Antimicrobial Agents Flashcards by Darpan Rekhi

What are some of the ideal characteristics of an Antimicrobial Agent

Selective toxicity against microbial target
Minimal toxicity to host
Kills micro-organisms
Long plasma half-life
Good tissue distribution
Low binding to plasma proteins
Oral and parental preparations
No adverse interactions with other drugs

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Name some mechanisms that antibiotics use to kill microbes

Inhibition of cell wall synthesis
Inhibition of protein synthesis
Inhibition of nucleic acid synthesis
Inhibition of folate synthesis
Disruption of the cytoplasmic membrane

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What can microbes do to develop and show a resistance to antimicrobial agents

Production of enzymes
Alteration in the outer membrane permeability
Alteration of target sites
Efflux pumps
Alteration of metabolic pathways

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Name some types of enzymes that can be produced to show resistance to antimicrobial agents

Beta-lactamases
Aminoglycoside - modifying enzymes
Chloramphenicol acetyl transferase

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What problems arise from human use of antibacterials

Adverse side effects
Drug interactions
Rising rate of resistance
Few organisms have become virtually untreatable
Superinfection - candida albicans and C.Diff

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What are the main features of the chemical structure of the penicillin family of drugs

Acyl side chain
Beta lactam ring
Thiazolidine ring

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What are the 6 groups drugs in penicillin family

Benzylpenicillin
Orally absorbed penicillin
Anti-staphylococcal penicillin
Extended spectrum penicillin
Antipseudomonal penicillin
B-lactamase resistant penicillins

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Give an example of an orally absorbed penicillin

Penicillin V

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Give an example of an anti-staphylococcal penicillin

Flucloxacillin

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Give an example of an extended spectrum penicillin

Amoxicillin

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Give an example of an anti-pseudomonal penicillin

Ticracillin

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What is the mechanism of penicillins

Inhibiting cell wall synthesis by binding to penicillin binding proteins and inhibiting transpeptidation of peptidoglycan

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How do microbes show resistance to penicillins

Resistance by beta-lactamases, failure to penetrate the outer membrane of gram negative bacteria, efflux and low affinity binding of antibacterial to target PBP

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What are the potential side effects of drugs in the penicillin family

Allergic reaction like anaphylactic reaction or delayed hypersensitivity
GI problems like diarrhoea and enterocolitis
Renal - interstitial nephritis or haemorrhagic cystitis
CNS - encephalopathy or seizures - rare and occurs with renal failure or high prolonged doses

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Name a beta lactamase inhibitor that can be administered with penicillins

Clavulanic acid

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Describe the structure of cephalosporins

Beta lactam ring

Six membered Dihydrothiazine ring but modified at certain positions to produce different compounds

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When are cephalosporins used in place of penicillins

When the patient is allergic to penicillins there is a low chance that they are also allergic to cephalosporins

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Give examples of macrolides

Erythromycin, Clarithromycin and Azithromycin

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What does bacteriostatic mean

Prevents the growth of bacteria

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How do microbes show resistance to macrolides

They decrease their outer membrane permeability
efflux
alteration in rRNA
enzymatic inactivation by phosphotransferases

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Are macrolides bacteriocidal or bacteriostatic

Bacteriostatic

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What is the general mechanism of macrolides

They inhibit RNA dependent protein synthesis (50S ribosomes)

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What are the potential side effects of Macrolides

GIT symptoms
Skin rash
fever
eosinophilia
cholestatic jaundice
transient hearing loss
potential for increase effect of warfarin because it inhibits its metabolism and clearance

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What is the spectrum of activity for macrolides

Gram positive bacteria
Mycoplasma
Legionella
Chlamydia

AY BAWS CAN I HABE DE NOTE PLZ

Macrolides can be used as an alternative to penicillin in penicillin-allergic patients

Give an example of Lincosamide

Clindamycin

Describe the general mechanism of Lincosamides

Inhibits RNA-dependent protein synthesis (50S)

How do microbes show resistance to Lincosamides

- Decrease outer membrane permeability - Alteration in rRNA - Alteration in 50S ribosomal proteins of the receptor sites - Enzymatic inactivation by transferase

What is the spectrum of activity for Lincosamides

Gram positive and anaerobic bacteria

What are some side effects

- C. Diff colitis - Allergic reaction - Transient hepatitis - Neutopenia - Thrombocytopenia

Give some examples of Tetracyclines

- Tetracycline - Chlortetracycline - Oxytetracycline - Doxycycline - Tigecycline

What is the mode of action of Tetracyclines

- Inhibits bacterial protein synthesis (30S)

Are tetracyclines bacteriocidal or bacteriostatic

bacteriostatic

What is the spectrum of activity for tetracyclines

- Broad spectrum for gram positive - Gram negative - Intracellular organisms

How can microbes show resistance to tetracyclines

- Efflux - Ribosomal protection protein - Enzymatic inactivation

What are the potential side effects of Tetracyclines

- GIT symptoms - Photosensitivity - Pigmentation (skin, nail and sclera) - Deposition in growing bone and teeth - Hepatotoxicity - Exacerbate renal impairment - Superinfection - Allergy

What is the general mechanism of Nitroimidazoles (metronidazole)

DNA synthesis inhibitor that interacts with nucleic acids and proteins causing breakage, destabilisation and cell death

What is the spectrum of activity for nitroimidazoles (metronidazole)

- Anaerobic - Facultative anaerobic bacteria - Protozoa

What are the potential side effects of Nitroimidazoles (metronidazole)

- Metallic taste - GIT symptoms - Peripheral neuropathy - Disulfiram-like reaction with alcohol - Allergic reaction - Genitourinary - Increase effect of warfarin

What are the effects of a disulfiram like reaction

``` Nausea Vomiting Flushing Tachycardia Hypotension Confusion Psychosis Sudden death ```

What are polyenes

Antifungal ting

Name some examples of polyenes

Amphotericin (IV) | Nystatin (PO)

What do polyenes interact with and what effect does this have on fungal cells

- Interacts with ergosterol and forms a transmembrane ion channel - Increases membrane permeability, leakage of cell contents and cell death

How are polyenes able to show a selective action on the fungi

As the main sterol in the human cells is cholesterol and not ergosterol

How is Nystatin (polyene) administered and why

Only used topically on the skin and mucous membrane, does not get absorbed from the GI tract

What are some potential side effects of amphotericin

``` Anaphylaxis Nephrotoxicity GIT upset Muscle and joint pain Anaemia Cardiovascular toxicity ```

How can resistance be shown to polyenes

Intrinsic resistance like in dermatophytes, acquired resistance is rare

What are the 2 categories of Azole

Imidazoles | Tiazoles

What are some types of Imidazoles

- Ketoconazole - Miconazole* - Clotimazole

What are some types of tiazoles

- Itraconazole - Fluconazole - Voriconazole - Posaconazole - Ravuconazole

What is the general mechanism of azoles

They inhibit the synthesis of ergosterol

When should imidazoles not be used

In patients with hepatic impairment, pregnancy or breast feeding ketoconazole is associated with fatal hepatotoxicity

What side affects and adjustments need to be made when administering Fluconazole

- Fluconazole can cause abnormal Liver Function Test (LFT) | - Fluconazole dose needs to be reduced in renal impairment

What azole is candida krusei resistant to

Fluconazole

What targets in viruses are there for antiviral agents to attack

- Attachment - Viral entry - Viral uncoating - Nucleic acid synthesis - Assemble and release of viral particle (protease and neuraminidase inhibitors)

What viruses is Aciclovir effective against

- Herpes Simplex Virus (HSV) | - Vesicular Stomatitis Virus (VSV)

What are the side effects of Aciclovir

- Skin irritation when used topically - High dose IV can cause nephrotoxicity - GIT disturbance - Confusion and hallucinations

Describe the mechanism of Aciclovir

- Aciclovir = analogue of guanosine - Phosphorylated by the thymidine kinase enzyme of HSV and VZV - Becomes trapped in the infected cell - Two further phosphate groups are added so becomes triphosphate by cellular kinase - Triphosphate compound is a potent and selective inhibitor of HSV DNA polymerase - DNA chain termination