Cimetidine suppression of nocturnal gastric secretion in active duodenal ulcer

A Prospective Review of Cimetidine use

A prospective-drug-use analysis was conducted on the first 60 patients receiving cimetidine in a general hospital. Only 18 percent had FDA-approved cimetidine indications, although another 62 percent received the drug for reasons supported by the medical literature. Other than a few cases of use for inappropriate reasons, the major limitation was that almost all patients received intensive antacid therapy along with cimetidine before being given an adequate trial with either drug alone. Thus, an assessment of cimetidine's efficacy was impossible.

Fluctuation in therapeutic control associated with interchange of prednisolone tablet formulations: assessment of bioequivalence by dissolution test

A 47-year-old woman received combination therapy with prednisolone (PSL), danazol, cepharanthin, ascorbic acid, and cimetidine for the treatment of idiopathic thrombocytopenic purpura. The platelet count was well controlled for over 1 year. Then the PSL tablet formulation was altered from Tablet A to Tablet B with the same treatment regimen, but the platelet counts fell drastically thereafter. However, the platelet counts recovered by changing the PSL tablet formulation back from Tablet B to Tablet A. In vitro dissolution testing was undertaken to assess bioequivalence between Tablet A and Tablet B. PSL in Tablet B was released more slowly compared with that in Tablet A regardless of the medium pH conditions, and the difference in the release rate between the two tablet formulations increased with increasing medium pH value. The difference exceeded the allowance limit (15%) for judgment of bioequivalence under conditions above pH 4, indicating that Tablet A and Tablet B might be nonbioequivalent. The intragastric pH of the patient was probably raised due to coadministration of cimetidine. Therefore the present results suggest that the disparity in the immunosuppressive effects between the two PSL tablet formulations was attributable to the difference in their dissolution behavior in the gastrointestinal tract. We consider that it is better to avoid interchanging PSL tablet formulations in clinical practice.

Novel oral medication delivery system for famotidine

A famotidine wafer that rapidly disperses on the tongue without water is a novel alternative to other histamine2 (H2)-antagonist dosage forms. Benefits associated with such a dosage form include convenience and potentially improved compliance for patients who dislike or have difficulty taking tablets and capsules. This report describes the research of three studies on the famotidine wafer dosage form. In the first trial, the bioequivalence and tolerability of the new 40-mg famotidine wafer and the marketed 40-mg famotidine tablet were studied in a 2-period crossover study (n = 18). The two formulations were bioequivalent as assessed by area under the plasma concentration versus time curve and maximum plasma concentration of famotidine. The plasma concentration of famotidine associated with 50% inhibition of pentagastrin stimulated gastric acid secretion (EC50; 10 ng/mL) was attained on average within 0.5 hours post-dose for the wafer and tablet. In a second trial, the tolerability of the famotidine 20-mg and 40-mg wafers or placebo given twice daily (bid) for 14 days were evaluated (n = 192). Both wafer strengths were well and equally tolerated. In a third trial of 450 subjects, the 40-mg wafer was preferred over tablets by 75% of the subjects, when they were asked to consider the method of administration and flavor. When used as an alternative to tablets and other conventional dosage forms, the wafers have the potential therapeutic benefit of improved compliance. It is concluded that similar systemic exposure, excellent tolerability, palatability, and preference make the famotidine wafer a clinically acceptable and convenient dosage from for patients on H2-antagonist therapy.

Effect of Histamine H2Receptor Antagonists on the Secretion of Cerebrospinal Fluid in the Cat

Following a recent report that epithelial cells of the choroid plexus possess histamine H2 receptors, the effect of cimetidine and ranitidine, histamine H2 receptor antagonists, on the secretion and electrolyte content of CSF was examined. Fifty cats were divided into one control (n = 6) and six experimental groups. CSF was collected by puncture of the cisterna magna following pentobarbital anesthesia, and its volume, concentrations of Na+, K+, Cl-, and pH were determined. Cimetidine or ranitidine (50, 20, or 10 mg/kg) was injected intravenously 2 h after the start of the test, and their concentrations were measured in hourly blood samples and in 30-min aliquots of CSF in the 50 mg/kg experimental groups. Whereas the secretion of CSF did not change over 6 h in the control group, it decreased significantly by 30-60 min after injection of cimetidine or ranitidine and remained low for the following 6 1/2 h in all experimental groups except the 10-mg ranitidine group. Peak cimetidine and ranitidine concentrations in CSF in the 50-mg experimental groups were noted 60 and 90 min, respectively, after intravenous injection. CSF electrolyte concentrations and pH did not change during the test in any group. We conclude that intravenous cimetidine or ranitidine can significantly reduce CSF secretion in the cat, possibly by competitive inhibition of the histamine effect on H2 receptors located on the choroid plexus epithelial cell, or by a direct effect on the capillaries of the choroid plexus.

Determination of cimetidine and related impurities in pharmaceutical formulations by high-performance liquid chromatography

The analytical characteristics of cimetidine tablets were studied. A high-performance liquid chromatographic method was developed in order to assay cimetidine and its related impurities simultaneously. A reversed-phase system and diode-array detector were used.

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.

Effects of low-dose cimetidine on nocturnal acid secretion in healthy subjects

The effects of 100 mg and 200 mg bedtime doses of cimetidine on nocturnal gastric acid secretion were examined in nine healthy subjects in a double blind, placebo controlled, randomised three way crossover study. Treatment was given at 23.00 hours and the gastric contents continually aspirated from midnight until 07.00 hours the following morning. Hourly aliquots were analysed for pH and acid output. Relative to placebo the 100 mg and 200 mg doses of cimetidine respectively increased mean pH by 2.22 and 2.63 units/h (P less than 0.001) with mean acid output decreasing by 0.95 and 0.98 mmol/h (P less than 0.001). Whilst mean pH was higher and mean acid output was lower for 200 mg cimetidine compared to 100 mg cimetidine the difference was not statistically significant. Mean hourly pH was consistently above pH 3 for 100% of the time for both doses of cimetidine whereas mean pH failed to reach this value at anytime on placebo. Low doses of cimetidine taken at bedtime effectively reduced nocturnal gastric acid secretion in healthy individuals.

The pharmacology of antiulcer drugs

The use of medications for the treatment of gastrointestinal ulcers has evolved to a great extent since the early days of therapy with diet and antacids. Today a number of different agents are available to treat the causative factors of ulcer formation. Currently, antacids, histamine2-receptor antagonists, and sucralfate are considered frontline therapies suitable for most patients. The future also looks promising for newer agents, such as omeprazole and prostaglandin analogs. The purpose of this article is to provide practitioners with an understanding of the achieved more efficiently and effectively.

Rebound nocturnal hypersecretion after four weeks treatment with an H2 receptor antagonist

Daytime intragastric pH, fasting and meal stimulated serum gastrin and nocturnal acid output were studied in eight male duodenal ulcer patients before, during and two days after completing nizatidine 300 mg nocte (20:00 h) for four weeks. Median nocturnal acid output (mmol/10 h) decreased during treatment to 11.6 (range 0.4-26.7) compared with pretreatment value of 39.4 (9.8-91.2); median acid inhibition 77% (p less than 0.01) which was strongest between 24:00 and 04:00 h. Two days after discontinuing treatment, nocturnal acid output increased to 74.1 (11-181). Compared with the pretreatment value this represents median rebound hypersecretion of 77% (p less than 0.05), caused by increased H+ concentration and volume of secretion. Overall median daytime intragastric pH (09:00-21:00 h) was unchanged on the final day of treatment and two days after completing therapy, compared with the pretreatment values. Fasting serum gastrin measured between 09:30 and 10:00 h and the integrated gastrin response to an OXO breakfast taken out at 10:00 h were also similar during and after treatment, compared with pretreatment values. The rebound nocturnal hypersecretion may be relevant to the high ulcer relapse rates after stopping H2 receptor antagonists.

Parietal cells in duodenal ulcer disease: a histochemical study of the effects of omeprazole and ranitidine on mitochondrial activities

H2-Receptor antagonists and omeprazole, a H-K ATPase inhibitor, inhibit acid secretion from the parietal cells. The ultrastructural changes of the parietal cells after treatment have been described, but the changes in the mitochondrial activity which reflect the energetic metabolism were not well defined. To study the effect of omeprazole and H2-receptor antagonists on the mitochondrial activity of the parietal cells, endoscopic biopsies were taken from nine patients with duodenal ulcer before and after treatment with either 10 mg or 20 mg omeprazole each morning, or 150 mg ranitidine twice daily for 2 weeks, given in a double-blind randomized manner. Three patients with healed duodenal ulcer who were on maintainence treatment with 150 mg ranitidine nightly for 1 year had an endoscopy performed after 4 and 12 months and two non-ulcer dyspeptic patients were recruited as controls. Three biopsies were taken during each endoscopy from the body of the stomach. The mitochondrial activity was assessed by the reaction of succinic dehydrogenase with nitroblue tetrazolium and of cytochrome oxidase with naphthoic acid mixed with N-phenyl-p-phenylenediamine, according to the intensity of the staining reaction. After treatment with omeprazole or ranitidine, the mitochondrial activity decreased appreciably and returned to the pretreatment level on cessation of treatment. Patients on maintainence ranitidine showed decreased mitochondrial activities after 4 months, which, however, returned to pretreatment levels in two patients. It is concluded that short-term treatment with omeprazole or ranitidine resulted in reversible suppression of mitochondrial activity while long-term treatment with ranitidine resulted in an initial suppression followed by a tendency to return to pretreatment level despite continued treatment.

Plasma prolactin, sex steroids and gastrin in human volunteers treated for 2 weeks with therapeutic doses of cimetidine or the new histamine H2-receptor antagonist ramixotidine (CM 57755A)

Three groups of eight healthy male volunteers received placebo for 2 days, then daily morning doses either of cimetidine 800 mg, ramixotidine 750 mg (CM 57755A), or placebo, for 14 days, and then were all returned to placebo for one more day. Plasma levels of prolactin, testosterone and 17 beta-estradiol were measured on Days 2, 3, 16 and 17 in blood samples taken 30 and 15 min before and 0, 60, 120, 180, 240 and 300 min after treatment. Gastrin was assayed in blood collected on the same days 180 min after treatment. Mean pre- and post-treatment areas under the time-concentration curves of the first three hormones were not significantly different in the three groups on any test day, or within the same group throughout the four test days. Mean plasma gastrin levels ranged between 27 and 42 pg/ml, respectively, in the placebo and cimetidine treated groups on test day 3, and intermediate values were found in the group receiving CM 57755A. There was no statistically significant difference in gastrin level between the groups on any test day or within the same group throughout the four test days. No subjective side-effects attributable to the treatments were reported, and there were no abnormalities in blood pressure, heart rate or standard laboratory tests.

Pharmacodynamics and pharmacokinetics of parenteral histamine (H2)-receptor antagonists

Parenteral histamine (H2)-receptor antagonists are frequently used to prevent upper gastrointestinal bleeding caused by stress-induced gastric mucosal damage in critically ill patients. It is generally agreed that the goal of therapy in this syndrome is the consistent elevation of gastric pH levels above a certain value, often set at 4, in order to prevent the underlying mucosal damage from progressing to bleeding. The three H2-receptor antagonists currently available in a parenteral form and suitable for this mode of prophylaxis are cimetidine, ranitidine, and famotidine. The pharmacodynamic and pharmacokinetic properties of these agents, as they relate to their use in prevention of stress ulceration bleeding, are discussed here. These agents are more noted for their pharmacodynamic and pharmacokinetic similarities in acid suppression, elimination, and metabolism than for their differences. Ranitidine and famotidine are more potent than cimetidine, and famotidine has a slightly longer half-life than do cimetidine and ranitidine, but current dosing recommendations take these differences into account so that the agents have equivalent efficacy. Cimetidine and ranitidine have been widely used in this application. Less experience has been obtained, to date, with famotidine. Recent studies with primed, continuous infusions of cimetidine indicate that dosing schedule may be the key to obtaining better efficacy in prophylaxis of stress-related mucosal damage. Similar studies with ranitidine have not yielded results as promising as those with cimetidine, however, and few data are available on famotidine.

Comparison of two antimuscarinic drugs, pirenzepine and propantheline, on gastric acid secretion, serum gastrin concentration, salivary flow and heart rate in patients with duodenal ulcer disease

Effects of orally-administered pirenzepine and propantheline bromide on food-stimulated gastric acid secretion, serum gastrin concentration, salivary flow and heart rate were compared in 10 duodenal ulcer patients in a placebo-controlled, double-blind study. Pirenzepine inhibited acid secretion by 25, 36 and 44% at doses of 50, 100, and 150 mg, respectively, while propantheline inhibited acid secretion by 32 and 41% at doses of 15 and 45 mg, respectively. None of the doses of pirenzepine affected food-stimulated serum gastrin concentrations, whereas 45 mg propantheline increased serum gastrin concentration significantly above placebo control. Enhancement of gastrin release by propantheline was not due to its antisecretory effect since intragastric pH after the meal was held constant at 5.0 by intragastric titration in vivo. Pirenzepine had no significant effect on heart rate and little or no inhibitory effect on salivary volume, depending on the dose administered. By contrast, both doses of propantheline increased heart rate and reduced salivary volume significantly (P less than 0.05). Thus, pirenzepine and propantheline in the doses administered inhibited acid secretion to approximately the same extent but pirenzepine had fewer effects on other organs.

Effect of bedtime ranitidine on overnight gastric acid output and intragastric pH: dose/response study and comparison with cimetidine

A dose/response study has been carried out in seven patients with endoscopically proven duodenal ulcers in symptomatic remission, measuring intragastric pH and gastric acid output overnight after a bedtime dose of ranitidine (75 mg, 150 mg, and 300 mg); and the results have been compared with placebo and with bedtime cimetidine 400 mg. The currently recommended ranitidine maintenance dose (150 mg) was the optimum because it was significantly more effective than ranitidine 75 mg in terms of intragastric pH but not of acid output, and there was no difference from 300 mg in terms of either measurement. It was also significantly more effective than the currently recommended cimetidine maintenance dose (400 mg) in terms of inhibiting overnight acid output (92% vs 80% inhibition, p less than 0.05), and of maintaining intragastric pH above 5 (100% vs 17% of the overnight period, p less than 0.001).

Gastroesophageal reflux disease. Acute and maintenance treatments with cimetidine

The comparative efficacy of a 12-week acute treatment with 800 and 1600 mg cimetidine daily and the effectiveness of a 400-mg single-dose maintenance treatment versus placebo lasting 6 months were studied in a double-blind fashion in 30 and 24 patients, respectively, with gastroesophageal reflux (GER) disease. Cimetidine in a dose of 800 or 1600 mg daily resulted in a significant symptomatic improvement and a decrease in the extent of endoscopic esophagitis. An improvement in the gastroesophageal sphincter function during treatment was suggested by a significant decrease in the frequency of reflux, as evaluated by isotope scintigraphy. No significant differences were found between the two doses of cimetidine. The overall initial improvement tended to be maintained during maintenance treatment, but no significant differences were found between cimetidine and placebo. The present study thus supports the use of 800 mg of cimetidine daily for short-term treatment of GER disease but provides no support for maintenance treatment with a low dose. The study further suggests that cimetidine treatment, by reducing the tendency to GER, may induce long-lasting remission of the disease.

Effects of oral cimetidine on plasma concentrations of phenylbutazone in horses

Phenylbutazone was administered to six Thoroughbred horses in a cross-over study in which the horses received cimetidine pretreatment or no cimetidine pretreatment. Blood samples were collected at various times for 48 h after phenylbutazone administration and the plasma was analysed for phenylbutazone. Cimetidine pretreatment elevated phenylbutazone plasma concentrations during the first 8 h after phenylbutazone administration. The absorption rate, maximum phenylbutazone plasma concentrations and AUC were significantly greater with cimetidine pretreatment. The half-life of phenylbutazone did not change with cimetidine pretreatment; however, lower plasma concentrations of the metabolite gamma-hydroxyphenylbutazone were observed with cimetidine pretreatments. Plasma concentrations of the metabolite oxyphenbutazone were unchanged with cimetidine pretreatment compared to control values. Twenty-four-hour plasma concentrations of phenylbutazone were not different from control values with cimetidine pretreatment. This study suggests that concurrent treatment with cimetidine and phenylbutazone 24 h before race time does not result in elevations of plasma phenylbutazone concentrations above control values.

Misoprostol, a synthetic PGE1 analog, in the treatment of duodenal ulcers. A multicenter double-blind study

Misoprostol, a synthetic analog of prostaglandin E1, inhibits gastric acid production and is cytoprotective at doses well tolerated by patients in preliminary trials. This multicenter double-blind study was performed in out-patients with endoscopically demonstrated duodenal ulcers, to compare the efficacy in ulcer healing and the safety of two dosages of misoprostol and placebo. Up to six antacid tablets daily were permitted for pain. 308 patients enrolled and were randomized to three treatment groups: placebo, misoprostol 50 micrograms and misoprostol 200 micrograms. After two weeks of treatment, the three groups had similar percentages of patients with complete ulcer healing. However, after four weeks, 76.6% of patients taking misoprostol 200 micrograms q.i.d. had complete healing, compared with 42.6% on misoprostol 50 micrograms q.i.d. and 51% on placebo (P less than 0.001, 200 micrograms versus placebo). Patients taking misoprostol 200 micrograms used less antacid than the others. Diarrhea, mild and self-limiting, was present in 13% of the 200 micrograms group versus 5% on placebo. We conclude that misoprostol 200 micrograms q.i.d. is effective, safe and well tolerated in the treatment of duodenal ulcers.

Anti-ulcer therapy. Past to present

Until 1950 the clinical treatment of peptic ulcer disease relied on dieting and antacids. However, recent controlled studies suggest that the natural course of peptic ulcer disease is not affected by diet. Antacids are primarily used to relieve distress, although high- and low-dose antacid regimens have been reported to promote duodenal ulcer healing. Initial favorable reports following the introduction of synthetic anticholinergic drugs have not been confirmed. Pirenzepine is an anticholinergic compound with a specific action on the muscarinic receptors of the parietal cells. Although pirenzepine appears effective in peptic ulcer, the results obtained in different centers have not been uniform. Sucralfate and tripotassium dicitrato bismuthate both act locally by coating the ulcer crater, the latter agent also liberating prostaglandins. Most prospective studies suggest that both drugs are effective when compared with placebo. Carbenoxolone heals 70% of gastric ulcers but is less effective against duodenal ulcers, and has a high incidence of side-effects. Treatment of peptic ulcer in the 1980s has been dominated by the advent of the H2-blockers, cimetidine and ranitidine. Peptic ulcer healing rates are similar with both drugs, and the main problem is how often and how much should be given in order to provide acceptable healing and to prevent ulcer recurrence. Other H2-blockers are being tested and they may be more effective either by healing more ulcers or healing them earlier. The clinical treatment of peptic ulcers will in future be advanced by the addition of two new classes of drugs, the prostaglandins and the benzimidazole derivatives, which are currently being investigated and appear extremely promising.

Omeprazole inhibition of nocturnal gastric secretion in patients with duodenal ulcer

We studied the effect of single 08.00 h doses of omeprazole or placebo on gastric acid secretion during the following night, 14 to 23 h after administration, in seven male subjects with duodenal ulcer. The drug was given orally, double-blind, in randomized order. Omeprazole 20 mg, 40 mg and 80 mg reduced mean total overnight acid output by 43%, 73% and 91% respectively and median pH increased from 1.4 with placebo to 1.6, 3.1 and 7.0 respectively. The inhibitory effect was maintained throughout the study period. No clinical side effects or abnormalities of laboratory screening tests were seen. Omeprazole is well tolerated and administration at 08.00 h produces prolonged dose related inhibition of acid output during the following night.

Radionuclide imaging of Meckel's diverticulum: cimetidine versus pentagastrin plus glucagon

The aim of this study was to investigate the effects of prior administration of cimetidine in radionuclide imaging of Meckel's diverticulum. In three groups of seven rats with artificial Meckel's diverticulum, containing ectopic gastric mucosa, the effects of pentagastrin + glucagon plus 99mTc-pertechnetate, as well as cimetidine premedication plus 99mTc-pertechnetate, and 99mTc-pertechnetate alone were compared to attain improved radionuclide imaging of Meckel's diverticulum. This experimental model suggests that the use of cimetidine seemed to have some advantages: (a) nontarget (intestinal) radioactivity was diminished by cimetidine, (b) the target to nontarget (Meckel's diverticulum to intestinal activity) ratio increased with cimetidine pretreatment. This resulted in an enhanced accumulation of pertechnetate in the ectopic gastric mucosa, and reduced excretion of the radionuclide into the lumen. Consequently, better scintiphotograms and a low rate of false results added to the validity of this method.

Twice-daily cimetidine does not increase gastric bacterial flora

Thirty patients with peptic ulcer (20 duodenal, 10 gastric) underwent glucose-hydrogen (H2) breath tests before and after 6 weeks treatment with cimetidine, 400 mg twice daily. For the group as a whole, basal breath H2 and integrated H2 output over a 2.5 hr test period was unchanged by cimetidine treatment. We conclude that there was no evidence of significant gastric bacterial colonization following twice daily cimetidine treatment.

Cimetidine in anesthesia: does it minimize the complications of acid aspiration?

The use of cimetidine, an H2-receptor antagonist, to minimize the complications of acid aspiration pneumonia is reviewed. Since Mendelson's early description of acid aspiration in 66 obstetrical patients, attempts have been made to decrease gastric acidity by administering perioperative antacids and/or antihistamine drugs such as atropine and glycopyrrolate. In this review of the literature, strict attention is given to study design and subject selection, methods of collecting gastric samples and reporting both pH and volume measurements, and medications taken on admission, given preoperatively, and as anesthetics. Clinical trials evaluating cimetidine alone and compared with other prophylactic regimens were reviewed, detailing the timing, route, and frequency of drug administration. Cimetidine appears to be effective in minimizing complications of acid aspiration since gastric acidity (pH less than 2.5) is a contributing factor in both the morbidity and mortality of this disease state. In general terms, cimetidine 300 mg po 1.5-2.0 h prior to intubation or 45-60 minutes iv before surgery will decrease gastric acidity below the critical level. This effect may be maintained for up to three hours. Perioperative cimetidine administration, to minimize the complications of acid aspiration, appears to be safe in terms of drug-drug interactions and effects on labor, the fetus, and the newborn child.

Daytime acid secretion after a single dose of ranitidine and cimetidine--a double blind crossover study

The purpose of the study was to evaluate the duration of inhibition of acid secretion by single oral doses of cimetidine and ranitidine. Basal and postprandial acid secretion in 6 healthy volunteers were measured for 14h by intermittent aspiration and prolonged intragastric titration. 400 mg cimetidine reduced daytime acid secretion by 22% and 150 mg ranitidine produced 38% inhibition. Although the elimination half lives of the drugs were similar, ranitidine led to more pronounced inhibition of acid secretion during the later part of the day. The longer duration of pronounced acid inhibition by ranitidine appears to be due solely to its greater potency.

Cimetidine or vagotomy? Comparison of the effects of proximal gastric vagotomy, cimetidine and placebo on nocturnal intragastric acidity and acid secretion in patients with cimetidine resistant duodenal ulcer

Nocturnal pH, acid output and volume of gastric secretion have been measured in a group of patients who were referred for surgery because of a poor clinical response to cimetidine. Patients were studied after no treatment, cimetidine 1 g/day and proximal gastric vagotomy. Although pH and acid output were controlled better with cimetidine than no treatment this was not true for volume of secretion. Vagotomy was significantly better than cimetidine in controlling pH, acid output and volume of gastric secretion. The results suggest that cimetidine non-responders should have a good result from proximal gastric vagotomy, making more radical forms of gastric surgery unnecessary.

Clinical pharmacokinetics of cimetidine

Cimetidine is the first histamine H2-receptor antagonist with wide clinical application. It is a weak base and a highly water-soluble compound which can be measured in biological fluids by a number of high-pressure liquid chromatographic methods. Following intravenous administration, the plasma concentration profile follows multicompartmental characteristics. The total systemic clearance is high (500 to 600 ml/min) and is mainly determined by renal clearance. The volume of distribution (Vd beta or Vdss) is of the order of 1 L/kg and this about equals bodyweight. Elimination half-life is approximately 2 hours. Following oral administration of cimetidine, 2 plasma concentration peaks are frequently observed, probably due to discontinuous absorption in the intestine. The absolute bioavailability in healthy subjects is about 60%. In patients with peptic ulcer disease, bioavailability is around 70%, but the variation is much greater than in healthy subjects. Absorption and clearance of cimetidine are linear after 200 and 800mg doses. Mean steady-state plasma concentrations on a standard 1000mg daily dose are 1.0 microgram/ml (range 0.64-1.64 micrograms/ml) and are reproducible after treatment periods of up to 2 years. When taken with food, the extent of absorption is unaltered, but a delay occurs and only 1 peak in the plasma concentration curve is apparent. Partial gastrectomy (Billroth I, II) causes an increase in systemic availability of cimetidine by an unclear mechanism. Distribution of cimetidine leads to extensive uptake into kidney, lung and muscle tissues. It distributes into the cerebrospinal fluid (CSF) at a ratio of 0.1 to 0.2 compared with plasma. The mean saliva to plasma ratio is 0.2 (range 0.1-0.55). Plasma protein binding is 20%, and there is no relevant effect of changes in binding on the pharmacokinetics of cimetidine. Uptake of cimetidine into red blood cells leads to concentrations equal to those in plasma. Between 50 and 80% of the dose administered intravenously is recovered in urine as unchanged cimetidine. This fraction is less after oral doses, but is independent of the amount of the dose. In ulcer patients, 40% is recovered unchanged in urine after oral administration. Biliary excretion of cimetidine accounts for only 2% of the dose.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cimetidine and oxmetidine on 24-h gastric acid and pepsin in patients

The 24-h intragastric pH, titrated hydrogen ion concentration, and pepsin concentration were studied in nine peptic ulcer patients during administration of placebo and of 800 mg cimetidine given as two or four equal doses. Cimetidine, 400 mg twice daily, was more effective in reducing acidity during morning (p less than 0.05) and overnight (p less than 0.01) than cimetidine, 200 mg four times daily, which, however, was the most effective regimen during the afternoon (p less than 0.05-0.01). During the 24-h period pH values equal to or above 5 were observed for less than 1 h with placebo treatment, for 1.8 h with cimetidine, 200 mg four times daily, and for 4.7 h with cimetidine, 400 mg twice daily. A new histamine H2-receptor antagonist, oxmetidine, was studied in six other patients, also during a 24-h period. Both 400 mg twice daily and 200 mg four times daily of oxmetidine were superior to placebo (p less than 0.05) in reducing intragastric acidity during the entire 24-h period.

Intragastric nitrites, nitrosamines, and bacterial overgrowth during cimetidine treatment

A six week course of cimetidine (1 g/day) healed peptic ulcers in 20 of 23 patients (14 with duodenal ulcer, nine with gastric ulcer). Reduction of basal acid output by 73% and peak acid output by 36% led to a rise in concentrations of intragastric aerobic bacteria and nitrate-reducing bacteria. While the mean intragastric concentration of nitrate was unchanged by treatment, there were statistically significant rises in nitrite and N-nitrosamine concentrations. The conversion from nitrates to nitrites was closely related to the occurrence of nitrate-reducing bacteria. In three patients the intragastric milieu had returned to normal two months after cimetidine treatment had been discontinued. Mean nitrite and N-nitrosamine concentrations did not return to pre-treatment levels in the group of eight patients who remained on maintenance cimetidine (0.4 g at night-time) for three months after the full dose treatment. This study shows that cimetidine treatment can create an intragastric milieu resembling that of atrophic gastritis. Large scale and long-term studies are necessary to establish whether these findings have any clinical significance.

The effect of cimetidine on basal gastric acid secretion in the rat

1. The effect of cimetidine on the basal gastric acid secretion of the rat has been investigated in an anaesthetized lumen-perfused preparation. 2. Six rats previously given large doses of cimetidine orally showed no significant difference in basal gastric acid secretion when compared with six control rats. 3. Intravenous administration of 1 mg and 8 mg of cimetidine failed to inhibit significantly basal gastric acid secretion. 4. Although rats with a basal gastric acid secretion above 2.5 micro Eq/10 min. showed a consistent small reduction in basal gastric acid secretion after intravenous cimetidine, this was not seen in rats with a basal gastric acid secretion below 2.5 micro Eq/10 min. 5. THese results contrast sharply with the pronounced inhibition of basal gastric acid secretion by cimetidine in man and the possible reasons for this are discussed. 6. The results are also contrasted with previous work on gastric fistula rats which showed higher basal gastric acid secretion and significant inhibition by cimetidine.

Role of H2-receptors in gastrogenic hyperglycemia and hyperinsulinemia in dogs

Recent studies have demonstrated that an acidified liver meal stimulates insulin release and raises plasma glucose levels. To examine the mechanism of these changes, a liver extract test meal at either pH 7 or at pH 2 was instilled into the stomach of dogs with a bisected pylorus and a gastric fistula during the infusion of either cimetidine, a specific H2-receptor antagonist, or a saline control. In response to the meal at pH 2 insulin, glucagon and glucose levels rose significantly and were not significantly changed by the infusion of cimetidine. In response to the liver meal at pH 7 a late rise in plasma glucagon levels was observed while plasma insulin and glucose did not change significantly; however, during the infusion of cimetidine a significant rise in plasma insulin and glucose levels occurred. The present data suggest that H2-receptors participate in an inhibitory mechanism with respect to the insulin and glucose response during the gastric phase of a neutral meal, but they do not seem to be involved in the rise in insulin and glucose observed in response to an acidified gastric meal.

Cimetidine as an oral antacid before elective Caesarean section

The H2-receptor antagonist cimetidine was used as a pre-operative antacid in 64 women scheduled for elective Caesarean section. All were given cimetidine 400 mg 90-215 minutes before induction, with 20 of them having an extra 400 mg dose the previous night. The intragastric pH at induction of anaesthesia was reliably above 2.5 if the treatment was given 90-150 minutes beforehand. The volume of gastric contents was reduced when compared with a control series of women receiving either no pre-operative antacid or 30 ml magnesium trisilicate mixture BPC. No adverse effects on mothers or infants were detected.

Nocturnal gastric acid secretion in duodenal ulcer: inhibition by cimetidine

The inhibitory effect of cimetidine 200 mg, cimetidine 400 mg, cimetidine 200 mg + oxyphenonium bromide 10 mg and placebo was studied on nocturnal gastric acid secretion in 10 patients with duodenal ulcer. Each patient was studied over a period of four nights and trial medication was given in a randomized sequence. Cimetidine in both doses significantly inhibited the nocturnal gastric acid secretion. The drug reduced both the H+ concentration and gastric juice volume but the reduction of H+ concentration was more impressive. Mean percentage inhibition of nocturnal acid output with cimetidine 400 mg (89.6 +/- 2.868) was significantly higher than cimetidine 200 mg (80.3 +/- 4.085; p less than 0.01). Combination of cimetidine 200 mg and oxyphenonium bromide 10 mg was significantly better than cimetidine 200 mg alone (p less than 0.05) and this combination produced inhibition of gastric juice volume, H+ concentration and acid output comparable to cimetidine 400 mg.

Cimetidine and the potential risk of postoperative sepsis

The gastric microflora of patients receiving cimetidine for duodenal ulceration has been investigated and the results compared with those from a group of untreated patients. Cimetidine-induced hypochlorhydria allows bacterial proliferation in the stomach; 75 per cent of aspirates from 44 fasting patients taking cimetidine 1 g daily were found to contain bacteria 2--4 h after the last dose. Of 41 patients taking cimetidine 400 mg at night, 34 per cent still had bacteria in their aspirates 12--13 h later. Patients treated with cimetidine are likely to be at an increased risk of postoperative sepsis. The drug should either be withdrawn before gastric surgery is undertaken or patients with gastric contents of pH 4 or above should receive antibiotic cover.

The direct excitatory effects of cimetidine on the smooth muscle of guinea pig ileum

1. Cimetidine produced dose-dependent contractions in isolated guinea pig ileum and these responses were not blocked by mepyramine the H1-receptor antagonist. 2. Atropine competitively inhibited the cimetidine-induced contractions in the guinea pig ileum. 3. Cimetidine-induced responses were potentiated in the presence of eserine. Magnesium ions non-competitively inhibited the contractions due to cimetidine. Our findings suggest that cimetidine excites the guinea pig ileum through muscarinic receptors by releasing acetylcholine.

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.

Cimetidine abrogates suppressor T cell function in vitro

Cimetidine increased the [3H] thymidine incorporation of normal human mononuclear cells in culture both when unstimulated or when under the stimulus of phytohemagglutinin or pokeweed mitogen (PWM). It also increased their supernatant immunoglobulin production under PWM stimulus. These effects were higher when the cells were preincubated with cimetidine than when it was added simultaneously. To determine if this effect of cimetidine reflects an abrogation of suppression we studied concanavalin-A-induced suppressor function of normal mononuclear cells using both [3H] thymidine incorporation and immunoglobulin synthesis as indicator systems and found that preincubation with cimetidine caused significant decrease in suppressor cell function in both systems.

Cimetidine is unlikely to increase formation of intragastric N-nitroso-compounds in patients taking a normal diet

Studies in fasting subjects have suggested that cimetidine therapy might lead to nocturnal hypochlorhydria, allowing bacterial overgrowth and the production of intragastric carcinogens. This hypothesis was investigated in normal subjects taking full-dose and maintenance cimetidine with food. Nocturnal hypochlorhydria wa rarely found and the incidence of bacterial overgrowth was correspondingly low; gastric-juice nitrite concentrations were rarely raised. These findings suggest that long term treatment with cimetidine is unlikely to promote gastric cancer as a result of bacterial metabolic activity.

Role of histamine H2-receptors in gastric and pancreatic release of somatostatin-like immunoreactivity during the gastric phase of meal

The present study was designed to determine the role of H2-receptors in the postprandial release of somatostatin-like immunoreactivity (SLI) from the gastric fundus and antrum and from the pancreas. In dogs subjected to laparotomy, the pylorus was bisected and a gastric fistula was created, following which 250 ml 20% liver extract (LE) at pH 7 or 2 were instilled intragastrically. In the fundic vein the incremental SLI rise in response to LE at pH 7 was 2423 plus or minus 540 pg/ml during a control infusion of saline and 4780 plus or minus 863 pg/ml during the infusion of cimetidine (1 mg/kg per h) (P less than 0.05). In the antral vein the incremental SLI in response to LE at pH 7 was 2182 plus or minus 530 pg/ml during the saline control but did not rise significantly during cimetidine infusion. In the pancreatic vein the incremental SLI level after LE at pH 7 was 1953 plus or minus 358 pg/ml in the control experiments and 4430 plus or minus 1024 pg/ml during cimetidine infusion (P less than 0.025). The incremental inferior vena cava SLI level was approximately 925 pg/ml in both groups (not significant). The instillation of LE at pH 2 during the saline control lowered fundic vein SLI by 500 pg/ml; this decline was abolished during cimetidine infusion. In the antral vein the incremental SLI level of 15 750 plus or minus 2514 pg/ml during saline was lowered to only 6728 plus or minus 2257 pg/ml during cimetidine (P less than 0.025). After LE at pH 2 the incremental pancreatic vein SLI level of 5641 plus or minus 1175 pg/ml during the control infusion was also significantly reduced to 2392 plus or minus 559 pg/ml by cimetidine (P less than 0.05). The incremental SLI in the inferior vena cava was reduced from 1270 plus or minus 280 pg/ml during saline to 680 plus or minus 190 pg/ml when cimetidine was infused (P less than 0.05). The present data suggest a histaminergic influence via stimulation of H2-receptors upon the regulation of gastric and pancreatic somatostatin release during the gastric phase of a meal.

Inhibition by pirenzepine of nocturnal gastric acid secretion in duodenal ulcer patients

Ten patients with endoscopically proven duodenal ulcers participated in a double-blind, placebo-controlled, cross-over trial to investigate the effect of pirenzepine on nocturnal gastric acid secretion. Pirenzepine, 50 mg orally at bedtime, inhibited acid secretion all night long: the overall volume secreted and acid output (midnight to 7 a.m.) were significantly less than after placebo. The decrease in acid output per hour was significant at 1,2,3,6, and 7 a.m. It was concluded that controlled clinical trials of maintenance therapy for prevention of relapse of healed duodenal ulcers should be carried out with pirenzepine taken at bedtime.

Preoperative cimetidine--effects on gastric fluid

A double blind study of 44 patients (24 placebo, 20 cimetidine) was undertaken to determine tha effect of cimetidine on the pH and volume of gastric fluid during anaesthesia. The pH was significantly higher on cimetidine-treated patients than placebo-treated patients at 0, 15, 30 and 45 minutes following intubation. At induction of anaesthesia, mean pH on cimetidine was 4.5 and on placebo mean H was 2.0. Approximately 70% of patients on cimetidine and 20% on placebo recorded a pH above 2.5 during anaesthesia. The reason for a pH recording of less than 2.5 in seven patients on cimetidine could not be ascertained. Mean volume of gastric aspirate was slightly lower in the cimetidine group at 0, 15, 30 and 45 minutes, but the differences were not significant.

Controlled trial of cimetidine in reflux esophagitis

In an eight-week double-blind trial, the effectiveness of cimetidine (1.6 g/day) was compared to placebo in 34 patients with symptomatic esophagitis confirmed by endoscopy with biopsies and/or by acid infusion test. Patients treated with cimetidine had significantly less symptomatic days during the first six weeks and less symptomatic nights during the first two weeks, and they consumed less antacids during the whole trial period. Endoscopic evaluation of 17 patients on cimetidine and of 15 patients on placebo did not show any significant difference in severity and extent of esophageal lesions after eight weeks, but histological assessment of 16 patients on cimetidine and 13 patients on placebo showed a significant improvement after eight weeks of cimetidine (P < 0.025). These results show that cimetidine has a rapid effect on symptoms of reflux esophagitis and that, in some cases, it may reduce the esophageal lesions after eight weeks.

Randomized prospective evaluation of cimetidine and antacid control of gastric pH in the critically ill

One hundred forty-four critically ill patients admitted to an intensive care setting were randomly assigned to cimetidine or antacid treatament groups. Gastric pH was monitored hourly. One hundred twenty-three (85%) patients demonstrated a fall in pH to less than 4 and were considered to require prophylaxis. Prophylaxis was considered adequate if the measured pH could then be maintained at greater than or equal to 4. Fifty-eight patients received antacids alone, the average requirement being 41 cc/hour. Sixty-five patients received cimetidine. Seventeen (26%) of the cimetidine prophylaxis patients failed to raise their pH and were than placed on hourly administration of antacid with successful elevations of pH to greater than or equal to 4 in all cases on an average supplementary dose of 53 cc/hour. Risk factors, including sepsis, hypotension, head injury, respiratory failure, degree of trauma, and age, were not statistically different in the two treated groups. Using these same criteria, responders to cimetidine could not be differentiated from nonresponders. All patients were protected from significant stress bleeding while on this study. Significant complications of either treatment were minimal. Antacids offered consistent protection against gastric acidity and were 100% effective. A routine schedule of 300 mg every six hours of cimetidine was effective in only 47% of patients, and the maximum dose of cimetidine was effective in only 74% of patients. Hourly measurement of intragastric pH is required for monitoring the response to prophylaxis of stress bleeding in severely ill patients.

Malabsorption of protein-bound cobalamin but not unbound cobalamin during cimetidine administration

The suppressive effects of cimetidine on acid, pepsin, and intrinsic factor secretion have been well documented; however, the effect of cimetidine on cobalamin absorption has not been assessed. The absorption of both unbound [57Co]cyanocobalamin and protein-bound [57Co]cyanocobalamin was evaluated in 12 patients with duodenal ulcer disease during and after discontinuation of cimetidine therapy. Cimetidine administration did not lead to malabsorption of unbound cobalamin but caused malabsorption of protein-bound cobalamin (0.22 +/- 0.08%, [mean +/- 1 SEM] versus 2.3 +/- 0.10% in control subjects, P less than 0.01). This malabsorption was reversible upon discontinuation of cimetidine. Patients on cimetidine therapy malabsorb protein-bound cobalamin and, during long-term treatment, are at risk for developing cobalamin deficiency. This malabsorption was reversible upon discontinuation of cimetidine. Patients on cimetidine therapy malabsorb protein-bound cobalamin and, during long-term treatment, are at risk for developing cobalamin deficiency. This malabsorption of protein-bound cobalamin is not detectable by the usual tests of cobalamin absorption which employ unbound cobalamin.

The influence of cimetidine on the acid gastro-oesophageal reflux in duodenal ulcer patients

Using a method described earlier, an investigation of the gastro-oesophageal region was made on duodenal ulcer patients before and during cimetidine treatment. During cimetidine treatment there was a small increase in the gastro-oesophageal sphincter pressure (p less than 0.05), although the pressure still was lower than in normal individuals (p less than 0.05). The acid perfusion test and the acid-clearing test were unchanged. The intensity of the acid gastro-oesophageal reflux at pH less than or equal to 4 was reduced p less than 0.05) but still greater than in normal individuals (p less than 0.05). A tendency to an increase of the intragastric pH postprandially (0.05 less than p less than 0.01) was found during treatment, whereas the intragastric pH fasting 12 h after the intake of the last tablet was unchanged. There was no change in the number of amplitudes registered at the proximal and distal pressure catheters (p greater than 0.1), whereas the reversed peristaltic activity still was increased compared with normal individuals (p less than 0.00u). Before treatment a reflux episode at pH less than or equal to 3 needed longer time and greater peristaltic activity to be cleared than was the case during treatment. Nineteen of 20 patients improved their symptoms during treatment. Cimetidine increased the gastro-oesophageal sphincter pressure in duodenal ulcer patients, which may be due to either the reduced intragastric acid secretion or to a direct influence on the gastro-oesophageal region. The reduction in the acid gastro-oesophageal reflux is partly due to an increased gastro-oesophageal sphincter pressure and partly due to a reduced output of acid reflux material. Low pH and the volume of the reflux material in the distal part of the oesophagus are important in regulating the peristaltic activity in duodenal ulcer patients.