Fosphenytoin Alleviates Herpes Simplex Virus Infection-Induced Provoked and Spontaneous Pain-Like Behaviors in Mice.

In this study, we investigated the effects of fosphenytoin (fPHT), a water-soluble prodrug of phenytoin, on the pain responses of a mouse herpes zoster (HZ) pain model. Transdermal herpes simplex virus type 1 (HSV-1) inoculation induced mechanical allodynia and hyperalgesia of the hind paw and spontaneous pain-like behaviors, such as licking the affected skin. Intravenous injection of fPHT (15 and 30 mg/kg) alleviated HSV-1-induced provoked pain (allodynia and hyperalgesia). The suppressive effects of fPHT on provoked pain were weaker than those of diclofenac and pregabalin which were used as positive controls. fPHT, diclofenac, and pregabalin significantly suppressed HSV-1-induced spontaneous pain-like behaviors. Among them, high-dose fPHT (30 mg/kg) showed the strongest suppression. Intravenous fPHT may become a viable option for an acute HZ pain, especially for spontaneous pain.

Clinical Manifestation and Nerve Block Effect of Acute Herpes Zoster Associated Pain and Postherpetic Neuralgia

OBJECTIVE: To assess the clinical manifestation of acute herpes zoster associated pain (AHP) and postherpetic neuralgia (PHN) and nerve block effect in AHP and PHN. METHOD: We assessed twenty eight patients by physical examination and pain questionairre, and nerve block effect in thirty one patients. We injected local anesthetics and triamcinolone into nerve root or trunk in study group, and saline in control group. The effect was assessed by visual analogue scale. RESULT: 1. Clinical manifestation: There was high incidence in thoracic dermatome. AHP and PHN patients expressed "sharp" pain. Pain rating index of AHP and PHN were 32.9, 33.0. 2. Nerve block effect: There was no nerve block effect in AHP (p>0.05) and PHN (p>0.05), but four patients of PHN patients in study group had significant pain relief, who suffered from pain during 2 month, 10 month, 6 years, 8 years. CONCLUSION: AHP and PHN had variable clinical manifestation but no difference between them. There was no nerve block effect in AHP and PHN but we can consider nerve block as a additive method for pain relief of PHN because some patients responded to nerve block and there was no significant complication in nerve block.