Hello,
Shingles or Herpes zooster is common in old age due to reduced immunity and reactivation of lesions.
The pain due to
post herpetic neuralgia is too severe and treatment if started a bit late can cause much neural damage resulting in pain for a longer duration.
Pain can persist for upto one to three months.
If the lesions are healed - for topical purpose
you can try
capsaicin cream
Lidocaine patch at the healed location
For oral purpose - (You need prescription from you doctor for these)
If it is still painful, amitryptiline with a dosage of 25 mg at night can be started and increased upto four times slowly as necessary. or
Gabapentin 100 mg or upto 300 mg three times daily until pain is brought under control.
Dosage should be increased slowly to avoid side effects.
Prostate cancer would not interfere with any of the drugs. It could have been the reason leading on to stress/reduced immunity and thereby Herpes zooster.
But without it also, according to studies 50% of elderly are prone to develop shingles once in their life time.
Hope I was able to answer your query. Take care. If you have any further queries, happy to help