Famotidine Enhances Rifampicin Activity against Acinetobacter baumannii by Affecting OmpA

The development of novel antibiotic adjuvants is imminent because of the frequent emergence of resistance in Gram-negative bacteria, which severely restricts the efficiency and longevity of commonly used clinical antibiotics. It is reported that famotidine, a clinical inhibitor of gastric acid secretion, enhances the antibacterial activity of rifamycin antibiotics, especially rifampicin, against Gram-negative bacteria and reverses drug resistance. Studies have shown that famotidine disrupts the cell membrane of Acinetobacter baumannii and inhibits the expression of the outer membrane protein ompA gene, while causing a dissipation of the plasma membrane potential, compensatively upregulating the pH gradient and ultimately increasing the accumulation of reactive oxygen species by leading to increased bacterial mortality. In addition, famotidine also inhibited the efflux pump activity and the biofilm formation of A. baumannii. In the Galleria mellonella and mouse infection models, the combination of famotidine and rifampicin increased the survival rate of infected animals and decreased the bacterial load in mouse organs. In conclusion, famotidine has the potential to be a novel rifampicin adjuvant, providing a new option for the treatment of clinical Gram-negative bacterial infections. IMPORTANCE In this study, famotidine was discovered for the first time to have potential as an antibiotic adjuvant, enhancing the antibacterial activity of rifamycin antibiotics against A. baumannii and overcoming the limitations of drug therapy. With the discovery of novel applications for the guanidine-containing medication famotidine, the viability of screening prospective antibiotic adjuvants from guanidine-based molecules was further explored. In addition, famotidine exerts activity by affecting the OmpA protein of the cell membrane, indicating that this protein might be used as a therapeutic drug target to treat A. baumannii infections.

Esomeprazole induces structural changes and apoptosis and alters function of in vitro canine neoplastic mast cells

Histamine-2 receptor antagonists such as famotidine and proton pump inhibitors such as esomeprazole are commonly used in canine MCT disease, but direct effects on dog MCs have not been evaluated. Omeprazole is a proton pump inhibitor which has been demonstrated to cause structural and functional changes to in vitro murine mast cells (MCs). It has not yet been determined if esomeprazole, the commercially available and commonly prescribed S-isomer of omeprazole, has similar effects. Our primary study objective was to evaluate and compare the effects of acid suppressants (esomeprazole and famotidine) on MC ultrastructure, viability, and function in vitro using both healthy and neoplastic MCs. Murine bone marrow derived mast cells (BMMC), human LAD2, and canine C2 and BR cells, were used for these studies, representing a single healthy (i.e., BMMCs) MC model and multiple neoplastic MC models (i.e., LAD2, C2, BR), respectively. The rat basophilic leukemic (RBL-2H3) and canine B cell lymphoma 17-71 cell lines served as granulocytic and agranulocytic control lines for experiments, respectively. The treatment effect of acid suppressants on MC ultrastructure was assessed via both light and transmission electron microscopy. Differences in MC viability was assessed between groups via MTS-based, colorimetric assays and flow cytometry. Degranulation was assessed by quantification of β-hexosaminidase (i.e., LAD2 and RBL-2H3). Esomeprazole-treated MCs of all lines exhibited dramatic time and concentration-dependent alterations in ultrastructure (i.e., increased vacuolization, compromise of cell membrane), increased apoptosis, and altered degranulation responses in comparison to famotidine and vehicle-treated cells. The canine B cell lymphoma cells consistently exhibited either no significant (i.e., cytotoxicity assays) or greatly diminished treatment responses (i.e., apoptosis) compared to MCs. Esomeprazole, but not famotidine, induces significant cytotoxicity, as well as alterations to cell structure and function to multiple lines of in vitro neoplastic MCs. Continued in vitro work investigating the specific mechanisms by which proton pump inhibitors induce these effects, as well as prospective, in vivo work comparing the treatment effects of acid suppressants on canine MCTs, are warranted.

Prediction of Permeability Coefficients of Compounds Through Caco-2 Cell Monolayer Using Artificial Neural Network Analysis

Artificial neural network (ANN) analysis was used to predict the permeability of selected compounds through Caco-2 cell monolayers. Previously reported models, which were shown to be useful in the prediction of permeability values, use many structural parameters. More complex equations have also been proposed using both linear and non-linear relationships, including ANN analysis and various structural parameters. But proposed models still need to be developed using different neuron patterns for more precise predictions and a better understanding of which factors affect the permeation. To develop a simple and useful model or method for easy prediction is also a general need. Permeability coefficients (log kp) were obtained from various literature sources. Some structural parameters were calculated using computer programs. Multiple linear regression analysis (MLRA) was used to predict Caco-2 cell permeability for the set of 50 compounds (r2=0.403). A successful ANN model was developed, and the ANN produced log kp values that correlated well with the experimental ones (r2=0.952). The permeability of a compound, famotidine, which has not previously been studied, through the Caco-2 cell monolayer was investigated, and its permeability coefficient determined. It was then possible to compare the experimental data with that predicted using the trained ANN with previously determined Caco-2 cell permeability values and structural parameters of compounds. The model was also tested using literature values. The developed and described ANN model in this publication does not require any experimental parameters; it could potentially provide useful and precise prediction of permeability for new drugs or other penetrants.

Spectrophotometric determination of H(2)-receptor antagonists via their oxidation with cerium(IV)

A simple, accurate and sensitive spectrophotometric method has been developed and validated for determination of H(2)-receptor antagonists: cimetidine, famotidine, nizatidine and ranitidine hydrochloride. The method was based on the oxidation of these drugs with cerium(IV) in presence of perchloric acid and subsequent measurement of the excess Ce(IV) by its reaction with p-dimethylaminobenzaldehyde to give a red colored product (lambda(max) at 464nm). The decrease in the absorption intensity of the colored product (DeltaA), due to the presence of the drug was correlated with its concentration in the sample solution. Different variables affecting the reaction were carefully studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9990-0.9994) were found between DeltaA values and the concentrations of the drugs in a concentration range of 1-20microgml(-1). The assay limits of detection and quantitation were 0.18-0.60 and 0.54-1.53microgml(-1), respectively. The method was validated, in terms of accuracy, precision, ruggedness and robustness; the results were satisfactory. The proposed method was successfully applied to the determination of the investigated drugs in pure and pharmaceutical dosage forms (recovery was 98.3-102.6+/-0.57-1.90%) without interference from the common excipients. The results obtained by the proposed method were comparable with those obtained by the official methods.

Different transport properties between famotidine and cimetidine by human renal organic ion transporters (SLC22A)

Histamine H2 receptor antagonist famotidine and cimetidine are commonly used for treatment of gastrointestinal ulcer diseases. Inasmuch as these drugs are mainly secreted by renal tubules, dosages have been adjusted according to renal function. Although many studies have been performed on the molecular mechanisms of renal handling of cimetidine, little is known about that of famotidine. In this study, to examine the recognition and transport of famotidine by human organic anion transporters (OATs; hOAT1, hOAT3) and human organic cation transporter (OCT; hOCT2), the uptake studies using Xenopus laevis oocytes were performed in comparison with cimetidine. The half-maximal inhibitory concentrations of famotidine for [3H]estrone sulfate transport by hOAT3 and [14C]tetraethylammonium transport by hOCT2 (300 microM and 1.8 mM, respectively) were higher than those of cimetidine (53 and 67 microM, respectively). While cimetidine inhibited p-[14C]aminohippurate transport by hOAT1 in a concentration dependent manner, famotidine did not affect it at 5 mM. In addition, hOAT3 mediated famotidine uptake, but hOAT1 and hOCT2 did not show famotidine transport. These results indicate that there are marked differences between famotidine and cimetidine in the recognition and transport by organic ion transporters and that hOAT3 contributes to the renal tubular secretion of famotidine. Present findings should be useful information to understand the renal handling of famotidine and cimetidine.

Carrier-mediated uptake of H2-receptor antagonists by the rat choroid plexus: involvement of rat organic anion transporter 3

The choroid plexus (CP) acts as a site for the elimination of xenobiotic organic compounds from the cerebrospinal fluid (CSF). The purpose of the present study is to investigate the role of rat organic anion transporter 3 (rOat3; Slc22a8) in the uptake of H(2)-receptor antagonists (cimetidine, ranitidine, and famotidine) by the isolated rat CP. Saturable uptake of cimetidine and ranitidine was observed in rOat3-LLC with K(m) values of 80 and 120 microM, respectively, whereas famotidine was found to be a poor substrate. The steady-state concentration of the H(2)-receptor antagonists in the CSF was significantly increased by simultaneously administered probenecid, although it did not affect their brain and plasma concentrations. Saturable uptake of cimetidine and ranitidine was observed in the isolated rat CP with K(m) values of 93 and 170 microM, respectively, whereas 50% of the uptake of famotidine remained at the highest concentration examined (1 mM). The K(i) value of ranitidine for the uptake of cimetidine by the isolated CP (50 microM) was similar to its own K(m) value, suggesting that they share the same transporter for their uptake. The inhibition potency of organic anions such as benzylpenicillin, estradiol 17beta-glucuronide, p-aminohippurate, and estrone sulfate for the uptake of cimetidine by the isolated rat CP was similar to that for benzylpenicillin, the uptake of which has been hypothesized to be mediated by rOat3, whereas a minimal effect by tetraethylammonium excludes involvement of organic cation transporter(s). These results suggest that rOat3 is the most likely candidate transporter involved in regulating the CSF concentration of H(2)-receptor antagonists at the CP.

Secretory transport of ranitidine and famotidine across Caco-2 cell monolayers

The secretory transport of the H(2)-antagonists, ranitidine and famotidine, across Caco-2 cell monolayers was found to be a saturable process. Both drugs exhibited greater permeability in the basolateral (BL) to apical (AP) direction than in the AP to BL direction, indicating apically directed secretion; BL to AP transport was inhibited by P-glycoprotein (P-gp) inhibitors verapamil and cyclosporin A. The cellular uptake of ranitidine across the BL membrane was saturable and temperature dependent, indicative of carrier-mediated transport. The K(m) and V(max) for the uptake process were estimated to be 66.9 mM and 20.9 nmol/mg of protein/min, respectively. The uptake of [(14)C]ranitidine across the BL membrane was inhibited by unlabeled ranitidine and structurally diverse organic cations. The tetraethylammonium (TEA)-sensitive organic cation transporters are not involved in the uptake of ranitidine and famotidine across the BL membrane of Caco-2. This conclusion was based on the evidence that functionally active TEA-sensitive organic cation transporters did not exist in the BL membranes of the Caco-2 cells, whereas the functionally active TEA-sensitive organic cation transporter(s) in LLC-PK(1) cells did not contribute to the transport of ranitidine or famotidine across the cell monolayers. Thus, we conclude that the secretory transport of ranitidine and famotidine across Caco-2 cell monolayers is mediated by 1) a carrier in the BL membrane that is distinct from the TEA-sensitive organic cation transporter(s) and 2) P-gp in the apical membrane.

Susceptibility of the H2-receptor antagonists cimetidine, famotidine and nizatidine, to metabolism by the gastrointestinal microflora

The H(2)-receptor antagonist ranitidine has previously been shown to be a substrate for colonic bacterial metabolism. The objective of the present study was to assess the in vitro stability of the other H(2)-receptor antagonists, cimetidine, famotidine and nizatidine, to colonic bacteria. One hundred milligrams of each drug were introduced into individual batch culture fermenters (100 ml) consisting of buffer medium inoculated with freshly voided human faeces (10% w/v). Control experiments, equivalent drug quantities in buffer medium without the presence of faeces, were also run in parallel. Samples were removed at set time intervals over a 24 h period and were subsequently analysed by HPLC. A selection of the samples removed from the fermenters was also subjected to analysis by UV spectroscopy and mass spectrometry. Following an initial dissolution phase in the fermentation system, a marked decline in nizatidine concentration was noted over time with virtually no drug remaining after 12 h, thereby suggesting degradation and metabolism of the drug by colonic bacteria. No such decline in concentration was noted for cimetidine or famotidine or for any of the drugs in the control buffer systems. The metabolic reaction pathway for nizatidine was complex, although UV and mass spectrometry analysis indicated that metabolism was initiated via cleavage of an N-oxide bond within the molecule. These results in combination with those obtained from a previous study indicate that of the four commercially available H(2)-receptor antagonists, nizatidine and ranitidine are susceptible to metabolism by colonic bacteria, which in turn has ramifications for drug delivery and absorption.

New findings on degradation of famotidine under basic conditions: identification of a hitherto unknown degradation product and the condition for obtaining the propionamide intermediate in pure form

The degradation behavior of famotidine (1) was investigated in 25% ammonia solution and in 2 M NaOH. The hydrolysis of the drug in ammonia resulted in separation of [3-[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]propionamide (3), an impurity listed in British Pharmacopoeia. The treatment with 2 M NaOH resulted in formation of [3-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]propionyl]sulfamide (2) and 3. These products further decomposed to [3-[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]propionic acid (4) and a heretofore unknown product, 5. The latter separated out in the reaction mixture as brown shiny crystals. Proton and carbon-13 nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis of the charcoal-treated product established the structure. The formation of 5 is postulated to involve abstraction of a proton from the alpha-carbon of intermediates 2 and 3 followed by elimination of the thiol moiety.

Neurotoxic convulsions induced by histamine H2 receptor antagonists in mice

Convulsive potency was evaluated to investigate the mechanism of neurotoxic convulsion induced by histamine H2 receptor antagonists (H2 blockers). Four H2 blockers, cimetidine (721-1236 nmol), ranitidine (477-954 nmol), famotidine (7.4-44 nmol), and nizatidine (226-603 nmol) were administered intracerebrally (i.c.) to mice. Dose dependency of clonic and/or tonic convulsion was observed, and the ED50 values of convulsive occurrence for cimetidine, ranitidine, famotidine, and nizatidine were 997, 662, 23.4, and 404 nmol, respectively. Intraperitoneal pretreatment of muscimol, aminooxy acetic acid, diazepam, (+/-)2-amino-7-phosphonoheptanoic acid (APH), or (+)MK801 suppressed the tonic convulsion after i.c. administration of ranitidine, but had no effect on clonic convulsion. Furthermore, the convulsive threshold concentration in the brain determined by constant rate infusion of ranitidine was not affected by the pretreatment of muscimol, diazepam, APH, and MK801. Ed50 values for convulsive occurrence after i.c. administration of four H2 blockers correlated well with the EC50 values for gastric acid secretion inhibition. The convulsive threshold concentrations of cimetidine and ranitidine in the brain were 11 and 2.5 microM, respectively, which were similar to the dissociation constants determined from the inhibition of gastric acid output in mice. From these results, tonic convulsion induced by H2 blockers can be suppressed by GABAergic or glutamatergic anticonvulsants, while clonic convulsion induced by H2 blockers may be associated with the blockade of H2 receptor in the brain and not be directly associated with the GABA and glutamate-mediated neurotransmission.

Stability and compatibility of anakinra with intravenous cimetidine hydrochloride or famotidine in 0.9% sodium chloride injection

We designed a study to evaluate the stability and compatibility of anakinra (recombinant human interleukin-1 receptor antagonist) with cimetidine hydrochloride or famotidine in 0.9% sodium chloride injection during a 4-h period at room temperature (22 degrees C) and light. Anakinra was diluted in 0.9% sodium chloride to concentrations of 4 and 36 mg/ml. At each concentration, anakinra was mixed with 3 mg/ml cimetidine or with 1 mg/ml famotidine, in a 50:50 proportion and stored in plastic culture vials with polypropylene caps. The mean concentrations of anakinra, cimetidine hydrochloride, and famotidine exceeded 95% of initial concentrations throughout the study. No changes were noted in the physical appearance, pH, or the chromatograms during the study period. Thus, anakinra appears to be stable and compatible with cimetidine hydrochloride or famotidine when diluted into 0.9% sodium chloride injection for 4 h at ambient room temperature and light.

H2-receptor antagonists are scavengers of oxygen radicals

Potential oxygen radical scavenging properties of the H2-receptor antagonists cimetidine, ranitidine and famotidine were investigated. These drugs, although ineffective against superoxide anion and hydrogen peroxide, can scavenge hydroxyl radical (OH.) with a very high rate constant, which is about tenfold higher than that of the specific scavenger mannitol for famotidine (1.7 x 10(10) mol-1 s-1) and cimetidine (1.6 x 10(10) mol-1 s-1), ranitidine displaying a rate constant of 7.5 x 10(9) mol-1 s-1. These OH. savenging effects are significant beginning from 10, 28 and 100 mumol l-1 concentration for famotidine, cimetidine and ranitidine, respectively, thus suggesting that the drugs may effectively act as OH. scavengers in vivo especially in the gastric lumen. Only cimetidine can apparently bind and inactivate iron, which further emphasizes its antioxidant capacity. Moreover, all drugs, even at 10 mumol l-1 concentration, show powerful scavenging effects on hypochlorous acid and monochloramine, which are cytotoxic oxidants arising from inflammatory cells, such as neutrophils. These data suggest that some therapeutical effects of H2-receptor antagonists in peptic ulcer may also be related to their antiradical-antioxidant capacity, and that these drugs could potentially be used in other disease entities characterized by free radical-mediated oxidative stress in vivo.

Structural characteristics of histamine H2 receptor antagonists that scavenge hypochlorous acid

Gastric and duodenal ulcers are characterized by hypersecretion of gastric acid and pepsin, inflammation of the mucosa and an influx of neutrophils. These cells can produce reactive oxygen species after stimulation. Particularly hydroxyl radicals and hypochlorous acid (HOCl) can be cytotoxic and damage the gastroduodenal mucosa. It has been shown that histamine H2 receptor antagonists such as cimetidine, ranitidine and famotidine are good hydroxyl radical scavengers. This study was undertaken to investigate whether these agents were able to scavenge the cytotoxic HOCl, and if so, which part of the molecule could be responsible for this action. It appears that the sulfur atom in the compound is of importance for scavenging HOCl. This finding should be taken into consideration in the development of new anti ulcer drugs, as HOCl is a detrimental factor in the pathophysiology of gastroduodenal ulcers.

Pharmacokinetics of cefpodoxime proxetil and interactions with an antacid and an H2 receptor antagonist

Cefpodoxime proxetil is a new oral esterified cephem antibiotic with a broad antibacterial spectrum. The dissolution of cefpodoxime proxetil is pH dependent. The objectives of this study were to characterize the pharmacokinetics of cefpodoxime proxetil in two different oral doses and to examine possible interactions with an antacid, aluminum magnesium hydroxide (Maalox 70), and an H2 receptor antagonist, famotidine. Two studies involving the same 10 healthy volunteers were performed. In the first study, cefpodoxime proxetil was administered in two doses, 0.1 and 0.2 g. In the second study, two interventions were performed in a randomized crossover design. For one intervention, the volunteers were pretreated with 40 mg of famotidine 1 h before 0.2 g of cefpodoxime proxetil was administered. In the second trial, participants were given 10 ml of Maalox 70 2 h and 10 ml of Maalox 70 15 min before they received 0.2 g of cefpodoxime proxetil. Serum and urine concentrations were determined by high-performance liquid chromatography. For the statistical evaluation, these data were tested by using the pharmacokinetics of 0.2 g of cefpodoxime proxetil from the first study. The maximum concentrations were 1.19 +/- 0.32 mg/liter after 0.1 g of cefpodoxime proxetil and 2.54 +/- 0.64 mg/liter after 0.2 g of cefpodoxime proxetil. The elimination half-lives were 149 min for 0.1 g and 172 min for 0.2 g of cefpodoxime proxetil. The total increase in the area under the concentration-time curve (AUC) was dose dependent. Combination with Maalox 70 caused a reduction in the AUC from 14.0 +/- 3.9 to 8.44 +/- 1.85 mg.h/liter. After famotidine, the AUC decreased to 8.36 +/- 2.0 mg . h/liter. Corresponding changes were registered for the maximum concentration of drug in serum, 24-h urine recovery, and the time to maximum concentration of drug serum. Cefpodoxime proxetil was well tolerated without any seriously adverse drug reactions.

Time-dependent interaction of a new H2-receptor antagonist, IT-066, with the receptor in the atria of guinea pig

3-Amino-4-[4-[4-(1-piperidinomethyl)-2-pyridyloxy]-cis-2- butenylamino]-3-cyclobutene-1,2-dione hydrochloride (IT-066) showed a highly potent and long lasting H2-receptor blocking action in guinea pig atria. The inhibitory effect of IT-066 on the histamine-induced positive chronotropic response increased concentration- and time-dependently. A short period of treatment with IT-066 shifted the concentration-response curve of histamine to the right in parallel, without decreasing the maximal response to histamine. With prolongation of the treatment, the concentration-response curve shifted further to the right with time-dependent suppression of the maximal response to histamine. The inhibitory effect of IT-066 was irreversible. The dissociation constant for histamine (KA) was not changed by prolongation of the time of incubation with IT-066. The dissociation constant for IT-066 (KB) was decreased with the prolongation of the treatment. Kinetic analysis of the time-dependent inhibition showed a two-step reaction: the first was reversible and the second was irreversible. Preincubation of the atria with ranitidine, however, protected the H2-receptor from the apparently irreversible antagonism of IT-066. These results suggest that IT-066 has a time-dependent and irreversible interaction with the H2-receptor and that the interaction may be responsible for the potent and long lasting H2-receptor blocking action of IT-066.