Tiotidine, a new long-acting histamine H2-receptor antagonist: comparison with cimetidine

The effects of tiotidine, a new histamine H2-receptor antagonist, and cimetidine on food-stimulated gastric acid secretion were evaluated in duodenal ulcer patients. Homogenized steak meals were infused immediately after, 1 h after, 5 h after, and 10 h after an oral dose of medication, and food-stimulated acid secretion was measured by in vivo intragastric titration. Tiotidine and cimetidine had a similar onset of action; however, tiotidine was more potent and had a longer duration of effect. Increased potency was demonstrated by the fact that from 1 to 2 h after medication 150 mg tiotidine inhibited acid secretion to approximately the same extent as did 300 mg cimetidine, and by the fact that for a given percent inhibition of acid secretion, plasma tiotidine concentration was eight to nine times lower than plasma cimetidine concentration. Longer duration of effect was demonstrated by the fact that from 5 to 7 h after medication, acid secretion was inhibited by 80% and 97% with 150 and 300 mg tiotidine, respectively, whereas 300 mg cimetidine inhibited acid secretion by only 22%. Also, 10-12 h after medication, 150 and 300 mg tiotidine inhibited acid secretion by 22% and 53%, respectively, while 300 mg cimetidine had no inhibitory effect. The long duration of effect was due in part to increased potency and in part to a plateau in plasma concentration of tiotidine, which was maintained from 2 to 6 h after medication. Neither tiotidine nor cimetidine had a significant effect on food-stimulated gastrin release or gastric emptying of a nonabsorbable marker.     

Famotidine,a new H2-receptor antagonist

We studied pentagastrin-stimulated acid and pepsin secretion with three doses (5, 10, and 20 mg) of a new H₂-receptor antagonist (famotidine) administered orally to normal male volunteers. A dose response was identified: 2 hr after oral dosing, 5 mg famotidine suppressed stimulated acid secretion to 60% of control and was comparable to 300 mg cimetidine (55% suppression). Higher doses of famotidine yielded significantly more suppression of acid secretion (10 mg yielding 70% and 20 mg, 90%). Pentagastrinstimulated acid secretion remained decreased (50% of control) 12 hr after oral dosing with 20 mg famotidine. The reduction in pepsin output paralleled the reduction in acid secretion and was primarily due to a reduction in the volume of secretion and not to a change in pepsin concentration. We calculated the components of gastric secretion (acid from parietal cells) and bicarbonate secretion (from nonparietal cells) and found that the primary effect of the H₂-receptor antagonists was a dramatic reduction in parietal cell output without a significant decrease in nonparietal secretion. Famotidine proved to be a potent inhibitor of both the parietal component of gastric acid and pepsin output. Famotidine was significantly more potent than cimetidine; 5 mg of famotidine was comparable to 300 mg of cimetidine.This study was supported by the Veterans Administration and by a grant from Merck Sharp and Dohme Research Laboratories, West Point, Pennsylvania.     

Gastric neuroendocrine cell hyperplasia after treatment with the long-acting, potent H2-receptor antagonist SK&F 93479

The time course and dose response of the neuroendocrine cell hyperplasia in the oxyntic mucosa of the rat was examined after treatment with the potent, long-acting H2-receptor antagonist SK&F 93479 at doses of 0 and 1000 mg/kg orally for 1, 3, 7, and 14 days and at doses of 0, 40, 200, and 1000 mg/kg orally for 1 and 6 months. The number of oxyntic neuroendocrine cells (chromogranin-positive) increased after 7 days of treatment. In the 1- and 6-month studies with doses of 1000 mg/kg, the grading for the number of oxyntic chromogranin-positive cells was 2.5 to 3 times the control levels, and they were distributed mostly throughout the mucosa, whereas at lower doses, which did not produce carcinoid tumours at 2 years, the neuroendocrine cells were distributed in the lower half of the mucosa with 1.5- to 2-fold increases in grades for cell numbers. Increases in cell numbers and cell distribution may be useful factors in the evaluation of the neuroendocrine cell hyperplasia found in, for example, the Zollinger-Ellison syndrome and chronic atrophic gastritis, in which hypergastrinaemia and fundic neuroendocrine cell hyperplasia are present.     

Influence of a meal on the absorption of cimetidine. A new histamine H2-receptor antagonist.

Absorption of an oral dose of 300 mg of Cimetidine was studied after an overnight fast in six healthy male volunteers on three separate occasions, 20 min before, during, and 2 h after a standard breakfast. Compared to the doses taken before and after the meal, the dose taken with the meal showed a significant delay in the time taken to reach therapeutic blood concentrations of the drug with no reduction in the period of time during which this concentration was maintained. We, therefore, suggest that the drug should be taken with a meal to achieve optimal acid inhibition in the interdigestive period.     

Effects of cimetidine,a histamine H2-receptor antagonist,on various experimental gastric and duodenal ulcers

The effects of cimetidine, a new histamine H₂-receptor antagonist, on the development of experimental gastric and duodenal ulcers were studied. It was found that either by the oral, intraduodenal, or intraperitoneal route this agent had a marked inhibitory activity on stress-, aspirin-, indomethacin-, or histamine-induced gastric ulcers in rats and guinea pigs. The effects of cimetidine on stress-, aspirin-, and indomethacin-induced gastric ulcers were dose-dependent in many cases. Pylorus-ligation ulcers, reserpine-or serotonin-induced gastric ulcers were little influenced by cimetidine. Duodenal ulcers induced by continuous infusion of carbachol-histamine were significantly inhibited by a simultaneous infusion of cimetidine. An analysis of gastric contents in pylorus-ligated rats after stressing indicated a decreased volume and acid output as the result of intraduodenal cimetidine treatment. In contrast, cimetidine exerted little influence on gastric secretion in rats treated with aspirin or in guinea pigs treated with histamine. Thus, the mechanism of action of cimetidine in preventing gastric or duodenal ulcers is likely to occur by suppression of gastric secretory function in a duodenal ulcer model but by suppression of other unknown ulcerogenic factors in gastric ulcer models.     

The effect of the new H2-receptor antagonist mifentidine on gastric secretion, gastric emptying and experimental gastric and duodenal ulcers in the rat: comparison with cimetidine and ranitidine

The new H2-receptor antagonist mifentidine (DA 4577) was tested for its antisecretory and gastric motor effects in comparison with cimetidine and ranitidine. The Shay rat preparation (5 h) was used for studying gastric secretion; the gastric emptying of a liquid meal was chosen for studying gastric motility. All the three compounds inhibited acid secretion in a dose-dependent fashion. Calculated ED50s were 2.3, 12.2 and 92.8 mg X kg-1 for mifentidine, ranitidine and cimetidine, respectively. Therefore, in this animal model, mifentidine was about 40 times more potent than cimetidine and 5 times more potent than ranitidine. As far as gastric emptying is concerned, the effect of equiactive antisecretory doses (i.e. the respective ED50s calculated from the previously established dose-response curves) of all the three antagonists was completely different. Cimetidine delayed emptying rate, whereas ranitidine accelerated it and mifentidine was completely ineffective. However, at higher doses, also this compound affected emptying rate by reducing it dose-dependently. Gastric and duodenal ulcers were induced in the rat by dimaprit (100 mg X kg-1 intravenously) and cysteamine (250 mg X kg-1 subcutaneously), respectively. As far as gastric ulcer is concerned, the ED50s (the effective dose which protected 50% of the animals from lesions) were 0.23, 4.40 and 9.70 mg X kg-1 for mifentidine, ranitidine and cimetidine, respectively. As regards duodenal ulcer, the ED50 was 4.48 for mifentidine and 150.00 mg X kg-1 for ranitidine. In this animal model, the efficacy of cimetidine was very low. Therefore an ED50 could not be determined. In conclusion, results of the present investigation demonstrated that mifentidine is a potent antisecretory compound and an effective anti-ulcer agent in the rat.     

Effectiveness of omeprazole in seven patients with Zollinger-Ellison syndrome resistant to histamine H2-receptor antagonists

The inhibitory effect of omeprazole, a benzimidazole derivative, on gastric acid secretion was investigated in seven patients with Zollinger-Ellison syndrome resistant to treatment with large doses of histamine H₂-receptor antagonists administered alone or in combination with pirenzepine. In two patients with an acute form of the syndrome, rapid control of acid overproduction was achieved with 180-mg intravenous and 120-mg oral daily doses, respectively. The other five patients, who were free of complication, initially received a standard regimen of omeprazole 60 mg orally once a day; dosage was subsequently adjusted until the basal acid output, measured 1 hr before the next dose of the drug, was less than 10 mmol/hr. The initial daily dose proved to be adequate in three patients and had to be increased to 80 mg and 60 mg bid, respectively in the remaining two patients. In all patients omeprazole therapy resulted in clinical recovery and rapid healing of mucosal lesions. The seven patients have now been followed up for 4–24 months (average 15 months). The adequacy of the daily dosage was periodically reassessed by measuring basal acid output in the hour preceding the morning dose. In one patient initially treated with 180 mg/day, dosage could be reduced to 60 mg/day. In three others, who were initially controlled with 60 mg/day, dosage had to be increased during follow-up. Despite adequate control of gastric acid secretion, one patient underwent total gastrectomy and tumor resection and another died of extensive liver metastases. The five patients still receiving omeprazole remain free of symptoms and mucosal lesions. No side effects or laboratory abnormalities ascribable to the drug were observed. It is concluded that omeprazole therapy is a good alternative in patients with Zollinger-Ellison resistant to currently available antisecretory drugs. Its safety and effectiveness in long-term therapy remain to be evaluated.     

The effect of cimetidine, a new histamine H2-receptor antagonist, on meal-stimulated acid secretion, serum gastrin, and gastric emptying in patients with duodenal ulcer.

Meal-stimulated acid secretion, measured by in vivo intragastric titration, was progressively inhibited by increasing oral doses of cimetidine (25 to 400 mg). Four hundred milligrams suppressed acid secretion by 73% for the first 3 hr after the meal, whereas it inhibited acid secretion by 94% during the 30-min period of maximal inhibition. The dose of cimetidine required to suppress acid secretion by 50% during the 30-min period of maximal inhibition was 25 mg. The duration of action of a 300-mg dose was at least 7 hr. Cimetidine was equally effective in inhibiting meal-stimulated acid secretion at two physiological intragastric pH levels (5.0 and 2.5). Cimetidine had no effect on serum gastrin concentration when intragastric pH was maintained at 5.0, but when pH was allowed to seek its own level, serum gastrin concentration was higher after cimetidine than after placebo. Cimetidine had no effect on gastric emptying. No side effects were noted in any patients.     

Is the time of dosing of a potent long-acting H2-receptor antagonist critical? Twenty-four-hour pH measurements with SKF-94482.

Reduction of daytime as well as nighttime acidity is important in the healing of duodenal ulceration and reflux oesophagitis. The importance of the time of dosing of potent, long-acting H2 blockers for optimal suppression of intragastric acidity is unknown. The efficacy of different oral dosage regimens of SKF-94482, a new, competitive and long-acting H2-receptor antagonist, in reducing daytime and nighttime intragastric acidity was studied with 24-h pH-monitoring in 3 double-blind, randomized, crossover trials in 45 fed, healthy subjects. In study A 200 mg, 400 mg, or 600 mg SKF-94482 or placebo was given at 0830 h for 6 days. In study B the above doses were taken at 1830 h. In study C 200 mg or 300 mg of SKF-94482 or placebo was given at 0830 and 1830 h for 6 days. SKF-94482, 400 mg, was the most effective dose, and twice daily dosing was of no additional pharmacodynamic benefit. When 400 mg SKF-94482 was given at 0830 h, the median 24-h, day (0800-1800 h) and night (1800-0800 h) pH (interquartile range) were 2.6 (2.2-3.2), 2.3 (2.1-3.8), and 2.6 (1.8-3.6), respectively. When the time of dosing was 1830 h with 400 mg SKF-94482, median 24-h, day and night pH were 3.4 (2.5-4.0), 3.4 (3.1-4.3), and 3.7 (2.8-5.9), respectively. Early-evening dosing of this long-acting H2 antagonist resulted in substantially greater suppression of intragastric acidity than morning dosing.     

Effect of the histamine H2-receptor antagonist, cimetidine, on gastric secretion and serum gastrin during insulin infusion in Man.

Cimetidine infusion (100 mg h-1) reduced the acid secretory response to insulin infusion (0.03 units Kg-1h-1) when compared to paired control tests in 6 healthy volunteers. There was no significant difference between cimetidine and control tests in terms of pepsin output or serum gastrin concentrations. Cimetidine also reduced the acid secretory response when administered after 90 minutes of insulin had established a secretory response in extended tests in 3 additional volunteers. Cimetidine may have therapeutic potential in the peptic ulcer diathesis.     

Early clinical experience with metiamide,a histamine H2-receptor antagonist,in patients with duodenal ulcer

The clinical, endoscopic, and biochemical effects of metiamide, a histamine H₂-receptor antagonist, in therapeutic dosage have been studied in a 28-day open trial in patients with duodenal ulcer disease. A good symptomatic response, combined with a 72% ulcer healing rate was observed. There were small but significant rises in plasma creatinine, serum glutamic oxaloacetic transaminase, and serum lactate dehydrogenase during treatment. Small quantities of amino acids appeared in the urine, and the heart size increased slightly. It is concluded that histamine H₂-receptor antagonism may be an important therapeutic approach to duodenal ulcer disease.     

Oxmetidine: clinical pharmacological studies with a new H2-receptor antagonist.

The gastric antisecretory effects of oxmetidine, a new H2-receptor antagonist, have been studied in 33 healthy subjects. The relative potency of oxmetidine compared with that of cimetidine depended on the route of administration and the experimental conditions. Oxmetidine intravenously infused was approximately four times as potent as cimetidine, weight for weight, in inhibiting impromidine stimulated gastric acid secretion but was twice as potent when food was used as a stimulus. After oral administration there were no differences in the weight-for-weight potency of oxmetidine and cimetidine, although oxmetidine was twice as potent on a molar basis. These apparent differences according to the route of drug administration are probably due to first pass metabolism of oxmetidine. There were no differences in the duration of action of oxmetidine and cimetidine. Twenty-four hour monitoring of intragastric pH showed that oxmetidine 400 mg twice daily reduced mean hourly 24 hour intragastric pH by 59%, suggesting that a twice daily dosage regimen should be evaluated in the treatment of duodenal ulceration.     

Tiotidine,a new H2-receptor antagonist,is a potent inhibitor of nocturnal acid secretion in duodenal ulcer patients

The efficacy of tiotidine, a new H₂-receptor antagonist, in reducing nocturnal acid secretion of duodenal ulcer patients (N=12, ages 21–60 years) was investigated. Different doses of tiotidine, 25, 50, 100, and 150 mg or placebo, were given as a single oral dose and acid secretion collected overnight. Tiotidine produced a significant, prolonged, and dose-related reduction of the nocturnal acid secretion without important side effects. The inhibition of cumulative H⁺ secretion after 25, 50, 100, and 150 mg tiotidine was 80, 89, 96, and 98% of that observed after placebo, while 300 mg of cimetidine caused an 87% inhibition. Compared to cimetidine, tiotidine appears to be approximately eight times more potent on a molar basis than cimetidine as an inhibitor of acid secretion, and the tiotidine effect is more prolonged. This strong and safe H₂-receptor antagonist may be an important addition to the treatment of acid hypersecretory states.     

CP-66,948: An antisecretory histamine H2-receptor antagonist with mucosal protective properties

CP-66,948 is a histamine H₂-receptor antagonist with gastric antisecretory activity and mucosal protective properties. The affinity of CP-66,948 for the guinea pig atria histamine H₂-receptor is 15 times greater than that of cimetidine and seven times greater than that of ranitidine.In vivo, the ED₅₀ value for inhibition of gastric acid secretion in pylorusligated rats is 2 mg/kg intraduodenally, and in histamine or pentagastrin-stimulated Heidenhain pouch dogs the antisecretory ED₅₀ values are 0.3 mg/kgper os and 1.0 mg/kgper os, respectively. CP-66,948 also inhibits ethanol-induced gastric hemorrhagic lesions in rats following either oral or systemic administration (ED₅₀ values of 12 mg/kgper os and 6 mg/kg subcutaneously). In addition, the mucosal protective activity is independent of prostaglandin synthesis. CP-66,948 inhibits gastric acid secretion in man, and its mucosal protective activity may provide additional benefits in peptic ulcer therapy.     

Famotidine,a histamine-2-receptor antagonist,inhibits the increase in rat gastric H+/K+-ATPase mRNA induced by intravenous infusion of gastrin 17 and histamine

We examined the effects of gastrin and histamine on rat gastric H⁺/K⁺-ATPase, the enzyme responsible for H⁺ secretion, gene expressionin vivo. Gastrin 17 (G 17) or histamine dihydrochloride (histamine) was continuously infused through the femoral vein of anesthetized rats. Gastric H⁺/K⁺-ATPase mRNA levels were measured using northern blot analysis. Infusion of G 17 and histamine increased the H⁺/K⁺-ATPase mRNA level significantly compared with basal control level or vehicle control level (P<0.01). However, pretreatment with famotidine, a potent histamine-2 (H₂)-receptor antagonist, inhibited the increase of rat gastric H⁺/K⁺-ATPase mRNA following G 17 and histamine infusion. These findings indicate that both histamine and G 17 increase expression of H⁺/K⁺-ATPase mRNA by activating H₂ receptor on the parietal cell.     

Inhibition of gastric acid secretion in the dog by the H2-receptor antagonists, ranitidine, cimetidine, and metiamide.

The new H2-receptor antagonist, ranitidine, has been compared with cimetidine and metiamide as an inhibitor of gastric acid secretion in the dog. All three compounds were effective both intravenously or by mouth in inhibiting secretion induced by histamine, pentagastrin, or bethanechol. This inhibition was mainly attributable to a reduction in the volume of secretion, although there was also a significant reduction in the concentration of acid secreted. Metiamide was slightly less active than cimetidine, but ranitidine was four to nine times more potent than cimetidine, depending on the secretagogue used. The antisecretory activity of ranitidine does not result from a limitation in blood flow to the gastric mucosa.     

Inhibition of the histamine-stimulated gastric secretion in healthy subjects by the H2-receptor antagonist ranitidine

The gastric secretion was examined for 30 min before and 120 min during intravenous infusion of 3 microgram/kg/h of histamine dihydrochloride. In eight subjects physiological saline solution was given as infusion in addition to histamine (controls), whereas nine subjects received ranitidine in doses increased every half hour--0.06, 0.12, 0.24, and 0.48 mg/kg/h. The infusion of ranitidine resulted in a significant reduction of volume of gastric juice both when compared with the unstimulated periods before histamine and with those of subjects receiving the saline solution. Similarly, the acid output was reduced still more significantly during infusion of ranitidine, the output being about zero in the last hour. The ranitidine dose used was about five time lower than that previously used of cimetidine. No side effects were observed.