Antivirals

Bacteria are independent cells with their own machinery, so antibiotics have plenty of unique targets. Viruses are different: they hijack the *host cell’s* own machinery to replicate, so a drug that blocks viral copying risks harming our cells too. The art of antiviral design is finding the few steps unique to the virus — a viral enzyme, a viral entry protein — and hitting those. This is why antivirals are virus-specific (an anti-herpes drug does nothing for flu) and why most of them suppress replication rather than eradicate the virus, which can lie latent beyond the drug’s reach.

The cleanest example is acyclovir for herpes. It is a fake building block (a guanosine analog) that is inert until a viral enzyme, thymidine kinase, activates it — an enzyme only present in infected cells. Once activated, it jams the viral DNA polymerase and terminates the growing viral DNA chain. That two-step selectivity — activated only in infected cells, then blocking a viral enzyme — is what makes it powerful against the virus yet gentle on the patient. Valacyclovir is simply acyclovir with a chemical handle that improves absorption (a prodrug).

A few families cover most of what a nurse sees. Anti-herpes (acyclovir, valacyclovir, famciclovir) treat HSV and shingles; CMV agents (ganciclovir/valganciclovir) are more toxic cousins. Anti-influenza drugs are mostly neuraminidase inhibitors (oseltamivir/Tamiflu, zanamivir/Relenza) that block the enzyme flu uses to release new virions from infected cells — halting spread. Their catch is timing: they only help if started within ~48 hours of symptom onset, and they shorten flu by roughly a day — an adjunct to vaccination, not a substitute.

Antiretrovirals (ART) for HIV attack the virus at several steps — reverse transcriptase (the -NRTIs/NNRTIs), protease (the -navir drugs), and integrase (the -tegravir drugs) — combined into regimens that drive the viral load to undetectable. But like herpes, HIV is controlled, not cured, so adherence is everything: missed doses let the virus rebound and develop resistance. The great exception to "suppress not cure" is hepatitis C: modern direct-acting antivirals (the -buvir/-asvir/-previr combos, e.g., Mavyret, Epclusa) achieve a genuine virologic cure (~95%+) in weeks — a landmark distinction worth knowing.

The nursing safety story is short and high-yield. The dominant one is acyclovir and the kidney: the drug can crystallize in the renal tubules, causing crystalluria and acute kidney injury, especially when given IV, rapidly, or to a dehydrated patient. The countermeasures are pure nursing — hydrate the patient well, give IV acyclovir slowly over at least an hour (never a bolus), and dose-adjust and monitor renal function; in renal impairment it can also cause neurotoxicity (confusion, tremor, hallucinations). A related caution: valacyclovir at high doses in the immunocompromised has caused TTP/HUS (a Warning, not a boxed warning).

The other points cluster by drug. Zanamivir is inhaled and can cause bronchospasm — avoid it in asthma/COPD. Oseltamivir has reports of neuropsychiatric events (monitor children/teens for abnormal behavior). And several antivirals carry agent-specific boxed warnings worth flagging: valganciclovir/ganciclovir (bone-marrow suppression, carcinogenicity — handle as hazardous), abacavir (a hypersensitivity reaction tied to the **HLA-B*5701 gene — screen before use), older NRTIs (lactic acidosis/hepatomegaly), and the hepatitis-C DAAs (hepatitis-B reactivation — screen for HBV first). Across all of them, the through-line for teaching is: start early, hydrate, and never stop HIV therapy on your own** — adherence prevents resistance.