Pregabalin hypersensitivity in a patient treated for postherpetic neuralgia
A 40-year-old male patient was hospitalized for sharp, lancinating pain in his left loin, which was disrupting his daily routine for last 2 days. A week ago, the patient developed vesicular rash in the same area and was treated with topical and oral acyclovir for 1 week. The patient also experienced a burning sensation at the site of rash, which responded to etoricoxib 120 mg daily given for 5 days. The patient reported back after 5 days to the out-patient clinic due to persistent and severe left loin pain and was hospitalized. The investigations revealed normal hematology and biochemistry profile. Chest X-ray and ultrasonography (USG) abdomen were also normal. Serological tests for hepatitis B virus, human immunodeficiency virus, Epstein-Barr virus and herpes simplex virus were normal. herpes zoster virus IgM titer was 1:40 by immune fluorescent assay (normal value < 1:10). The patient was diagnosed as a case of post herpetic neuralgia and received intramuscular tramadol 50 mg as and when required. Etoricoxib was stopped and pregabalin 75 mg twice a day and paracetamol 1 g 3 times a day was started orally. In view of inadequate pain relief, the dose of pregabalin was increased to 150 mg twice a day. Remarkable improvement was noticed after increased dose of pregabalin. Hence, patient decided to go home. He was advised to continue pregabalin 150 mg twice a day and paracetamol orally whenever necessary.\nAfter 2 weeks, the patient came with complaints of low grade fever, itchy skin rash and swelling of lips and face since 3 day. Purpuric rash was observed on the face and exfoliative lesions were seen on the hands and feet, without any joint or mucosal involvement. He had raised erythrocyte sedimentation rate, C-reactive protein, peripheral eosinophilia (absolute eosinophil count of 1400/cm) and normal leukocyte and platelet counts. Dengue antigen (NS1) and malaria rapid tests were negative. Liver function tests revealed alanine transferase (ALT) 250 IU/L and aspirate transaminases (AST) 322 IU/L with normal bilirubin, alkaline phosphatase and gamma glutamyl transpeptidase, Anti-nuclear antibodies were negative. Ultrasonography did not reveal any liver abnormality. Serum pregabalin was 5 μg/mL; (N < 10 μg/mL; MedTox Lab Inc. USA, liquid chromatography/tandem mass spectrometry [MS]). The diagnosis of probable hypersensitivity to pregabalin was made.\nThe drug was stopped and patient was treated with topical betamethasone cream and oral prednisolone 40 mg daily for 10 days tapered over a period of 1½ months. He recovered completely. The casualty assessment by World Health Organization Uppsala Monitoring Center scale[] and Naranjo's algorithm[] (score 6) showed a probable relationship between the drug and the reaction.