Ketamine-induced cystitis: Lessons from a case of recreational use

To describe a case of ketamine-induced cystitis (KIC) in a middle-aged patient using ketamine recreationally, highlight diagnostic pitfalls that may lead to unnecessary antibiotics, and offer pharmacist-focused recommendations for assessment and management, including a formal causality assessment using the Naranjo algorithm.

A 56-year-old male with escalating recreational ketamine use (initial insufflation, later subcutaneous injections; ∼1 gram powder weekly) presented with 6 months of severe suprapubic pain, dysuria, urinary frequency, hematuria, and pain with bowel movements. Prior outpatient management included ciprofloxacin for suspected urinary tract infection, an antispasmodic that worsened pain, and urethral lidocaine gel without relief. In an attempt to self-manage symptoms, ketamine use increased. On admission, pain was 7/10 at rest and 12/10 with urination. Computed tomography (CT) abdomen/pelvis showed stranding/induration and fluid within the subcutaneous tissues of the pelvis/proximal thighs and mild asymmetric left renal atrophy with cortical scarring. Laboratory tests revealed acute kidney injury (serum creatinine 1.76→2.59 mg/dL; blood urea nitrogen (BUN )70 mg/dL). Urinalysis: 100 mg/dL protein, 3+ blood, red blood cells (RBC) >50, white blood cells (WBC) 26-50, small leukocyte esterase. Empiric ciprofloxacin was re-initiated while awaiting cultures; hydrocodone/acetaminophen then ibuprofen as needed were used for analgesia. On day 3, the patient insisted on discharge, reporting improved pain after non-steroidal anti-inflammatory drugs (NSAIDs); he denied suicidal ideation but carried relapse risk. A Naranjo algorithm assessment supported possible causality between ketamine and cystitis (score = 4; Table 1).

KIC can mimic infectious cystitis yet is often sterile; recognition prevents inappropriate antibiotics and supports harm-reduction counseling, ketamine cessation, non-opioid analgesia, anti-inflammatories, and specialty referral. Pharmacists play a central role in screening, differential diagnosis support, and care coordination for patients using ketamine medically or non-medically.