Approach
Treatment depends on the underlying cause. The most common cause is medications, but acute interstitial nephritis (AIN) can also occur in the context of infection and chronic inflammatory disease. Advice should be sought from a nephrologist. Patients who do not rapidly respond (in <1 week) to the withdrawal/treatment of the underlying cause should be referred to a nephrologist for prompt treatment and to exclude other diagnoses, especially where a kidney biopsy is indicated.
Medication related
The initial treatment is discontinuation of the triggering medication as soon as AIN is suspected. Longer duration of exposure to AIN-inducing medication is associated with worse chances of kidney function recovery.[3] After discontinuing the medication, most patients will have resolution of their acute kidney injury and a progressive return of kidney function.[1][11]
If the patient is taking several known triggering medications, it will not be clear which medication is the cause. In this situation, all medications should be switched to drugs from a different class. For example, a penicillin might be changed for a fluoroquinolone rather than a cephalosporin, and omeprazole might be changed for ranitidine rather than lansoprazole.
Supportive care includes attention to fluid and electrolyte balance. All patients should have serum electrolytes, urea, and creatinine monitored daily during the acute episode. Sodium and volume restriction may be required, along with limitation of potassium and phosphorus intake. Diuretics may be required for treatment of fluid retention. If a diuretic is suspected as the trigger, a diuretic from a different class should be used. Dialysis may be needed if the patient has severe symptoms, or severe fluid balance or metabolic derangement that is not responding to medical therapy.
There are currently no randomised controlled trials for the use of corticosteroids in AIN and the existing evidence is based on observational studies.[28] These studies show conflicting results. Two studies showed no benefit of corticosteroids on kidney function recovery; however, in one of these studies, the corticosteroid group had much worse kidney function at the time of biopsy than controls, whereas the other study initiated corticosteroids weeks after diagnosis.[29][30] Other studies show a benefit to kidney function recovery after AIN with corticosteroids, particularly if started within 1 to 2 weeks of diagnosis.[9][31][32] Based on these data, a short course of prednisolone should be considered in most patients whose kidney function does not improve rapidly after drug withdrawal, unless corticosteroid therapy is contraindicated.[33] This should be undertaken with the results of a kidney biopsy confirming the diagnosis of AIN and excluding other possible diagnoses. Corticosteroids should be continued for 1 to 1.5 months as much of the recovery of kidney function is expected in this period.
Chronic inflammatory disease related
Corticosteroids are the preferred therapy for interstitial nephritis associated with Sjogren syndrome, sarcoidosis, IgG4-related syndrome, systemic lupus erythematosus, and tubulo-interstitial nephritis with uveitis (TINU) syndrome.[4][14] AIN due to autoimmune conditions usually requires longer duration of treatment than drug-induced AIN and corticosteroids should be continued for 2 to 3 months. Patients with chronic inflammatory disease may also be taking known triggering medications, and these should be discontinued.
Supportive care is the same as for medication-related episodes (monitoring of electrolytes and renal function, sodium and volume restriction, diuretics, dialysis if needed).
If patients relapse on withdrawal of corticosteroid treatment, a repeat course should be given. A few patients have recurrence of renal failure every time corticosteroid therapy is discontinued; these patients are corticosteroid dependent and will require long-term treatment.
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