[H2-receptor antagonists and alcohol: clinical significance]

The aim of the review is to evaluate the putative clinical interactions between alcohol metabolism and the administration of H2-receptor antagonists. Places of the first-pass metabolism of ethanol in the body have been investigated as well. According to the in vitro experimental results the H2-receptor antagonists can inhibit the ethanol metabolism which may have clinical relevance. When low doses of alcohol (below 0.3 g/kg) are given per os, the administration of H2-receptor antagonists results in an increase in the blood ethanol concentrations. Since that challenged increase never exceeds the level of 0.3/1000 blood alcohol concentration, it has hardly any clinical or medico-legal significance.

Nizatidine accelerates gastric emptying of a solid meal in rats

Nizatidine, a new histamine-2-receptor antagonist, stimulates gastrointestinal motility in dogs and gastric emptying of liquids in rats. Effect of nizatidine on gastric emptying of a solid meal was investigated using a novel gastric emptying model in rats. Male Wistar rats (weighing 200-300 g) were supplied with powdered food containing 30 w/w% barium 14 hr before the beginning of the experiment and x-ray photography of rat stomach was taken under light ether anesthesia. Gastric emptying was assessed by percentage of a decrease in area 30 min after drug was injected intraperitoneally. There was a positive correlation between the area of the gastric outline and the weight of the gastric contents (r = 0.94, P < 0.01). Ether anesthesia itself did not affect gastric emptying. Nizatidine increased gastric emptying dose-dependently (emptied percentage; vehicle: 4.9 +/- 1.5%, 1 mg/kg: 7.2 +/- 0.4%, 3 mg/kg: 10.4 +/- 2.0%, 10 mg/kg: 16.7 +/- 4.9%, 30 mg/kg: 25.7 +/- 7.4%). N-Desmethyl nizatidine (NDM) also stimulated gastric emptying, but nizatidine S-oxide, cimetidine, an famotidine had no significant effects on gastric emptying. Nizatidine and neostigmine, but not NDM, at a subthreshold dose accelerated gastric emptying treated with a low dose of acetylcholine (0.1 mg/kg). Atropine (2 mg/kg, -30 min) did not modulate the gastroprokinetic action of nizatidine, but blocked that of NDM. These findings suggest that this noninvasive method may allow measurement of gastric emptying of solids accurately and that nizatidine and NDM facilitate gastric emptying probably mediated by a direct and/or an indirect (acetylcholinesterase inhibition) cholinergic mechanism.

Effect of nizatidine and ranitidine on 24 hour intragastric pH, pepsin, prostaglandin E2 and serum gastrin concentrations in healthy volunteers

In order to achieve possible greater therapeutic efficacy, ranitidine 300 mg bid (R2) may be given rather than 300 mg qhs (R1), or nizatidine 300 mg bid (N2) may be given rather than 300 mg qhs (N1). A randomized placebo-controlled crossover study was performed in six healthy volunteers (four males, two females) who ranged in age from 23 to 43 years, comparing R1, R2, N1 and N2 versus placebo (P), measuring 24 h intragastric pH by the aspiration technique, gastric juice pepsin and prostaglandin E2 (PGE2) concentrations, as well as serum gastrin concentrations. In all treatment groups, 24-h intragastric pH was higher than with P; the 24 h and daytime (0800-2200 h) pH was higher with N2 than with N1, but not with R2 versus R1. The percentage pH > or = 3 was greater with N2 than with N1 during the daytime. Night-time (2200-0800 h) and 24 h pepsin concentrations were higher in R2 than in R1, were similar in N1 and N2, and were lower in these treatment groups than in P. The gastric juice PGE2 concentration at night-time, but not at daytime, was increased in the four treatment groups compared with P. Despite the higher pH values at night-time in the treatment groups, the night-time concentrations of serum gastrin were unchanged, and yet during the daytime the higher values of pH were associated with increased gastrin concentrations when R2 or N2 were given, but not with R1 and N1. There was a negative correlation between intragastric juice pH and pepsin concentration during the daytime, and a positive correlation between pH and PGE2 concentration during the night-time. The slopes and y-axis intercepts between pH and pepsin or PGE2 concentrations differed between the placebo and the treatment groups, suggesting that these H2-receptor antagonists may have an effect on lowering pepsin and raising PGE2 concentrations in addition to their effects on pH. As the percentage of time over the 24 h period and night-time periods when the pH was greater than 3 was not different between ranitidine and nizatidine, the two regimens will likely have similar clinical efficacy.

Cimetidine inhibition of human gastric and liver alcohol dehydrogenase isoenzymes: identification of inhibitor complexes by kinetics and molecular modeling

Cimetidine, an H2-receptor antagonist, is one of the most commonly prescribed drugs in the world. It has been reported to increase blood alcohol concentrations in drinking individuals. To determine if this increase could be due to inhibition of alcohol dehydrogenase activity, the effect of the drug on ethanol oxidation by gastric sigma sigma alcohol dehydrogenase and liver beta 2 beta 2, pi pi, and chi chi alcohol dehydrogenase isoenzymes was observed. Cimetidine inhibited all isoenzymes studied except chi chi; the chi chi isoenzyme showed no inhibition up to 5 mM cimetidine. Inhibition of the alcohol dehydrogenase isoenzymes by the H2-receptor antagonists nizatidine, ranitidine, and famotidine was negligible. Docking simulations with the beta 2.NAD+.4-iodopyrazole X-ray structure indicated that cimetidine fit well into the substrate binding site. The substitution on the thiazole ring of nizatidine, however, prevented docking into the binding site. Cimetidine inhibition of ethanol oxidation by sigma sigma and beta 2 beta 2 was competitive with varied ethanol, exhibiting Ki values of 2.8 +/- 0.4 mM and 0.77 +/- 0.07 mM, respectively. Cimetidine inhibition of ethanol oxidation by pi pi was noncompetitive with varied ethanol (Ki = 0.50 +/- 0.03 mM). Inhibition of ethanol oxidation by sigma sigma and beta 2 beta 2 with varied NAD+ was competitive. These results, together with the cimetidine inhibition kinetics of acetaldehyde reduction by sigma sigma and beta 2 beta 2, with either varied NADH or varied acetaldehyde, are consistent with cimetidine binding to two enzyme species. These species are free enzyme and the productive enzyme.NAD+ complex.

Effects of oral nizatidine on preoperative gastric fluid pH and volume in children

We have studied the effect of oral nizatidine 6 mg kg-1 in total on preoperative gastric fluid pH and volume in children. One hundred and four healthy children, aged 4-11 yr, were allocated randomly to four groups (n = 26): placebo administered at 21:00 and 06:30 the night before and on the day of surgery, respectively (placebo-placebo: control); nizatidine 6 mg kg-1 at 21:00 and placebo at 06:30 (nizatidine-placebo); placebo at 21:00 and nizatidine 6 mg kg-1 at 06:30 (placebo-nizatidine); and nizatidine 3 mg kg-1 at 21:00 and 06:30 (nizatidine-nizatidine). Each child ingested a large volume of apple juice 3 h before estimated induction of anaesthesia. After induction of anaesthesia, pH and volume of gastric fluid obtained via an orogastric tube were measured. Mean pH in the placebo-nizatidine and nizatidine-nizatidine groups was significantly higher than that in the placebo-placebo group (5.7 (SEM 0.3), 6.0 (0.3) vs 1.8 (0.2), respectively) (P < 0.05). Mean pH in the nizatidine-placebo group was similar to that in the control group (2.3 (0.3) vs 1.8 (0.2)). The number of children with pH < 2.5 and volume > 0.4 ml kg-1 in the nizatidine-nizatidine (0%) and placebo-nizatidine (4%) groups was reduced compared with the control (46%) or nizatidine-placebo (38%) group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the H2-antagonists famotidine and nizatidine and the cytoprotectant misoprostol on human colonic and rat peritoneal mast cells

The H2-antagonists famotidine and nizatidine produced a dose-dependent inhibition of histamine release from human colonic mucosal and muscle mast cells stimulated with anti-IgE. The IC30 values were in the range 0.5-10 microM and the maximum inhibition approached 50%. The compounds showed similar efficacy against rat peritoneal mast cells but were more potent. The cytoprotectant misoprostol had a striking effect on the human colonic mast cells, producing more than 50% inhibition at concentrations of 0.1-1 nM, but was much less active against the rat cells.

H2-antagonists and alcohol. Do they interact?

There are conflicting data on the existence of significant first-pass metabolism of alcohol (ethanol) in the human stomach and its inhibition by histamine H2-receptor antagonists. Alcohol is predominantly metabolised in the liver by the microsomal alcohol oxidising system, alcohol dehydrogenase (ADH) and a catalase enzyme. Histochemical and kinetic studies have revealed several ADH isoenzymes in the gastric mucosa with different kinetic properties. After small oral doses of alcohol first-pass metabolism in the stomach occurs, as shown by reduced area under the plasma concentration-time curve (AUC) compared with intravenous or intraduodenal administration. The activity of gastric ADH is reduced in women, the elderly, Asian individuals, the fasting state, chronic alcoholism and after gastrectomy. The effect is only present with small (< or = 0.3 g/kg) alcohol doses and with a high alcohol concentration. In a number of studies, cimetidine in therapeutic doses over 7 days produced a significant increase in the AUC and in the peak plasma concentration after administration of alcohol 0.15 and 0.30 g/kg. This was related to an inhibition of gastric ADH activity, as shown by in vitro studies. Ranitidine inhibited gastric ADH to a similar extent on a molar basis, but its effect on alcohol levels in vivo was less constant in various studies. Nizatidine also reduced gastric alcohol first-pass metabolism, but famotidine and roxatidine did not show this effect. In other studies, H2-receptor antagonists did not change AUC and peak alcohol concentration. The controversy is not easy to resolve, since a number of the positive studies did not use a placebo-controlled, randomised, crossover design, while some of the negative studies did not exclude habitual alcohol consumers and included Oriental volunteers, although both groups have been shown to lack significant gastric ADH activity. In this case, when first-pass metabolism of alcohol does not exist, this by definition cannot be abolished by H2-antagonists. The inclusion of oral and intravenous dosage data of alcohol is mandatory to positively identify first-pass metabolism in any individuals. The significance of the effect of H2-antagonists on blood alcohol concentrations is minor. It only occurs in young, male, nonalcoholic, non-Asian individuals, and alcohol must be given in a small (social) dose, in a high concentration, and after meals. An increase in alcohol levels in predisposed patients during treatment with some H2-antagonists cannot be excluded, although the likelihood is small. Furthermore, carefully designed studies are needed to clarify fully the significance of this interaction.

Effect of nizatidine and ranitidine on the D-tubocurarine neuromuscular blockade in the toad rectus abdominis muscle

The influence of varying concentrations of the H2-receptor antagonists nizatidine and ranitidine on the acetylcholine- and carbachol-induced contractures on the toad rectus abdominis muscle, as well as the possible interaction between the above H2-receptor antagonists and D-tubocurarine were studied. Nizatidine and ranitidine at a concentration of 3.2 x 10(-4) mol l-1 augmented, and at 3.2 x 10(-3) mol l-1 inhibited, the acetylcholine-induced contractures on the toad rectus abdominis muscle, while at concentrations from 3.2 x 10(-4) to 3.2 x 10(-3) mol l-1 they inhibited the carbachol-induced contractures, in a concentration-dependent manner. In addition, nizatidine and ranitidine at a concentration of 3.2 x 10(-4) mol l-1 reversed the D-tubocurarine blocking activity on the acetylcholine-induced contractures, but at a concentration of 3.2 x 10(-3) mol l-1 they augmented it. These findings provide evidence that the above H2-receptor antagonists produce either cholinesterase inhibition or neuromuscular blockade, depending on their concentration. Thus, the D-tubocurarine neuromuscular blocking activity is potentiated at high concentrations of nizatidine and ranitidine, while it is reversed at lower ones.

Acid inhibitory characteristics of nizatidine in man: an overview

The antisecretory activity of nizatidine, an H2-receptor antagonist, has been extensively investigated in man both by quantitative acid secretory tests and by means of 24-h continuous ambulatory pH monitoring. Studies have shown that nizatidine is a potent inhibitor of basal, nocturnal and stimulated acid secretion. Particular modalities of nizatidine administration, such as early evening intake with supper or morning dosing, have been recently defined. Further studies are needed to clarify if rebound nocturnal acid hypersecretion may develop after abrupt withdrawal of nizatidine or if tolerance may develop during prolonged administration.

Drug interactions of H2-receptor antagonists

Three drug interactions of nizatidine and of other antisecretory agents were studied comparatively. First, the effects of nizatidine, cimetidine and ranitidine on the dispositional kinetics of theophylline were evaluated in chronic obstructive pulmonary disease (COPD) patients. Second, the effect of magnesium/aluminium hydroxide on the relative bioavailability of nizatidine, famotidine, cimetidine and ranitidine was evaluated in healthy volunteers. Finally, the effects of nizatidine and omeprazole on the dispositional kinetics of phenytoin were evaluated in healthy volunteers. Only cimetidine altered the steady-state kinetics of oral theophylline, slowing theophylline clearance by 25%. Each of the H2-receptor antagonists exhibited a modest decline in relative bioavailability when ingested with antacid. Antacid ingestion decreased the bioavailability of famotidine, ranitidine and cimetidine by 20-25%, and the bioavailability of nizatidine by 12%. Each of these effects was statistically significant. Finally, it was found that neither omeprazole nor nizatidine affected the single dose kinetics of phenytoin.

Absence of an inhibitory effect of omeprazole and nizatidine on phenytoin disposition, a marker of CYP2C activity

The effects of omeprazole (40 mg orally per day) and nizatidine (300 mg orally per day) on the disposition of phenytoin (4.5 mg kg(-1) p.o. single dose) were studied in 18 healthy, young adult males. Total and unbound plasma concentrations of phenytoin were measured for 48 h after each dose of phenytoin. Neither treatment altered the disposition kinetics of phenytoin, the hydroxylation of which is mediated specifically by cytochromes P450 of the 2C subfamily.

[Nizatidine: a meta-analytical study]

The medline database was applied to search all randomized clinical trials published from 1986 to 1992 concerning the use of Nizatidine, a powerful H2-antagonist, versus other treatments, including placebo, in the treatment of duodenal ulcer disease. Therapeutic efficacy of nizatidine is comparable to that of other H2-antagonists; with the use of meta-analysis, no significant differences were demonstrated, both in acute and long-term treatment of duodenal ulcer between nizatidine and ranitidine, but untoward side effects were less frequent with nizatidine than with ranitidine.

Changes in the effects of nizatidine and famotidine on cardiac performance after pretreatment with ranitidine

This was an open, randomized study of the cardiovascular effects of the histamine H2 receptor antagonists ranitidine, famotidine, and nizatidine after single oral doses alone or in combination in healthy volunteers. When compared with placebo ranitidine (450 mg) did not have any haemodynamic effects. Nizatidine (300 mg) caused significant falls in heart rate and cardiac output. Famotidine (40 mg) caused significant falls in stroke volume and cardiac output and an increase in pre-ejection period. Pretreatment with ranitidine abolished the haemodynamic effects of nizatidine and caused a time-shift of 2 h in the onset of the cardiovascular effects of famotidine. The difference in the results for nizatidine and famotidine can be explained by the longer half-life of famotidine. Vascular effects are assumed to be responsible for impairment of cardiac performance by famotidine.

[Effects of various histamine H2-receptor antagonists on gastrointestinal motility and gastric emptying]

Effects of various histamine H2-receptor antagonists (H2-RA) on gastrointestinal motility and gastric emptying were investigated. Ranitidine, nizatidine and cimetidine dose dependently induced contractions over the entire gastrointestinal tract, and the order of their effects was ranitidine > nizatidine > cimetidine. Roxatidine or famotidine had no effects on motility of the gastrointestinal tract. Ranitidine and nizatidine also induced contractions during the postprandial period and facilitated gastric emptying, while cimetidine, roxatidine or famotidine did not influence gastric emptying. Since acid reduction is thought to be the most important element of the treatment of peptic ulcer and reflux esophagitis, it was inferred that administration of a H2-RA selected with consideration of its property of facilitating gastrointestinal motility is effective in the treatment of patients with abnormal gastrointestinal motility.

Anti-oxidant properties of H2-receptor antagonists. Effects on myeloperoxidase-catalysed reactions and hydroxyl radical generation in a ferrous-hydrogen peroxide system

Ulcerogenesis of the gastroduodenal mucosa is caused by the digestive action of gastric juice and initially involves an inflammatory reaction with infiltration of phagocytes. The anti-inflammatory activity of many drugs have been attributed to the inhibition of the leukocyte enzyme, myeloperoxidase (MPO). In this study, the H2-antagonists in clinical use were found to be potent inhibitors of MPO-catalysed reactions (IC50 < 3 microM) under conditions resembling those in experiments with intact neutrophils. Since peak plasma concentrations of cimetidine, ranitidine and nizatidine are well within the micromolar range, after oral therapeutic dosing, our results may be of clinical relevance. The inhibitory actions of cimetidine and nizatidine were largely due to scavenging of hypochlorous acid (HOCl), a powerful chlorinating oxidant produced in the MPO-H2O2-Cl- system. In contrast to famotidine, ranitidine was also a potent scavenger of HOCl, while both drugs inhibited MPO reversibly by converting it to compound II, which is inactive in the oxidation of Cl-. The HOCl scavenging potencies of ranitidine and nizatidine were about three times higher than that of the anti-rheumatic drug, penicillamine, which had a potency similar to that of cimetidine. The rapid HOCl scavenging ability of penicillamine is thought to contribute to its anti-inflammatory effects. Using riboflavin as a probe, the H2-antagonists were found to be inhibitors of hydroxyl radical (.OH) generated in a Fe(2+)-H2O2 reaction mixture. Spectral analyses of the interaction of iron ions with the drugs and studies with chelators, suggest that the drugs were efficient chelators of Fe2+, in addition to their .OH scavenging abilities. Since the gastrointestinal tract can contain potentially reactive iron, the simultaneous presence of H2-antagonists may help to suppress iron-driven steps in tissue damage.

Dose-dependent heart rate reducing effect of nizatidine, a histamine H2-receptor antagonist

1. Twelve healthy subjects were treated in a randomised placebo-controlled crossover study with placebo, 150 mg, 300 mg, and 600 mg nizatidine, 100 mg pirenzepine, and 300 mg nizatidine plus 100 mg pirenzepine for 1 week each. 2. On the seventh treatment day, heart rate, blood pressure, systolic time intervals, impedance cardiographic and Doppler ultrasound variables were measured. 3. Stroke volume and blood pressure were not altered by nizatidine and/or pirenzepine. By contrast, heart rate and cardiac output significantly (P < 0.05) decreased in a dose-dependent manner 1.5 and 3 h after administration of 300 and 600 mg nizatidine. Treatment with 150 mg nizatidine led to similar though non-significant trends. 4. While a slightly insignificant rise in heart rate was detected with pirenzepine alone, heart rate and cardiac output remained unchanged upon combined nizatidine and pirenzepine treatment as compared with placebo and baseline values. 5. In conclusion, nizatidine reduced heart rate and cardiac output in a dose-dependent manner, whereas this negative chronotropic effect was counteracted by concurrent administration of the anti-cholinergic drug pirenzepine.

Histamine-2 receptor antagonists do not alter serum ethanol levels in fed, nonalcoholic men

OBJECTIVE

To determine whether the four histamine-2 receptor antagonists currently available for the treatment of acid-peptic disorders in the United States alter serum ethanol levels after moderate alcohol consumption.

DESIGN

Prospective, randomized crossover design comparing the effects of histamine-2 receptor antagonists and no treatment on serum ethanol levels. Each participant served as his own control.

PARTICIPANTS

Twenty-five healthy nonalcoholic men (21 to 35 years old); two participants were withdrawn before starting the study.

SETTING

University medical center.

INTERVENTION

Cimetidine (400 mg twice daily), famotidine (20 mg twice daily), nizatidine (150 mg twice daily), ranitidine (150 mg twice daily), and no treatment for 7 days. After the last dose of medication, participants ate a standard meal; 1 hour later they drank ethanol (0.3 g/kg body weight in 500 mL of orange juice) over 8 minutes.

MEASUREMENTS

Simultaneous measurements of breath and serum (headspace gas chromatography) ethanol were made before and 10, 20, 30, 45, 60, 90, 120, 150, and 180 minutes after ingestion of ethanol.

RESULTS

Peak ethanol levels did not differ (mmol/L; mean +/- SE) after cimetidine (3.0 +/- 0.3), famotidine (2.9 +/- 0.3), nizatidine (2.9 +/- 0.3), ranitidine (3.1 +/- 0.4), and no treatment (2.9 +/- 0.4). Similarly, there was no difference in the area under the curve (mmol/L.h; mean +/- SE) after cimetidine (4.3 +/- 0.5), famotidine (3.8 +/- 0.4), nizatidine (4.2 +/- 0.5), ranitidine (3.9 +/- 0.4), and no treatment (4.0 +/- 0.5).

CONCLUSIONS

In healthy nonalcoholic men, the histamine-2 receptor antagonists currently available in the United States do not alter serum ethanol levels following moderate alcohol consumption after an evening meal.

Early evening nizatidine intake with a meal optimizes the antisecretory effect

The importance of the temporal relationship between meal and nizatidine intake was studied in a six-armed, double-blind, placebo-controlled trial. Eleven healthy volunteers received early (18.00 hours) or late (21.00 hours) supper, with either placebo, early (18.00 hours) nizatidine, or late (21.00 hours) 300 mg nizatidine. Ambulatory 21-hour gastric pH-metry was performed and plasma nizatidine concentrations were determined by high pressure liquid chromatography. Early-nizatidine/early-supper (median pH 2.50), but not late-nizatidine/late supper (median pH 2.30), produced significantly higher median 21-hour pH values than did early-nizatidine/late-supper (median pH 1.90). Concomitant food delayed the absorption of nizatidine but did not change the drug's bioavailability. Oral nizatidine should be taken with food, preferably early in the evening, to optimize its anti-secretory effect.

Twenty-four-hour control of gastric acidity by twice-daily doses of placebo, nizatidine 150 mg, nizatidine 300 mg, and ranitidine 300 mg

This study was carried out to assess the effects on gastric acidity of placebo twice daily (bid), nizatidine 150 mg bid, nizatidine 300 mg bid, and ranitidine 300 mg bid by means of continuous 24-hour intragastric pH monitoring. Twelve patients with duodenal ulcer in remission were randomized to receive in single-blind fashion the above medications on four separate occasions, at least 1 week apart. The three active regimens produced higher pH values (P < .001) and maintained gastric pH above 3.0 units for a longer period (P < .001) than placebo in all time intervals but evening. Nizatidine 150 mg bid caused a lower rise in pH than nizatidine 300 mg bid (P < .01) and ranitidine 300 mg bid (P < .05) during both the daytime and the whole 24 hours. In these time windows also the time spent above 3.0 pH units was significantly shorter for the former regimen than for 300 mg bid of both nizatidine (P < .01) and ranitidine (P < .05). There was no difference between the latter two dosing schedules in terms of both potency and duration of action in all the time intervals considered. It is concluded that twice daily doses of H2 blockers are more effective than placebo in reducing gastric acidity. Three hundred milligrams twice daily of both nizatidine and ranitidine produce a significantly greater and longer-lasting acid suppression than 150 mg bid of nizatidine. Our study also confirms the greater effectiveness of H2 antagonists during nighttime than during day-time.

Gastroprokinetic activity of nizatidine, a new H2-receptor antagonist, and its possible mechanism of action in dogs and rats

We studied the anti-acetylcholinesterase (AChE) activity of a new H2-antagonist, nizatidine, in in vitro experiments and its gastroprokinetic action in the dog and rat in comparison with other H2-antagonists, neostigmine and cisapride. The IC50 of nizatidine for AChE was 6.7 x 10(-6) M, and this activity was reversible. The relative anti-AChE potency was in the following order: neostigmine > nizatidine > cimetidine >> famotidine. The inhibition of AChE by nizatidine was noncompetitive, with a Ki value of 7.4 x 10(-6) M. Gastrointestinal (GI) motility was examined during the interdigestive state in dogs with chronically implanted force transducers. Nizatidine (0.3-3 mg/kg, i.v.) significantly increased the motor index in a dose-dependent manner. It was of interest that the contractile response of the GI tract to nizatidine was similar to the interdigestive migrating contractions-like activity. At the doses used in this study, neither cimetidine nor famotidine had a significant effect on the motor index. Neostigmine at a higher dose of 0.06 mg/kg and cisapride at 0.3 mg/kg were found to stimulate GI contractions. Gastric emptying was determined in rats given phenol red as a liquid test meal. Nizatidine (3 mg/kg, i.p., or above) significantly increased gastric emptying, whereas the other H2-antagonists had no such effect. The ED50 and ED90 values of nizatidine for inhibition of gastric acid secretion were 0.18 and 3.22 mg/kg in dogs, and 2.94 and 19.6 mg/kg in rats, respectively. These findings suggest that nizatidine stimulates GI contractions and accelerates gastric emptying at gastric antisecretory doses.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of a single oral morning dose of nizatidine and ranitidine on intragastric pH under basal conditions and after pentagastrin stimulation

A comparison was made of the antisecretory activity of orally administered nizatidine and ranitidine by measuring intragastric pH under basal conditions and during and after pentagastrin stimulation. Intragastric pH values were measured with a bipolar glass electrode in 10 patients with healed duodenal ulcers treated with nizatidine or ranitidine according to a randomized single-blind design. The antisecretory activity of the two drugs was similar during the 4 h of monitoring following drug administration. Nizatidine, however, showed a more rapid inhibitory action than ranitidine, producing a significantly greater increase in pH with respect to basal values during pentagastrin infusion. In the period following infusion the pH values observed with ranitidine were higher than with nizatidine, but not significantly so. Under these experimental conditions, therefore, the antisecretory activity of nizatidine was shown to be more rapid than that of ranitidine and equally effective.

The effect of nizatidine on neuromuscular transmission

The effect of the H2-receptor antagonist, nizatidine, on neuromuscular transmission was investigated using sciatic nerve-gastrocnemius muscle preparations of rat in vivo. Nizatidine, administered by i.v. injection, potentiates the neuromuscular blockade induced by d-tubocurarine, pancuronium and the aminoglycoside antibiotic, kanamycin. Moreover, the drug alone is capable of producing a blockade on preparations stimulated at high frequency. The neuromuscular blockade induced by nizatidine is reversed by 4-aminopyridine but not by dimaprit.