---

ANTIVIRALS - COMPLETE MBBS LEARNING NOTE

From Absolute Beginner to Examination Mastery

---

SECTION 1: BIG PICTURE OVERVIEW

What problem does this drug class solve?

1. Block the virus from entering your cells
2. Block the virus from copying its genetic material
3. Block the virus from assembling new particles
4. Block the virus from leaving your cells and spreading

---

Why Do Viruses Cause Disease?

• Direct cell damage: The virus kills cells as it bursts out (cytopathic effect)
• Immune damage: Your immune system sends inflammation to fight the virus, but this collateral damage also injures your own tissues
• Immune evasion: Some viruses (like HIV) specifically destroy immune cells, leaving you vulnerable to all infections
• Persistence: Some viruses (like herpes viruses) hide inside cells in a dormant (sleeping) state for life, reactivating when you are stressed or immunosuppressed

---

SECTION 2: BUILD THE FOUNDATION

Part A: The Viral Life Cycle - Understanding the Target

STEP 1: ATTACHMENT (Adsorption)
Virus floats in blood/body fluids
↓
Virus finds a target cell with the right surface protein (receptor)
↓
Virus docks onto that receptor
Example: HIV docks onto CD4 protein on helper T-cells
Example: Influenza docks onto sialic acid on respiratory epithelium

STEP 2: PENETRATION (Entry/Fusion)
Virus merges with the cell membrane OR gets taken inside the cell
↓
The virus is now INSIDE your cell

STEP 3: UNCOATING
The virus sheds its outer coat (protein shell = capsid)
↓
Viral genetic material is now free inside the cell

STEP 4: REPLICATION
For DNA viruses: the virus uses the cell's nucleus and polymerases to copy its DNA
For RNA viruses: the virus brings its own RNA-dependent RNA polymerase to copy itself
SPECIAL CASE - Retroviruses (HIV):
   RNA virus → uses REVERSE TRANSCRIPTASE to convert RNA → DNA
   DNA then inserts into the HOST cell's genome (becomes a PROVIRUS)
   This is why HIV is almost impossible to eradicate

STEP 5: TRANSCRIPTION and TRANSLATION
Viral DNA → viral mRNA → viral proteins
These proteins become structural components and enzymes

STEP 6: ASSEMBLY
New viral particles are assembled inside the cell
Viral proteases cut large precursor proteins into active pieces

STEP 7: RELEASE (Budding/Lysis)
New virus particles bud out of the cell OR the cell explodes
Virus spreads to adjacent cells

Part B: Key Concepts You Must Understand

---

Part C: Classification of Viruses - Relevant to Drug Choice

---

SECTION 3: DRUG CLASS FRAMEWORK

OVERVIEW: Classification of Antiviral Drugs

ANTIVIRAL DRUGS
├── Anti-Herpes Drugs
│   ├── Acyclovir (prototype nucleoside analog)
│   ├── Valacyclovir (prodrug of acyclovir)
│   ├── Famciclovir (prodrug of penciclovir)
│   ├── Ganciclovir (for CMV)
│   ├── Valganciclovir (prodrug of ganciclovir)
│   ├── Cidofovir (nucleotide analog)
│   ├── Foscarnet (pyrophosphate analog - no viral kinase needed)
│   └── Trifluridine (topical - HSV keratitis)
│
├── Anti-Influenza Drugs
│   ├── Neuraminidase Inhibitors: Oseltamivir, Zanamivir, Peramivir
│   ├── Endonuclease Inhibitor: Baloxavir marboxil
│   └── M2 Ion Channel Blockers (Adamantanes): Amantadine, Rimantadine
│       (largely obsolete due to resistance)
│
├── Anti-HIV Drugs (Antiretrovirals - ARVs)
│   ├── NRTIs (Nucleoside Reverse Transcriptase Inhibitors)
│   ├── NtRTIs (Nucleotide RTIs)
│   ├── NNRTIs (Non-Nucleoside RTIs)
│   ├── PIs (Protease Inhibitors)
│   ├── INSTIs (Integrase Strand Transfer Inhibitors)
│   ├── Entry/Fusion Inhibitors
│   └── CCR5 Antagonists
│
├── Anti-Hepatitis Drugs
│   ├── Anti-HBV: Tenofovir, Entecavir, Lamivudine, Adefovir, Telbivudine
│   ├── Anti-HCV (DAAs): NS3/4A PIs, NS5B inhibitors, NS5A inhibitors
│   └── Immunomodulators: Interferon-alfa, Pegylated Interferon
│
├── Broad-Spectrum Antivirals
│   ├── Ribavirin (RSV, HCV, hemorrhagic fevers)
│   └── Interferons
│
└── Other/Special
    ├── Anti-COVID: Nirmatrelvir/ritonavir (Paxlovid), Remdesivir, Molnupiravir
    └── Anti-RSV: Palivizumab (monoclonal antibody)

---

CLASS 1: ANTI-HERPES DRUGS

Background: The Herpes Virus Family

---

DRUG 1: ACYCLOVIR (Prototype - Learn this first!)

STEP 1: (VIRAL ENZYME - HIGH SELECTIVITY)
Acyclovir (inactive)
↓ Herpes virus-specific thymidine kinase (TK)
Acyclovir monophosphate

STEP 2: (CELLULAR ENZYMES)
Acyclovir monophosphate
↓ Cellular kinases
Acyclovir diphosphate
↓ Cellular kinases
Acyclovir triphosphate (ACTIVE FORM)

STEP 3: (VIRAL DNA POLYMERASE INHIBITION)
Acyclovir triphosphate
↓ Competes with deoxyguanosine triphosphate (dGTP)
↓ Incorporated into viral DNA chain by viral DNA polymerase
↓ Chain termination (no 3'-OH available for next nucleotide)
↓ Also directly inhibits viral DNA polymerase
Viral DNA synthesis STOPS

• Oral bioavailability: Only 15-30% (poor). This is why valacyclovir was developed.
• Distribution: Good - crosses blood-brain barrier (important for encephalitis)
• Elimination: Kidney (dose reduction needed in renal impairment)

• Mutation or deletion of viral thymidine kinase gene → most common mechanism
• Mutation of viral DNA polymerase
• TK-deficient HSV strains are resistant to acyclovir, valacyclovir, AND famciclovir (all require TK for activation)
• Treatment of acyclovir-resistant herpes: Foscarnet (does not require TK activation)

---

DRUG 2: VALACYCLOVIR

• L-valyl ester prodrug of acyclovir
• Converted rapidly to acyclovir by intestinal/hepatic enzymes after absorption
• Oral bioavailability: ~55% (compared to 15-30% for acyclovir) - main advantage
• Same spectrum, mechanism, and toxicity as acyclovir
• Used for: genital herpes, cold sores, shingles
• Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) has been reported in severely immunocompromised patients receiving high doses

---

DRUG 3: FAMCICLOVIR

• Prodrug of penciclovir
• Similar mechanism to acyclovir (requires viral TK, then cellular kinases → penciclovir triphosphate → viral DNA polymerase inhibition)
• Key difference: penciclovir triphosphate has a much longer intracellular half-life than acyclovir triphosphate
• This means LESS frequent dosing
• Used for: genital herpes, shingles, cold sores

---

DRUG 4: GANCICLOVIR

• CMV retinitis in AIDS patients (most important use)
• CMV prophylaxis and treatment in transplant patients
• CMV pneumonitis, colitis, encephalitis in immunocompromised

---

DRUG 5: VALGANCICLOVIR

• Oral L-valyl ester prodrug of ganciclovir
• Converted to ganciclovir in intestine and liver
• Oral bioavailability ~60% (vs. <10% for oral ganciclovir)
• Same spectrum, uses, and toxicities as ganciclovir
• Preferred over oral ganciclovir for CMV prophylaxis in transplant patients

---

DRUG 6: CIDOFOVIR

• A nucleotide analog (not nucleoside - it already has a phosphate group attached)
• Key advantage: does NOT require viral kinase activation for initial phosphorylation
• Phosphorylation by cellular kinases only → cidofovir diphosphate → inhibits viral DNA polymerase
• Works against CMV including ganciclovir-resistant strains (since no UL97 kinase needed)
• Also active against HSV, VZV, HPV, adenoviruses

---

DRUG 7: FOSCARNET

• Pyrophosphate analog (STRUCTURALLY DIFFERENT from all nucleoside/nucleotide analogs)
• Does NOT require viral kinase activation
• Directly inhibits viral DNA polymerase AND RNA polymerase AND HIV reverse transcriptase by binding to the pyrophosphate binding site (instead of the nucleotide binding site)

FOSCARNET MECHANISM:
Normal DNA synthesis:
  Nucleotide triphosphate → DNA polymerase removes pyrophosphate → incorporates nucleotide
Foscarnet mimics pyrophosphate → blocks the pyrophosphate binding site of DNA polymerase
→ Viral DNA polymerase cannot function
→ Viral DNA synthesis halted

• Acyclovir-resistant HSV and VZV infections (most important indication)
• Ganciclovir-resistant CMV infections
• CMV retinitis when ganciclovir is contraindicated

---

CLASS 2: ANTI-INFLUENZA DRUGS

Background: Understanding Influenza

• Hemagglutinin (HA): Allows the virus to ATTACH to sialic acid residues on respiratory cells. Think of HA as the virus's "grappling hook."
• Neuraminidase (NA): An enzyme that cleaves sialic acid. It helps newly formed viruses ESCAPE from the infected cell and spread to new cells. Without NA activity, new viruses clump together on the dying cell's surface and cannot spread.

---

DRUG GROUP 1: NEURAMINIDASE INHIBITORS

Normal influenza life cycle - Release step:
  New virions bud out on cell surface
  → Neuraminidase cleaves sialic acid
  → Virions released and spread to new cells

With Neuraminidase Inhibitors:
  New virions bud out on cell surface
  → Neuraminidase BLOCKED by drug
  → Sialic acid NOT cleaved
  → New virions STUCK to cell surface
  → Cannot spread to new cells
  → Infection contained

• Treatment of influenza A and B (must start within 48 hours of symptom onset for significant benefit)
• Post-exposure prophylaxis of influenza

• Oseltamivir: Nausea, vomiting (take with food); rare: neuropsychiatric effects (especially in children)
• Zanamivir: Bronchospasm (contraindicated in reactive airway disease)
• Peramivir: Diarrhea

• Mutations in neuraminidase gene (e.g., H275Y mutation in H1N1)
• Seasonal influenza A(H1N1) became virtually 100% resistant to oseltamivir worldwide in 2007-2009 (before the pandemic strain replaced it)
• Resistant mutants are often less virulent than wild-type

---

DRUG GROUP 2: BALOXAVIR MARBOXIL (Novel mechanism)

• Active against Influenza A and B, including strains resistant to neuraminidase inhibitors
• Given as a single oral dose (half-life ~79 hours)
• Must be taken within 48 hours of symptom onset
• Drug interaction: Chelation with divalent cations (calcium, iron, magnesium) reduces absorption - avoid dairy, antacids, mineral supplements

---

DRUG GROUP 3: ADAMANTANES (Now Largely Obsolete)

• Active ONLY against Influenza A (Influenza B has no M2 protein)
• Currently NOT recommended due to widespread resistance (point mutation in M2 gene)
• Amantadine has additional use in Parkinson's disease (dopaminergic effect)
• Adverse effects: CNS (insomnia, dizziness, confusion - more with amantadine), anticholinergic effects

---

CLASS 3: ANTI-HIV DRUGS (ANTIRETROVIRALS)

Background: HIV Pathophysiology - You Must Understand This Deeply

HIV LIFE CYCLE AND DRUG TARGETS

1. CD4/CCR5 (or CXCR4) BINDING
   HIV gp120 binds to CD4 on helper T-cells
   Co-receptor binding (CCR5 or CXCR4)
   ← DRUG TARGET: CCR5 antagonists (Maraviroc)
   ← DRUG TARGET: Attachment inhibitors (Ibalizumab)

2. FUSION
   HIV gp41 mediates membrane fusion
   HIV enters the cell
   ← DRUG TARGET: Fusion inhibitors (Enfuvirtide)

3. UNCOATING
   Viral RNA is released into cell cytoplasm

4. REVERSE TRANSCRIPTION
   HIV RNA → DNA (via reverse transcriptase - unique to retroviruses!)
   ← DRUG TARGET: NRTIs, NtRTIs, NNRTIs

5. NUCLEAR IMPORT
   Viral DNA enters the nucleus

6. INTEGRATION
   Viral integrase inserts HIV DNA into host chromosome (PROVIRUS)
   ← DRUG TARGET: Integrase strand transfer inhibitors (INSTIs)

7. TRANSCRIPTION
   Host RNA polymerase reads proviral DNA
   HIV mRNA produced

8. TRANSLATION
   Long polyprotein chains produced

9. PROTEASE CLEAVAGE
   HIV protease cleaves polyproteins into active proteins
   ← DRUG TARGET: Protease inhibitors (PIs)

10. ASSEMBLY
    New viral particles form

11. BUDDING
    New virions bud off the cell
    (CCR5/CXCR4 now become gp120 targets again)

---

HIV DRUG CLASS 1: NUCLEOSIDE/NUCLEOTIDE REVERSE TRANSCRIPTASE INHIBITORS (NRTIs / NtRTIs)

• NRTIs: Zidovudine (ZDV/AZT), Lamivudine (3TC), Emtricitabine (FTC), Abacavir (ABC), Didanosine (ddI), Stavudine (d4T) - older
• NtRTIs: Tenofovir disoproxil fumarate (TDF), Tenofovir alafenamide (TAF)

NRTI Activation (same logic as acyclovir but no viral TK needed):
  NRTI prodrug
  ↓ Cellular kinases (3 phosphorylation steps)
  NRTI triphosphate (active form)
  ↓ Competes with natural dNTPs
  ↓ Incorporated into HIV DNA chain by reverse transcriptase
  ↓ Chain termination (NRTIs lack 3'-OH group)
  Reverse transcription STOPS

---

HIV DRUG CLASS 2: NON-NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS (NNRTIs)

NNRTIs - Non-competitive inhibition:
  NNRTI binds to allosteric site on HIV reverse transcriptase
  ↓ Enzyme shape changes (conformational change)
  ↓ Active site distorted
  ↓ Enzyme slows dramatically
  HIV RNA → DNA conversion impaired

• Active ONLY against HIV-1 (not HIV-2)
• A single point mutation in the reverse transcriptase gene can confer resistance to multiple NNRTIs at once (low genetic barrier to resistance)
• Cross-resistance is common among NNRTIs

• Efavirenz and nevirapine are CYP3A4 inducers (decrease levels of other drugs metabolized by CYP3A4)
• Rilpivirine and etravirine are CYP3A4 substrates
• This creates many clinically significant interactions (rifampicin reduces NNRTI levels; interaction with protease inhibitors)

---

HIV DRUG CLASS 3: PROTEASE INHIBITORS (PIs)

HIV replication - late stage:
  HIV polyprotein (Gag-Pol) produced as one long chain
  ↓ HIV PROTEASE cleaves polyprotein into:
    - Structural proteins (capsid, matrix)
    - Functional enzymes (protease, RT, integrase)
  ↓ Mature, infectious virions produced

With Protease Inhibitors:
  PI binds to active site of HIV protease
  ↓ Protease cannot cleave polyprotein
  ↓ Only IMMATURE, non-infectious viral particles produced
  (Virus buds out but is incapable of infecting new cells)

---

HIV DRUG CLASS 4: INTEGRASE STRAND TRANSFER INHIBITORS (INSTIs)

HIV DNA integration:
  HIV DNA enters nucleus
  ↓ HIV integrase performs 2 steps:
    a) 3'-processing: Cleaves 2 nucleotides from each end of HIV DNA
    b) Strand transfer: Inserts HIV DNA into host chromosome
  ↓ HIV DNA permanently integrated (PROVIRUS)

With INSTIs:
  Drug binds to integrase-DNA complex (chelates Mg2+ in active site)
  ↓ Strand transfer BLOCKED
  ↓ HIV DNA cannot integrate into host genome
  ↓ HIV DNA degraded
  ↓ No provirus formed

• High potency (rapid and deep viral suppression)
• High genetic barrier to resistance (especially dolutegravir and bictegravir)
• Excellent tolerability
• Minimal drug interactions (especially dolutegravir - not CYP3A4 substrate)

• Bictegravir/Tenofovir alafenamide/Emtricitabine (Biktarvy) - highly preferred in most patients
• Dolutegravir + Tenofovir/Emtricitabine
• Dolutegravir + Lamivudine (2-drug regimen for selected patients)

---

HIV DRUG CLASS 5: ENTRY AND FUSION INHIBITORS

• A 36-amino acid synthetic peptide
• Binds to HR1 region of HIV gp41 (a viral envelope protein)
• Prevents conformational change needed for membrane fusion → HIV cannot fuse with T-cell membrane → entry blocked
• Route: Subcutaneous injection only (cannot be taken orally - degraded in GI tract)
• Adverse effect: Injection site reactions (almost universal), hypersensitivity reactions
• Reserved for treatment-experienced patients with multidrug-resistant HIV

• Binds to the human CCR5 co-receptor (not the virus itself)
• HIV needs to bind BOTH CD4 AND a co-receptor (CCR5 or CXCR4) to enter the cell
• By blocking CCR5, maraviroc prevents the conformational change needed for fusion
• Tropism testing MANDATORY before use: Must confirm the patient's virus is "R5-tropic" (uses CCR5) not "X4-tropic" (uses CXCR4) - maraviroc does NOT work against X4-tropic HIV
• Adverse effects: Hepatotoxicity, cardiovascular events, cough; increased risk of infections (CCR5 is important in some immune responses)

• Monoclonal antibody against CD4 (the HIV receptor on T-cells)
• Blocks HIV from using CD4 for entry even after initial attachment
• Given IV every 2 weeks
• For treatment-experienced patients with multidrug-resistant HIV

---

CLASS 4: ANTI-HEPATITIS DRUGS

Anti-HBV (Hepatitis B) Drugs

• Suppress HBV DNA (reduce viral load)
• Achieve HBeAg seroconversion (loss of HBeAg, appearance of anti-HBe)
• Prevent cirrhosis and hepatocellular carcinoma
• Treatment is often long-term or lifelong

---

Anti-HCV (Hepatitis C) Drugs - Direct-Acting Antivirals (DAAs)

• NS3/NS4A serine protease: Cleaves the HCV polyprotein; essential for RNA replication
• NS5B RNA-dependent RNA polymerase: The sole RNA polymerase for HCV replication
• NS5A protein: A multifunctional protein essential for RNA replication and viral assembly

• NS3/4A protease inhibitors: end in "-previr" (grazoprevir, glecaprevir, voxilaprevir)
• NS5B polymerase inhibitors: end in "-buvir" (sofosbuvir)
• NS5A inhibitors: end in "-asvir" (ledipasvir, elbasvir, velpatasvir, pibrentasvir)

• Generally well tolerated
• NS3/4A protease inhibitors: Rash, pruritus, nausea, anemia; elevated ALT; contraindicated in decompensated cirrhosis (increased drug exposure → hepatic decompensation)
• Sofosbuvir + amiodarone: Severe symptomatic bradycardia (contraindication)
• NS5A inhibitors: Drug interactions via P-gp and CYP450 inhibition
• Ribavirin (when used): Hemolytic anemia (dose-limiting), teratogenicity (Category X)

---

CLASS 5: BROAD-SPECTRUM ANTIVIRALS

RIBAVIRIN

1. Inhibits inosine monophosphate dehydrogenase (IMPDH) → depletes guanosine triphosphate (GTP) pools → less raw material for viral RNA synthesis
2. Inhibits viral RNA-dependent RNA polymerase
3. Prevents capping of viral mRNA (mRNA cap is needed for translation)
4. Induces viral mutagenesis (error catastrophe) - incorporates into viral RNA and causes lethal mutation rate

• Severe RSV infection in infants/young children (inhaled aerosol via SPAG device)
• Chronic Hepatitis C (in combination with interferon or DAAs)
• Lassa fever and other viral hemorrhagic fevers
• Hantavirus infection

---

INTERFERONS

• Interferon alfa (IFN-α): Antiviral and antiproliferative
• Pegylated interferon alfa (Peg-IFN-α): IFN-α attached to polyethylene glycol (PEG) - longer half-life, once-weekly dosing

• Degrade viral RNA (RNase L activation)
• Block viral protein synthesis (PKR activation → phosphorylates eIF2α → translation halted)
• Induce immune responses (NK cells, cytotoxic T cells activated)

• Chronic Hepatitis B (Peg-IFN alfa-2a) - finite therapy, no long-term nucleoside analog
• Chronic Hepatitis C (largely replaced by DAAs, now rarely used)
• Some hematologic malignancies, multiple sclerosis (IFN-β)

• Decompensated liver disease (can worsen hepatic function)
• Severe psychiatric disorders
• Autoimmune hepatitis
• Pregnancy
• Uncontrolled thyroid disease
• Severe cytopenias

---

CLASS 6: ANTI-COVID-19 DRUGS

Nirmatrelvir/Ritonavir (Paxlovid)

• Nirmatrelvir: A protease inhibitor that blocks the SARS-CoV-2 main protease (Mpro/3CLpro), preventing cleavage of viral polyprotein
• Ritonavir: A pharmacokinetic booster (CYP3A4 inhibitor) co-administered to increase nirmatrelvir blood levels
• Given orally, within 5 days of symptom onset
• Reduces hospitalization risk in high-risk patients by ~90%
• Major concern: Extensive drug interactions due to ritonavir (CYP3A4 inhibition)

Remdesivir (Veklury)

• Adenosine nucleoside analog prodrug
• Activated intracellularly to triphosphate form
• Inhibits SARS-CoV-2 RNA-dependent RNA polymerase (RdRp), causing chain termination
• Given IV; used in hospitalized patients requiring supplemental oxygen
• Also active against Ebola, filoviruses, hepatitis C

Molnupiravir (Lagevrio)

• Prodrug of beta-D-N4-hydroxycytidine (NHC)
• Incorporates into viral RNA and causes RNA virus mutagenesis (error catastrophe)
• Oral; within 5 days of symptom onset
• Contraindicated in pregnancy (potential teratogenicity via mutagenic mechanism)
• Less effective than nirmatrelvir/ritonavir

---

SECTION 4: TEACH USING ANALOGIES

The Master Analogy Collection for Antivirals

---

SECTION 5: STEP-BY-STEP CLINICAL REASONING

Clinical Scenario 1: Patient with Herpes Simplex Encephalitis

• Renal function (nephrotoxicity - crystalluria)
• Adequate hydration (prevents crystal deposition in tubules)
• Infuse over at least 1 hour (slow infusion to reduce crystallization risk)

---

Clinical Scenario 2: HIV-Positive Patient Starting Treatment

---

Clinical Scenario 3: CMV Retinitis in an AIDS Patient

• Switch to Foscarnet (does not require UL97 kinase; different toxicity profile - nephrotoxicity, electrolyte disturbances)
• Or Cidofovir (also does not require viral kinase; nephrotoxic)

---

Clinical Scenario 4: Chronic Hepatitis C

• HCV genotype (some regimens are genotype-specific)
• Fibrosis/cirrhosis status (decompensated cirrhosis: NS3/4A protease inhibitors contraindicated)
• Drug interactions (especially NS5A inhibitors with P-gp substrates)

---

SECTION 6: MEMORY TOOLS

Mnemonic 1: Anti-Herpes Drugs - "ACE GAP FCT"

• Acyclovir
• Ganciclovir
• Valganciclovir
• Famciclovir/Foscarnet
• Cidofovir

Mnemonic 2: Acyclovir Activation - "3 V's"

Mnemonic 3: NRTIs Toxicities - "ZEST LAD"

• Zidovudine → Zap the marrow (anemia, neutropenia)
• Emtricitabine → Easy (well tolerated)
• Stavudine → Spinal/peripheral neuropathy + lipoatrophy
• Tenofovir → Tubular (kidney) toxicity
• Lamivudine → Low toxicity
• Abacavir → Allergy (hypersensitivity - check HLA-B*5701)
• Didanosine → Damage pancreas (pancreatitis)

Mnemonic 4: DAA Naming Endings

• -previr = NS3/4A Protease inhibitor (it "prevents" the protease from working)
• -buvir = NS5B (polymerase) inhibitor ("B" for B in NS5B)
• -asvir = NS5A inhibitor ("A" for A in NS5A)

Mnemonic 5: HIV Drug Classes - "NICE PIN"

• NRRTIs (Non-Nucleoside RTIs)
• Integrase inhibitors
• CCR5 antagonists
• Entry/fusion inhibitors
• Protease inhibitors
• INRTIs (Nucleoside RTIs)
• NtRTIs (Nucleotide RTIs)

Mnemonic 6: Foscarnet Toxicities - "SHARK HEN"

• Seizures
• Hypocalcemia
• Anemia
• Renal toxicity (nephrotoxicity)
• Kauses (causes) electrolyte disturbances
• Hypomagnesemia
• Electrolyte imbalance (general)
• Nausea

Memory Story: "The Virus Hotel"

• Block the doorman → Entry inhibitors
• Block the receptionist → CCR5 antagonists (Maraviroc)
• Jam the photocopier → NRTIs/NNRTIs
• Lock the filing clerk → INSTIs (integrase inhibitors)
• Blunt the kitchen knives → Protease inhibitors
• Seal the mail room → Neuraminidase inhibitors (oseltamivir)

Comparison Table: Acyclovir vs Ganciclovir vs Foscarnet vs Cidofovir

---

SECTION 7: EXAMINER'S CORNER

Most Tested Facts in Antivirals

1. Acyclovir mechanism - the three phosphorylation steps, viral thymidine kinase selectivity
2. Acyclovir resistance - TK mutation; treatment = foscarnet
3. Ganciclovir for CMV - why not acyclovir? (CMV lacks HSV TK; UL97 kinase instead)
4. Ganciclovir toxicity - myelosuppression (neutropenia), teratogenicity
5. Foscarnet - no kinase required; pyrophosphate analog; toxicities (nephrotoxicity, hypocalcemia, seizures)
6. Oseltamivir - neuraminidase inhibitor; for influenza A and B; must start within 48 hours
7. HIV drug classes - all five classes and their mechanisms
8. HAART principle - why combination therapy? (prevent resistance; target multiple steps)
9. Abacavir hypersensitivity - HLA-B*5701 testing mandatory
10. DAA naming conventions - -previr, -buvir, -asvir
11. Ribavirin - hemolytic anemia; teratogenicity (Category X for both sexes)
12. Interferon toxicities - flu-like syndrome, depression, thyroid disorders

---

Most Likely Essay Questions

1. "Discuss the mechanisms of action, clinical uses, and adverse effects of acyclovir. What is the basis for its selective toxicity?"
2. "Classify antiretroviral drugs. Describe the mechanism of action of each class. What is the rationale for combination antiretroviral therapy (HAART)?"
3. "Write short notes on: (a) Neuraminidase inhibitors (b) Direct-acting antivirals in Hepatitis C (c) Ganciclovir"
4. "Compare and contrast acyclovir and ganciclovir with respect to mechanism, spectrum, and toxicity."
5. "Discuss the pharmacotherapy of HIV infection."

---

Most Likely Short Note Topics

• Acyclovir
• Oseltamivir
• Zidovudine (AZT)
• Ganciclovir
• Foscarnet
• Ribavirin
• Interferon-alpha
• Direct-acting antivirals in Hepatitis C
• Integrase inhibitors
• Baloxavir marboxil

---

Most Likely Viva Questions

1. "What is the mechanism of selective toxicity of acyclovir?"
2. "A patient with acyclovir-resistant herpes - what drug would you use?" → Foscarnet
3. "Why is ganciclovir used for CMV and not acyclovir?" → CMV lacks HSV TK; requires UL97 kinase
4. "What is the most important toxicity of ganciclovir?" → Myelosuppression (neutropenia)
5. "Name two adverse effects of foscarnet that result from its chelation of divalent cations" → Hypocalcemia, hypomagnesemia
6. "Before prescribing abacavir, what test must you perform?" → HLA-B*5701 genotyping
7. "What does HAART stand for and why is it used?" → Highly Active Antiretroviral Therapy; combination to prevent resistance and achieve deeper viral suppression
8. "What is the mechanism of action of NNRTIs? How do they differ from NRTIs?" → NNRTIs: allosteric (non-competitive) inhibitors; no phosphorylation needed; bind hydrophobic pocket. NRTIs: competitive; need phosphorylation; cause chain termination
9. "Name a drug that does not need viral kinase activation but still inhibits viral DNA polymerase" → Foscarnet (and Cidofovir)
10. "What is the mechanism of ribavirin-induced hemolytic anemia?" → Ribavirin triphosphate accumulates in RBCs (cannot be exported); causes oxidative stress and hemolysis

---

Most Likely MCQs with Answers

---

---

---

---

---

---

---

---

---

---

Common Traps Students Fall Into

1. "Acyclovir works against CMV" - FALSE. Acyclovir has minimal activity against CMV. Ganciclovir is the CMV drug.
2. "Acyclovir resistance means use ganciclovir" - FALSE. TK-deficient HSV is also resistant to ganciclovir (ganciclovir also needs TK for initial phosphorylation). The answer is FOSCARNET.
3. "Neuraminidase inhibitors only work for influenza A" - FALSE. They work for BOTH influenza A and B. (Adamantanes only work for influenza A.)
4. "NNRTIs are activated like NRTIs (phosphorylation)" - FALSE. NNRTIs act directly (no phosphorylation needed). Only NRTIs require phosphorylation.
5. "Any antiretroviral can be used as monotherapy" - FALSE. Monotherapy rapidly selects resistant mutants. Always use combination therapy (≥3 drugs from ≥2 classes).
6. "Ribavirin alone treats hepatitis C" - FALSE. Ribavirin alone has minimal efficacy against HCV. It is always used in combination (with DAAs or interferon).
7. "Acyclovir is safe in pregnancy" - Generally considered safe, but this question in the context of "which antiviral is teratogenic" should prompt you to think ribavirin (Category X), ganciclovir (teratogenic), and efavirenz (neural tube defects in first trimester).
8. "Zanamivir can be used in asthma" - Caution/contraindication. Zanamivir is inhaled and can cause bronchospasm in asthmatics.

---

SECTION 9: HIGH-YIELD REVISION SHEET

╔══════════════════════════════════════════════════════════════════╗
║          ANTIVIRALS - ONE-PAGE HIGH-YIELD REVISION              ║
╠══════════════════════════════════════════════════════════════════╣
║ ANTI-HERPES                                                      ║
║ Acyclovir: Guanosine analog → requires HSV TK (Step 1)          ║
║   → cellular kinases → acyclovir-TP → viral DNA pol inhibition  ║
║   → chain termination                                           ║
║ Toxicity: Nephrotoxicity (crystalluria) - hydrate!              ║
║ Valacyclovir = prodrug of acyclovir (better bioavailability)    ║
║ Ganciclovir = CMV (requires CMV UL97 kinase)                    ║
║   Toxicity: MYELOSUPPRESSION (dose-limiting), teratogenic       ║
║ Foscarnet = pyrophosphate analog; NO kinase needed              ║
║   Use: acyclovir-resistant HSV; ganciclovir-resistant CMV       ║
║   Toxicity: Nephrotoxicity + Electrolyte disturbances           ║
║   (hypocalcemia, hypoMg, seizures, arrhythmias)                 ║
║ Cidofovir = nucleotide (no viral kinase) → severe nephrotoxicity║
║                                                                  ║
║ ANTI-INFLUENZA                                                   ║
║ Oseltamivir/Zanamivir/Peramivir: Neuraminidase inhibitors       ║
║   Active vs Influenza A + B; Start within 48 hrs                ║
║   Zanamivir: Bronchospasm (avoid in asthma)                     ║
║ Baloxavir: PA endonuclease inhibitor; single oral dose          ║
║ Adamantanes (amantadine): M2 channel blocker; Flu A ONLY        ║
║   Largely obsolete - widespread resistance                      ║
║                                                                  ║
║ ANTI-HIV (HAART = ≥3 drugs, ≥2 classes)                        ║
║ NRTIs: Chain terminators (need phosphorylation by cellular      ║
║   kinases); backbone of all regimens                            ║
║   AZT→anemia; d4T→neuropathy; ddI→pancreatitis                 ║
║   Abacavir→hypersensitivity (HLA-B*5701 test mandatory!)        ║
║   TDF→nephrotoxicity; TAF→safer than TDF                       ║
║ NNRTIs: Allosteric RT inhibition; no phosphorylation needed     ║
║   Active only vs HIV-1; low genetic barrier to resistance       ║
║   Efavirenz→CNS effects, teratogenic (1st trimester avoid)      ║
║   Nevirapine→rash (SJS), hepatotoxicity                        ║
║ PIs: Block viral protease; immature virions produced            ║
║   Ritonavir = CYP3A4 booster; used to boost other PIs          ║
║   Toxicity: Metabolic syndrome, lipodystrophy, GI effects       ║
║   Atazanavir: Nepholithiasis; Indirect hyperbilirubinemia       ║
║ INSTIs (Preferred first-line now):                              ║
║   Raltegravir, Dolutegravir, Bictegravir                        ║
║   Inhibit strand transfer step of integration                   ║
║   High genetic barrier (DTG, BIC); well tolerated               ║
║ Fusion inhibitors: Enfuvirtide (SC injection)                   ║
║ CCR5 antagonist: Maraviroc (tropism test needed!)               ║
║                                                                  ║
║ ANTI-HBV                                                        ║
║ Preferred: Tenofovir (TDF/TAF) or Entecavir                    ║
║ Lamivudine: High resistance rate (not preferred)                ║
║ Interferon: Finite therapy; many side effects                   ║
║                                                                  ║
║ ANTI-HCV (DAAs)                                                 ║
║ -previr = NS3/4A protease inhibitor                             ║
║ -buvir = NS5B polymerase inhibitor (sofosbuvir)                 ║
║ -asvir = NS5A inhibitor                                         ║
║ >95% cure with 8-12 weeks oral DAA therapy                      ║
║ NS3/4A PIs: Contraindicated in decompensated cirrhosis          ║
║ Sofosbuvir + amiodarone: Severe bradycardia (avoid)             ║
║                                                                  ║
║ RIBAVIRIN                                                        ║
║ Broad spectrum; mechanism: multiple (IMPDH inhibition, etc.)    ║
║ Toxicity: HEMOLYTIC ANEMIA; TERATOGENIC (Category X)            ║
║   Contraception needed for months after stopping                ║
║                                                                  ║
║ INTERFERONS                                                      ║
║ Mechanism: JAK-STAT signaling → antiviral state in cells        ║
║ Toxicity: Flu-like, depression/suicide, myelosuppression,       ║
║   thyroid dysfunction, autoimmune, retinopathy                  ║
║ Contraindicated: Decompensated liver disease, severe psych.     ║
╚══════════════════════════════════════════════════════════════════╝

---

SECTION 10: SELF-ASSESSMENT - 10 Short-Answer Questions

---

---

---

---

---

---

---

---

1. Flu-like syndrome (fever, myalgia, fatigue, headache): Interferons bind to cellular receptors and activate JAK-STAT signaling, inducing production of inflammatory cytokines (TNF, IL-1, IL-6) - the same mediators responsible for flu symptoms. This is virtually universal and is managed by taking interferon at bedtime and using paracetamol.
2. Depression and psychiatric effects (suicidal ideation): IFN activates the IDO enzyme (indoleamine 2,3-dioxygenase) which diverts tryptophan toward the kynurenine pathway away from serotonin synthesis. This leads to serotonin depletion in the brain, contributing to depression. Direct effects on cytokine-signaling in the brain also play a role.
3. Myelosuppression (neutropenia, thrombocytopenia): IFN suppresses myeloid progenitor cell proliferation in bone marrow.
4. Thyroid dysfunction (hypothyroidism or hyperthyroidism): IFN can trigger anti-thyroid autoantibodies (anti-TPO, anti-Tg) through immunomodulatory effects, leading to autoimmune thyroiditis (Hashimoto's or Graves' disease).

---

• -previr: NS3/NS4A serine protease inhibitors (e.g., grazoprevir, glecaprevir, voxilaprevir)
• -buvir: NS5B RNA-dependent RNA polymerase inhibitors (e.g., sofosbuvir)
• -asvir: NS5A replication complex inhibitors (e.g., ledipasvir, velpatasvir, pibrentasvir)

---

---

---