Analgesic nephropathy

Alternative names:

nephropathy - analgesic; phenacetin nephritis

Definition:

Damage to the kidney caused by overexposure to mixtures of medications, especially over-the-counter (OTC) pain remedies.

Causes, incidence, and risk factors:

Analgesic nephropathy is one type of toxic injury to the kidney. It is usually a result of prolonged or chronic ingestion of analgesics, especially OTC medications that contain phenacetin or acetaminophen - oral and nonsteroidal antiinflammatory drugs (NSAIDs) including aspirin (see salicylates - oral) or ibuprofen. The ingestion may have been excessive, with as much as 2 or more kg (4 - 5 pounds) total medication ingested over a period of years, or about 3 pills per day for 6 years. This frequently occurs as a result of self-medication, often for some type of chronic pain.

Analgesic nephropathy occurs in about 4 out of 100,000 people, mostly women over 30 years old. The incidence has decreased significantly since phenacetin is no longer widely available in OTC preparations. Risk factors include use of OTC analgesics containing more than one active ingredient, chronic headache, chronic backache or musculoskeletal pain, pain with menstrual periods, emotional and/or behavioral changes, and history of dependent behaviors including smoking, alcoholism, and excessive use of tranquilizers. There may also have been a history of previous urinary tract infection (see UTI - acute), interstitial nephritis, renal calculi, prerenal azotemia, congestive heart failure, or blood volume depletion (such as dehydration).

The damage occurs within the internal structures of the kidney. There is interstitial nephritis and renal papillary necrosis, eventually leading to acute renal failure or chronic renal failure. The tissue of the kidney may slough off into the urine. There may be blood and pus in the urine with or without positive urine cultures or other signs of infection, and there may be minimal or no loss of protein in the urine.