Antivirals

Acyclovir won't help your patient if you destroy their kidneys giving it. Timing and hydration determine whether these antivirals heal or harm.

Acyclovir and oseltamivir target different viruses through different mechanisms but share a critical nursing principle: timing is everything. Acyclovir treats herpes simplex (HSV) and varicella-zoster (VZV) by inhibiting viral DNA polymerase — it gets activated only inside infected cells by viral thymidine kinase, which is why it selectively targets virus-infected cells while sparing healthy ones. It must be infused slowly (over at least 1 hour) with aggressive IV hydration because acyclovir crystallizes in renal tubules, causing nephrotoxicity. Monitor BUN, creatinine, and urine output throughout therapy. Dose must be adjusted in renal impairment. Also monitor for neurotoxicity (confusion, tremors, seizures), especially in elderly or renally impaired patients. Oral acyclovir is less nephrotoxic but still requires adequate fluid intake. Oseltamivir (Tamiflu) is a neuraminidase inhibitor that blocks influenza virus release from infected cells, limiting viral spread. It must be started within 48 hours of symptom onset to be effective. Common side effects include nausea and vomiting — give with food to reduce GI distress. Neither drug cures the virus; both reduce severity and duration of illness.

Key Distinctions

Don't confuse acyclovir's nephrotoxicity mechanism (crystal precipitation in tubules) with amphotericin B's nephrotoxicity (direct tubular damage) — acyclovir nephrotoxicity is prevented by hydration, not by slowing infusion alone. Students mix up the 48-hour window: oseltamivir must start within 48 hours of flu symptoms, while acyclovir for shingles is most effective within 72 hours of rash onset. Don't assume completing a full acyclovir course eliminates the virus — HSV and VZV remain latent in dorsal root ganglia and can reactivate. Patients need education that recurrence is possible.

Clinical Pearl

Acyclovir crystals love dry kidneys — push fluids like the renal tubules depend on it, because they do. Oseltamivir needs a clock: no benefit after 48 hours.