The role of dosage form in aspirin-induced gastrointestinal bleeding

Review: acute human models of gastric mucosal injury

The use of acute human models of gastric mucosal injury has been stimulated by a need to understand more fully the problems of non-steroidal anti-inflammatory drugs but such models have other applications. None is ideal and they all share certain drawbacks. For none of them has a precise relationship to clinical events been established and they have all tended to be employed on a population of young healthy subjects who are not those at greatest clinical risk. Of individual methods mucosal potential difference is an indirect measure which is too often affected by other influences to be acceptable as a measure of mucosal injury when used alone, although it has some value as an adjunct to other measurements. Assay of DNA in gastric washings is a suitable technique for quantifying desquamation of gastric epithelial cells occurring in response to acute injury; on present evidence its significance is much more difficult to assess in the context of continuing challenge over several days. By contrast, measurement of microbleeding is more suitable for quantifying injury over several days of NSAID ingestion; little bleeding is recorded with a single acute challenge. Endoscopy can demonstrate macroscopic lesions which result from mucosal injury--injury which is quantified more easily and sensitively by measurements of cellular exfoliation or bleeding. Paradoxically, endoscopy's strength has been to underline the scientific weakness of acute models because it shows that it is rare for ulcers, which are the lesions of clinical concern to develop in these studies.

Role of misoprostol in reducing aspirin-induced gastrointestinal blood loss in arthritic patients

Nonsteroidal anti-inflammatory drugs are used to control pain and inflammation in arthritic disorders. When used at recommended anti-inflammatory dose levels, however, they often produce injury to the gastric and duodenal mucosa and concomitant blood loss. A double-blind, parallel, placebo-controlled study was conducted to assess the effectiveness of misoprostol, a synthetic analogue of prostaglandin E1, in preventing gastrointestinal blood loss induced by acetylsalicylic acid in patients with degenerative joint disease. Forty-five arthritic patients (22 women and 23 men) were admitted to the study. All patients had received treatment with 3,900 mg of acetylsalicylic acid per day in four divided doses for at least two weeks and continued to receive that regimen for the duration of the study. Red blood cells were tagged with chromium-51, and fecal blood loss was determined from Days 4 to 7. Patients with a mean blood loss of at least 1.5 ml per day were randomly allocated to receive either placebo or 200 micrograms of misoprostol four times daily for seven days. Fecal blood loss was measured daily, and the results were compared with baseline determinations. Of 41 patients who completed the study, 19 were treated with misoprostol. Of these, 11 patients (57.9 percent) had at least a 50 percent reduction in blood loss. Of 22 patients receiving placebo, only one had a 50 percent reduction in blood loss (p = 0.003; Fisher's exact test). Mean blood loss in patients using misoprostol was reduced from 3.65 +/- 2.51 to 1.57 +/- 0.86 ml per day, whereas among those taking placebo, mean blood loss did not significantly change (2.98 +/- 1.24 to 2.79 +/- 1.63 ml per day). The difference in blood loss between the misoprostol and placebo groups was significant (p = 0.0023; Wilcoxon test). In those patients who completed the study, no significant changes were detected on laboratory tests. In conclusion, misoprostol effectively reduced fecal blood loss in arthritic patients treated with acetylsalicylic acid.

Gastrointestinal intolerance and bleeding with non-narcotic analgesics

Aspirin and paracetamol (acetaminophen) are the most commonly used minor analgesics, but their effects on the gastrointestinal tract differ widely. The effects of other nonsteroidal anti-inflammatory drugs (NSAIDs), including phenylbutazone, are intermediate. Aspirin is significantly associated with major upper gastrointestinal haemorrhage, whereas paracetamol is not. Short term use of aspirin produces erythema, erosions and occasionally ulcers; paracetamol does not, while other NSAIDs do so to varying degrees. Chronic gastric ulcer is linked to aspirin intake in patients with rheumatic disease, and epidemiologically in all heavy aspirin users. In only one epidemiological study was a paradoxical significant association reported between paracetamol intake and chronic gastric ulcer. Faecal occult blood loss is increased in most regular aspirin users but not in those taking paracetamol. Although formal studies in children have apparently not been made, in isolated small clinical series it has been reported that gastrointestinal bleeding and anaemia do occur in the paediatric age group after the use of aspirin. Pathophysiologically, aspirin alters the gastric mucosal barrier to hydrogen ions and lowers gastric potential difference; paracetamol has no effect on these parameters. Such changes correlate ultrastructurally with damage in surface epithelial cells and microerosions after the use of aspirin, but not after the use of paracetamol. Aspirin and other NSAIDs cause a dramatic reduction in the ability of gastric mucosa to generate protective prostaglandins; however, paracetamol also reduces prostaglandins. Other postulated mechanisms of aspirin damage include reduction in gastric mucosal secretion, reduction in bicarbonate output, and alteration of cell turnover. Because damage to gastric mucosa by aspirin and NSAIDs is often 'silent', the clinician needs a high level of suspicion and awareness regarding this problem. In patients prone to gastric damage, or in those with a past history of aspirin-induced gastric damage, paracetamol is the drug of choice when a minor, non-inflammatory problem requires an analgesic.

Pharmacological studies in the rat with [2-(1,3-didecanoyloxy)-propyl]2-acetyloxybenzoate (A-45474): an aspirin pro-drug with negligible gastric irritation

A triglyceride of aspirin, A-45474: [2-(1,3-didecanoyloxy)-propyl]2-acetyloxybenzoate, was developed to reduce the direct gastric irritant properties of aspirin. Studies in the rat show that oral administration of A-45474 produces anti-inflammatory activity comparable to aspirin with negligible gastric irritation. Compared with aspirin, plasma salicylate levels of A-45474 appeared less rapidly and were more sustained. It is concluded that incorporation of aspirin in the 2-position of a triglyceride bearing n-decanoyl groups in the 1- and 3-positions markedly reduces the gastric irritating properties of aspirin while maintaining its pharmacological effects.

Beneficial effects of methionine and histidine in aspirin solutions on gastric mucosal damage in rats

Amino acids methionine and histidine, which are soluble in propylene glycol, were investigated for their purported beneficial effects on aspirin-induced gastric mucosal damage in the rat. The pathognomonic changes observed microscopically in the fundic region of the stomach of animals administered daily doses (100 mg/kg), for up to 15 days, of aspirin solutions (0.36 M) in propylene glycol incorporated with the amino acids were compared with those of animals given equivalent quantities of aspirin in an aqueous suspension combined with an aluminum hydroxide antacid. A "delayed" onset of aspirin-induced cellular damage due to the presence of amino acids, analogous to that associated with the use of antacids, was found as determined partly by differences in the staining ability of injured cells with hematoxylin and eosin.

Gastro-intestinal blood loss during administration of indoprofen, aspirin and ibuprofen

The acute effect of three non-steroidal anti-inflammatory drugs, ibuprofen, acetylsalicylic acid (ASA) and indoprofen, on faecal blood loss was investigated in 15 subjects by means of 51Cr-labelled erythrocytes. Ibuprofen (900 mg/day for 5 days) and indoprofen capsules and tablets (300 mg and 600 mg/day for 5 days, respectively) slightly increased the amount of blood eliminated in faeces. The increase was of the same order of magnitude for both doses of indoprofen. ASA (1,500 mg/day for 5 days) caused about a 6-fold increase in blood loss. Four days after withdrawal of ASA, faecal blood was still about twice as high as in faeces of subjects given ibuprofen and indoprofen. The method appears sensitive and reliable for comparison of the immediate effect of anti-inflammatory drugs on gastro-intestinal mucosa.

Aspirin-induced gastritis and gastrointestinal bleeding

Aspirin-induced gastritis and gastrointestinal hemorrhage were reviewed and discussed on the basis of currently available literature. Acute hemorrhagic gastritis occurs in from 50% to 70% of all patients taking aspirin, is not directly related to dose size, and can be severe enough to cause death in a few cases. No tolerance appears to ever develop. The mechanism that causes this bleeding is not definite, but the back diffusion of H+ ions accross the gastric barrier seems to bear primary responsibility, with physical erosion, prolonged platelet bleeding, and the effect of low pH values also being possible explanations. There appears to be less acid present in the stomach when bleeding occurs, but this is a masking effect of the aspirin that causes increased absorption of the H+ ions. Factors important in determining pharmaceutical formulation are method of administration, particle size of the aspirin, duration of contact between the drug and the mucosa, presence of buffers in the drug to raise the gastric pH, dissolution rate of the drug in the stomach, and ionization characteristics of the drug itself. Gastrointestinal blood loss caused by aspirin can be minimized by administering the drug in one of these forms:--a dilute solution of acetylsalicylate;--an intravenously injected solution;--a very rapidly dissolving and rapidly absorbed tablet;--a solution with sufficiently large amounts of antacid added;--a fine-grain, highly buffered aspirin tablet;--an enteric-coated tablet that does not dissolve in the stomach; or--an aspirin substitute such as acetaminophen.

Drugs and gastric damage

The effects of aspirin, salicylate formulations and substitutes, smoking (nicotine), indomethacin, corticosteroids, phenylbutazone, ethanol, caffeine and reserpine on the gastric mucosa are discussed. The damaging effects of the drugs are considered in terms of the gastric mucosal barrier, gastric erosions, microbleeding and haematemesis and melaena and finally whether they cause peptic ulcer. There is suggestive evidence that unbuffered aspirin is a cause of haematemesis and melaena and of gastric ulcer but the incidence rates for hospital admission are low, being 10 to 15 per 100,000 heavy users per year. Aspirin in solution as acetylsalicylate buffered to maintain a neutral pH protects against gastric damage. Newer aspirin substitutes (mefenamic acid, fenoprofen, naproxen, tolmetin and ibuprofen) appear to cause less faecal blood loss than aspirin but their long-term effects have not been fully evaluated. Smoking is definitely associated with peptic ucler but the mechanism is unknown. Corticosteroids are probably not ulcerogenic despite clinical bias that they are. Indomethacin and phenylbutazone may be ulcerogenic but there is insufficient evidence to make firm judgements. Ethanol, caffeine and reserpine, on available evidence, are probably not ulcerogenic.

Effect of naproxen on gastrointestinal microbleeding following acetylsalicylate medication

This study was undertaken to determine if substitution of naproxen for ASA does influence salicylate-induced gastrointestinal bleeding. Twelve normal volunteers were selected and given increasing doses of salicylate until guaiac tests were consistently positive. Autologous labeling of their red blood cells with 51-Cr was used to quantitate the microbleeding. After two weeks on ASA, six subjects were double blindly switched to naproxen and six to placebo for another two weeks of observation. Two-way analysis of variance on the raw data shows a significant treatment effect associated with a significant interaction in both groups. Final analysis on a logarithmic scale permits orthogonal contrasts to be accurately made without any significant remaining interaction. It is concluded that substitution of naproxen for ASA at a dose of 500 mg daily is accompanied by a rapid reduction of microbleeding to "normal" levels.