Esketamine Combined Pregabalin and Duloxetine for Postherpetic Neuralgia

Inclusion Criteria: 1. Ages more than 18 years; 2. Pain present for more than 3 months after healing of a herpes zoster skin rash; 3. Has an average pain score of at least 4 on a Numeric Rating Scale (NRS, 0= no pain, 10= worst possible pain)； 4. Failed to respond to or tolerate the effective dose of pregabalin monotherapy. Exclusion Criteria: 1. Obstructive sleep apnoea syndrome; 2. Those who receive interventional treatments; 3. A history of systemic immune diseases, organ transplantation, or cancers; 4. A history of severe cardiopulmonary, hepatic or renal dysfunction; 5. A history of schizophrenia, epilepsy, or myasthenia gravis, delirium; 6. Currently using monoamine oxidase inhibitors (MAOIs); 7. Having untreated angle-closure glaucoma; 8. Those suffering from increased intracranial pressure； 9. Comorbid hyperthyroidism or phaeochromocytoma; 10. Suspected or confirmed history of drug abuse; 11. Having contraindications to esketamine, pregabaline or duloxetine; 12. Communication difficulties; 13. Women who are preparing for pregnancy, in the pregnancy or lactation period.