The failure of high doses of aspirin to produce renal lesions in pigs

Analgesic nephropathy in rodents

While it is clear that humans suffer from "classic" analgesic nephropathy, the causative agents and mechanisms are still not known. A review of the literature revealed that chronic acetaminophen exposure does not produce renal papillary necrosis in rodents or humans. In contrast, while chronic aspirin exposure to rodents results in renal papillary necrosis with renal morphological and functional changes similar to that described in humans, epidemiological studies do not implicate aspirin alone in human analgesic nephropathy. The difference in the effects of aspirin in humans and rats may be due to the inability of epidemiological studies to detect aspirin-induced analgesic nephropathy or more likely to the fact that species differences exist, with the rat being more sensitive than humans. With respect to combinations of aspirin and acetaminophen, with or without caffeine, there are minimal tightly controlled studies. In addition, there is little evidence of enhanced renal papillary necrosis in rodents treated with aspirin and acetaminophen combinations. In summary, it remains to be determined what chemical entities cause "classic" analgesic nephropathy in humans and the mechanisms of this toxicity such that preventative measures can be instituted. Elucidation of the mechanisms of analgesic nephropathy has been hampered due to the lack of animal models that closely mimic the human disease. Rodents do not appear to be an appropriate model.

Does aspirin cause acute or chronic renal failure in experimental animals and in humans?

There are conflicting reports on the ability of aspirin as a single agent to cause acute or chronic renal failure in experimental animals. Chronic administration of aspirin alone over 18 to 68 weeks in doses of 120 to 500 mg/kg/d has been reported to cause renal papillary necrosis in rats. However, some investigators have been unable to produce renal papillary necrosis in other species or in rats given lower divided doses comparable to therapeutic doses used in humans. In a variety of rat strains, aspirin administered as a single high dose intravenously or by oral gavage produces acute tubular necrosis of proximal tubules, rarely accompanied by renal papillary necrosis in susceptible strains. Several human studies have addressed the chronic nephrotoxicity of aspirin alone or relative risk of end-stage renal disease in association with aspirin use after correction for other analgesics. With the exception of one case control study demonstrating a low, but statistically significant risk of end-stage renal disease in association with aspirin use, all other case control studies and several prospective studies have been unable to identify a significant risk of chronic renal failure in patients using aspirin alone in therapeutic doses. In healthy adults, short-term aspirin administration in therapeutic doses has no effect on creatinine clearance, urine volume, osmolar clearance, or sodium and potassium excretion. However, in predisposed individuals with glomerulonephritis, cirrhosis, and chronic renal insufficiency, and in children with congestive heart failure, short-term aspirin use in therapeutic doses may precipitate reversible acute renal failure. Acute aspirin intoxication (>300 mg/kg) frequently causes acute renal failure and doses of 500 mg/kg may be lethal. Chronic salicylate intoxication has been reported to cause reversible or irreversible acute renal failure in association with a pseudosepsis syndrome.

The effect of acetaminophen on pig kidneys with a 2-bromoethanamine-induced papillary necrosis

Large White pigs were used to investigate the effects of acetaminophen (paracetamol) on normal kidneys or those with an existing renal papillary necrosis. Pairs of young female animals were treated with either a single iv dose of 50 mg/kg 2-bromoethanamine (BEA), 100 mg/kg/day acetaminophen po for 28 days, or a combination of BEA followed by the acetaminophen treatment. Two pigs served as untreated controls. Kidney length, diameter and parenchymal thickness were measured by ultrasound scans, and glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) assessed by 99mTc-DTPA and 131I-hippuran renography prior to treatment and on day 26. Acetaminophen only caused no renal pathology. Despite the lack of a gross RPN, hyperplasia of the pelvic and ureteric urothelia (with extensive vacuolation) was observed following BEA, but BEA followed by acetaminophen for 28 days did not enhance the lesion. The BEA and BEA-acetaminophen groups (but not acetaminophen only) showed an increased ERPF compared with age-matched controls, but there was no significant difference in the overall GFR between the groups.

Analgesic-associated nephropathy

Although the question of whether or not analgesic abuse leads to a certain type of nephropathy has been investigated since 1953, no conclusive answer has been forthcoming. Epidemiologic investigations on the correlation between analgesic abuse and renal function as well as experimental animal studies have given contradictory results concerning the possibility of analgesic-associated kidney damage. However, studies on the correlation between analgesic abuse and papillary necrosis have demonstrated that this lesion coincides in 69% of the cases with an analgesic history. Follow-up studies of patients with analgesic nephropathy have shown that renal function deteriorates in 60% of the patients with continued abuse and that it stabilizes in 80% of the patients after cessation of abuse. Studies on the legislative restriction of phenacetin/acetaminophen, carried out mostly in Scandinavian countries since 1965, show a 50%-90% decline in signs of analgesic nephropathy (papillary necrosis) following a reduction in the sale of these drugs. The prevalence of analgesic abuse may be underestimated, since up to 80% of the abusers tend to deny their analgesic intake. Obviously, only a small percentage of analgesic abusers (approximately 1%) finally develop nephropathy. Even though the results of epidemiologic and experimental studies are contradictory, the results of investigations on papillary necrosis and on legislative prevention as well as of patient follow-ups tend to indicate a correlation between analgesic abuse and a well-defined type of nephropathy.

Renal toxicity of non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs represent the most heavily prescribed and used class of drugs in human medicine. Most are derivatives of either salicylates, propionic acid, indoleacetic acid, anthranilic acid, pyrazolone, or oxicams. They depress the synthesis of prostaglandins from arachidonic acid by reversible inhibition of the enzyme cyclooxygenase. In the kidney, prostaglandins PGE2 and PGI2 modulate the vasoconstrictor effects of angiotensin II, norepinephrine, and vasopressin. In the presence of volume contraction, anesthesia, or disease states associated with high levels of these hormones, prostaglandins regulate glomerular filtration, vascular resistance, and renin secretion. They additionally influence urine volume and sodium content. In man, a syndrome of analgesic abuse that has been identified worldwide occurs more frequently in females than males and can result in severe renal damage, most notably renal papillary necrosis. Most common laboratory animals are relatively resistant to developing the renal lesion associated with NSAIDs unless high doses are given over long periods of time and some withholding of water is introduced into the protocol. Diuresis with 5% dextrose and water is protective. Studies of paracetamol and salicylate have demonstrated that these compounds concentrate in the papillary tip of the kidney at concentrations of 4 to 13 times the plasma levels in dogs and rabbits, respectively. Renal papillary necrosis has been described in horses on maintenance doses of phenylbutazone where dehydration or reduced water consumption has occurred. The lesion can be reproduced experimentally if water is withheld during a portion of the dosing interval. An increased incidence of uroepithelial tumors have been reported in patients with a history of analgesic abuse.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological mechanisms of analgesic nephropathy

The situation in the experimental field is unresolved; too many factors require clarification before the critical experiment can be conducted to settle the matter once and for all. However, as there is now plentiful evidence to convince any reasonable physician that commonly available analgesics, when abused, carry a significant health risk, one may resonably ask whether any further experimental evidence is needed? The object of this review is in no sense divisive, i.e., by pointing out discrepancies in the available data to thereby cloud the issue rather than resolve them. The problem of abuse lies properly in the field of public health education, and the first step to this would surely be an appropriate worning on the packaging of all commonly used analgesics. For future research, however, government health authorities should be guided in their preclinical testing requirements for mild antiinflammatory analgesics, and enough is now known to draw up guidelines for good laboratory practice in this field.

Experimental renal papillary necrosis

Review of experimental work indicates that renal papillary necrosis (RPN) is more readily induced by mixtures of analgesics which include phenacetin or paracetamol, than by either of the latter drugs alone. In an experiment in which moderate doses of analgesics were given to rats over a long period, it was shown that aspirin had a greater nephrotoxic effect than either phenacetin or paracetamol although less than in combination with either. In a study of the evolution of aspirin-induced damage, the earliest changes were shown to occur in the interstitial cells. There was also loss of medullary mucopolysaccharides. Occlusive lesions were demonstrated in the vasa recta. Using partial papillectomy, it was shown that the development of analgesic-induced cortical lesions did not depend on the presence of papillary necrosis. It was suggested that the early papillary changes might be due to ischemia, medullary blood flow being reduced as a result of aspirin's action as an inhibitor of prostagladin synthesis. The lesions in the vasa recta might cause ischemia at a late stage, leading to total RPN.

Aspirin, phenacetin, and the kidney: a rheumatism clinic study

In a rheumatism clinic study in Brisbane, the consumption of aspirin and phenacetin compounds (APC) containing more than one kilogram of aspirin and phenacetin was significantly associated with overt renal papillary necrosis (RPN) and with a renal score, but when more than one kilogram of aspirin was taken without phenacetin there was no such association. Analysis and comparison with the parallel New Zealand study showed an overall risk of RPN of at least 10-6% when more than one kilogram of aspirin was taken in APC form, and 0-3% when aspirin was taken without phenacetin. An additive interaction of phenacetin and aspirin is postulated. It is concluded that phenacetin use should be severely restricted.

Analgesic abuse and kidney disease

The analgesic syndrome, comprising renal disease, hypertension, peptic ulcer, anaemia and recurrent headache, accounts for wide-spread morbidity and mortality especially in Queensland and New South Wales. Epidemiological and clinical evidence gathered from many Western societies implicates unsupervised consumption of compound analgesic preparations, particularly those containing phenacetin, in the causation of the majority of cases. Laboratory experiments so far have failed to produce an entirely satisfactory model of clinical analgesic nephropathy. In small animals, papillary necrosis results from prolonged feeding with large doses of aspirin and a number of other anti-inflammatory agents more readily than when phenacetin, paracetamol or phenazone is given alone. The apparently conflicting deductive and experimental data may be reconciled if, as indicated by preliminary observations, salicylates enhance the toxicity of phenacetin derivatives. In planning a programme of prevention for the analgesic syndrome, the central aetiological role of non-narcotic drug dependency must be recognized. As the analgesics to which addiction commonly occurs are the compound powders and tablets, or those containing a stimulant, these preparations should be available only in circumstances where their use can be monitored. Suspected unsupervised and unwarranted consumption of analgesics should be checked by urinary testing for drug metabolites. Because the underlying problem of analgesic dependency is behavioural and environmental in origin rather than medical, the physician must combine forces with the social engineer to devise a definitive solution for this condition.