The kidneys contain tubules, which are structures in the kidneys that are involved in filtering fluids. Tubulointerstitial nephritis is inflammation that affects the tubules and the tissue surrounding them, called “interstitial tissue.” Onset of tubulointerstitial nephritis may be acute (sudden) or chronic (gradual) and often results in kidney failure. Which of the following is the most common cause of acute tubulointerstitial nephritis?