem |
| Mutation | -A random chromosomal genetic mutation that occurs spontaneously in a place that controls susceptibility to AMA - |
| Transfer | -Extra-chromosomal genetic material→ transfer of genetic material containing antibiotic-resistance→ by plasmid-mediated conjugation |
| -Plasmid | -piece of extra-chromosomal DNA that carry genes coding for resistance “R-factor” -plasmid-mediated resistance is the most important mechanism clinically as it can spreads / transferred easily among bacteria |
| Transfer takes place & occurs by :: | Transduction Conjugation Transformation |
| Transduction | -Is the transfer of plasmid DNA from one bacteria to another through bacteriophage “virus that infects bacteria” -e.g: transfer of drug-resistance among the strains of Staph. aureus |
| Conjugation: | -Is the direct cell-to-cell transfer of extrachromosomal genetic material (plasmids / R-factor) between bacteria during mating by direct contact bridge e.g: Enterococcal species |
| Transformation | Is the transfer of genetic material (R-factor) that released from resistant-bacteria into the medium through naked DNA which taken up by other sensitive bacteria e.g: Penicillin-resistance in pneumococci |
| Cross-resistance: | When MO develops resistance to one drug → it’s also show resistance to other drugs. -Share a MOA or a similar mode of binding site of action -Share the same group or family (closely-chemically related drugs) |
| To minimize the emergence of resistance | - Only use AB when they are clearly indicated - Use narrow-spectrum AB - Use effective dose & adequate duration of AB - Use older chemotherapeutic drugs whenever possible - Use Multiple-Drugs combination Therapy (MDT) |
Created by:
ahmad445
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