The first case was of a 72-year-old male whose somatic anamnesis was unremarkable and no prior intake of medications. He was hospitalized for localized zoster in the right groin and front thigh for 23 days. Eight days after tooth extraction, the patient developed a local rash with pinching pain and was diagnosed with extensive HZ of dermatomes T12 to L2 by a dermatologist. The oral medication was initially 200 mg celecoxib twice a day, 75 mg pregabalin, and 250 mg of famciclovir three times a day, for 7 days, respectively. The patient-reported visual analogue scale (VAS) score was controlled, no more than 6. On the 19th day after the appearance of the rash, the patient developed severe breakthrough pain, with more than ten attacks per day (about 5-6 outbreaks at night), each episode lasting 5-8 minutes, accompanied by a tremor of the right lower limb. The VAS pain score was 10 in the onset of breakthrough pain and 0 in the resting. The initial dermatologist tried to increase the dosage of pregabalin, but the patient reported intolerable dizzy and lethargy without any alleviation of his breakthrough pain. Therefore, the patient was admitted and prescribed 75 mg pregabalin three times a day, as well as 100 mg tramadol hydrochloride every 12 hours. Two days after hospitalization, the patient reported no reduction of the intensity and number of episodes of breakthrough pain, after which epidural blockade was performed to resolve the pain. However, during the process, breakthrough pain recurred and the patient was unable to keep his lateral position and switched to a supine position; therefore, the treatment was suspended. The patient received repetitive infusions of 4 g of vitamin C in 250 ml of physiological saline solution, without adjusting the dosage of pregabalin and tramadol hydrochloride. On the second night, there were still 5 episodes of breakthrough pain, but the duration of each attack did not exceed 3 minutes, and the VAS dropped to 8. On the fourth day, although the daily attack frequency did not decrease markedly, the duration had dropped to about 1 minute and the VAS was 6. On the seventh day, the second attempt of epidural blockade using 10 ml 1% lidocaine with 40 mg methylprednisolone was performed successfully. Although the patient suffered an attack of breakthrough pain after lying in the lateral position, the pain intensity was tolerable and lasted for merely 1.5 minutes. During the first 24 hours after the epidural blockade, there were 5 times of attacks, each time lasting for no more than 1 minute and the pain intensity remaining, with a VAS of 3-4. On the tenth day after intravenous administration of vitamin C, the patient had only one attack in the daytime, lasting for half a minute, with a VAS of 1-2. The next day, he was totally pain-free and was discharged from the hospital with an oral prescription for 75 mg pregabalin three times a day for two days. At 1-week and 3-month follow-up, there was no pain recurrence.