Effect of intravenous omeprazole on intragastric pH during intravenous infusion of amino acids

alpha-Amino acid derivatives as proton pump inhibitors and potent anti-ulcer agents

In a program to identify new anti-ulcer compounds, a series of N-acyl derivatives of alpha-amino acids were screened for their in vitro H(+)/K(+) ATPase inhibitory activity, and in vivo efficacy in Pylorus ligation model. 3D-QSAR studies were carried out and a representative compound 13 was studied for the nature of its proton pump inhibition.

Omeprazole treatment of Korean patients: effects on gastric pH and gastrin release in relation to CYP2C19 geno- and phenotypes

This study aimed to investigate the effect of omeprazole on intragastric pH and gastrin release as well as the plasma concentration of omeprazole in relation to CYP2C19 genotypes after repeated doses in Korean patients. Twenty-six Korean patients with acid related disease were genotyped for CYP2C19 by allele specific PCR (wt/wt, CYP2C19*1/*1; wt/mut, CYP2C19*1/*2 or *1/*3; mut/mut, CYP2C19*2/*2, *2/*3 or *3/*3). Intragastric pH was monitored during 24 hr, and the plasma concentrations of omeprazole, hydroxyomeprazole, omeprazole sulfone and meal-stimulated gastrin were measured during 4 hr before and after 8 consecutive daily doses of 20 mg omeprazole. Unexpectedly the AUCs of omeprazole in the three genotypes were similarly high on Day 8. The mean 24 hr pH increased significantly in all three genotypes (paired t-test; P<0.0001), and the AUCs (4 hr) of gastrin in all patients increased markedly from 129+/-73 to 298+/-142 pMhr (P<0.0001). However, there was no statistically significant difference between the three genotypes in the mean pH and gastrin AUCs on Day 8. After 8 consecutive doses of 20 mg omeprazole, the gastric pH and the plasma gastrin were increased significantly in all three CYP2C19 genotypes, which were confirmed by high plasma concentrations of omeprazole in all three genotype groups. We suggest that the reason why the wt/wt had high concentrations of omeprazole similar to those in the other two genotype groups is that some of them were old with low CYP2C19 activity. In these patients omeprazole accumulated from the first to the eighth dose similar to that in the heterozygotes.

Stress-related mucosal disease: risk factors and prophylactic therapy

BACKGROUND

The term stress-related mucosal disease (SRMD) represents a continuum of conditions ranging from stress-related injury (superficial mucosal damage) to stress ulcers (focal deep mucosal damage). Caused by mucosal ischemia, SRMD is most commonly seen in critically ill patients in the intensive care unit (ICU). Prophylaxis of stress ulcers may reduce major bleeding but has not yet been shown to improve survival.

OBJECTIVES

This article reviews currently available agents for the prophylaxis of SRMD and discusses their uses and potential adverse effects.

METHODS

Relevant articles in the English-language literature were identified through a MEDLINE search (1968-2003) using the key words stress-related mucosal disease, stress-related injury, ulcer, prophylaxis, intensive care unit, and upper gastrointestinal bleeding.

RESULTS

The most widely used drugs for stress-related injury are the intravenous histamine(2)-receptor antagonists. These drugs raise gastric pH but are associated with the development of tolerance and possible drug interactions and neurologic manifestations. Sucralfate, which can be administered by the nasogastric route, can protect the gastric mucosa without raising pH, but may decrease the absorption of concomitantly administered oral medications. The prostaglandin misoprostol has not been shown to be of benefit in the prophylaxis of SRMD. Antacids lower the risk of gastrointestinal bleeding, but large volumes of antacids are required and treatment is labor intensive. Proton pump inhibitors (PPIs) are the most potent acid-suppressive pharmacologic agents available. Esomeprazole, lansoprazole, omeprazole, pantoprazole, and rabeprazole substantially raise gastric pH for up to 24 hours after a single dose. The availability of an intravenous formulation of pantoprazole may help improve the treatment of SRMD in ICU patients, particularly those receiving mechanical ventilation. Tolerance does not develop, and few adverse effects have been reported.

CONCLUSIONS

Recent studies of PPIs have shown promising results in high-risk patients, making this class of drugs an option for the prophylaxis of SRMD.

EFEITO DA RANITIDINA E DO OMEPRAZOL SOBRE O pH GÁSTRICO EM CÃES

O objetivo deste trabalho foi investigar o efeito da ranitidina e omeprazol sobre o pH gástrico em 24 cães adultos, machos, sem raça definida, distribuídos em 3 grupos: grupo A - controle, grupo B - ranitidina e grupo C - omeprazol. O pH gástrico foi medido, após coleta do suco gástrico, com seringa, em cães submetidos a gastrotomia. Esta medida foi feita no grupo controle nos tempos zero, 30, 60, 90 e 120 minutos, no grupo ranitidina a medida foi feita no tempo zero, seguida de aplicação de 0,85 mg/kg de ranitidina por via endovenosa, sendo realizada nova medida nos tempos 30, 60, 90 e 120 minutos e, no grupo omeprazol a medida foi feita no tempo zero, seguida de aplicação de 0,68 mg/kg de omeprazol por via endovenosa, sendo realizada nova medida nos tempos 30,60, 90 e 120 minutos. A comparação entre os grupos mostrou um aumento significante do pH gástrico após o uso de ranitidina e omeprazol. Entretanto, os efeitos comparados da ranitidina e omeprazol não apresentaram diferenças significantes na variação do pH.

Current guidelines on stress ulcer prophylaxis

Acute uppergastrointestinal bleeding in intensive care unit (ICU) patients may occur due to peptic ulcer disease, adverse drug effects, gastric tube lesions, acute renal failure, liver failure or stress-induced gastric mucosal lesions. Gastric acid hypersecretion can be observed in patients with head trauma or neurosurgical procedures. Gastric mucosal ischaemia due to hypotension and shock is the most important risk factor for stress ulcer bleeding. Preventive strategies aim to reduce gastric acidity (histamine H2 receptor antagonists, antacids), strengthen mucosal defensive mechanisms (sucralfate, antacids, pirenzepine) and normalise gastric mucosal microcirculation (sucralfate, pirenzepine). However, the most important prophylactic measure is an optimised resuscitation and ICU regime aiming to improve oxygenation and microcirculation. All drugs approved for stress ulcer prophylaxis in Europe (H2 antagonists, antacids, pirenzepine, sucralfate) have been shown to be effective in prospective controlled randomised trials. However, due to insufficient clinical data, prostaglandins and omeprazole cannot be recommended for this use. Stress ulcer prophylaxis is indicated only in patients at risk, and not in every ICU patient. The selection of drugs today depends not only on efficacy but also on possible adverse effects and on costs. In this regard, the most cost-effective drug is sucralfate. The clinical relevance of nosocomial pneumonia due to gastric bacterial overgrowth has decreased during the past decade due to several changes in the management of critically ill patients.

Effect of repeated boluses of intravenous omeprazole and primed infusions of ranitidine on 24-hour intragastric pH in healthy human subjects

The aim of this study was to identify dosage regimens using intravenous omeprazole and ranitidine that would elevate and consistently maintain intragastric pH > 6 in the first 24 hr of therapy. In 19 healthy, fasting human subjects using continuous 24-hr gastric pH-metry, we studied two dosages of primed infusions of ranitidine (50 mg bolus followed by infusion of either 3 or 6 mg/kg body wt/24 hr) and six regimens of intravenous omeprazole (80-200 mg in 24 hr in two to five boluses). Only the two ranitidine infusions and high doses of omeprazole (> or = 160 mg/day as four or five boluses) raised the intragastric median pH above 5.4. There was no significant difference in the median intragastric pH after high dose ranitidine and high doses of omeprazole. Considerable interindividual variation in intragastric pH was observed after omeprazole therapy. The percentage of intragastric pH > 6.0 during the 24-hr study was lower after omeprazole (35-42%) than after high-dose ranitidine (58%). We conclude that it is possible to raise intragastric pH > 6.0 by use of either primed ranitidine infusion or by repeated boluses of omeprazole. However, maintenance of this high pH in the first 24 hr is difficult with both, more so with omeprazole.

Individual and group dose-responses to intravenous omeprazole in the first 24 h: pH-feedback-controlled and fixed-dose infusions

1. Individual responses to intravenous boli of omeprazole have shown considerable variability. Data on the individual responses to the new omeprazole infusion formulation are lacking. 2. Individual dose-responses in the first 24 h of fixed-dose and pH-feedback-controlled infusions of omeprazole were assessed in two randomised, third-party blinded, cross-over studies, using two separate groups of eight healthy subjects. In study A, feedback-controlled infusions of omeprazole (target pH 5, dose range 0-12 mg h-1) and fixed-dose infusions (8 mg h-1) were compared, both with an initial bolus of 80 mg. Omeprazole plasma concentrations were measured. Study B assessed the effect on individual pH-control of a loading bolus of either 40 mg or 80 mg omeprazole, followed by feedback-controlled infusions. 3. Study A: the median % time of pH > 5 was 71.2 (total range: 48.9-83.2) with feedback infusions and 57.9 (28.0-95.3) with fixed-dose infusions (P = 0.06). The mean 24 h infusion doses were 173.1 mg (44.5-253.1) in the feedback group and 192 mg in the fixed-dose group. The AUC of omeprazole plasma concentrations ranged widely, but correlated with the % time of pH > 5 during fixed-dose infusions. Study B: initial boli of 40 mg and 80 mg of omeprazole resulted in similar 24 h median % of time with pH > 5, 69.2 (49.9-78.8) and 69.6 (44.4-87.7), respectively. Mean omeprazole doses infused by feedback pump were 187.6 mg (83.1-253.6) after 40 mg boli and 159.9 mg (61.8-227.0) after 80 mg boli.(ABSTRACT TRUNCATED AT 250 WORDS)

Do continuous infusions of omeprazole and ranitidine retain their effect with prolonged dosing?

BACKGROUND/AIMS

Prolonged infusions of H2-antagonists are commonly used in intensive care units, although little is known about their antisecretory efficacy beyond the initial 24 hours of dosing. The aim of this study was to assess the antisecretory effects of infusions of ranitidine and omeprazole for a period of 72 hours.

METHODS

Twelve healthy volunteers received individually titrated 72-hour intravenous infusions of omeprazole, ranitidine, or placebo in a double-blind, crossover study. Gastric pH and dosing requirements were compared.

RESULTS

The median percentage of time with pH > 4 (interquartile range) was 93% (88%-95%) on day 1 and 96% (94%-99%) on day 3 with omeprazole and 67% (56%-78%) and 43% (31%-51%), respectively, with ranitidine (both P < 0.001 vs. omeprazole). The mean doses (+/- SD) required on days 1 and 3 for omeprazole were 235.8 +/- 44 mg and 134.0 +/- 37 mg (P < 0.0001), and ranitidine doses were 502.5 +/- 76 mg and 541.8 +/- 25 mg, respectively (P = 0.05).

CONCLUSIONS

Omeprazole infusions consistently maintained gastric pH above 4 over a period of 72 hours with progressively lower doses. Significant tolerance to the antisecretory effect of ranitidine infusion developed in 72 hours, which was not overcome despite individually titrated doses of more than 500 mg/24 hours. Consequently, application of pharmacodynamic results of single-day H2-blocker and proton-pump inhibitor studies to prolonged infusion trials for stress ulcer-related bleeding is inappropriate.

Effects of indomethacin on intragastric pH and meal-stimulated serum gastrin secretion in rheumatoid arthritis patients

The effects of oral indomethacin on intragastric pH and serum gastrin were investigated in rheumatoid arthritis patients. Nine patients (1 male, 8 female) without a history of peptic ulcer disease and 6 patients with a history of peptic ulcer disease (5 male, 1 female) were studied. To obviate Helicobacter pylori infection as a confounding factor, only patients with positive H. pylori serology were included. After a 5-day period of placebo treatment and after a 5-day period of indomethacin (50 mg t.d.s.; total dose 750 mg), 24-h intragastric pH and basal and meal-stimulated serum gastrin levels were measured in a double-blind placebo controlled cross-over study. There were no differences in the median 24-h pH values between placebo and indomethacin users irrespective of peptic ulcer disease history. Indomethacin resulted in a higher basal and stimulated gastrin response than placebo in patients with a history of peptic ulcer disease. The basal and incremental responses were lower in patients with a history of peptic ulcer disease than in patients without a history of peptic ulcer disease, both during indomethacin and placebo. The same basal and stimulated incremental serum gastrin responses were found during placebo and indomethacin treatment in patients without a history of peptic ulcer disease. No correlation was established between median 2-h post-prandial intragastric pH and post-prandial incremental serum gastrin concentration. We conclude that indomethacin does not influence the intragastric pH of rheumatoid arthritis patients irrespective of history of peptic ulcer disease.

Gastric acid secretion and intragastric acidity: measurement in health and disease

Gastric acid secretion tests have limited use in clinical practice. For practical purposes, a pH measurement on a fasting gastric aspirate will provide strong evidence of the presence or absence of achlorhydria. Tests of gastric acidity, in particular 24-h acidity studies, have provided considerable insight into normal and abnormal gastric physiology, and have largely determined the dosing regimens for the management of acid-peptic diseases. Acid tests may be simple to perform, so much so that they have been suggested as 'practicals' for student teaching (Nicol et al, 1991). However, reproducible and meaningful results require careful attention to detail, and the appropriate mathematical analysis is still subject to some debate. It is important that the presentation of the data should allow the reader to assess the response over the 24-h period, and also the range of individual responses. Despite the many years of research into gastric acid secretion, only recently have the effects of age, sex, diet, smoking and mental stress been identified. In addition, many data need to be reviewed in the light of the effects of H. pylori infection on gastrin release. H2-receptor antagonists had been studied extensively before and since their first clinical use in 1974, but surprisingly only recently have the issues of tolerance and rebound been defined. The 24-h intragastric acidity profile remains an essential study before the start of clinical trials on any new drug to be used for the treatment of acid-peptic diseases.

Repeated intravenous bolus injections of omeprazole: effects on 24-hour intragastric pH, serum gastrin, and serum pepsinogen A and C

We determined the effect of four times daily dosing with intravenous omeprazole on 24-h intragastric acidity, serum gastrin, and serum pepsinogen A and C in 10 fasting subjects (median age, 23.5 years). Two dose regimens (80-20-20-20 mg and 80-40-40-40 mg) were compared in a randomized placebo-controlled crossover study. Intragastric pH was continuously monitored during 24 h, using combined glass electrodes, and blood samples were taken every 6 h. Repeated boluses of omeprazole every 6 h significantly increased (p less than 0.01) the median 24-h intragastric pH compared with placebo (median pH, 3.7 (140 mg/day), 4.3 (200 mg/day), and 1.4 (placebo)) but failed to continuously raise pH levels above 4.0 in 8 (140 mg/day) or 9 (200 mg/day) of 10 subjects. No advantage of the 200-mg dose over the 140-mg dose was demonstrated. A cumulative effect of intravenous omeprazole was shown after repeated boluses but also a marked interindividual variation in response, which was correlated with the omeprazole area under the plasma concentration time curve. A significant elevation of serum gastrin coincided with the increased pH levels, which was followed after 12-18 h by a significant increase of both serum pepsinogens.