Module 11 - Antimicrobials Continued

Question 1

Antifungal Agents:

Answer 1

-few in number
-selective toxicity is difficult (fungi are eukaryotes, like human cells)
-have ergosterol - a lipid in fungal membranes (humans have cholesterol)
-some times no single antifungal is ideal (ringworm infection of the nails or recurrent vaginal candidiasis are frequently intractable)
-resistance occurs

Question 2

Azoles or Imidazoles:

Answer 2

-Inhibits cell membrane synthesis (ergosterol)
-Small molecule, easily absorbed
-Clotrimazole (Lotrimin) and miconazole (Monistat) are useful topical preparations
-Fluconazole used increasingly to treat Candida (avoid in 1st trimester especially)*
-Ketoconazole (Nizoral) is the agent of choice for serious infections*
-issues in pregnancy

Question 3

Ketoconazole:

Answer 3

-Effective orally but can be used topically
-3-20% report nausea when given orally
-Hepatic toxicity can be a problem
-Teratogenic
(can cause congenital defects)
-Syndactyly and polydactyly
-CONTRAINDICATED during pregnancy (unless no choice)
-At high doses may block steroid levels:
Oestrogen and progesterone: may affect contraceptive function
Testosterone: may lead to gynecomastia

Fluconazole- another family member also has evidence of teratogenicity at high dose (Category D at high doses)- low dose less evidence of an issue

Question 4

Polyenes:

Answer 4

-amphotericin B and nystatin (mycostatin)
-inhibit cell membrane function:
-bind to cell membrane and cause leakage of cell products and cell death (breaks ergosterol and not cholesterol)
-selective toxicity because humans do not have the binding site
-used to treat serious systemic fungal infections
-Amphotericin B given IV, orally, or topically
Used to treat serious infections
Side effects: fever, nausea, malaise, chills
*Safe during pregnancy (category B)
-Nystatin topical only (category A)
Used to treat Candida in mouth, mucous membranes (vaginal)
Athlete’s foot (cutaneous mycosis)
Minimal side effects

Question 5

Antivirals:

Answer 5

-During the last 20 years a range of new antivirals for HIV, Hepatitis B and C and influenza have been discovered
-All are virustatic not virucidal→ they suppress replication, not kill viruses
-Difficulty with antivirals is how to interfere with viral activity in the cell and not harm the host
-We know viruses depend on host’s protein synthesis machinery

Question 6

Antiviral Site of Action:

Answer 6

1. Absorption (T-20- binds HIV gp41 site to stop attachment)
2. Penetration and uncoating (amantadine)
3. Viral DNA/RNA synthesis (aciclovir,
   nevirapine)
4. Viral protein synthesis (interferons)
5. Assembly (protease inhibitors)
6. Release (no therapy available)

Question 7

Anti Herpesvirus Agents: Nucleoside Inhibitors:

Answer 7

-Aciclovir, ganciclovir, valaciclovir
-Inhibits DNA polymerase of one or more members of the herpesvirus family
Acyclovir is used in the treatment of HSV and VZV infections
Ganciclovir is used in CMV as well HSV/VZV
Valacyclovir (a derivative of acyclovir) is used for genital herpes
-Minimal toxic-side effects for it is active only in infected cells

Question 8

Antivirals for HSV and pregnancy:

Answer 8

-people with known recurrent genital HSV infection should be offered aciclovir or valaciclovir suppression at 36 weeks’ gestation to decrease the risk of clinical lesions and viral shedding at the time of delivery and therefore decrease the need for Caesarean section

Question 9

Nucleoside Inhibitors: Mechanism of Action
slide 12

Question 10

Antiretroviral Therapy:

Answer 10

-Aim is to keep plasma HIV-1 load low to maintain the CD4 count
-Many different types of agents used to achieve this including nucleoside and nucleotide reverse transcriptase inhibitors(RTI), non-nucleoside RTI, Protease/fusion/integrase inhibitors, Chemokine receptor antagonists
-Therapy with combinations of antiretroviral drugs is referred to as antiretroviral therapy (ART)

Question 11

Anti-influenza Agents:

Answer 11

-Can target Influenza A alone or both A and B viruses
-Amantadine (A only):
Inhibits an early step in viral replication, probably viral uncoating
For some strains, they also alter hemagglutinin processing
Can be given prophylactically during outbreaks
Can also use as treatment: if given within 48 hrs of symptoms it reduces disease severity
May cause minor neurological disturbances, insomnia

Zanamivir/Oseltamivir
-Neuraminidase Inhibitors
-Targets the surface glycoprotein neuraminidase
-Acts against strains A and B
-Same usage as amantadine

Question 12

slide 15

Question 13

Antihepatitis Agents:

Answer 13

-the aim of of treatment is to reduce risk of liver cirrhosis and carcinoma by keeping BHV/HCV levels low
-Hepatitis B-IFN or nucleoside and nucleotide analogues (lamivudine)
-hepatitis C
-Direct acting antivirals have recently become approved to treat chronic HCV – prevents virus replication and can “cure” in 90% of cases
*currently not approved in pregnancy, but may become of use in the future

Question 14

Resistance:

Answer 14

In comparison to antibiotics, resistance to antiviral agents is uncommon

Question 15

Vaccines: General Concepts:

Answer 15

-Vaccines provide active immunisation, because the adaptive immune system responds to antigens in the vaccine a produces memory B and T cells. These cells are then available to respond quickly (memory) if an infection with that pathogen occurs after immunisation.
Antibodies generated by vaccination (or repeated vaccination) are directly available to fight the pathogen when an infection occurs

-Passive immunisation is provided by antiserum or other immunoglobulin (what B cells would normally make) based treatments that provide antibodies to protect from (or treat) infection, but do not induce memory response, and provide only temporary immunity

Question 16

What is a Vaccine:

Answer 16

-a biological preparation that is designed to induce an adaptive immune response to a pathogen so that upon subsequent exposure to that pathogen the individual will be protected

Question 17

Edward Jenner

Answer 17

• 1796: cowpox to immunise against smallpox
• now there is a worldwide eradication of smallpox

Question 18

Aims of Vaccination:

Answer 18

For individuals:
Reduce or prevent symptoms of infectious disease

For society as a whole:
Prevent transmission of infectious disease (avoid epidemics or pandemics)
Eradicate disease from humans (long-term lofty goal)

Question 19

Basic Types of Approved Vaccines (6 total types- 8 with new COVID Vaccines):

Answer 19

1.Live attenuated
2.Inactivated (primarily good at inducing antibodies)
A) Whole
B) Fractional:
1. Subunit
2. Toxoid
3. Polysaccharide based- Whole/conjugate

3.mRNA *
4.Viral-vectored*
-* New classes that have been approved with COVID

Question 20

1. Live Attenuated Type Vaccines

Answer 20

-Attenuated virus still infects humans and replicates
-Usually it has reduced replication, assembly or release
-They generally stay within the local injection site
-This allows an immune response to occur to clear the virus without a large spread or load of infection

Question 21

How are attenuated viruses produced? Slide 31

Question 22

Live Attenuated Type Vaccines:

Answer 22

BENEFITS:
-Works well for viruses (harder for bacteria)
-Because it mimics infection, it develops a full immune response against the pathogen
-Both antibody mediated and cellular mediated
-Most potent vaccine type so it doesn’t usually require adjuvants

RISKS/NEGATIVES:
-Risk of reversion to wild type virulent strain
-Can’t be given to everyone- dangerous for immunocompromised and not recommended for pregnant women
-Needs to be kept cold to maintain activity

Question 23

SLIDE 33

Question 24

Live Attenuated Vaccine Use in Pregnancy:

Answer 24

-pregnancy is reduced cellular immunity
-Nearly all live attenuated vaccines pose risk to the foetus and sometimes the mother.
-Most are contraindicated.
MMR
Varicella
Smallpox
Typhoid
Yellow Fever
Nasal influenza (should not use)

Question 25

Live Attenuated Type Vaccine Examples:

Answer 25

1. Currently available and commonly used examples include vaccines against measles, rubella, varicella and zoster
2. Bacterial attenuated vaccine: bacille Calmette-Guerin (BCG) for tuberculosis- made from attenuated mycobacterium bovis
   -most are given intramuscular, sometimes subcutaneous, sometimes oral (less common), intranasal is a new concept

Question 26

2. Inactivated Whole Vaccine:

Answer 26

-Microorganism is killed or inactivated with heat or chemicals (formaldehyde, Β -propiolactone, phenol, acetone) which makes it unable to replicate
-The goal is anti-pathogen antibodies
-examples of whole vaccines:
1.Viral - polio, hepatitis A, rabies, Ex. Killed Polio Vaccine (Salk): - chemical “fixation” with formaldehyde
2.Bacterial: available for pertussis, typhoid, cholera and plague but not widely used
-all subcutaneous or intramuscular currently

Question 27

Inactivated- Fractional: Subunit Vaccine

Answer 27

-Vaccine contains specific protein antigens from the microorganism that can elicit an immune response
-These can be isolated from the microorganism or created by recombinant DNA technology
-The goal is anti-pathogen antibodies
Examples of subunit vaccines:
1.Influenza Vaccines: isolated surface hemagglutinin and neuraminidase proteins
2.HPV Vaccine-Gardasil 4 or 9: recombinant capsid proteins from several strains of HPV with adjuvant (3X)
-all subcutaneous or intramuscular

Question 28

Ask for slides on toxoid, polysaccharide,

Question 29

Recombinant Protein Vaccines Against Human Papilloma Virus (HPV):

Answer 29

-Gardasil: recombinant capsid proteins, from several strains of HPV in aggregated particulate form, with adjuvant
-Given i.m. with adjuvant, repeated 3x for maximum effect
-IgG antibody to protect reproductive tract, female and male
-Side effects: mild and typical for i.m. injected killed/protein vaccines with adjuvants
-Considered safe in pregnancy – a clinical trial showed no higher frequency of foetal abnormalities BUT currently not recommended due to limited data(Public Health Agency of Canada)

Question 30

Fractional: Polysaccharide Based Vaccine:

Answer 30

Examples of Polysaccharide based vaccines:
Pure polysaccharide vaccines to pneumococcal disease, meningococcal disease and Salmonella typhi
Conjugate polysaccharide vaccines-
Hib Vaccine-
Hemophilus influenza - Tetanus or Diphtheria toxoids linked to polysaccharide coat of Haemophilus influenzae
Pneumococcal
Meningococcal
-currently all intramuscular

Question 31

Inactivated Vaccines:

Answer 31

-benefits:
Stable- No risk of mutation
Possible for bacteria or virus (not toxoid/polysaccharide for virus)
Very little chance of adverse reactions (specific reactions except whole inactivated option)
-negatives:
Does not replicate so usually only antibody mediated responses are induced- usually weaker than from live attenuated (but this may be all you need!)
Require repeated doses (boosters)
Need adjuvant or to conjugate (polysaccharide)
Identification of best antigens for subunit vaccines may be difficult or impossible

Question 32

slide 44

Question 33

Adjuvants for i.m. Vaccines- Inactivated- whole/subunit vaccines:

Answer 33

-adjuvant means ‘to help’
-immunologic adjuvant = any substance that acts to accelerate, prolong, or enhance antigen-specific immune responses when used in combination with specific vaccine antigens
-For humans, nearly all injectable, intramuscular (i.m.) vaccines contain aluminium salts as adjuvant
-Aluminium salts cause local inflammation in injection site
-Enhances acquired immunity to vaccine protein or carbohydrate antigen components
-Typically provided increased IgG antibody response
-Small risk for side effects: fever, pain at injection site, headache
-Some natural oils, TLR ligands and recombinant “virosomes” in current trials as new adjuvants
-Adjuvants work by stimulating local tissue inflammation, and activating dendritic cells that then migrate to lymph nodes and present antigen to CD4 T cells

Question 34

slide 47

Question 35

Virus: SARS(severe acute respiratory syndrome-CoV(coronavirus)-2 Disease: COVID-19:

Answer 35

-Enveloped positive-sense RNA virus
-SARS-CoV-2 binds to ACE2 (angiotensin converting enzyme) on alveolar epithelial cells using the receptor binding domain (RBD) of its’ Spike protein
-Common symptoms: cough, fever/chills, difficulty breathing/shortness of breath, loss of sense of taste/smell, feeling very unwell, headache, GI symptoms, fatigue/muscle aches/weakness
-40-75% of infections may be asymptomatic (pre-symptomatic and asymptomatic can spread virus)

Question 36

3. mRNA Vaccines:

Answer 36

-mRNA encapsulated in a lipid nanoparticle to protect it from degradation
-Take up by APC, mRNA enters cytoplasm and makes spike protein
-Immune response to spike develops
-mRNA broken down after used
-Not approved for use prior to COVID
-RARE SIDE EFFECTS Pfizer/Moderna COVID Vaccine: myocarditis, Bell’s palsy

Question 37

4. Recombinant Viral Vector Vaccine:

Answer 37

-Replication deficient or attenuated replication competent viral backbone
-Engineered to express antigens from the pathogen
-Common viral backbones:
-Ad5 (human adenovirus type 5)
-ChAd (chimpanzee adenovirus)
-RARE SIDE EFFECTS Astrazeneca/Johnson Johnson COVID vaccine: Vaccine induced thrombocythemia (blood clots), Guillain Barre Syndrome

Question 38

RSV:

Answer 38

-Enveloped single-stranded RNA virus
-Causes respiratory tract disease- most common cause of bronchiolitis and pneumonia among infants
-Droplet and indirect transmission on surfaces

Question 39

Toxicity or Pathology from Vaccines:

Answer 39

Known pathology from vaccination:
1.Infection due to contaminated live virus or reversion of attenuated virus. Immunocompromised patients at risk
2. Chemicals that contaminate vaccine preparation may cause toxic effects
3. Co-isolated compounds that are allergens and can cause anaphylaxis.
(eg. egg albumin in some influenza vaccines)

Question 40

Pathologic Complications of Vaccine:

Answer 40

-egg sensitivity = live measle, mumps, killed measles, RSV
-convulsions, encephalitis = pertussis, measles
-meningitis = mumps
-arthritis = rubella

Question 41

Things we don’t have vaccines for yet:
chart