Analgesic nephropathy pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Pathophysiology

The scarring of the small blood vessels, called capillary sclerosis, is the initial lesion of analgesic nephropathy.[1] Found in the renal pelvis, ureter, and capillaries supplying the nephrons, capillary sclerosis is thought to lead to renal papillary necrosis and, in turn, chronic interstitial nephritis.[2][1]

How phenacetin and other analgesics lead to this damage is incompletely understood. It is currently thought that the renal toxicities of NSAIDs and the antipyretics phenacetin and paracetamol may combine to give rise to analgesic nephropathy. A committee of investigators reported in 2000 that there was insufficient evidence to suggest that non-phenacetin analgesics by themselves are associated with analgesic nephropathy.[3]

Aspirin and NSAIDs

Proper kidney function depends upon adequate blood flow to the kidney. Kidney blood flow is a complex, tightly regulated process that relies on a number of hormones and other small molecules, such as prostaglandins. Under normal circumstances, prostaglandin E2 (PGE2) produced by the kidney is necessary to support adequate blood flow to the kidney. Like all prostaglandins, PGE2 synthesis depends upon the cyclooxygenases.

Aspirin and other NSAIDs are inhibitors of the cyclooxygenases. In the kidney, this inhibition results in decreased PGE2 concentration causing a reduction in blood flow. Because blood flow to the kidney first reaches the renal cortex (outside) and then the renal medulla (inside), the deeper structures of the kidney are most sensitive to decreased blood flow. Thus the innermost structures of the kidney, called the renal papillae, are especially dependent on prostaglandin synthesis to maintain adequate blood flow. Inhibition of cyclooxygenases therefore rather selectively damages the renal papillae, increasing the risk of renal papillary necrosis.

Most healthy kidneys contain enough physiologic reserve to compensate for this NSAID-induced decrease in blood flow. However, those subjected to additional injury from phenacetin or paracetamol may progress to analgesic nephropathy.

Phenacetin and paracetamol

It is unclear how phenacetin induces injury to the kidney. Bach and Hardy have proposed that phenacetin's metabolites lead to lipid peroxidation that damages cells of the kidney.[4]

Paracetamol is the major metabolite of phenacetin and may contribute to kidney injury through a specific mechanism. In cells of the kidney, cyclooxygenases catalyse the conversion of paracetamol into N-acetyl-p-benzoquinoneimine (NAPQI).[5] NAPQI depletes glutathione via non-enzymatic conjugation to glutathione, a naturally occurring antioxidant.[6] With depletion of glutathione, cells of the kidney become particularly sensitive to oxidative damage.

References

  1. 1.0 1.1 Mihatsch MJ, Hofer HO, Gudat F, Knüsli C, Torhorst J, Zollinger HU (1983). "Capillary sclerosis of the urinary tract and analgesic nephropathy". Clin. Nephrol. 20 (6): 285–301. PMID 6641031. Unknown parameter |month= ignored (help)
  2. Mihatsch MJ, Khanlari B, Brunner FP (2006). "Obituary to analgesic nephropathy--an autopsy study". Nephrol. Dial. Transplant. 21 (11): 3139–45. doi:10.1093/ndt/gfl390. PMID 16891638. Unknown parameter |month= ignored (help)
  3. Feinstein AR, Heinemann LA, Curhan GC; et al. (2000). "Relationship between nonphenacetin combined analgesics and nephropathy: a review. Ad Hoc Committee of the International Study Group on Analgesics and Nephropathy". Kidney Int. 58 (6): 2259–64. doi:10.1046/j.1523-1755.2000.00410.x. PMID 11115060. Unknown parameter |month= ignored (help)
  4. Bach PH, Hardy TL (1985). "Relevance of animal models to analgesic-associated renal papillary necrosis in humans". Kidney Int. 28 (4): 605–13. PMID 3910912. Unknown parameter |month= ignored (help)
  5. Mohandas J, Duggin GG, Horvath JS, Tiller DJ (1981). "Metabolic oxidation of acetaminophen (paracetamol) mediated by cytochrome P-450 mixed-function oxidase and prostaglandin endoperoxide synthetase in rabbit kidney". Toxicol. Appl. Pharmacol. 61 (2): 252–9. PMID 6798713. Unknown parameter |month= ignored (help)
  6. Duggin GG (1996). "Combination analgesic-induced kidney disease: the Australian experience". Am. J. Kidney Dis. 28 (1 Suppl 1): S39–47. PMID 8669429. Unknown parameter |month= ignored (help)

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