Irritative activity of a new anti-inflammatory agent 4-(p-chorophenyl)-2-phenyl-5-thiazoleacetic acid (CH-800) on the gastrointestinal tract in rats (author's transl)

A single oral administration of CH-800 induced a dose-dependent irritation of the stomach and intestine. As determined from the UD50 value (the dose inducing ulceration by 50%), the potency of gastric irritation was as follows; indomethacin greater than diclofenac Na greater than ibuprofen greater than aspirin greater than CH-800 greater than phenylbutazone. Repeated administrations of CH-800 for 5 days induced a gastric irritation when given in doses from 3 to 100 mg/kg, however, the response was not dose-related. In contrast, the irritation of intestinal mucosa seen with CH-800 administration was dose-related. The degree of gastric or intestinal irritation seen with dosing of other drugs was as follows; indomethacin greater than diclofenac Na greater than ibuprofen greater than aspirin greater than phenylbutazone or indomethacin greater than CH-800 = diclofenac Na greater than ibuprofen greater than phenylbutazone, respectively. CH-800 given for 5 days significantly delayed the healing of active ulcers and the healed ulcers showed a tendency toward re-ulceration. However, the irritating activity of phenylbutazone, diclofenac Na and ibuprofen was more potent than that of CH-800. Thus, CH-800 appears to have a rather weak irritative activity on the gastrointestinal tract of rats without ulceration, in contrast to other commonly clinically prescribed drugs.     

Paracetamol potentiates stress-induced gastric ulceration in rats

The effect of paracetamol on gastric ulcers produced by restraint at 4 degrees C for 2 h (stress) was studied in rats. Paracetamol treatment s.c. or p.o., with a dose as high as 250 mg kg-1, did not produce any haemorrhagic lesions in the glandular mucosa. Oral administration with 250 mg kg-1, however, significantly reduced the mast cell count in the gastric glandular mucosa and potentiated haemorrhagic ulceration but not mast cell degranulation caused by stress. The potentiating action was maximum when paracetamol was given between 15 and 30 min before stress. Ranitidine, astemizole, dimethylsulphoxide, sucralfate and verapamil did not protect against the adverse action of paracetamol on stress-evoked lesions. This study suggests that paracetamol worsens stress-induced stomach ulceration by an action which appears not to be due to histamine release, free radical production or intracellular calcium disturbance in the gastric mucosa.     

Indomethacin and paracetamol: interaction with prostaglandin synthesis in the rat stomach

Using ex vivo incubation of mucosal strips the production of prostaglandins (I2- and E-like PGs) in the rat stomach was demonstrated by bioassay. Indomethacin inhibited this PG synthesis 1 and 4 h after oral drug administration. Paracetamol stimulated the production of PGs when given by itself but could not prevent the inhibitory action of indomethacin. Protection of the stomach by paracetamol against the injuring effect of indomethacin is therefore not due to preservation of the production of protective PGs.     

The comparative effects of paracetamol and indomethacin on renal function in healthy female volunteers.

1. Renal function was assessed in 10 healthy female volunteers during administration of placebo, paracetamol (acetaminophen) (4.0 g daily) and indomethacin (150 mg daily) for 3 days under conditions of controlled sodium and fluid intake. 2. Paracetamol and indomethacin had no significant effect on the glomerular filtration rate and effective renal plasma flow as measured by the renal clearances of inulin, creatinine and p-aminohippurate (PAH). 3. Compared with placebo, paracetamol reduced the mean urinary excretion of prostaglandin E2 by 43% on the second day and 58% on the third treatment day (P less than 0.01). With indomethacin the corresponding reductions were 73 and 80%. Paracetamol and indomethacin had much less effect on the excretion of prostaglandin 6-keto F1 alpha, and a significant decrease was observed only on the third day. 4. The decreased urinary excretion of prostaglandin E2, produced by paracetamol was associated with a reduction in sodium excretion of more than 50% (P less than 0.01) and delay in the onset of diuresis following an acute water load. 5. The renal effects of paracetamol and indomethacin appear to differ. Although indomethacin reduced prostaglandin excretion more than paracetamol it had a similar effect on sodium excretion and less initial antidiuretic action. Unlike paracetamol, indomethacin also reduced basal plasma renin activity. 6. Paracetamol reduced the total body clearance of PAH and increased its plasma half-life. This effect could be attributed to inhibition of the acetylation of PAH by paracetamol. 7. In normal use paracetamol does not appear to have the adverse renal effects associated with the non-steroidal anti-inflammatory analgesics and further studies are required to establish the clinical significance of these findings.     

Current concepts of the actions of paracetamol (acetaminophen) and NSAIDs

There is much uncertainty about the mechanism of action of paracetamol (acetaminophen). It is commonly stated that, unlike the non-steroidal anti-inflammatory drugs (NSAIDs), it is a weak inhibitor of the synthesis of prostaglandins. This conclusion is made largely from studies in which the synthesis of prostaglandins was measured in homogenized tissues. However, in several cellular systems, paracetamol is an inhibitor of the synthesis of prostaglandins with IC₅₀ values ranging from approximately 4 μM to 200 μM. Paracetamol is not bound significantly to plasma proteins and therefore the concentrations in plasma can be equated directly with those used in in vitro experiments. After oral doses of 1 g, the peak plasma concentrations of paracetamol are approximately 100 μM and the plasma concentrations are therefore in the range where marked inhibition of the synthesis of prostaglandins should occur in some cells. Paracetamol is metabolized by the peroxidase component of prostaglandin H synthase but the relationship of this to inhibition of the cyclooxygenase or peroxidase activities of the enzyme is unclear. Paracetamol is also metabolized by several other peroxidases, including myeloperoxidase, the enzyme in neutrophils which is responsible for the production of hypochlorous acid (HOCl). The metabolism of paracetamol by myeloperoxidase leads to the decreased total production of HOC1 by both intact neutrophils and isolated myeloperoxidase, even though the initial rate of production of HOC1 is increased. The IC₅₀ value, derived from inhibition of the total production of HOC1 by isolated myeloperoxidase, is 81 μM. Several NSAIDs inhibit functions of neutrophils in media containing low concentrations of protein but their effects, in contrast to that of paracetamol, are generally produced only at concentrations greater than those of the unbound drug in plasma during treatment with the NSAIDs. However, neutrophils isolated during treatment with NSAIDs, such as piroxicam, ibuprofen and indomethacin show decreased function. Paracetamol has little or no anti-inflammatory activity by itself but may potentiate the clinical activity of NSAIDs in the treatment of rheumatoid arthritis.     

Effects of aspirin,indomethacin, flufenamic acid and paracetamol on prostaglandin output from rat stomach and renal papilla in-vitro and ex-vivo

The effects of aspirin, indomethacin, flufenamic acid and paracetamol on prostaglandin (PG) biosynthesis were studied in whole cell preparations of rat renal papilla and stomach in-vitro and ex-vivo. In the ex-vivo experiments a low dose aspirin was a potent inhibitor of PGE output from the stomach but not the renal papilla, while in-vitro renal PGE output was inhibited by aspirin to a greater extent than gastric PGE. Indomethacin and flufenamic acid inhibited both renal papillary and gastric PGE outputs in-vitro and ex-vivo. Paracetamol enhanced PGE output from the stomach more than twice ex-vivo, and to a lesser extent in-vitro. It also augmented PGE output from the papilla ex-vivo but not in-vitro. In view of the possible contribution of cellular organization and pharmacokinetic processes to the ultimate effect, it is suggested that studies on the effects of anti-inflammatory and antipyretic agents on PG biosynthesis should not be restricted to fully in-vitro systems.     

The role of direct tissue contact in the production of gastrointestinal ulcers by anti-inflammatory drugs in rats

The role of direct contact and systemic activity of phenylbutazone, indomethacin, and ibuprofen in the production of gastrointestinal lesions was studied in the rat comparing the ulcerogenic effects of these drugs after oral and intravenous administration. Phenylbutazone was shown to be more toxic on the stomach than on the intestine but no differences were observed between the two administration routes. Indomethacin was more toxic on the stomach by the oral route than by the intravenous route; the opposite occurred on the intestine. Of the three drugs tested, ibuprofen was the only one which proved to be more toxic orally than intravenously both on the stomach and intestine. In contrast, the anti-inflammatory effects of ibuprofen were equally marked with both routes of administration. The practical implications of these experiments are discussed.     

The influence of excipients on the diffusion of ibuprofen and paracetamol in gastric mucus

The aim of this study was to examine the diffusion of commonly administered analgesics, ibuprofen and paracetamol, through gastric mucus. As ibuprofen and paracetamol are often formulated with alkalising excipients, or are commonly co-administered with antacids that have been demonstrated to alter their absorption, diffusion was also studied in the presence of a range of soluble and insoluble antacids or buffering agents. The effect of pH, which has been demonstrated to modify the properties of mucus, was also studied. Mucus was a significant barrier to diffusion for both drugs, compared to an unstirred aqueous layer with diffusion rates significantly lower in the presence of a mucus barrier for both drugs; ibuprofen diffusion also demonstrated a significant increase in the lag time. Paracetamol diffusion was not significantly affected by addition of any antacid, whereas ibuprofen rates were affected and the diffusion lag time for ibuprofen was significantly reduced in all cases. Isolated increases in pH increased the rate and reduced the lag time for ibuprofen diffusion. It was shown that mucus acts as a passive barrier in the case of paracetamol diffusion, and an interactive barrier to ibuprofen diffusion. Changes in mucus viscosity at different pH values may be responsible for the observed changes in ibuprofen diffusion rate.     

Effect of suspending agents on the characteristics of some anti-inflammatory suspensions

The effect of suspending agents on the physical stability and in vitro availability of mefenamic acid, flufenamic acid, glafenine, ibuprofen and azapropazone suspensions was studied. The ulcerogenic effect of these formulated suspensions on the stomach of rats was also investigated. The results revealed that 2% veegum and 2% sorbitol gave the best formulated suspension for glafenine as compared to other formulations. On the other hand, 2% veegum, 2% sobitol and 1% avicel was found to improve the physical stability of mefenamic acid and flufenamic acid suspensions. Also, the combination of 1% veegum, 1% sorbitol and 1% algin produced excellent suspension for ibuprofen and azapropazone as compared to other combinations. The results of in vitro release data proved an optimal availability of the above mentioned formulations. In addition, significant reduction in the gastric erosions in stomach of rats was observed in all mentioned suspensions except glafenine suspension.     

Effects of phenacetin,paracetamol and caffeine on the erosive activity of acetylsalicylic acid in the rat stomach: dose-response relationships,time course of erosion development and effects on acid secretion

Adult male and female Wistar rats were equally susceptible to gastric injury induced with acetylsalicylic acid (aspirin). Both in male and in female rats simultaneous administration of caffeine and aspirin caused significantly more gastric erosions than the same dose of aspirin alone; likewise addition of paracetamol to aspirin decreased the incidence of gastric lesions in either sex, and addition of phenacetin to aspirin had no effect. The potentiation by caffeine and the inhibition by paracetamol were both dose-dependent and only markedly influenced the development of erosions after 3–4 h. Pretreatment with phenacetin or paracetamol 1 h before administration of aspirin did not affect its erosive activity. Administration of benorylate caused no more gastric erosions than the vehicle or than equivalent mixtures of aspirin and paracetamol. The histamine-stimulated acid output of the stomach during gastric perfusion with aspirin was rapidly diminished. Neither paracetamol nor caffeine initially affected this decrease in acid output. However, 30 min after perfusion with aspirin and caffeine, acid secretion increased approximately as strongly as after caffeine alone. Caffeine potentiates aspirin-induced erosions by its stimulatory effect on acid secretion whereas paracetamol inhibits these erosions by preventing their growth.     

The protective effect of tinoridine against carbon tetrachloride hepatotoxicity

The effect of tinoridine, an anti-inflammatory drug with a potent anti-peroxidative ability, on CCl₄ hepatotoxicity was investigated in rats. CCl₄ administration to rats produced not only marked increases in serum glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase but also decreases in liver microsomal cytochrome P-450 and glucose-6-phosphatase. These CCl₄-induced alterations in the enzyme activities were markedly decreased by pretreatment with tinoridine. The protective effect of tinoridine was also ascertained by histologic evaluation. α-Tocopherol also showed a similar protection, but anti-inflammatory drugs such as phenylbutazone, indomethacin, ibuprofen, and prednisolone failed to protect against the CCl₄-induced hepatotoxicity. These findings suggest that the anti-peroxidative action of tinoridine contributes to the protective effect against CCl₄ hepatotoxicity.     

Pharmacokinetic interactions between indomethacin and paracetamol in the rat

The influence of concurrent administration of paracetamol with indomethacin on the plasma concentrations of these drugs was studied in rats. Orally administered paracetamol reduced the plasma levels of indomethacin during the first 2 hours after oral administration. Later, 16 and 24 hours after administration of indomethacin, the plasma levels exceeded the control values due to the concurrent oral administration of paracetamol. These data suggest that paracetamol delayed the absorption of indomethacin. In contrast the plasma concentrations of paracetamol were not influenced substantially by indomethacin. When paracetamol was co-administered subcutaneously with oral indomethacin, the plasma levels of the latter drug were not influenced. It is concluded that the protective effect of paracetamol against the gastric injuring side effect of indomethacin, which also occurs with subcutaneous administration of paracetamol, cannot be solely due to lowered plasma concentrations of indomethacin.     

Inhibition of prostanoid synthesis by human gastric mucosa

Non-steroidal anti-inflammatory drugs (NSAIDs) damage the gastric mucosa, and an important part of this effect is probably due to inhibition of prostaglandin synthesis. We have therefore studied various drugs for their ability to reduce prostaglandin and thromboxane formation by human isolated gastric mucosa. The overall relative potencies for inhibiting the endogenous production of PGE, 6-keto-PGF1 alpha and thromboxane B2 by mucosal pieces was generally: indomethacin = naproxen greater than ibuprofen greater than piroxicam; diflunisal, the prodrug sulindac, and the analgesic paracetamol usually had small or variable effects. This rank order was mainly similar to the inhibition of gastric microsomal PGE2 formation from exogenous arachidonic acid, the relative potencies being: indomethacin greater than naproxen greater than ibuprofen = piroxicam = diflunisal; again sulindac and paracetamol had little or no effect. The relative propensity of NSAIDs to cause gastric mucosal damage is controversial, but aspirin and indomethacin may be worst, and ibuprofen seems to be among the safest. Potency as an inhibitor of prostaglandin synthesis correlates better with the reported propensity for damage than does potency x dose. For reasons that are given in the discussion, this may indicate that gastric mucosal damage by NSAIDs with short or moderate half-lives is due largely to locally absorbed drug. Whereas inhibition of prostaglandin synthesis is probably the major cause of the damage, the simultaneous reduction of thromboxane formation might be advantageous for gastric mucosal integrity. Various implications arise from our hypotheses concerning the design of anti-inflammatory drugs.     

Serum deprivation and re-addition: effects on cyclooxygenase inhibitor sensitivity in cultured glia

A number of drugs were assessed for their ability to inhibit stimulus-evoked prostanoid synthesis in cultured glia. These drugs included non-selective cyclooxygenase (COX) inhibitors and those considered to be selective for the inducible isoform of this enzyme (COX-2). Experiments were carried out on normal cultures and those which had been maintained in serum-free growth medium for four days then re-exposed to serum for a further seven days. All of the drugs tested elicited concentration-dependent inhibitions of arachidonic acid (AA)-stimulated thromboxane B₂ (TXB₂) accumulation in normal cultures with the following rank order of potency: indomethacin > piroxicam > nimesulide = NS398 > ibuprofen ≫ aspirin > paracetamol. In cultures which had been deprived of serum for four days, basal and AA-stimulated TXB₂ production was considerably reduced, as was the amount of COX immunoreactivity determined by Western blotting. Basal and AA-stimulated TXB₂ production together with COX immunoreactivity were restored to control levels by the re-addition of serum to serum-deprived cultures for 7 days. In these cultures, the rank order of potency was: indomethacin > piroxicam ≫ ibuprofen > nimesulide = NS398 ≫ aspirin > paracetamol; however, there were marked charges in the apparent IC₅₀ values for particular drugs. Indomethacin, piroxicam and aspirin were very similar to control, but the potencies of ibuprofen (3-fold), NS398 (30-fold) and nimesulide (40-fold) were found to be decreased when compared to control. Paracetamol, on the other hand, was found to be almost 3-fold more potent under these conditions. Glia appear to express a COX with a novel sensitivity to particular inhibitors following serum deprivation and re-addition.     

EFFECTS OF FIVE NON-STEROIDAL ANTI-INFLAMMATORY DRUGS ON THE RENAL AND SYSTEMIC RESPONSES TO ARACHIDONATE IN CONSCIOUS DOGS

1. The effects of five different non-steroidal anti-inflammatory drugs (NSAID) on the renal blood flow responses to arachidonate were compared. 2. Arachidonate (5-200 micrograms/kg) injected into the renal arteries of conscious dogs caused dose-related renal vasodilatation with no systemic effects. 3. Aspirin (35 mg/kg), phenylbutazone (12 mg/kg) and ibuprofen (25 mg/kg) all markedly reduced arachidonate-induced renal vasodilatation. 4. In contrast, neither indomethacin (3 mg/kg) or its related drug sulindac sulphide (6 mg/kg) significantly reduced arachidonate-induced renal vasodilatation. 5. All NSAID abolished the hypotensive response to intravenous injection of arachidonate (10 mg). 6. Thus, indomethacin and sulindac did not block the effects of renal artery injections of arachidonate but did abolish the systemic effects. Aspirin, phenylbutazone and ibuprofen greatly reduced responses to both renal artery and intravenous arachidonate. 7. Indomethacin and aspirin both reduced the production of prostaglandin E2 and 6-keto-PGF1 alpha by dog renal cortical microsomes in vitro. 8. Thus, indomethacin and sulindac had different effects to other NSAID on arachidonate-induced renal vasodilatation. The results are compatible with the hypothesis that some sites of prostaglandin production in the kidneys of conscious dogs may be relatively resistant to inhibition by indomethacin and sulindac.     

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.     

Investigation of the vasodilator and antisecretory role of prostaglandins in the rat gastric mucosa by use of non-steroidal anti-inflammatory drugs.

1 The effects of non-steroidal anti-inflammatory drugs on gastric acid secretion and mucosal blood flow were studied in the rat. 2 Indomethacin, in ulcerogenic doses, caused a dose-dependent rise in pentagastrin-stimulated acid secretion, but decreased mucosal blood flow per unit acid secretion. 3 During resting conditions, indomethacin had no significant effect on acid output, but reduced mucosal blood flow. 4 Pretreatment with indomethacin, phenylbutazone or meclofenamate potentiated the secretory response to dibutyryl cyclic adenosine 3',5'-monophosphate. 5 Indomethacin markedly reduced the mucosal prostaglandin-like activity at a time when mucosal erosion formation had reached steady levels. 6 These results provide evidence that prostaglandins have a local role in the regulation of blood flow and acid secretion in the rat gastric mucosa, and suggest that non-steroidal anti-inflammatory drugs cause mucosal erosions by disrupting these processes.     

In Vitro Effect of Anti-Inflammatory Agents on Phagocytosis and Bacterial Killing by Human Neutrophilic Leukocytes

The phagocytosis of killed Staphylococcus epidermidis by neutrophilic leukocytes was inhibited in vitro by indomethacin in a concentration of 3 × 10^-4M, and by hydrocortisone, phenylbutazone, and paracetamol in a concentration of 10^-3M. Phagocytosis was slightly stimulated by 10^-7M phenylbutazone. Acetylsalicylic acid, mefenamic acid, and phenacetin had no effect. The bactericidal activity of leukocytes against live Staphylococcus epidermidis was reduced by 10^-4M phenacetin, 5 × 10^-4M mefenamic acid, and 10^-3M phenylbutazone and indomethacin, whereas concentrations of 10^-5M and above of paracetamol enhanced bacterial killing by leukocytes. Hydrocortisone and acetylsalicylic acid were ineffective. It is probable that concentrations of anti-inflammatory agents sufficient to affect phagocytosis and bacterial killing by neutrophils are as a rule not attained in the organism during treatment, although inhibition may occur locally, for example in inflamed tissue, as a consequence of a low pH, which potentiates the effect of acid anti-inflammatory drugs. This inhibition may be a factor in the mechanism of action of anti-inflammatory compounds.     

The antinociceptive activity of paracetamol in zymosan-induced peritonitis in mice: the role of prostacyclin and reactive oxygen species.

1. Oral administration of high doses of paracetamol (600 mg kg-1 or more) resulted in inhibition of the writhing and reduced the levels of prostacyclin (PGI2, measured as 6-keto-PGF1 alpha) induced by intraperitoneal administration of zymosan in mice. The high oral doses of paracetamol required were accompanied by behavioural toxicity which may have contributed to the inhibition of writhing. 2. The number of writhes per mouse and the proportion of mice writhing at least once correlated significantly with the levels of 6-keto-PGF1 alpha. However, inhibition of writhing by paracetamol occurred at higher levels of 6-keto-PGF1 alpha than was previously observed with acidic non-steroidal anti-inflammatory agents. 3. When injected i.p., PGI2, carbacyclin and iloprost (agonists at the PGI2 receptor) induced writhing. Intraperitoneal injection of PGI2 reversed the inhibition of writhing induced by indomethacin (1 mg kg-1, p.o.) but not that induced by oral administration of paracetamol. 4. Paracetamol at 800 mg kg-1, p.o., inhibited carbacyclin-induced writhing but indomethacin at 1 mg kg-1 p.o. did not. Paracetamol administered i.p. at 100 mg kg-1 reduced the peritoneal levels of 6-keto-PGF1 alpha and inhibited zymosan-induced but not carbacyclin-induced writhing and did not produce behavioural toxicity. 5. The in vitro potency of paracetamol as a prostaglandin synthesis inhibitor is known to be reduced by the presence of lipid peroxides. However, no lipid peroxides, measured as thiobarbituric acid reactive material, were detected in the peritoneal lavage fluid of zymosan-injected mice.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of indomethacin, ibuprofen and paracetamol on the TRH induced TSH secretion in the rat

1. The response of TSH to TRH and the TRH content of the hypothalamus, following indomethacin, ibuprofen and paracetamol treatment, was measured in male rats. 2. Daily treatment of indomethacin (3 mg/kg)) for 3 days markedly reduced T4 concentration in the serum, the TRH content of the hypothalmus gland and inhibit Pituitary TSH response to the low T4 level in the blood. 3. Ibuprofen (12 mg/kg) and paracetamol (50 mg/kg) did not influence T4 or TSH levels of the serum nor the TRH content of the hypothalmus. 4. TRH-induced TSH secretion was not influenced by indomethacin, ibuprofen or paracetamol treatment.