A 49-year-old female patient (weight: 60 kilos; height: 1.63 metres) consulted the emergency department for 5 days of left lumbar pain, burning and electric type, intensity 10/10 on a verbal analogue scale. The pain is episodic, exacerbated by movement and does not improve with the administration of tramadol and diclofenac. Physical examination revealed erythematous, vesicular lesions with dermatomatous distribution on the skin of the lumbar region and left buttock. The rest of the physical examination was normal. She has a history of lumbar disc disease, arterial hypertension and hypothyroidism under medical treatment. The patient denies any history of renal disease.
The patient was assessed by the infectious diseases department, who considered it to be a case of herpetic neuritis and decided to hospitalise the patient due to the severity of the symptoms. During the first day and prior to the hydration protocol (500 ml of 0.9% saline solution), an infusion of intravenous acyclovir 10 mg/kg every 8 hours (600 mg) was started. Consultation with the pain clinic was requested, who started an analgesic programme with acetaminophen + codeine (500 + 30 mg orally every 6 h), morphine in case of severe pain (2 mg per dose) and pregabalin (150 mg/12 h). The patient initially presented adequate analgesia with no side effects, rating her pain at 4/10.
On the second day of hospitalisation she presented dizziness, nausea, emesis, somnolence and dysarthria. The symptoms were considered to be a side effect of the analgesics and it was decided to discontinue the acetaminophen with codeine and pregabalin. Morphine doses of 2 mg were prescribed in case of severe pain after assessment of consciousness. On the third day of hospitalisation, without receiving any opioid dose, the patient persisted with deterioration of her general condition, with progression to stupor, tachypnoea, desaturation and respiratory distress. She was transferred to the Intensive Care Unit. The picture is compatible with acute pulmonary oedema and renal failure with serum potassium at 5.7 mEq/L, BUN 50 mg/dl (admission value of 17.2), creatinine 5.01 mg/dl (admission value of 0.66) and arterial blood gases with metabolic acidosis. Nephrology confirmed the diagnosis of acute renal failure secondary to administration of acyclovir, with the need for haemodialysis. The patient required a single session of haemodialysis with improvement in azo levels. Analgesic management continued with acetaminophen 500 mg and codeine 30 mg; the patient did not require new doses of morphine. She was discharged on the sixth day of hospitalisation with controlled pain and normal renal function tests.