The kidneys are two organs that sit in the small of the back on either side of the spinal cord. The kidneys filter toxic substances from the blood; help balance fluid, acid, and electrolyte levels; and reabsorb water and nutrients back into the body. The kidneys produce urine from excess water and waste products, which is stored in the bladder until eliminated. Because the kidneys filter toxic substances, including some drugs, they are susceptible to damage if these substances build up in the proximal tubules, the site where reabsorption of excess water takes place.

Some anti-HIV drugs have been linked to kidney toxicity, particularly tenofovir (Viread) and indinavir (Crixivan).