Herpes resistant to acyclovir is treated by
**Core Concept**
The development of acyclovir resistance in herpes simplex virus (HSV) or varicella-zoster virus (VZV) infection necessitates the use of alternative antiviral agents. This phenomenon is due to mutations in the viral thymidine kinase (TK) gene or the viral DNA polymerase gene, compromising the antiviral activity of acyclovir.
**Why the Correct Answer is Right**
The correct treatment option for acyclovir-resistant herpes involves the use of drugs that are not metabolized by the viral thymidine kinase or are not dependent on viral DNA polymerase for their antiviral activity. Foscarnet is a potent inhibitor of viral DNA polymerase and is effective against acyclovir-resistant HSV or VZV infections. Foscarnet does not require activation by viral thymidine kinase and can directly inhibit viral DNA replication.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify a treatment for acyclovir-resistant herpes.
* **Option B:** This option is incorrect as it does not accurately represent a treatment for acyclovir-resistant herpes.
* **Option D:** This option is incorrect as it does not accurately represent a treatment for acyclovir-resistant herpes.
**Clinical Pearl / High-Yield Fact**
Foscarnet is a high-risk medication for electrolyte imbalances, particularly hypocalcemia, and requires careful monitoring of serum calcium levels during treatment.
**Correct Answer: C. Foscarnet**