Analgesic Nephropathy (Phenacetin nephritis)

What is Analgesic Nephropathy?

Analgesic Nephropathy is a condition resulting from damage to the kidney caused by overexposure to mixtures of medications, especially over-the-counter pain medication.

Statistics on Analgesic Nephropathy?

This condition occurs throughout the world, ranking as one of the most common causes of chronic renal insufficiency in Australia and Western Europe. It is twice as common in females than in males, and present most commonly in patients of middle-age. The incidence of this condition has fallen in recent times since the identification and withdrawal of certain analgesics from public access. These include phenacetin and analgesic "cocktails" containing phenacetin.

Risk Factors for Analgesic Nephropathy

1. Long term use of analgesics (usually combination preparations).2. Chronic illness requiring long term analgesia.3. Chronic dehydration in combination with excessive use of analgesics.

Progression of Analgesic Nephropathy

Analgesic nephropathy is a chronic renal disease that arises from an excessive long term intake of analgesics. The injury accumulates over many years, causing the insidious development of symptoms such as anaemia, chronic renal failure, symptoms of urinary infection or urinary tract obstruction. Urinary tract infection complicates around 50% of cases. The sloughing of necrotic papillae may result in complete urinary tract obstruction, which may result in acute renal failure. With continued use of analgesics, this condition may result in chronic renal failure. With appropriate withdrawal and alternative pain management, renal function may stabilise or even improve with time.In rare cases, patients may develop transitional papillary carcinoma of the renal pelvis despite their discontinuation of the offending analgesic. This condition must be treated surgically to remove the tumour. The prognosis is good, provided an early diagnosis is made of a superficial tumour.

How is Analgesic Nephropathy Diagnosed?

1. Assessment of baseline renal function: Bloods - Urea and electrolytes, Serum creatinine.2. Investigate for urinary tract obstruction: Renal imaging - x-ray (KUB), Intravenous pyelogram, Renal ultrasound.

Prognosis of Analgesic Nephropathy

The damage to the kidney may be acute and temporary, or chronic and long term. The level of complication caused to the kidney will ultimately provide a prognosis.

How is Analgesic Nephropathy Treated?

1. Consumption of long-term analgesics should be discouraged. If necessary, prescribe simple paracetamol or dihydrocodiene. Avoid combination analgesics. 2. Antimicrobial therapy for urinary tract infection if present.3. Monitor and treat hypertension if present.4. Monitor and treat urinary tract obstruction if present - Refer to urological surgery if obstruction present and monitor for acute renal failure with regular assessment of creatinine, urea and electrolyte (esp. potassium.) The acute development of flank pain is indicative of urinary tract obstruction which should prompt immediate urographic/ultrasound assessment of the urinary tract with referral to urological surgery if obstructed.5. Monitor and treat electrolyte disturbance - Salt wasting is likely as the kidneys will lose their ability to resorb sodium. Assess daily and manipulate fluids as appropriate.

Analgesic Nephropathy References

[1] Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison's Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001.[2] Cotran, Kumar, Collins 6th edition. Robbins Pathologic Basis of Disease. WB Saunders Company. 1999.[3] Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002 Pg 545-549.[4] Longmore M, Wilkinson I, Torok E. OXFORD HANDBOOK OF CLINICAL MEDICINE. Oxford Universtiy Press. 2001.