Biopsy-proven acute interstitial nephritis, 1993-2011: a case series.

BACKGROUND: Acute interstitial nephritis (AIN) is an important cause of acute kidney injury, especially in hospitalized patients. The cause and outcome of AIN, particularly that due to drugs, is changing with prevalent medication use. The effectiveness of steroids for treatment of AIN is debated.

STUDY DESIGN: Case series.

SETTING & PARTICIPANTS: 133 patients with biopsy-proven AIN from 1993 through 2011 at a single center.

OUTCOMES: Recovery of kidney function by 6 months, either complete, partial, or none. Complete recovery was defined as improvement in serum creatinine level to within 25% of baseline (or < 1.4 mg/dL), and partial recovery, as a ≥ 50% decrease in serum creatinine level from its peak value but not reaching within 25% of its baseline value.

RESULTS: Causes of AIN included drugs (70%), autoimmune diseases (20%), and infections (4%). Drug-induced AIN was due to antibiotics in 49%, proton pump inhibitors (PPIs) in 14%, and nonsteroidal anti-inflammatory drugs (NSAIDs) in 11%. Overall, the top 3 drug causes were omeprazole (12%), amoxicillin (8%), and ciprofloxacin (8%). Patients with drug-induced compared to non-drug-induced AIN were older and had higher baseline kidney function, but more severe acute kidney injury. Patients with PPI-induced AIN were older, were less symptomatic, and had longer durations of drug exposure and longer delays in getting kidney biopsy and steroids than for antibiotic-induced or NSAID-induced AIN. At 6 months postbiopsy, 49% of patients with drug-induced AIN treated with steroids achieved complete recovery; 39%, partial recovery; and 12%, no recovery. Correlates of poor recovery included a longer duration of drug exposure (15 vs 30 vs 130 days for complete, partial, and no recovery, respectively; P = 0.04) and longer delay in starting steroid therapy (8 vs 11 vs 35 days, respectively; P = 0.05).

LIMITATIONS: Retrospective study, selection bias in patients who had kidney biopsy, single-center experience.

CONCLUSIONS: The cause of AIN may be shifting; PPIs are emerging as an important contributor to this disease. Delays in discontinuation of the culprit drug and in initiating steroid treatment adversely affect recovery of kidney function.