Some drugs are wholly or partially eliminated through the kidney. Any other drug that interferes with this process may increase or decrease the blood levels of the first drug. For example, probenecid will decrease the amount of AZT (zidovudine, Retrovir) excreted in the urine, thus increasing blood levels and effects. This may be useful, as the number of AZT capsules taken daily can be decreased when taken in combination with probenecid and this decreases dosing amounts and drug costs.