Pharmacology Quiz: Herpesvirus Antivirals
20 questions · exam conditions
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Herpesvirus AntiviralsQuestion 1 of 20

A 72-year-old patient with a creatinine clearance of 25 mL/min is being treated for herpes zoster. Which of the following antiviral regimens requires the most careful dose adjustment and carries the highest risk of adverse central nervous system effects, such as confusion and hallucinations?

Topical penciclovir cream.
Oral famciclovir.
Oral valacyclovir.
Topical docosanol cream.
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Pharmacology Quiz

Pharmacology Quiz: Herpesvirus Antivirals

Practice Herpesvirus Antivirals in Pharmacology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Herpesvirus Antivirals, giving you a quick way to practice the rules, question types, and explanations that matter most for Pharmacology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A 72-year-old patient with a creatinine clearance of 25 mL/min is being treated for herpes zoster. Which of the following antiviral regimens requires the most careful dose adjustment and carries the highest risk of adverse central nervous system effects, such as confusion and hallucinations?

  1. Topical penciclovir cream.
  2. Oral famciclovir.
  3. Oral valacyclovir. (correct answer)
  4. Topical docosanol cream.
Explanation: Both famciclovir and valacyclovir are systemic agents whose active metabolites (penciclovir and acyclovir, respectively) are eliminated by the kidneys, requiring dose adjustment in renal impairment. However, acyclovir (from valacyclovir) is more strongly associated with neurotoxicity, particularly in the elderly and those with poor renal function, due to accumulation of the parent drug and its metabolites. Topical agents have minimal systemic absorption and do not pose a significant risk of systemic toxicity.

Question 2

A liver transplant recipient on immunosuppressive therapy develops CMV viremia. The patient is started on intravenous ganciclovir. Monitoring for which of the following dose-limiting adverse effects is most critical during the initial phase of treatment?

  1. Acute crystalline nephropathy.
  2. Severe neutropenia. (correct answer)
  3. Drug-induced pancreatitis.
  4. Peripheral neuropathy.
Explanation: The most significant and common dose-limiting toxicity of ganciclovir and its prodrug valganciclovir is myelosuppression, manifesting as neutropenia, thrombocytopenia, or anemia. This requires frequent monitoring of complete blood counts, especially when initiating therapy. Crystalline nephropathy is a classic toxicity of high-dose intravenous acyclovir, not ganciclovir. Pancreatitis and neuropathy are less common.

Question 3

A patient is receiving valacyclovir 1000 mg orally once daily for suppression of genital herpes. The plasma half-life of the active drug, acyclovir, is approximately 3 hours. Despite this short plasma half-life, once-daily dosing provides effective suppression primarily because...

  1. the intracellular concentration of the active acyclovir triphosphate is maintained for many hours. (correct answer)
  2. valacyclovir is a slow-release formulation that provides sustained acyclovir levels over 24 hours.
  3. acyclovir causes irreversible covalent inhibition of the viral DNA polymerase.
  4. the parent drug is highly protein-bound, creating a long-lasting reservoir in the plasma.
Explanation: When you encounter questions about drug dosing that seems to contradict pharmacokinetic principles, focus on the difference between plasma drug levels and the actual site of drug action. Valacyclovir is a prodrug that's rapidly converted to acyclovir in the body. Once acyclovir enters virus-infected cells, it undergoes sequential phosphorylation by viral and cellular kinases to form acyclovir triphosphate - the true active antiviral compound. This triphosphate has a much longer intracellular half-life (up to 20-24 hours) than acyclovir's plasma half-life of 3 hours. The triphosphate accumulates in infected cells and provides sustained viral DNA polymerase inhibition throughout the dosing interval, making answer A correct. Answer B is wrong because valacyclovir is an immediate-release formulation, not sustained-release. The once-daily efficacy isn't due to prolonged drug release. Answer C mischaracterizes the mechanism - acyclovir triphosphate competitively inhibits viral DNA polymerase and causes chain termination, but this isn't irreversible covalent inhibition. The enzyme can be regenerated. Answer D is incorrect because acyclovir actually has low protein binding (15-30%), so plasma protein binding doesn't explain the prolonged effect. Remember this key principle: the pharmacokinetics of the active metabolite at its site of action can differ dramatically from the parent drug's plasma pharmacokinetics. Always consider where and how the drug actually works, not just its behavior in plasma.

Question 4

A 60-year-old male with a history of recurrent herpes zoster is managed with suppressive oral valacyclovir. He is now diagnosed with end-stage renal disease (ESRD) and begins hemodialysis three times a week. Which adjustment is necessary for his valacyclovir therapy?

  1. The dose should be increased to compensate for anticipated drug removal during dialysis sessions.
  2. The drug should be switched to topical penciclovir as systemic therapy is now contraindicated.
  3. The drug should be switched to famciclovir, which is primarily metabolized by the liver and not cleared by the kidneys.
  4. The dosing frequency should be reduced, and a supplemental dose should be administered after each dialysis session. (correct answer)
Explanation: When you encounter questions about antiviral dosing in renal disease, focus on how kidney function affects drug clearance and the impact of dialysis on medication removal. Valacyclovir is a prodrug that converts to acyclovir, which is primarily eliminated by the kidneys. In end-stage renal disease, acyclovir accumulation can occur, leading to potential neurotoxicity. Additionally, acyclovir is efficiently removed during hemodialysis due to its low protein binding and small molecular size. This creates a two-part dosing challenge: you need to reduce the baseline dose due to impaired clearance, but then replace what's lost during dialysis. Answer D correctly addresses both issues. Reducing dosing frequency prevents accumulation between dialysis sessions, while supplemental post-dialysis doses maintain therapeutic levels after drug removal during treatment. Answer A is dangerous because increasing the dose would worsen drug accumulation and increase toxicity risk in a patient with no renal clearance. Answer B incorrectly suggests systemic antivirals are contraindicated in ESRD - they're not, they just require adjustment. Topical penciclovir also wouldn't provide the systemic suppression needed for recurrent zoster. Answer C contains a critical error: famciclovir is also converted to penciclovir, which is renally eliminated just like acyclovir, so it faces the same dosing challenges. Remember: most antivirals (acyclovir, valacyclovir, famciclovir) are renally cleared and dialyzable. In ESRD patients on hemodialysis, always consider both dose reduction for impaired clearance and post-dialysis supplementation for drug replacement.

Question 5

A 68-year-old male with chronic kidney disease is receiving intravenous acyclovir for HSV encephalitis. Co-administration of which of the following drugs would most significantly increase the risk of acyclovir-induced nephrotoxicity?

  1. Probenecid. (correct answer)
  2. Allopurinol.
  3. Rifampin.
  4. Atorvastatin.
Explanation: Acyclovir is primarily eliminated from the body by glomerular filtration and active tubular secretion in the kidneys. Probenecid is a known inhibitor of the organic anion transporters (OATs) in the renal tubules, which are responsible for the active secretion of many drugs, including acyclovir. By blocking its secretion, probenecid can significantly increase the plasma concentration and half-life of acyclovir, thereby increasing the risk of concentration-dependent toxicities like nephrotoxicity and neurotoxicity.

Question 6

Acyclovir demonstrates potent activity against Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV), but has minimal activity against Cytomegalovirus (CMV). This difference in susceptibility is best explained by...

  1. CMV's ability to rapidly clear acyclovir from infected cells via P-glycoprotein efflux pumps.
  2. the absence of a suitable DNA polymerase target in CMV for acyclovir triphosphate.
  3. inefficient initial phosphorylation of acyclovir by the CMV-encoded protein kinase UL97. (correct answer)
  4. the inability of host cell kinases to convert acyclovir monophosphate to triphosphate in CMV-infected cells.
Explanation: The primary reason for acyclovir's poor activity against CMV is the inefficient initial phosphorylation step. HSV and VZV encode a thymidine kinase that efficiently phosphorylates acyclovir. CMV does not encode a thymidine kinase; instead, it encodes a different protein kinase (UL97 phosphotransferase) which is a very poor substrate for acyclovir. This lack of efficient activation prevents the formation of the active triphosphate metabolite, rendering the drug ineffective.

Question 7

Acyclovir, ganciclovir, and penciclovir all function as nucleoside analogues that must be phosphorylated by viral and/or host kinases to become active inhibitors of viral DNA synthesis. This mechanism of activation fundamentally distinguishes them from which of the following anti-herpesvirus agents?

  1. Idoxuridine.
  2. Trifluridine.
  3. Vidarabine.
  4. Foscarnet. (correct answer)
Explanation: Foscarnet is a pyrophosphate analogue, not a nucleoside analogue. It directly inhibits viral DNA polymerase by binding to the pyrophosphate-binding site, preventing the cleavage of pyrophosphate from the incoming deoxynucleotide triphosphate. This mechanism does not require any prior phosphorylation or activation. In contrast, idoxuridine, trifluridine, and vidarabine are all older nucleoside analogues that, like the acyclovir class, must be phosphorylated to their triphosphate forms to be active.

Question 8

A patient with AIDS and a CD4 count of 40 cells/μL has been treated for CMV retinitis with valganciclovir for 6 months. They now present with progressive vision loss. Viral genotype analysis reveals a mutation in the UL54 gene, but no mutation in the UL97 gene. This finding suggests resistance has developed due to an alteration in the...

  1. viral phosphotransferase responsible for initial drug activation.
  2. drug's oral bioavailability due to gastrointestinal pathology.
  3. viral DNA polymerase, the ultimate target of the active drug. (correct answer)
  4. host cell guanylate kinase responsible for diphosphorylation.
Explanation: Resistance to ganciclovir (the active form of valganciclovir) occurs via two primary mechanisms: mutations in the viral phosphotransferase gene (UL97) or mutations in the viral DNA polymerase gene (UL54). Since the UL97 gene is normal, resistance is not due to impaired drug activation. The presence of a mutation in UL54 indicates an alteration in the viral DNA polymerase, which is the direct target of ganciclovir triphosphate. This alteration reduces the drug's ability to inhibit viral DNA synthesis.

Question 9

An immunocompromised patient with recurrent orolabial herpes shows a poor clinical response to high-dose oral valacyclovir. A viral isolate is obtained. The most common molecular basis for this clinical resistance would be a mutation in the gene encoding...

  1. viral DNA polymerase.
  2. a host cell nucleoside kinase.
  3. viral thymidine kinase. (correct answer)
  4. the host L-valyl esterase responsible for prodrug conversion.
Explanation: The most common mechanism of resistance to acyclovir and its prodrugs is an alteration in the viral thymidine kinase (TK) gene, leading to deficient or absent enzyme activity. Since TK is required for the initial, rate-limiting phosphorylation of acyclovir, its absence or alteration prevents the drug's activation. Mutations in the viral DNA polymerase can also confer resistance but are less common. Host enzymes are not the site of viral resistance mutations.

Question 10

A physician is choosing between famciclovir and valacyclovir for a patient with herpes zoster. Which statement represents a correct pharmacological distinction between the ultimate active forms of these two prodrugs?

  1. Acyclovir achieves significantly higher intracellular triphosphate concentrations than penciclovir. (correct answer)
  2. Acyclovir (from valacyclovir) is a more potent competitive inhibitor of VZV DNA polymerase than penciclovir (from famciclovir).
  3. Penciclovir is a strict chain terminator, whereas acyclovir allows for limited DNA strand elongation.
  4. Acyclovir undergoes significant hepatic metabolism via CYP enzymes, while penciclovir is cleared unchanged by the kidneys.
Explanation: When comparing antiviral prodrugs, you need to understand both their bioavailability advantages and how their active metabolites differ at the cellular level. Both famciclovir and valacyclovir are prodrugs that improve oral absorption compared to their active forms, but their ultimate mechanisms show important distinctions. The key difference lies in intracellular accumulation. Acyclovir (from valacyclovir) achieves significantly higher intracellular triphosphate concentrations than penciclovir (from famciclovir). This occurs because acyclovir triphosphate has a longer intracellular half-life, allowing it to accumulate to higher steady-state concentrations within infected cells. This enhanced accumulation translates to more sustained antiviral activity. Looking at the incorrect options: Option B is wrong because both drugs have similar potency as competitive inhibitors of viral DNA polymerase once converted to their triphosphate forms. Option C reverses the actual mechanism - acyclovir acts as a chain terminator due to its lack of a 3'-hydroxyl group, while penciclovir allows some limited chain elongation before termination. Option D incorrectly describes the clearance pathways - both acyclovir and penciclovir are primarily eliminated unchanged through the kidneys, not through hepatic CYP metabolism. For pharmacology exams, remember that prodrug questions often test your understanding of what happens after the prodrug converts to its active form. Focus on learning the specific cellular pharmacokinetics and mechanisms of action for the active metabolites, not just the bioavailability benefits of the parent prodrugs.

Question 11

A clinical trial compares equimolar oral doses of acyclovir and valacyclovir for the treatment of recurrent genital herpes. The study is most likely to find that the valacyclovir group exhibits a significantly higher...

  1. incidence of crystalline nephropathy.
  2. time to peak plasma concentration (Tmax) of the parent drug.
  3. area under the curve (AUC) for the active metabolite, acyclovir. (correct answer)
  4. rate of first-pass hepatic metabolism of the administered drug.
Explanation: Valacyclovir is an L-valyl ester prodrug of acyclovir. Its primary advantage is enhanced oral bioavailability (around 55%) compared to acyclovir (15-20%). This increased bioavailability means that for an equimolar dose, a greater amount of acyclovir reaches the systemic circulation, resulting in a significantly higher area under the plasma concentration-time curve (AUC) for acyclovir. The risk of nephrotoxicity is dose-dependent, but higher AUC is the direct pharmacokinetic consequence. Tmax is not significantly different. Valacyclovir is converted by intestinal/hepatic esterases, not extensive first-pass metabolism in the traditional sense.

Question 12

An immunocompromised patient with recurrent orolabial herpes shows a poor clinical response to high-dose oral valacyclovir. A viral isolate is obtained. The most common molecular basis for this clinical resistance would be a mutation in the gene encoding...

  1. viral DNA polymerase.
  2. a host cell nucleoside kinase.
  3. viral thymidine kinase. (correct answer)
  4. the host L-valyl esterase responsible for prodrug conversion.
Explanation: The most common mechanism of resistance to acyclovir and its prodrugs is an alteration in the viral thymidine kinase (TK) gene, leading to deficient or absent enzyme activity. Since TK is required for the initial, rate-limiting phosphorylation of acyclovir, its absence or alteration prevents the drug's activation. Mutations in the viral DNA polymerase can also confer resistance but are less common. Host enzymes are not the site of viral resistance mutations.

Question 13

A 72-year-old patient with a creatinine clearance of 25 mL/min is being treated for herpes zoster. Which of the following antiviral regimens requires the most careful dose adjustment and carries the highest risk of adverse central nervous system effects, such as confusion and hallucinations?

  1. Topical penciclovir cream.
  2. Oral famciclovir.
  3. Oral valacyclovir. (correct answer)
  4. Topical docosanol cream.
Explanation: Both famciclovir and valacyclovir are systemic agents whose active metabolites (penciclovir and acyclovir, respectively) are eliminated by the kidneys, requiring dose adjustment in renal impairment. However, acyclovir (from valacyclovir) is more strongly associated with neurotoxicity, particularly in the elderly and those with poor renal function, due to accumulation of the parent drug and its metabolites. Topical agents have minimal systemic absorption and do not pose a significant risk of systemic toxicity.

Question 14

Acyclovir demonstrates potent activity against Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV), but has minimal activity against Cytomegalovirus (CMV). This difference in susceptibility is best explained by...

  1. CMV's ability to rapidly clear acyclovir from infected cells via P-glycoprotein efflux pumps.
  2. the absence of a suitable DNA polymerase target in CMV for acyclovir triphosphate.
  3. inefficient initial phosphorylation of acyclovir by the CMV-encoded protein kinase UL97. (correct answer)
  4. the inability of host cell kinases to convert acyclovir monophosphate to triphosphate in CMV-infected cells.
Explanation: The primary reason for acyclovir's poor activity against CMV is the inefficient initial phosphorylation step. HSV and VZV encode a thymidine kinase that efficiently phosphorylates acyclovir. CMV does not encode a thymidine kinase; instead, it encodes a different protein kinase (UL97 phosphotransferase) which is a very poor substrate for acyclovir. This lack of efficient activation prevents the formation of the active triphosphate metabolite, rendering the drug ineffective.

Question 15

A patient with AIDS and a CD4 count of 40 cells/μL has been treated for CMV retinitis with valganciclovir for 6 months. They now present with progressive vision loss. Viral genotype analysis reveals a mutation in the UL54 gene, but no mutation in the UL97 gene. This finding suggests resistance has developed due to an alteration in the...

  1. viral phosphotransferase responsible for initial drug activation.
  2. drug's oral bioavailability due to gastrointestinal pathology.
  3. viral DNA polymerase, the ultimate target of the active drug. (correct answer)
  4. host cell guanylate kinase responsible for diphosphorylation.
Explanation: Resistance to ganciclovir (the active form of valganciclovir) occurs via two primary mechanisms: mutations in the viral phosphotransferase gene (UL97) or mutations in the viral DNA polymerase gene (UL54). Since the UL97 gene is normal, resistance is not due to impaired drug activation. The presence of a mutation in UL54 indicates an alteration in the viral DNA polymerase, which is the direct target of ganciclovir triphosphate. This alteration reduces the drug's ability to inhibit viral DNA synthesis.

Question 16

A 68-year-old male with chronic kidney disease is receiving intravenous acyclovir for HSV encephalitis. Co-administration of which of the following drugs would most significantly increase the risk of acyclovir-induced nephrotoxicity?

  1. Probenecid. (correct answer)
  2. Allopurinol.
  3. Rifampin.
  4. Atorvastatin.
Explanation: Acyclovir is primarily eliminated from the body by glomerular filtration and active tubular secretion in the kidneys. Probenecid is a known inhibitor of the organic anion transporters (OATs) in the renal tubules, which are responsible for the active secretion of many drugs, including acyclovir. By blocking its secretion, probenecid can significantly increase the plasma concentration and half-life of acyclovir, thereby increasing the risk of concentration-dependent toxicities like nephrotoxicity and neurotoxicity.

Question 17

A patient is prescribed oral famciclovir. For this drug to exert its antiviral effect against herpes zoster, it must undergo sequential metabolic conversion. Which of the following best describes this two-step process?

  1. Hydrolysis by host esterases to acyclovir, followed by phosphorylation by viral kinase.
  2. Deacetylation and oxidation by host enzymes to penciclovir, followed by phosphorylation by viral kinase. (correct answer)
  3. Initial phosphorylation by viral kinase, followed by conversion to penciclovir by host kinases.
  4. Direct phosphorylation by viral kinase to famciclovir monophosphate within infected cells.
Explanation: Famciclovir is a prodrug that requires a two-step conversion to its active form. First, during and after absorption, host enzymes (esterases and aldehyde oxidase) deacetylate and oxidize famciclovir to penciclovir. This is the active nucleoside analogue. Second, within virus-infected cells, penciclovir is phosphorylated by viral thymidine kinase to penciclovir monophosphate, and subsequently to the active triphosphate form by host kinases. Famciclovir itself is not a substrate for viral TK.

Question 18

A hematopoietic stem cell transplant recipient develops a VZV infection that is unresponsive to IV acyclovir. Genotyping of the virus reveals a thymidine kinase (TK) deficiency. Which of the following antiviral agents would most likely also be ineffective against this specific viral strain?

  1. Foscarnet.
  2. Cidofovir.
  3. Letermovir.
  4. Ganciclovir. (correct answer)
Explanation: When you encounter antiviral resistance questions, focus on the mechanism of action and whether drugs share the same activation pathway. This VZV strain has thymidine kinase (TK) deficiency, making it resistant to acyclovir, which requires viral TK for phosphorylation to its active form. Ganciclovir (D) is correct because it also depends on viral thymidine kinase for initial phosphorylation. Like acyclovir, ganciclovir must be converted to its monophosphate form by viral TK before cellular kinases can complete activation. Since this VZV strain lacks functional TK, ganciclovir would be equally ineffective. Foscarnet (A) is wrong because it doesn't require phosphorylation at all. It directly inhibits viral DNA polymerase by mimicking pyrophosphate, so TK deficiency doesn't affect its activity. Cidofovir (B) is wrong because it's phosphorylated by cellular kinases, not viral TK, making it effective against TK-deficient strains. Letermovir (C) is wrong because it targets the viral terminase complex involved in DNA packaging, completely bypassing the need for TK-dependent activation. The key insight is that TK-deficient viruses remain susceptible to antivirals that either don't require phosphorylation (foscarnet) or use cellular rather than viral kinases for activation (cidofovir). Study tip: Group antivirals by activation mechanism: TK-dependent (acyclovir, ganciclovir, famciclovir), cellular kinase-dependent (cidofovir), and direct inhibitors (foscarnet). TK-deficient resistance affects only the first group, making this a high-yield pattern for pharmacology exams.

Question 19

A patient is receiving valacyclovir 1000 mg orally once daily for suppression of genital herpes. The plasma half-life of the active drug, acyclovir, is approximately 3 hours. Despite this short plasma half-life, once-daily dosing provides effective suppression primarily because...

  1. the intracellular concentration of the active acyclovir triphosphate is maintained for many hours. (correct answer)
  2. valacyclovir is a slow-release formulation that provides sustained acyclovir levels over 24 hours.
  3. acyclovir causes irreversible covalent inhibition of the viral DNA polymerase.
  4. the parent drug is highly protein-bound, creating a long-lasting reservoir in the plasma.
Explanation: When you encounter questions about drug dosing that seems to contradict pharmacokinetic principles, focus on the difference between plasma drug levels and the actual site of drug action. Valacyclovir is a prodrug that's rapidly converted to acyclovir in the body. Once acyclovir enters virus-infected cells, it undergoes sequential phosphorylation by viral and cellular kinases to form acyclovir triphosphate - the true active antiviral compound. This triphosphate has a much longer intracellular half-life (up to 20-24 hours) than acyclovir's plasma half-life of 3 hours. The triphosphate accumulates in infected cells and provides sustained viral DNA polymerase inhibition throughout the dosing interval, making answer A correct. Answer B is wrong because valacyclovir is an immediate-release formulation, not sustained-release. The once-daily efficacy isn't due to prolonged drug release. Answer C mischaracterizes the mechanism - acyclovir triphosphate competitively inhibits viral DNA polymerase and causes chain termination, but this isn't irreversible covalent inhibition. The enzyme can be regenerated. Answer D is incorrect because acyclovir actually has low protein binding (15-30%), so plasma protein binding doesn't explain the prolonged effect. Remember this key principle: the pharmacokinetics of the active metabolite at its site of action can differ dramatically from the parent drug's plasma pharmacokinetics. Always consider where and how the drug actually works, not just its behavior in plasma.

Question 20

A 60-year-old male with a history of recurrent herpes zoster is managed with suppressive oral valacyclovir. He is now diagnosed with end-stage renal disease (ESRD) and begins hemodialysis three times a week. Which adjustment is necessary for his valacyclovir therapy?

  1. The dose should be increased to compensate for anticipated drug removal during dialysis sessions.
  2. The drug should be switched to topical penciclovir as systemic therapy is now contraindicated.
  3. The drug should be switched to famciclovir, which is primarily metabolized by the liver and not cleared by the kidneys.
  4. The dosing frequency should be reduced, and a supplemental dose should be administered after each dialysis session. (correct answer)
Explanation: When you encounter questions about antiviral dosing in renal disease, focus on how kidney function affects drug clearance and the impact of dialysis on medication removal. Valacyclovir is a prodrug that converts to acyclovir, which is primarily eliminated by the kidneys. In end-stage renal disease, acyclovir accumulation can occur, leading to potential neurotoxicity. Additionally, acyclovir is efficiently removed during hemodialysis due to its low protein binding and small molecular size. This creates a two-part dosing challenge: you need to reduce the baseline dose due to impaired clearance, but then replace what's lost during dialysis. Answer D correctly addresses both issues. Reducing dosing frequency prevents accumulation between dialysis sessions, while supplemental post-dialysis doses maintain therapeutic levels after drug removal during treatment. Answer A is dangerous because increasing the dose would worsen drug accumulation and increase toxicity risk in a patient with no renal clearance. Answer B incorrectly suggests systemic antivirals are contraindicated in ESRD - they're not, they just require adjustment. Topical penciclovir also wouldn't provide the systemic suppression needed for recurrent zoster. Answer C contains a critical error: famciclovir is also converted to penciclovir, which is renally eliminated just like acyclovir, so it faces the same dosing challenges. Remember: most antivirals (acyclovir, valacyclovir, famciclovir) are renally cleared and dialyzable. In ESRD patients on hemodialysis, always consider both dose reduction for impaired clearance and post-dialysis supplementation for drug replacement.