Comparative investigation of the influence of nizatidine, ranitidine, and cimetidine on the steady-state pharmacokinetics of theophylline in COPD patients

The influence of usual regimens of the H2 blocking drugs, cimetidine, ranitidine, and nizatidine on the steady-state plasma concentrations and pharmacokinetic characteristics of theophylline was studied in seventeen patients with chronic obstructive pulmonary disease (COPD). Patients were dosed to steady-state with an oral, sustained-release formulation of theophylline given in therapeutic doses twice daily for 2 weeks. Over the next 4 weeks, each patient received a week-long regimen of each H2 blocker concomitantly with theophylline, and a week-long regimen of theophylline alone (control). At the end of each of the latter 4 weeks the steady-state pharmacokinetics of theophylline were assessed. Neither ranitidine nor nizatidine treatment altered the steady-state pharmacokinetics of theophylline relative to the control phase (i.e. no H2 blocker treatment). Values for theophylline C(ave), Cssmax, AUC0-12, and CLoral were significantly different during cimetidine treatment compared with all other treatments (ranitidine, nizatidine, and control). Cimetidine increased theophylline Cssmax, AUC0-12 and Cave by approximately 32%, and decreased theophylline oral clearance by approximately 23%. The authors conclude that cimetidine alters the steady-state pharmacokinetics of theophylline in COPD patients, whereas ranitidine and nizatidine are without effect.

Comparative Study of the H2-Receptor Antagonists Cimetidine, Ranitidine, Famotidine and Nizatidine on the Rabbit Stomach Fundus and Sigmoid Colon

The H2-receptor antagonists, cimetidine, ranitidine, famotidine and nizatidine, were tested for their effect on the isolated smooth muscle strips from the rabbit stomach fundus and sigmoid colon. These H2-receptor antagonists were found to possess a concentration-dependent contractile effect on the above smooth muscle preparations and the order of potency was: ranitidine = nizatidine > famotidine > cimetidine. In addition, the smooth muscle preparations from the sigmoid colon were significantly more sensitive to the above compounds than the smooth muscle preparations from the stomach fundus.

Rebound intragastric hyperacidity after abrupt withdrawal of histamine H2 receptor blockade

In a series of 24 hour studies, intragastric acidity and plasma gastrin concentration were measured simultaneously in 46 healthy subjects before, during, and 24 to 48 hours after abrupt withdrawal of a histamine H2 receptor antagonist regimen. For 34 days subjects were given either cimetidine 800 mg at night (n = 8), ranitidine 150 mg twice daily (n = 10), ranitidine 300 mg at night (n = 12), nizatidine 300 mg at night (n = 8), or famotidine 40 mg at night (n = 8). All subjects responded to H2 blockade by a decrease in 24 hour intragastric acidity. Withdrawal of H2 blockade resulted in a significant rise in median nocturnal integrated intragastric acidity in 42 of 46 subjects (+36%; 95% CI +19, +55%) compared with prestudy values, but this rise was not associated with a significant change in the median integrated plasma gastrin concentration (+1%; 95% CI -12, +13%). A statistically significant rise in nocturnal acidity was observed after all regimens, except after dosing with famotidine. After stopping, median daytime integrated acidity and plasma gastrin concentrations in the whole group were raised, but not significantly: values were +15% (95% CI +4, +34%) and +5% (95% CI -2, +12%), respectively. A statistically significant increase in daytime acidity was observed only after dosing with ranitidine. In conclusion, intragastric hyperacidity occurs in most subjects after abrupt withdrawal of a histamine H2 receptor blocker, but this phenomenon is not associated with hypergastrinaemia.

Effects of H2-receptor antagonists on gastric alcohol dehydrogenase activity

Inhibition of gastric alcohol dehydrogenase (ADH) activity by cimetidine results in elevated blood levels of ethanol after moderate consumption. To search for alternative H2-blockers lacking such an effect, we compared cimetidine, ranitidine, nizatidine, and famotidine. They inhibited rat gastric ADH noncompetitively, with a Ki for ethanol oxidation of 0.68 mM for cimetidine, 0.5 mM for ranitidine, 1 mM for nizatidine, and 4.5 mM for famotidine. These concentrations are higher than therapeutic plasma levels, but intracellular concentrations in the gastric mucosa (assessed with [3H]cimetidine and [14C]famotidine) were at least 10- and 2-fold greater than in the blood, respectively. These results suggests that, given at therapeutic doses in vivo, the degree of inhibition by cimetidine and ranitidine should be significant and comparable, that by nizatidine should be smaller, and that by famotidine should be negligible. These drugs also exerted either mixed or competitive inhibition of rat hepatic ADH, but the effects of cimetidine and famotidine were observed at concentrations unlikely to occur in vivo. Thus, in alcoholics and in social drinkers who require treatment with H2-receptor antagonists, famotidine might be preferable to the other H2 blockers tested.

Effects of various concomitant medications on gastric alcohol dehydrogenase and the first-pass metabolism of ethanol

Inhibition of gastric alcohol dehydrogenase (ADH) has been shown to enhance alcohol absorption in man under certain circumstances. To determine whether various medications might affect alcohol absorption, we screened 18 compounds for an effect on ADH. Salicylic acid, acetaminophen, propranolol, ethacrynic acid, and three H2-receptor antagonists all inhibited rat gastric ADH in vitro, indicating that several commonly used medications have the potential to enhance alcohol absorption. Of these, cimetidine, ranitidine, and nizatidine were studied further to define their effect on alcohol absorption in man and to assess the clinical relevance of the effect. Both ranitidine and nizatidine enhanced the absorption of small doses of alcohol (0.15 g/kg) in the morning by 63% and 64% and increased Cmax by 48% and 54% respectively (p less than 0.001), effects similar to those reported by others for cimetidine. The effect of ranitidine given before dinner was greatly attenuated with increases in Cmax of 8% (NS) and AUC of 21% (p = 0.02). Cimetidine 800 mg hs did not affect the absorption of 0.15 g/kg alcohol given in the evening, and cimetidine 400 mg bid decreased absorption by 14% (p = 0.11). Cimetidine 300 mg qid had no effect on larger doses of alcohol given at dinner. We conclude that many commonly used medications affect gastric ADH, but that the increase in the actual amount of alcohol absorbed is quite small, and demonstrable only under special conditions.

Comparison of the effects of oral nizatidine and ranitidine on gastric volume and pH in patients undergoing gynaecological laparoscopy

Ninety patients who presented for elective gynaecological laparoscopy as day cases were allocated at random to three groups and studied on a double blind basis to compare the effects of nizatidine, ranitidine or placebo on gastric secretion. All the patients received the active drugs or placebo orally at least 45 minutes before the induction of anaesthesia. After tracheal intubation gastric fluid was aspirated via an orogastric tube and the volume and pH of the aspirate were measured. Venous blood samples were obtained at the times of gastric sampling to determine the plasma levels of the drugs. The proportion of patients with both pH greater than 2.5 and volume less than 25 ml were 100%, 90%, and 92.9% in the nizatidine, ranitidine and placebo groups respectively. There was no difference in volume between groups. Two patients in the nizatidine group without a measurable aspirate had blood levels less than the therapeutic range. The median pH values in both treated groups were significantly greater than in the placebo group, but there were no differences between the two treated groups. There were 19 (67.8%) patients in the placebo group with pH less than 2.5. This was significantly higher than the 2 (7.4%) and 6 (20%) in the nizatidine and ranitidine groups respectively. When the time interval between drug administration and induction of anaesthesia was divided arbitrarily into 45-90 minutes and greater than 90 minutes, all the patients in the nizatidine and ranitidine groups with pH less than 2.5 were given the drugs in the 45-90 minute interval; this suggests a latent period is required before the gastric pH increases. Nizatidine may be an effective protective agent against acid aspiration syndrome.

Effects of successive doses of nizatidine, cimetidine and ranitidine on serum gastrin level and gastric acid secretion

Nizatidine (N-[2-[[[2-[(dimethylamino)methyl]- 4-thiazolyl]methyl]thio]ethyl]-N'-methyl-2-nitro-1,1-ethenediamine , CAS 76963-41-2) is a new histamine H2-receptor antagonist which shows suppression of gastric acid secretion and antiulcer activity. In the present experiment, the effects of single s.c. administration of nizatidine, cimetidine and ranitidine on serum gastrin levels were studied in fasted rats. Nizatidine at 100 mg/kg increased serum gastrin level 3 h after administration, which however, returned to basal level 6 h after administration. Cimetidine and ranitidine at respective doses of 250 and 100 mg/kg markedly increased serum gastrin levels 3 and 6 h after administration. In a previous study, the suppressive effect of nizatidine on basal gastric acid secretion was 82.8% at a dose of 100 mg/kg s.c. in rat pylrus-ligated model. On the basis of these findings, changes in basal gastric acid secretion and serum gastrin level after withdrawal of nizatidine, cimetidine and ranitidine administered for 14 consecutive days were studied. One day after withdrawal, nizatidine at 100 mg/kg showed a tendency to increase the basal gastric acid secretion. However, 3 and 7 days after administration, almost no changes were obtained. Cimetidine at 250 mg/kg showed a tendency to increase the basal gastric acid secretion 7 days after withdrawal of the drug. Ranitidine at 100 mg/kg induced no changes in basal gastric acid secretion after withdrawal. No obvious influences of all drugs on serum gastrin level after withdrawals were obtained. These results indicate that consecutive administration of nizatidine may cause only a transient increase of gastric acid secretion but no hypergastrinaemia after its withdrawal.

Effects of the new anti-ulcer drug nizatidine on prostaglandins in the rat gastric mucosa

The effects of nizatidine (N-[2-[[[2-[(dimethylamino)methyl]- 4-thiazolyl]methyl]thio]ethyl]-N'-methyl-2-nitro-1,1-ethenediamine , CAS 76963-41-2), a new histamine H2-receptor antagonist, on the content of prostaglandins (PGs) in the rat gastric mucosa at doses that inhibit basal gastric acid secretion were compared with those of two other histamine H2-receptor antagonists, cimetidine and ranitidine. Nizatidine did not inhibit basal gastric acid secretion at a dose of 0.4 mg/kg but showed dose-dependent inhibition at doses of 10, 30, and 100 mg/kg. This drug had no effects on the content of PG in the gastric mucosa when subcutaneously administered at doses of 0.4, 10, 30 and 100 mg/kg once daily for 5 days. Cimetidine and ranitidine administered at doses that markedly inhibit basal gastric acid secretion (250 and 100 mg/kg/d, respectively) had no effects on the content of PG in the gastric mucosa. On the other hand, nizatidine, cimetidine, or ranitidine at concentrations of 1-100 mumols/l did not inhibit in vitro PGE2 synthesis using sheep seminal vesicle microsomes. These results suggest that nizatidine did not affect in vitro PGE2 synthesis and even doses that markedly inhibit gastric acid secretion had no effects on the content of PGs in the gastric mucosa.

Rebound hypersecretion after H2-antagonist withdrawal--a comparative study with nizatidine, ranitidine and famotidine

Our previous study demonstrated rebound nocturnal acid hypersecretion after a 4-week course of nizatidine. Nocturnal acid output was increased by 77% two days after discontinuing treatment compared with pretreatment values. To confirm this effect with other H2-blockers we assessed daytime intragastric pH, fasting and meal-stimulated plasma gastrin and nocturnal acid output in 9 duodenal ulcer patients in remission before, during and two days after treatment with three different drugs. Each patient received 4-week courses of 300 mg ranitidine, 40 mg famotidine or 300 mg nizatidine, taken at 20.00 hours in randomized order with a 'washout' period of 4 weeks between each course of drug. Median nocturnal acid output (mmol/10 h) decreased during treatment with ranitidine to 3 (range 0-17), famotidine to 4 (1-12) and nizatidine 6 (0-40) compared with the respective pre-treatment values, 49 (20-126; P less than 0.01), 52 (22-105; P less than 0.01) and 32 (23-114; P less than 0.01). Two days after discontinuing treatment nocturnal acid output was increased after ranitidine at 77 (28-237; P less than 0.04) and after nizatidine at 64 (17-130; P less than 0.05) compared with pre-treatment values. There was no significant change in nocturnal acid output after famotidine at 57 (27-107) compared with the pre-treatment value. There was no change in daytime intragastric pH with any drug during or after treatment compared with the pre-treatment values. Fasting and meal-stimulated plasma gastrin concentrations were increased on the final treatment day with ranitidine and famotidine but had returned to pretreatment levels two days after treatment. The rebound acid hypersecretion may contribute to the high ulcer relapse rate after discontinuation of H2-receptor antagonists.