Treating Hepatitis And Parasitic Infections

Front 1

indication for hep B tx [3]

Back 1

Antiviral to clear virus/↓risk of chronic liver disease
1. serum HBV DNA level (>2000 IU/mL)
2. Serum ALT level (>ULN: upper limit normal)
3. severity of liver dx (assessed by bx)

Front 2

phase of chronic hep B infection [3]

Back 2

1. Immune tolerant
- HBeAg +ve, HBV DNA >200,000 IU/mL
- ALT normal
- normal/mild inflammation, scant fibrosis

2. Immune active [tx candidate]
- HBeAg +ve/-ve, HBV DNA usu >20, 000 IU/mL
- ALT elevated
- inflammation + fibrosis: degree varies

3. Inactive
- HBeAg negative, HBV DNA <2000 IU/mL
- ALT normal
- normal or mild inflammation

Front 3

approved drugs to treat chronic hep B
1. [2]
2. [5]

Back 3

1. Interferon (both antiviral + immunomodulatory)
*short-term, then follow-up [curative]
- conventional IFN-a
- Peg-IFN a-2a

2. Nucleoside/nucleotide analogue [antiviral]
*long-term suppressive
- lamivudine
- adefovir
- entecavir
- telbivudine
- tenofovir

Front 4

wrt life cycle of HBV,
how does IFN and NA work?

Back 4

IFN (interferon)
- activate intracellular enzymes: 2'5' oligoadenylate synthetase → degrade HBV mRNA
- ↑CMI to HBV: augment expression of HLA class 1 antigen presenting molecules

NA: (nucleoside/tide analogue)
- inhibit HBV DNA polymerase: interfere w. synthesis of HBV DNA strand

Front 5

action of IFN-a [4]

Back 5

1. Induce host resistance to viral infection
* inhibit viral penetration, translation, transcription, protein processing, maturation, release

2. ↑HLA class I display: facilitate immune recognition of infected cell

3. ↑NK cell activity

4. induce intracellular enzyme:
*2'5'-oligoadenylate synthetase (activate RNAse to cleave viral mRNA)
*induce protein kinase to inhibit 1st step of viral protein synthesis

Front 6

What is the IFN signaling pathway [4]

Back 6

1. IFN-a bind to & activate IFN-R1 & IFN-R2 receptors ax w. JAK & TYK2 enzymes

2. Activation → phosphorylation of latent cytoplasmic STAT family of proteins

3. STAT protein + IRF-9 → ISGF-3 complex.
*Translocates to nucleus,
*binds to ISRE (cis-acting DNA elements) in IFN-a inducible genes.
*Activates transcription of IFN-stimulated genes

4. Induces:
*2'5' oligo A synthase (w. ds RNA) → 2'5' oligo A
*induction of ribonuclease L (w. 2'5' oligo A) → mRNA degraded
*induction of protein kinase (w. ds RNA) → phosphorylated initiation factor (eIF-2) → inhibits protein synthesis

Front 7

IFN-a
- administration [3]
- effects [3]
- toxicity [3]

Back 7

Standard (IFN-a2b)
- IM or deep SC 3x/week for 3-6 months (ACUTE)
- pegylated formulation (pegIFN-alfa 2a)
- SC once weekly.

- Delays absorption, ↓clearance
- ↓subsequent liver disease, limits disease spread
- influenza-like symptoms: malaise, fever

Dose-limiting Toxicities:
- myelosuppression
- neurotoxicity: somnolence, behavioural disturbance
- severe fatigue, weight loss

Front 8

Chronic HBV infection?
- its effect on IFN-a tx [4]

Back 8

chronic HBV infection: lose HBV DNA, HBeAG, + develop anti-HBe antibody

- Predictors of response: low pre-therapy serum HBV DNA levels + high ALT levels

- serocoversion to anti-HBe usu ax with ↑ALT and hepatitis-like infection

- Remission: most px lose HBsAg, ↓risk of liver-related complications/mortality, histo improvement/stabilization

- HBV genotype A/B better response than C/D

Front 9

Agents to treat chronic Hep B
1.
2. (2 subtypes: give an example)

Back 9

1. IFN-a (standard, pegylated)

2. HBV polymerase inhibitors
a) L-Nucleosides
- lamivudine [L-nucleoside]
- telbivudine [L-nucleoside]

b) D-Cyclopentane [nucleoside]
- entecavir [D-cyclopentane]

c) Acyclic phosphonate [nucleotides]
- adevofir [acyclic phosphonate]
- tenofovir [acyclic phosphonate]

Front 10

Lamivudine (nucleoside analogue)
- mechanism [3]
- ADME [4]
- effects [3]

Back 10

- phosphorylated by host cellular enzymes to active triphosphate form:
- competitively inh. HBV DNA polymerase
- incorporated into viral DNA → proviral DNA chain termination

ADME:
- well absorbed orally, widely distributed
- mostly excreted urine (t1/2~9hr)
- dose reduction needed in renal insufficiency
- 2nd/3rd line due to resistance***

Effects:
- chronic tx: ↓HBV DNA levels, improved biochemical markers, ↓hepatic inflammation
- highest response in px with ↑serum ALT
- well tolerated, safe

Front 11

Primary antiviral drug resistance mutations
what is the mutation [2]

Back 11

Reverse transcriptase gene mutation: AA substitution

Lamivudine tx: mutation within
- tyrosine-methionine-aspartate-aspartate motif in C domain of reverse transcriptase region of HBV polymerase

- Primary mutation in motif
*replace methionine by valine or isoleucine at 204 codon, designated at rtM204V/I
*Ax compensatory mutations in B domain: restore higher replication capacity [rtV173L]

Front 12

MoA of adefovir (acyclic phosphate of HBV polymerase inhibitor) [3]

Back 12

- competitive inhibitor for HBV reverse transcriptase
- needs intracellular conversion to diphosphate form
- incorporated into DNA ~ acts as chain terminator, preventing DNA elongation

Front 13

Pharmacokinetics of adefovir dipivoxil (ADV)
- mechanism [2]
- ADME [5]

Back 13

Prodrug of acyclic phosphonate nucleotide analogue

- phosphorylated by cellular kinase to active metabolite adefovir diphosphate
- incorporated into viral DNA → terminate DNA synthesis and prevents viral replication

ADME:
- once a day, excreted in urine
- dose adjustment for renal dysfunction
- ↓viral load, improve liver function
- discontinuation → severe exacerbation of hepatitis
- resistance SLOWER than lamivudine***

Front 14

Telbivudine [nucleoside analogue]
- MoA [2]
- aDME [4]
- ADR [4]

Back 14

MoA:
- thymidine nucleoside analogue (L-form)
- intracellular → phosphorylated active form
- comp. inhibits HBV DNA polymerase → incorporation into viral DNA → chain termination

ADME
- more potent than lamivudine & adefovir
- highly effective against lamivudine-resistant HBV mutants
- taken orally once daily
- mainly eliminated by renal route

ADR
- lactic acidosis,
- severe hepatomegaly,
- steatosis,
- hep flare after discontinuation

Front 15

Entecavir [nucleoside analogue]
- MoA [3]
- ADME [4]
- ADR [3]

Back 15

- compete w. dGTP for HBV DNA polymerase
- intracellular phosphorylation → active triphosphate form
- inhibit base priming, reverse transcription of negative strand, synthesis of +ve strand of HBV DNA

ADME
- more potent than lamivudine & adefovir
- highly effective against lamivudine-resistant HBV mutants
- orally, once daily
- mainly eliminated by renal route

aDR
- severe acute exacerbation of hepatitis after discontinuation
- lactic acidosis
- hepatosteatosis

Front 16

Tenofovir (nucleoTide)
- ADME [4]

Back 16

- acyclic nucleotide analog of adenosine recently approved to treat chronic HBV

ADME:
- highly potent in antiretroviral action, less nephrotoxic
- taken orally once daily
- well tolerated
- less frequent resistance

Front 17

Timing/manifestations of antiviral resistance
- which hepatitis drug has most resistance ? (in order)

Back 17

Virologic breakthrough: Rise in HBV DNA level first sign of viral resistance
- precedes biochemical breakthrough/symptomatic flare

1. Lamivudine (1st gen): HIGH
2. Adefovir, telbivudine (2nd gen): MEDIUM
3. Entecavir, Tenofovir: Low (3rd gen) (LOW)

Front 18

Pros [3] and cons [4] of Pegylated-IFN

Back 18

Pros
- finite duration
- higher rate of anti-HBe & anti-HBs seroconversion w. 12 months of therapy
- absence of resistance

Cons
- moderate antiviral effect
- inferior tolerability
- risk of adverse events
- subcutaneous injections

Front 19

Pros [3] and cons [3] of NA

Back 19

Pros
- potent antiviral effect
- good tolerance
- oral admin

Cons
- indefinite duration
- RESISTANCE risk
- unknown long-term safety

Front 20

therapeutic goals of hep C treatment [5]

Back 20

- eradicate virus
- ↓HCV-associated morbidity/mortality
- normalize biochemical markers
- ↑clinical sx
- prevent spread of disease, progress to cirrhosis/HCC, end-stage liver

Front 21

How does HCV replicate? [6]

Back 21

1. HCV binds to receptor & enters hepatocyte

2. Uncoating & release of RNA

3. Internal ribosome entry site directs virus to host ER

4. Translation + processing of polyprotein precursors quire viral NS4/NS4a protease

5. Transcription + development of progeny virions in CAPSOMERE

6. Newly formed virus released from hepatocyte cell membrane

Front 22

Treatment for chronic HCV
[2]

Back 22

1. Dual therapy
- pegylated IFNa combined w. oral ribavirin
*for genotype II, III more responsive

2. Triple therapy
*for genotype I, as it's resistant to IFN therapy.
- peg-IFN, ribavirin + Telaprevir/boceprevir (HCV NS3/4A protease inhibitor)

Front 23

describe IFN-a

Back 23

1. IFN-a (non-specific antiviral environment in cell)
- induce IFN-stimulated genes
- immunomodulator against HCV
- Pegylated form: polyethylene glycol moiety covalently attached, conferring 10-fold longer serum half-life than parent drug

Front 24

MoA of ribavirin, (guanosine analogue) [6]

Back 24

effective against broad spectrum of RNA/DNA virus

1. phosphorylated intracellularly by host cell enzymes
2. Enhanced host T-cell immune clearance of HCV
3. Inhibit action of inosine 5'monophosphate dehydrogenase (IMPDH)
4. Deplete pools of GTP (needed for viral mrNA synthesis)
5. Directly inhibit viral RNA-dependent polymerase
6. RNA virus mutagenesis → reduced virion infectivity

Front 25

Direct acting antivirals?

Back 25

1. NS3/4A protease inhibitor
2. NS5B polymerase inhibitors

Front 26

NS3/4A protease inhibitor (direct acting antiviral)
- give examples
- MoA
- ADME
- ADR

Back 26

Example: boceprevir, telaprevir

MoA:
- inhibit NS3/4A serine protease (cleaves viral polyprotein after translation) in CYP450

ADME:
- Triple therapy: combined w. peginterferon & ribavirin for treatment-naive genotype 1 HCV patients
*higher sustained virologic response in tx-naive, relapsers and non-responders
- Resistance if either drug is monotherapy: must have triple therapy for full course

Front 27

Describe NS5B polymerase inhibitor
- example
- features

Back 27

- Sofosbuvir

- nucleotide analogue inhibitor of HCV polymerase (NS5B protein), an RNA-dependent RNA polymerase critical for viral cycle
- high genetic barrier to resistance development
- well tolerated

Front 28

Initial tx of chronic HCV

Back 28

1. Genotype I
- PegIFN + ribavirin + sofosbuvir
- PegIFN + ribavirin + simeprivir

2. Genotype I px who can't take IFN
- sofosbuvir + simeprevir ± ribavirin for 12 wks
- sofosbuvir + ribavirin for 24 wks

3. Genotype 2
- sofosbuvir + ribavirin for 12 wks
- simeprevir + pegIFN 12 wks, + ribavirin 24 wks

4. Genotype 3
- sofosbuvir + ribavirin 24 wks
- sofosbuvir + ribavirin + pegIFN 12 wks

Front 29

MoA of general antimalarial tx (Wrt to life cycle of plasmodium)
- 3 places (give one example)

Back 29

blood schizonticides kill asexual erythrocytic stage

1. Sporozoites injected into bloodstream
*DRUG AGAINST EXOERYTHROCYTIC FORM
- primaquine

2. Sporozoite → merozoite

3. Merozoite released → invade RBC
*DRUGS AGAINST ERYTHROCYTIC FORM
- artemisinin
- chloroquine
- quinine
- mefloquine
- pyrimethamine

4. in RBC, merozoite → trophozoite

5. Trophozoite multiple → new merozoite (RBC rupture)

6. Gametocytes
*DRUGS EFFECTIVE HERE:
- primaquine

Front 30

Blood schizonticides used [3]

Back 30

- chloroquine
- artemisinin
- sulphadoxine-pyrimethamine

Front 31

Chloroquine [3]
- ADR [4]

Back 31

- highly specific for ASEXUAL plasmodia: treat ERYTHROCYTIC P. falciparum malaria, except resistant strains
- treat extraintestinal amebiasis
- mefloquine & amodiaquine

ADR at high dose (toxicity)
- GI upset
- pruritus
- headaches
- blurred vision

Front 32

Artemisinin [3]

Back 32

- severe multidrug-resistant P. falciparum malaria
- antimalarial action → produce free radicals within plasmodium food vacuole
- short half-life precludes use in chemoprophylaxis

Front 33

Sulphadoxine-Pyrimethamine (fansidar) [2]

Back 33

- antifolate analogues selectively inhibit DHFR (plasmodial dihydrofolate reductase) at lower conc. than needed to inhibit mammalian enzyme
- problem of resistance

Front 34

What tissue schizonticide is used?
- features [3]
- adr [2]

Back 34

- lead to radical cures of P. vivax & P. ovale (remain in liver in exoerythrocytic form, after erythrocytic form of disease is eliminated)

- gametocytic forms destroyed in plasma/prevented from maturing later in the mosquito (interrupt transmission of disease)

- not effective against erythrocytic stage

ADR:
- drug-induced hemolytic anemia in G6PD deficiency
- contraindicated during pregnancy

Front 35

Sites of action of amoebicidal drugs in entamoeba histolytica [3]
- givean example

Back 35

1. Mixed amoebicides
- metronidazole, tinidazole
- Kill both luminal & systemic amoebae
- usually admin w. luminal amebicides (cure rate >90%)

2. Luminal amoebicides
- iodoquinol, diloxanide furoate, paramomycin
- Treat asymptomatic colonization state
- effective against amoebae in lumen of bowel
- Admin after tx invasive intestinal or extraintestinal amoebic disease is complete

3. Systemic amoebicides
- chloroquine, emetine
- effective vs amoebae in int. wall infection & liver abscess
- chloquine combined w. metronidazole and diloxanide furoate to tx/prevent amoebic liver abscess

Front 36

How to treat
- protozoal infection (amoebiasis, giardiasis)
- Nematode infection (hookworm, roundworm, pinworm, whipworm)
- trematode (schistosomiasis)
- cestode (tapeworm)

Back 36

- metronidazole

- mebendazole (interfere w. microtubules & glucose uptake)

- praziquantel (↑cell calcium permeability: contracture/paralysis of parasite)

- niclosamide (inhibit parasite's mitochondrial phosphorylation of ADP to generate ATP)