When are antiviral drugs appropriate to treat "shingles" and what is the first-line treatment for post-infection pain?
A 66-year-old man comes to see you complaining of a rash on his back and abdomen that began approximately three days ago. He reports that it is mildly uncomfortable but not really painful. When you examine him, you see the rash is along the distribution of the T10 nerve root and is relatively mild. You make a diagnosis of herpes zoster (HZ). His only other health issues are diabetes, which is well controlled with metformin, and hypertension, controlled with lisinopril.
1. Which of the following factors would lead you to initiate an antiviral medication to treat the HZ?
A. His age
B. The level of pain
C. The location of the rash
D. His current medications
Answer: A. His age.
It is recommended that patients over age 50 who are diagnosed with HZ should be started on an antiviral medication, even if their immune systems are not compromised. Other indications for antiviral therapy are pain or rash that is severe or involvement of an area of the body other than the trunk.
You treat the patient with acyclovir but he returns several weeks later and reports that while his rash has disappeared, he is having marked pain at the same site and that the pain is especially severe if something touches the skin. The symptoms are consistent with allodynia and you diagnose postherpetic neuralgia (PHN).
2. All but which of the following are considered first-line treatment for PHN?A. A tricyclic antidepressant (TCA) such as amitriptyline or nortriptyline
E. Lidocaine patch 5%
Answer: B. Oxycodone.
The TCAs, the gabapentinoid anticonvulsants pregabalin and gabapentin, and the lidocaine patch are considered the drugs most likely to be effective for PHN. Opioid analgesics may benefit some patients but are less likely to reduce symptoms and so should only be tried after these other drugs fail.
3. When considering whether to start a TCA, a gabapentinoid, or the lidocaine patch for this patient, which of the following would best help predict the agent’s efficacy for him?A. The level of the pain
B. The presence of allodynia
C. The time between the onsets of the rash and of PHN
D. There are no good predictive factors for determining which of the medications is most likely to be efficacious
Answer: D. There are no good predictive factors for determining which of the medications is most likely to be efficacious
As of yet, no predictive factors have been identified that help determine which class of drugs or which individual drug is most likely to be effective in treatment of PHN and there is scant research comparing the drugs to each other.
Haanpaa M, Rice ASC, Rowbotham MC. Treating herpes zoster and postherpetic neuralgia. Pain Clin Updates. 2015;23:1-8.