Assessment of Substrate-Dependent Ligand Interactions at the Organic Cation Transporter OCT2 Using Six Model Substrates.

Organic cation transporter (OCT) 2 mediates the entry step for organic cation secretion by renal proximal tubule cells and is a site of unwanted drug-drug interactions (DDIs). But reliance on decision tree-based predictions of DDIs at OCT2 that depend on IC50 values can be suspect because they can be influenced by choice of transported substrate; for example, IC50 values for the inhibition of metformin versus MPP transport can vary by 5- to 10-fold. However, it is not clear whether the substrate dependence of a ligand interaction is common among OCT2 substrates. To address this question, we screened the inhibitory effectiveness of 20 µM concentrations of several hundred compounds against OCT2-mediated uptake of six structurally distinct substrates: MPP, metformin, N,N,N-trimethyl-2-[methyl(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)amino]ethanaminium (NBD-MTMA), TEA, cimetidine, and 4-4-dimethylaminostyryl-N-methylpyridinium (ASP). Of these, MPP transport was least sensitive to inhibition. IC50 values for 20 structurally diverse compounds confirmed this profile, with IC50 values for MPP averaging 6-fold larger than those for the other substrates. Bayesian machine-learning models of ligand-induced inhibition displayed generally good statistics after cross-validation and external testing. Applying our ASP model to a previously published large-scale screening study for inhibition of OCT2-mediated ASP transport resulted in comparable statistics, with approximately 75% of "active" inhibitors predicted correctly. The differential sensitivity of MPP transport to inhibition suggests that multiple ligands can interact simultaneously with OCT2 and supports the recommendation that MPP not be used as a test substrate for OCT2 screening. Instead, metformin appears to be a comparatively representative OCT2 substrate for both in vitro and in vivo (clinical) use.

Stress ulcer prophylaxis in intensive care unit patients receiving enteral nutrition: a systematic review and meta-analysis.

BACKGROUND: Pharmacologic stress ulcer prophylaxis (SUP) is recommended in critically ill patients with high risk of stress-related gastrointestinal (GI) bleeding. However, as to patients receiving enteral feeding, the preventive effect of SUP is not well-known. Therefore, we performed a meta-analysis of randomized controlled trials (RCTs) to evaluate the effect of pharmacologic SUP in enterally fed patients on stress-related GI bleeding and other clinical outcomes. METHODS: We searched PubMed, Embase, and the Cochrane database from inception through 30 Sep 2017. Eligible trials were RCTs comparing pharmacologic SUP to either placebo or no prophylaxis in enterally fed patients in the ICU. Results were expressed as risk ratio (RR) and mean difference (MD) with accompanying 95% confidence interval (CI). Heterogeneity, subgroup analysis, sensitivity analysis and publication bias were explored. RESULTS: Seven studies (n = 889 patients) were included. There was no statistically significant difference in GI bleeding (RR 0.80; 95% CI, 0.49 to 1.31, p = 0.37) between groups. This finding was confirmed by further subgroup analyses and sensitivity analysis. In addition, SUP had no effect on overall mortality (RR 1.21; 95% CI, 0.94 to 1.56, p = 0.14), Clostridium difficile infection (RR 0.89; 95% CI, 0.25 to 3.19, p = 0.86), length of stay in the ICU (MD 0.04 days; 95% CI, -0.79 to 0.87, p = 0.92), duration of mechanical ventilation (MD -0.38 days; 95% CI, -1.48 to 0.72, p = 0.50), but was associated with an increased risk of hospital-acquired pneumonia (RR 1.53; 95% CI, 1.04 to 2.27; p = 0.03). CONCLUSIONS: Our results suggested that in patients receiving enteral feeding, pharmacologic SUP is not beneficial and combined interventions may even increase the risk of nosocomial pneumonia.

Stress Ulcer Prophylaxis in Neurocritical Care.

Stress ulcer prophylaxis (SUP) with acid-suppressive drug therapy is widely utilized in critically ill patients following neurologic injury for the prevention of clinically important stress-related gastrointestinal bleeding (CIB). Data supporting SUP, however, largely originates from studies conducted during an era where practices were vastly different than what is considered routine by today's standard. This is particularly true in neurocritical care patients. In fact, the routine provision of SUP has been challenged due to an increasing prevalence of adverse drug events with acid-suppressive therapy and the perception that CIB rates are sparse. This narrative review will discuss current controversies with SUP as they apply to neurocritical care patients. Specifically, the pathophysiology, prevalence, and risk factors for CIB along with the comparative efficacy, safety, and cost-effectiveness of acid-suppressive therapy will be described.

Experimental study of the rat for the assessment of barium coating on the gastric mucosa: efficacy of ranitidine and acetylcysteine administration.

PURPOSE: In order to improve the preparation method for barium examination of the stomach by ranitidine and acetylcysteine use, the effect on the rat gastric mucosa caused by the administration of ranitidine and acetylcysteine was studied. MATERIALS AND METHODS: Rat stomach that had been treated with ranitidine or acetylcysteine at different intervals and examined in vivo was excised and coated with a barium suspension. A radiograph was subsequently taken and evaluated in regard to the removal of gastric mucus and imaging of the areae gastricae (AG). The removal of mucus was assessed by six blind observers. The imaging of AG was estimated as a percentage of the imaged AG area per total gastric corpus. RESULTS: No change was seen on the radiograph with ranitidine preparation, while the mucus was distinctly removed and AG well-imaged in the group studied 15 minutes after the peroral administration of acetylcysteine. CONCLUSION: Proper preparation for barium study of the stomach should involve treatment with a mucolytic agent about 15 minutes before the examination. H2-blockers must be used supplementally in the short term.

Randomized trial of preoperative cimetidine in patients with colorectal carcinoma with quantitative assessment of tumor-associated lymphocytes.

BACKGROUND: Previous studies have suggested that cimetidine, a histamine-2 receptor antagonist with immunostimulatory effects, may improve survival in patients with colorectal carcinoma. This effect may be apparent by an increase in the number of peritumoral lymphocytes. A prospective, double blind, randomized, placebo-controlled trial of a short course of preoperative treatment with cimetidine in patients with colorectal carcinoma was performed to assess the effect of cimetidine on survival and on the number of peritumoral lymphocytes. METHODS: One hundred and twenty-five patients who were scheduled to undergo elective colon or rectal excision for carcinoma were randomized to receive either placebo or cimetidine preoperatively for 5 days. In addition to standard histopathology, immunohistochemistry and computer video image analysis were used to assess the number of peritumoral lymphocytes in an objective manner. Interim survival analysis according to the Kaplan-Meier method was performed. RESULTS: A trend toward a survival advantage in the group of patients receiving cimetidine (800 mg twice daily) compared with the placebo group was observed (P = 0.20, log rank test) that was most marked in patients with replication error negative tumors (P = 0.04). Similarly, in these two groups there was a trend toward an increase in the number of patients with a conspicuous lymphocytic infiltration (P = 0.10, chi-square test). However, there was no difference in the number of peritumoral lymphocytes as measured by image analysis. CONCLUSIONS: Based on the results of the current study, a short course of preoperative treatment with cimetidine does appear to have an effect on patient survival; however, the exact mechanism is unknown. The failure of this study to demonstrate a clear increase in the local lymphocyte response does not exclude an immunologic mechanism of action.

Daily variations of serum diamine oxidase and the influence of H1 and H2 blockers: a critical approach to routine diamine oxidase assessment.

OBJECTIVE AND DESIGN: Histamine in food has been shown to induce intolerance reactions mimicking food allergy. These reactions seem to be due to impaired histamine metabolism caused by reduced diamine oxidase activity. To validate routine serum diamine oxidase assessment, daily variations of diamine oxidase were evaluated. METHODS: Blood was drawn from each of 20 healthy volunteers (10 female, 10 male; mean age 32.5 years) every 2 h from 9 a.m. to 5 p.m., and diamine oxidase activity was measured using the C14 putrescine method. To assess possible influences of H1 and H2 blockers on diamine oxidase activity, diphenhydramine, ketotifen, cimetidine, and ranitidine were incubated at pharmacologic concentrations with human placental diamine oxidase (identical to neutrophilic and eosinophilic diamine oxidase). Inhibition of diamine oxidase activity was calculated as the percentage of inhibition versus control. In addition, the known diamine oxidase inhibitors, dihydralazine and aminoguanidine, were used as positive controls. RESULTS: Serum diamine oxidase levels showed no significant daily variations (0.041 +/- 0.025; 0.037 +/- 0.022; 0.041 +/- 0.023; 0.040 +/- 0.023; 0.038 +/- 0.025 nKat/l) and no significant sex differences (female 0.040 +/- 0.028 nKat/l versus male 0.039 +/- 0.019 nKat/l). Antihistamines had no influence on diamine oxidase activity except for cimetidine, which caused 25% inhibition at the highest dose tested ( p < 0.0002) (positive control: aminoguanidine 85% inhibition (p< 0.0001), dihydralazine 68% inhibition (p<0.0001)) and diphenhydramine, which caused 19% increase (p<0.0001) of enzyme activity. CONCLUSION: Serum diamine oxidase levels do not show daily variations allowing assessment anytime during office hours. However, diagnostic interpretation of serum diamine oxidase levels may be difficult.

The actions of the H2-blocker cimetidine on the toxicity and biotransformation of the phosphorothioate insecticide parathion.

Parathion, like most organophosphorus insecticides currently in use, must undergo cytochrome P450(P450)-dependent activation in order to exert its acute mammalian toxicity (cholinergic crisis). Since P450 isoforms play such an important role in mediating the toxicity of parathion and related insecticides, factors which significantly alter P450 activities, such as exposure to certain xenobiotics, can also be expected to affect the toxicity of these potentially hazardous insecticides. Cimetidine is a H2-histamine antagonist that has been shown to inhibit several P450-isoforms. In addition, administration of cimetidine has been reported to result in clinically significant pharmacokinetic interactions with a wide variety of drugs. In the present study coexposure to cimetidine and parathion resulted in a moderate increase in the toxicity of this pesticide. However, coexposure to cimetidine and paraoxon did not alter the toxicity of the organophosphate, indicating that cimetidine likely affected P450-dependent formation of paraoxon from parathion. In vitro incubations of mouse hepatic microsomes demonstrated that, in addition to reducing the velocity of P450-dependent metabolism of parathion, cimetidine increased the proportion of paraoxon formed (activation). and decreased the proportion of p-nitrophenol formed (detoxification). Since parathion is not eliminated significantly by other routes in the mouse, the bulk of parathion in vivo was metabolized by P450 (although more slowly) in the presence of cimetidine, leading to a greater amount of paraoxon produced, and therefore greater toxicity. Incubations with individual P450 isoforms suggested that cimetidine could act by inhibition of P450 isoforms that detoxify parathion to a greater degree than cimetidine-resistant isoforms, and/or cimetidine could alter the proportions of detoxification versus activation of certain individual isoforms.

Synthesis and assessment of formamidines as new histamine H2-receptor antagonists.

Four series of compounds whose substructure contains a formamidine functionalized as a novel group in the chemistry of histamine H2-receptors have been synthesized. Series design, synthesis and pharmacological data including inhibition of histamine-stimulated acid secretion, inhibition of acid secretion p.o. and pA2 are reported. N-[(E)-[[2-[[[2](Diaminomethylene)amino]-4-thiazolyl] methyl]thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide (ebrotidine, CAS 100981-43-9, FI-3542) was selected for further research.

The role of proton pump inhibitors in the treatment of gastro-oesophageal reflux disease.

Efficacy (healing, symptom relief) and cost-effectiveness are the principal reasons for the rapidly increasing use of proton pump inhibitors (PPIs) for the management of gastro-oesophageal reflux disease. EFFICACY: Mean healing rates pooled from clinical trials are as follows: on omeprazole (OME) 20 mg vs. H2-receptor antagonist. H2RA (cimetidine (CIM) 1.6 g or ranitidine (RAN) 300 mg) (eight studies) at 4 weeks, 67% vs. 37%: at 8 weeks, 81% vs. 49%: on lansoprazole (LAN) 30 mg vs. H2RA (three studies), 83% vs. 47% and 91% vs. 63% at 4 and 8 weeks, respectively. The benefit is greatest in severe disease because the H2RAs are disproportionately less effective. Heartburn is more rapidly relieved and in a higher proportion: at 4 weeks, on OME 20 mg vs. H2RA. 77% vs. 47% and on LAN 30 mg vs. H2RA, 81% vs. 46%. Both PPIs are effective in H2RA-refractory disease, approximately 80% healing occurring in 8 weeks. Relapse rates after healing vary from 25% to 85% at 6 months. Maintenance therapy sustains remissions: relapse at 1 year is, on OME 20 mg vs. RAN 300 mg (2 studies), 12% vs. 79%, and 28% vs. 55% (and 38% on OME 10 mg); on LAN 30 mg vs. 10 mg vs. RAN 600 mg, 20% vs. 31% vs. 68%. The effectiveness of the lower dose allows for dose titration. COST EFFECTIVENESS: The higher drug costs for the PPIs are offset by their higher efficacy, making their use cost effective, particularly in severe disease. Efficacy and cost effectiveness are likely to further expand the use of PPIs at the expense of H2RAs as increasing numbers of patients with milder disease are treated.

Efficacy, safety, and cost issues in managing patients with gastroesophageal reflux disease.

The phases of therapy for gastroesophageal reflux disease (GERD) and the efficacy, safety, and cost of the various drugs used are discussed. The therapeutic goals for patients with GERD are to relieve pain, promote healing, avoid complications, and prevent recurrence. Sustained inhibition of gastric acid secretion is necessary to facilitate healing of eroded esophageal mucosa. Phase 1 treatment involves lifestyle changes to remove factors that may help to precipitate reflux, such as overeating, alcohol, and tobacco. Phase 2 involves pharmacologic manipulation of the secretion, concentration, and transport of gastric acid. The drugs used are antacids, alginic acid, the histamine H2-receptor antagonists, the prokinetic agents, sucralfate, and omeprazole. While all of these agents may provide symptomatic relief, only the H2 antagonists and omeprazole have been convincingly shown to relieve symptoms and promote healing. The H2 antagonists differ in potency, pharmacodynamic effect, pharmacokinetics in certain patient groups, drug interactions, and adverse effects. The H2 antagonists may not be effective at standard dosages in patients who secrete especially large quantities of gastric acid. Because of its mechanism of action, omeprazole provides greater inhibition of gastric acid than any other antisecretory drug. Omeprazole may also be the most cost-effective treatment. The availability of omeprazole may reduce the number of patients for whom clinicians must resort to phase 3 treatment, surgery. Although many drugs provide symptomatic relief in patients with GERD, the healing that is necessary to break the cycle of damage and symptoms is promoted only by the H2 antagonists and omeprazole.

Radiographic assessment of nocturnal gastric juice secretion after administration of roxatidine acetate hydrochloride.

Adult patients with symptoms of gastric disease were randomly assigned to a treatment group (n = 103) or untreated control group (n = 89). The treatment group received 75 mg of roxatidine acetate hydrochloride at 9 PM and 12 to 13 hours later gastric juice secretion was measured with gastric x-ray films in both groups. Mean gastric juice secretion was significantly lower in the treated group (16.1 ml/12 hrs) than in the untreated controls (49.8 ml/12 hrs). Gastric juice suppression by roxatidine was 90% in patients with gastric ulcer, 74% in patients with duodenal ulcer, 63% in patients with gastritis, and 70% in patients with no evidence of disease. It is concluded that 150 mg of roxatidine daily would be adequate to treat patients with gastric diseases.

[Interaction between drugs. A critical assessment of various controlling factors in relation to clinical significance--exemplified by cimetidine]. / Interaktion mellan läkemedel. En kritisk genomgång av några styrande faktorer i förhållande till klinisk betydelse--exemplet cimetidin.

Interactions between pharmaceutical preparations are common and can occur at almost every stage in a substance's metabolic clearance but frequently lack clinical significance. Different factors must be considered in the assessment of data on interactions. This article compares interactions between H2-antagonists from various aspects: the disposition of the study, the mechanism of operation, the pharmacokinetics and pharmaco-dynamics etc. Several pharmaceutical interactions are dose-related so that the questions of equipotent dosage, the length of the period of treatment etc are crucial. The principal interaction mechanism for this group of drugs pertains to absorption, interference with the oxidative metabolism and excretion via the kidneys. Important measures to avoid interaction problems are individualization of the dose (lower dose = less risk), scrupulous clinical observation, and determination of the concentration in the blood of the drug concerned, if an analytical method exists. Under these circumstances any of the H2 antagonists may be used.

Assessment of intragastric acidity in man: modern aspects, reproducibility of intragastric pH-monitoring, and pharmacodynamic results obtained with H2-receptor antagonists.

Unlike other methods for assessing intragastric pH or total acid output, the reproducibility of ambulatory pH-monitoring is excellent but is critically dependent on the electrode system and the recording device. In three double-blind randomized studies in normal volunteers the effects of different dosage regimens of roxatidine acetate were compared with placebo and ranitidine. Roxatidine acetate, 75 mg twice daily, raised median 24-h gastric pH from 1.6 to 3.2 and median nocturnal pH from 1.5 to 3.0 Roxatidine acetate, 150 mg at bedtime, raised median 24-h pH to 2.4 and nocturnal pH to 5.9. Roxatidine acetate, 150 mg at bedtime, was as effective as ranitidine, 300 mg at night, in raising median nocturnal pH. However, when drugs were taken after the evening meal, 150 mg roxatidine acetate was less potent than 300 mg ranitidine or 300 mg roxatidine acetate.

Single bedtime dose of famotidine: assessment of its antisecretory action by 24-hour intragastric pH monitoring.

The antisecretory efficacy of a single bedtime dose of famotidine, a new potent H2-receptor antagonist, was evaluated by means of continuous 24-hour intragastric pH monitoring. Of 20 patients with duodenal ulcers, ten randomly received famotidine 40 mg at 10 PM and ten were monitored without medication for control. Famotidine regimen led to a remarkable reduction of gastric acidity in patients who were treated for duodenal ulcer and the drug-induced pH levels were significantly different (P less than .0001) from those of untreated controls. The antisecretory action lasted for 12 hours, which comprised the nocturnal period, whereas no important difference was found between the two groups for the most part of the daytime. The drug was able to keep intragastric pH above 4 units during almost 50% of the whole 24-hour period. These results confirm that famotidine is a powerful and long-acting H2 blocker that relieves gastric acidity during the night and morning hours when administered as a single bedtime dose of 40 mg.

Relative effectiveness and costs of antiulcer medications as a basis for rational prescribing.

To be maximally effective, antiulcer medications should relieve ulcer symptoms rapidly and promote rapid healing of an ulcer crater; after the cessation of a course of treatment the ulcer should not recur. A wide variety of agents is available. These are of similar efficiency in the control of ulcer symptoms and in the acceleration of the healing of the ulcer crater. However, evidence exists of differences in the rate of the recurrence of duodenal ulcers on the cessation of these drugs. Surface-active agents (bismuth complexes, sucralfate, prostaglandins and carbenoxolone) are consistently superior to H2-histamine receptor antagonist drugs (cimetidine and ranitidine). A high relapse rate produces more patients with active disease at any one time, hence more patients will be exposed to the complications of the disease, and will require active investigation and therapy. Because of the increased rate of relapse, the use of H2-receptor antagonist drugs as first-line intermittent healing therapy can be shown to be associated with an eight-fold (800%) increase in cost of pharmaceutical agents as compared with first-line treatment with bismuth salts; a four-fold increase compared with the cost of using antacid drugs; and a two-fold increase compared with the cost of using sucralfate. When maintenance therapy with H2-receptor antagonist agents is given instead of intermittent therapy with bismuth complexes, a 14-fold increase in pharmaceutical costs is incurred, with inferior results that have already been demonstrated under the conditions of a controlled clinical trial. These considerations of efficacy and cost suggest that H2-receptor antagonist drugs ought not to be first-line therapy for duodenal ulcers; rather, surface-active agents such as colloidal bismuth or sucralfate should be prescribed initially.