Development and in vitro/in vivo evaluation of famotidine hydrochloride bioadhesive sustained release suspension

To develop a new kind of famotidine-resin microcapsule for gastric adhesion sustained release by screening out suitable excipients and designing reasonable prescriptions to improve patient drug activities to achieve the expected therapeutic effect. The famotidine drug resin was prepared using the water bath method with carbomer 934 used as coating material. Microcapsules were prepared using the emulsified solvent coating method and appropriate excipients were used to prepare famotidine sustained release suspension. Pharmacokinetics of the developed microcapsules were studied in the gastrointestinal tract of rats. The self-made sustained-release suspension of famotidine hydrochloride effectively reduced the blood concentration and prolonged the action time. The relative bioavailability of the self-made suspension of the famotidine hydrochloride to the commercially available famotidine hydrochloride was 146.44%, with an average retention time of about 5h longer, which indicated that the new suspension had acceptable adhesion properties. The findings showed that the newly developed famotidine-resin microcapsule increased the bioavailability of the drug with a significant sustained-release property.

Improved gastric residence time of famotidine by raft-forming drug delivery system using DOE

OBJECTIVE

This study investigated the raft-forming suspension of famotidine as an anti-reflux formulation to improve the oral bioavailability of narrow absorption window drugs by enhancing gastric residence time (GRT) and preventing gastro-esophageal reflux disease (GERD).

METHOD

Various combinations of raft-forming agents, such as Tragacanth gum (TG), guar gum (GG), and xanthan gum (XG), were evaluated alongside sodium alginate (SA) to develop an effective raft. Preformulation studies and preliminary screening were conducted to identify the most suitable raft-forming agent, and GG was chosen due to its mucilaginous properties. The formulation was optimized using a 32 full factorial design, with the quantities of GG and SA as independent factors and apparent viscosity and in-vitro drug release (%) as dependent factors. The in vivo floating behavior study was performed for optimized and stabilized formulation.

RESULTS

Among the tested batches, F6 was selected as the optimized formulation. It exhibited desirable characteristics such as adequate raft weight for extended floating in gastric fluid, improved apparent viscosity, and a significant percentage of drug release at 12 h. A mathematical model was applied to the in-vitro data to gain insights into the drug release mechanism of the formulation. The stability of the suspension was assessed under accelerated conditions, and it demonstrated satisfactory stability. The formulation remains floating in the Rabbit stomach for more than 12 h.

CONCLUSION

It concludes that the developed formulation has enhanced bioavailability in the combination of GG and SA. The floating layer of the raft prevents acid reflux, and the famotidine is retained for an extended period of time in the gastric region, preventing excess acid secretion. The developed formulations are effective for stomach ulcers and GERD, with the effect of reducing acid secretion by H2 receptor antagonists.

Spectroscopic interaction studies of H2 receptor antagonists with levocetirizine

Patients with allergic rhinitis may also suffer abdominal pain, gastritis or peptic ulcer. In this condition patient may use levocetirizine with famotidine or ranitidine. These drugs have potential to interact with another drug and form complex. The aim of the present study is to evaluate the possible drug drug interaction with each other which may cause increase or decrease of therapeutic effects. For this purpose, validity of Beer Lambert law was checked, lone availability of famotidine (20gm), ranitidine (150gm) and levocetirizine (5mg) were studied in pH simulated to gastric juice (pH 1), pH 4, pH 7.4 and in pH 9 and finally percent availabilities of these drugs were calculated with the help of simultaneous equation. Results showed high percentage of levocetirizine in all pH as 300.32%, 514.41%, 173.38% and 220.68% in presence of famotidine but very low availability of famotidine as 5.36%, 35.38%, 51.87% and 10.89% in presence of levocetirizine. In the case of levocetirizine and ranitidine interaction, zero percent levocetirizine was available at pH 1and 9, 56.28% in pH 4 and 191.1% in pH 7.4. On the other hand, ranitidine was available as 95.36%, 127.93%, 41.47% and 144.3%. These results showed that percentage of all drugs were altered in presence of each other due to drug-drug interaction. This may be due to the charge transfer binding capabilities of the drugs which resulted in significantly changed availability of famotidine, ranitidine as well as levocetirizine.

Effect of gastric acid-reducing agents on the pharmacokinetics and efficacy of lemborexant

Lemborexant is a dual orexin receptor antagonist approved for treating insomnia. As the solubility of lemborexant is pH-sensitive, the impact of the gastric acid-reducing agent (ARA), famotidine, on lemborexant pharmacokinetics was evaluated in a Phase 1 study. Additionally, post hoc analysis of data from Phase 3 studies examined the potential effect of concomitant ARAs on patient-reported/subjective sleep onset latency (sSOL) in subjects with insomnia. Coadministration of lemborexant 10 mg with famotidine decreased the maximum observed concentration by 27% and delayed time of maximum observed concentration by 0.5 hours. Famotidine did not affect overall lemborexant exposure based on comparison of area under the concentration curves. Concomitant ARA use in the Phase 3 studies did not impact the effect of lemborexant on sSOL; the change from baseline during the last 7 nights of 1 month of treatment with lemborexant 10 mg was -17.1 minutes with vs -17.9 minutes without ARAs. Collectively, these results indicate that lemborexant can be coadministered with ARAs.

Class A G Protein-Coupled Receptor Antagonist Famotidine as a Therapeutic Alternative Against SARS-CoV2: An In Silico Analysis

The pandemic associated with Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV2) and its disease named COVID-19 challenged the scientific community to discover effective therapeutic solutions in a short period. Repurposing existing drugs is one viable approach that emphasizes speed during these urgent times. Famotidine, a class A G protein-coupled receptor antagonist used for the treatment of gastroesophageal reflux was recently identified in an in silico screening. Additionally, a recent retrospective clinical report showed that the treatment with famotidine provided a good outcome in patients infected with SARS-CoV2. A clinical trial testing effectiveness of famotidine in combination with hydroxychloroquine is currently ongoing in the United States (US). In the 1990s, famotidine was described as an antiviral agent against human immunodeficiency virus (HIV). Interestingly, some HIV protease inhibitors are presently being used against SARS-CoV2. However, it is not clear if famotidine could be effective against SARS-CoV2. Thus, by using a computational analysis, we aimed to examine if the antiviral effect of famotidine could be related to the inhibition of proteases involved in the virus replication. Our results showed that famotidine could interact within the catalytic site of the three proteases associated with SARS-CoV2 replication. However, weak binding affinity of famotidine to these proteases suggests that a successful famotidine therapy could likely be achieved only in combination with other antiviral drugs. Finally, analysis of famotidine's pharmacokinetic parameters indicated that its effect against SARS-CoV2 infection could be reached only upon intravenous administration. This work will contribute to the pharmacological knowledge of famotidine as an antiviral agent against SARS-CoV2.

In vitro Spectroscopic studies on drug interaction of cefpodoxime proxetil and H2 receptor blockers

One of the relatively advance 3rd generation cephalosporins, cefpodoxime proxetil, is being used all-around. Generally, these are used for the cure of infections allied to urinary and respiratory tract. These cephalosporins have showed a remarkable in vitro activity against many strains of bacteria which are resistant to other orally used active medicinal substances. It is the first oral 3rd generation cephalosporin to be used in the cure of skin infections. The practice of H2 receptor antagonists, concerning lots of treatments recommended in patients with different types of ulcers and allergic urticarial condition, is raising hazards of unwanted secondary outcomes and drug interactions. Learning of in-vitro interaction between cefpodoxime poxetil and H2 blockers (Ranitidine, Famotidine and Cimetidine) were examined applying UV/Visible spectrophotometry and Infrared spectrometry. In the existence of H2 receptor blockers, the cefpodoxime proxetil availability was found to be decreased in vitro only under specific conditions. Furthermore, complexes of Cefpodoxime proxetil-H2 receptor antagonists were manufactured approving the interaction of these drugs. Finally, the above mentioned spectrophotometric techniques were employed to examine the complexes formed (Cefpodoxime proxetil-cimetidine, cefpodoxime proxetil-famotidine and cefpodoxime proxetil-ranitidine).

Monitoring simultaneous photocatalytic-ozonation of mixture of pharmaceuticals in the presence of immobilized TiO2 nanoparticles using MCR-ALS: Identification of intermediates and multi-response optimization approach

The present study has focused on the degradation of a mixture of three pharmaceuticals, i.e. methyldopa (MDP), nalidixic acid (NAD) and famotidine (FAM) which were quantified simultaneously during photocatalytic-ozonation process. The experiments were conducted in a semi-batch reactor where TiO2 nanoparticles (crystallites mean size 8nm) were immobilized on ceramic plates irradiated by UV-A light in the proximity of oxygen and/or ozone. The surface morphology and roughness of the bare and TiO2-coated ceramic plates were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). An analytical methodology was successfully developed based on both recording ultraviolet-visible (UV-Vis) spectra during the degradation process and a data analysis using multivariate curve resolution with alternating least squares (MCR-ALS). This methodology enabled the researchers to obtain the concentration and spectral profiles of the chemical compounds which were involved in the process. A central composite design was used to study the effect of several factors on multiple responses namely MDP removal (Y1), NAD removal (Y2) and FAM removal (Y3) in the simultaneous photocatalytic-ozonation of these pharmaceuticals. A multi-response optimization procedure based on global desirability of the factors was used to simultaneously maximize Y1, Y2 and Y3. The results of the global desirability revealed that 8mg/L MAD, 8mg/L NAD, 8mg/L FAM, 6L/h ozone flow rate and a 30min-reaction time were the best conditions under which the optimized values of various responses were Y1=95.03%, Y2=84.93% and Y3=99.15%. Also, the intermediate products of pharmaceuticals generated in the photocatalytic-ozonation process were identified by gas chromatography coupled to mass spectrometry.

Release mechanisms behind polysaccharides-based famotidine controlled release matrix tablets

Polysaccharides, which have been explored to possess gelling properties and a wide margin of safety, were used to formulate single-unit floating matrix tablets by a direct compression technique. This work has the aim to allow continuous slow release of famotidine above its site of absorption. The floating approach was achieved by the use of the low density polypropylene foam powder. Polysaccharides (kappa-carrageenan, gellan gum, xyloglucan, and pectin) and blends of polysaccharides (kappa-carrageenan and gellan gum) and cellulose ethers (hydroxypropylmethyl cellulose, hydroxypropylcellulose, sodium carboxymethyl cellulose) were tried to modulate the release characteristics. The prepared floating tablets were evaluated for their floating behavior, matrix integrity, swelling studies, in vitro drug release studies, and kinetic analysis of the release data. The differential scanning calorimetry and Fourier transform infrared spectroscopy studies revealed that changing the polymer matrix system by formulation of polymers blends resulted in formation of molecular interactions which may have implications on drug release characteristics. This was obvious from the retardation in drug release and change in its mechanistics.

Caco-2 Cell Culture as a Model for Famotidine Absorption

The aim of the study was to determine penetration properties of Famotidine fro the formulations through colon adenocarcinoma (Caco)-2 cell monolayers and to compare in vitro with in vivo test results. It also aimed to determine the effect of particle size on the penetration properties of Famotidine when microsphere formulations were used. Famotidine was chosen as a model drug and Caco-2 cell culture model was used. Biodegradable Famotidine microspheres of poly(lactide-co-glycolide)(PLGA) polymer (50:50) were prepared by using multiple emulsion technique. Microspheres were coded according to their particle size and polymer[LHIV:60 microm Famotidine-PLGA(high viscosity), SHIV:6 microm Famotidine PLGA(high viscosity), LLIV:60 microm Famotidine-PLGA (low viscosity), SLIV:6 microm Famotidine-PLGA (low viscosity)]. Famotidine solution(5 mg/ml) and microsphere formulations were administered orally to mice and blood drug levels were determined and compared with the Caco-2 cell experiments. Permeability values of Famotidine through Caco-2 cells from various formulations were determined (log k(solution) = 7,274 +/- 0,010,log kSHIV = -3,884 +/- 0,033,log kLHIV = -2,300 +/- 0,009,log kSLIV = -4,076 +/- 0,208,log kLLIV = 3,525 +/- 0,045). Our results showed that H2 receptor antagonists alter the barrier properties of the Caco-2 cell monolayer by causing an increment in the tightness of the tight junctions. Therefore, amount of the H2 receptor antagonist-like drug at the site of action was found to be important as well as polymer type and particle size of microspheres for drug permeation. Permeation of the drug was lower when higher amounts of Famotidine were present at the diffusion site. A controlled release dosage form of H2 receptor antagonist-like drugs may be beneficial for long-term treatments.

Which has superior acid-suppressive effect, 10 mg omeprazole once daily or 20 mg famotidine twice daily? Effects of single or repeated administration in Japanese Helicobacter pylori-negative CYP2C19 extensive metabolizers

Low-dose omeprazole is superior to full-dose famotidine in maintenance therapy for gastroesophageal reflux disease, whereas "on-demand" famotidine is more effective for relief of episodes of heartburn. To explain this apparent discrepancy, intragastric pH was measured for 24-hr seven times in eight Japanese Helicobacter pylori-negative cytochrome P450 2C19 extensive metabolizers; on Days 1, 8, and 15 of repeated administration of 10 mg of omeprazole once daily and of 20 mg of famotidine twice daily and before medication. During repeated administration of omeprazole, mean intragastric pH and % time that intragastric pH > 4.0 were significantly higher and became greater. With famotidine, although these parameters were significantly higher, the degrees became smaller. Consequently, acid-suppressive effect was in the order; omeprazole < famotidine on Day 1, omeprazole approximately famotidine on Day 8, and omeprazole >famotidine on Day 15. This discrepancy possibly results from the "potentiation" of acid-suppressive effect of omeprazole and the "tolerance" phenomenon in respect to famotidine.

Initial 48-hour acid inhibition by intravenous infusion of omeprazole, famotidine, or both in relation to cytochrome P450 2C19 genotype status

BACKGROUNDS AND AIMS

Faster and stronger acid inhibition is required for the treatment of hemorrhage from peptic ulcers. We compared the effects of intravenous infusion regimens of a proton pump inhibitor (PPI) alone, a histamine 2 receptor antagonist (H2RA) alone, and the combination of a PPI with an H2RA on acid inhibition in the early postadministration phase in relation to cytochrome P450 (CYP) 2C19 genotype status.

METHODS

Fifteen Helicobacter pylori-positive volunteers with 3 different CYP2C19 genotypes were administered twice-daily intravenous infusions of 20 mg famotidine alone, 20 mg omeprazole alone, 10 mg omeprazole plus 10 mg famotidine (half-concomitant regimen), and 20 mg omeprazole plus 20 mg famotidine (full-concomitant regimen) for 2 days. The subjects underwent 48-hour intragastric pH monitoring.

RESULTS

In homozygous extensive metabolizers (EMs) the median first 24-hour intragastric pH with the full-concomitant regimen was 4.8 (range, 4.5-5.4), which was significantly higher than that with omeprazole alone (3.9 [range, 2.6-4.7], P=.043) or famotidine alone (4.4 [range, 3.8-4.9], P=.043). In heterozygous EMs and poor metabolizers the respective median first 24-hour pH values attained with omeprazole alone (5.8 [range, 4.3-6.3] and 6.1 [range, 5.3-7.4]) and the full-concomitant regimen (5.8 [range, 5.1-6.4] and 5.8 [range, 5.4-6.2]) were significantly higher than those attained with famotidine alone (4.1 [range, 3.9-6.5] and 4.7 [range, 3.7-5.7], P=.043 for all).

CONCLUSIONS

For faster and stronger acid inhibition, the concomitant infusion regimen of a PPI and an H2RA appears to be therapeutically useful in homozygous and heterozygous EMs, but omeprazole alone appears to be sufficient in poor metabolizers of CYP2C19.

Pharmacokinetic and Pharmacodynamic Properties of Lafutidine after Postprandial Oral Administration in Healthy Subjects: Comparison with Famotidine

Lafutidine, a histamine H(2)-receptor antagonist, inhibits gastric acid secretion during the daytime, however, the relationship between the plasma concentration and the drug response remains unclear. The aim of this study was to compare the pharmacokinetic and pharmacodynamic properties of lafutidine and famotidine following postprandial oral administration. After a lafutidine tablet (10 mg), famotidine tablet (20 mg), or water only (control) was administered, blood samples were taken and intragastric pH was measured. The plasma concentrations of lafutidine and famotidine were determined by HPLC, and the median intragastric pH values per 30 min were used as the degrees of gastric acid suppression. Data were analyzed based on a one-compartment pharmacokinetic model and a sigmoid E(max) pharmacodynamic model. Lafutidine plasma concentrations rapidly increased after administration; famotidine required some time to increase the plasma concentrations, requiring an absorption lag time in the pharmacokinetic model. Between the plasma concentration and DeltapH (the difference in intragastric pH by the drug vs. control), lafutidine showed an anticlockwise hysteresis loop which indicated equilibration delay between the plasma concentration and effect site, requiring an effect site compartment in the pharmacodynamic model; famotidine showed more parallel relationship. These results indicated that the pharmacokinetic and pharmacodynamic properties of lafutidine after postprandial oral administration were different from those of famotidine at least 4.5 h after dosing.

Formulation and Evaluation of Famotidine Floating Tablets

The purpose of this investigation was to prepare a gastroretentive drug delivery system of famotidine. Floating tablets of famotidine were prepared employing two different grades of methocel K100 and methocel K15M by effervescent technique; these grades of methocel were evaluated for their gel forming properties. Sodium bicarbonate was incorporated as a gas-generating agent. The floating tablets were evaluated for uniformity of weight, hardness, friability, drug content, in vitro buoyancy and dissolution studies. The effect of citric acid on drug release profile and floating properties was investigated. The prepared tablets exhibited satisfactory physico-chemical characteristics. All the prepared batches showed good in vitro buoyancy. The tablet swelled radially and axially during in vitro buoyancy studies. It was observed that the tablet remained buoyant for 6-10 hours. Decrease in the citric acid level increased the floating lag time but tablets floated for longer duration. A combination of sodium bicarbonate (130mg) and citric acid (10mg) was found to achieve optimum in vitro buoyancy. The tablets with methocel K100 were found to float for longer duration as compared with formulations containing methocel K15M. The drug release from the tablets was sufficiently sustained and non-Fickian transport of the drug from tablets was confirmed.

[Drug release mechanism of famotidine time-controlled release pellets]

AIM

To study the drug release mechanism of famotidine time-controlled release pellets and to explore the mechanism of "organic acid-induced type drug delivery system".

METHODS

The effects of dissociated and undissociated forms of succinic acid on the drug release behavior of famotidine time-controlled release pellets were studied from the following aspects: ion-exchange reaction, hydration, etc.

RESULTS

The dissociated succinic acid created new ionic circumstances by ion-exchange reaction with Eudragit RS100. Whereas undissociated succinic acid increased the flexibility of the film by distribution in the hydrophobic segment of Eudragit RS100. Effects of both forms of the succinic acid could improve the hydration of Eudragit RS film. As a result, the permeability of the film was improved evidently.

CONCLUSION

The lag time of famotidine time-controlled release pellets is induced by the hydrophobicity of the film. After water dissolve the organic acid, the dissociated and undissociated forms of succinic acid interact with the film through different ways. These interactions can change the structure of the film. Therefore the permeability of the film will be improved markedly.

Variability in renal clearance of substrates for renal transporters in chinese subjects

The authors evaluated the inter- and intraindividual variability in the renal clearance of substrates of organic anion transporters (OAT) or organic cation transporters (OCT) using repeated drug application procedures. Two OAT substrates (ampicillin and cephalexin) and 2 OCT substrates (famotidine and metformin) were selected. Each drug was administered orally twice to healthy subjects, with sample sizes ranging from 12 to 28 (using bioequivalent formulations of each drug). The inter-(delta(inter)) and intrasubject (delta(intra)) variances in renal clearance were estimated based on analysis of variance, and the genetic contribution (r(GC)) was calculated as (delta(inter - intra))/delta(inter). The renal clearances of ampicillin, cephalexin, famotidine, and metformin averaged 5.21 (range, 2.87-11.20), 3.01 (range, 1.50-3.82), 4.96 (range, 2.84-8.17), and 9.44 (range, 5.66-15.43) mL/min/kg, with mean intraindividual coefficients of variation of 17.7%, 7.3%, 13.5%, and 9.0% and r(GC) values of 0.75, 0.89, 0.81, and 0.93, respectively. These high r(GC) values suggest a potential significant genetic contribution by the renal OATs and OCTs in Chinese subjects. Further studies in a larger population are needed to confirm the importance of these results as well as to identify specific genetic variants in these transporters responsible for such variability.

Is the Monkey an Appropriate Animal Model to Examine Drug-Drug Interactions Involving Renal Clearance? Effect of Probenecid on the Renal Elimination of H2Receptor Antagonists

The renal drug-drug interaction between famotidine (an H(2) receptor antagonist) and probenecid has not been reproduced in rats. We have proposed that this is caused by a species difference in the transport activity by human/rat organic anion transporter (OAT) 3 and the expression of organic cation transporter (OCT) 1 in the rodent kidney. Since monkey OATs (mkOATs) exhibit similar transport activities to human orthologs, it is hypothesized that in vivo studies in monkeys will allow a more precise prediction of renal drug-drug interactions in humans. Famotidine and cimetidine were efficiently taken up by mkOAT3-expressing human embryonic kidney cells (Km, 154 and 71 microM, respectively), and their uptake was strongly inhibited by probenecid (Ki, 3.0-5.7 microM). Quantification of mkOCT1 and mkOCT2 mRNAs in the monkey kidney using real-time reverse transcription-polymerase chain reaction revealed their predominant expression in the liver and kidney, respectively. Crossover studies were conducted in cynomolgus monkeys. Famotidine was given by i.v. administration, with or without probenecid. Probenecid treatment caused a 65% reduction in the renal clearance (0.426 +/- 0.079 versus 0.165 +/- 0.027 l/h/kg) and a 90% reduction in the tubular secretion clearance (0.275 +/- 0.075 versus 0.0230 +/- 0.0217 l/h/kg), whereas it had no effect on the renal clearance of cimetidine. In contrast to the species-dependent effect of probenecid, allometric scaling using animal data (rat, dog, and monkey) successfully predicted the renal and tubular secretion clearance of famotidine in humans. These results suggest that monkeys are more appropriate animal species for predicting the renal drug-drug interactions in humans.

Comparative study of the speed of acid-suppressing effects of oral administration of cimetidine and famotidine

BACKGROUND AND AIM

H2 histamine receptor antagonists (H2RAs) are widely used in patients with acid-related diseases, and the onset of antisecretory activity of H2RAs is reported to be faster than that of proton pump inhibitors (PPIs). The aim of this study was to compare the rapidity of onset of antisecretory activity of cimetidine and famotidine when orally administered.

METHODS

Fifteen healthy male Japanese volunteers (five H. pylori-positive and 10 H. pylori-negative) participated in a randomized cross-over study. All subjects were examined three times by ambulatory 6-h pH monitoring (from 17:30 to 23:30) with no medication or oral administration of 400 mg of cimetidine or 20 mg of famotidine. Drugs were administered at 19:30 after eating a standard meal, and plasma concentrations were also examined for 4 h periods.

RESULTS

The plasma concentration of cimetidine increased rapidly after oral administration, while that of famotidine increased gradually. Intragastric pH was increased and percentage time with pH < 4.0 decreased significantly 2 h after administration of either cimetidine or famotidine. There was no statistically significant difference in acid-suppressing effect between cimetidine and famotidine during the short-term post-administration period.

CONCLUSION

Rapidity of antisecretory activity did not differ between oral cimetidine and famotidine administered orally.

Pharmacokinetics of Famotidine in Infants

BACKGROUND

Although famotidine pharmacokinetics are similar in adults and children older than 1 year of age, they differ in neonates owing to developmental immaturity in renal function. Little is currently known about the pharmacokinetics of famotidine in infants aged between 1 month and 1 year, a period when renal function is maturing.

OBJECTIVE

To characterise the pharmacokinetics of famotidine in infants.

DESIGN

This was a two-part multicentre study with both single dose (Part I, open-label) and multiple dose (Part II, randomised) arms.

PATIENTS

Thirty-six infants (20 females and 16 males) who required treatment with famotidine and who had an indwelling arterial or venous catheter for reasons unrelated to the study.

METHODS

Infants in Part I were administered a single dose of famotidine 0.5 mg/kg; the dose was intravenous or oral according to the judgement of the attending physician. Infants receiving 0.5 mg/kg intravenously were divided into two groups by age, and pharmacokinetic parameters in infants 0-3 months and >3 to 12 months of age were compared. Infants in Part II were randomised to one of the following treatments: 0.25 mg/kg/dose intravenously or 0.5 mg/kg/dose orally on day 1 and subsequent days, or 0.25 mg/kg/dose intravenously or 0.5 mg/kg/dose orally on day 1 followed by doses of either 0.5 mg/kg/dose intravenously or 1 mg/kg/dose orally on subsequent days. From day 2 onwards, age-adjusted dose administration regimens (once daily in infants <3 months of age and every 12 hours in infants >3 months of age) were used; the total number of famotidine doses ranged from 3 to 11 and the total number of days of dose administration ranged from two to eight.

RESULTS

In infants <3 months of age, plasma and renal clearance of famotidine were decreased compared with infants >3 months of age. Pharmacokinetic parameters for the older infants (i.e. those >3 months) were similar to those previously reported for children and adults. Approximate dose-proportionality, no accumulation on multiple dosing and an estimated bioavailability similar to adult values were also observed.

CONCLUSION

A short course of famotidine therapy in infants appears generally well tolerated, and the characteristics of famotidine pharmacokinetics during the first year of life are explained to a great degree by the development of renal function, the primary route of elimination for this drug.

Photoaffinity Labeling of the Anionic Sites in Caco-2 Cells Mediating Saturable Transport of Hydrophilic Cations Ranitidine and Famotidine

The H(2) antagonists, ranitidine and famotidine, exhibit saturable absorptive transport across Caco-2 cell monolayers and human intestine via a yet unidentified mechanism. A photoreactive derivative of famotidine has been synthesized and evaluated as a photoaffinity probe for the putative transporter protein(s). The probe irreversibly inhibited ranitidine transport across Caco-2 cell monolayers and irreversibly increased the transepithelial electrical resistance (TEER) after UV activation. Photoaffinity labeling was protected by a molar excess of famotidine.

Effect of Relative Humidity on the Photocatalytic Activity of Titanium Dioxide and Photostability of Famotidine

Titanium dioxide (TiO2) has been widely used as a pharmaceutical excipient and is also known to be a strong photocatalyst. An investigation into the relationship between the photocatalytic activity of TiO2 and the photostability of famotidine, which is known as an H2-blocker, is presented. The photocatalytic activity of the anatase form of TiO2, as measured by the four-probe method, is approximately 1.5 times higher than that of the rutile form. Discoloration of famotidine in a binary system containing TiO2 depends significantly on both the wavelength of the irradiating light and the crystal form of the TiO2, with the degree of discoloration of anatase higher than that of the rutile form. Discoloration of famotidine also depends on relative humidity. The relationship between discoloration rate constant and water vapor pressure is linear. These results demonstrate that famotidine is easily discolored by the photocatalytic activity of TiO2 and suggest that the solid-state photocatalytic activity of TiO2 is strongly affected by relative humidity.

[Preparation of famotidine microemulsion and its quality evaluation]

OBJECTIVE

To study the preparation of famotidine microemulsion (FM) and its quality evaluation, thereby to establish the quality-control criteria for this preparation.

METHODS

The formulations of the FM were optimized by studying the pseudoternary phase diagrams and its absorption in rat jejunum using in situ perfusion method. The morphology, particle size distribution, famotidine concentration and stability of the FM were studied.

RESULTS

The optimization of formulation was completed successfully. Electron microscopy presented the FM as small spherical drops, with a mean diameter of 65 nm. The average recovery as determined by high-performance liquid chromatography was 97.63%, its mean RSD being 0.72%.

CONCLUSION

The FM is easy to prepare with consistent quality, whose reliable determination method may be easily reproduced.

Famotidine disposition in children and adolescents with chronic renal insufficiency

The pharmacokinetics of intravenous famotidine (0.5 mg/kg, maximum 20 mg) were evaluated in 18 pediatric patients (ages 1-18 years) with stable, chronic renal insufficiency. Subjects were stratified by calculated creatinine clearance (Clcr) into mild (Clcr > or = 50 to < 90 mL/min/1.73 m2), moderate (Clcr > or = 25 to < 50 mL/min/1.73 m2), and severe (Clcr < or = 10 mL/min/1.73 m2) renal insufficiency groups. Significant differences between the mild, moderate, and severe groups were found for elimination rate (Kel), apparent elimination half-life (t1/2), area under the curve (AUC), and total plasma clearance (Clp) (p < 0.01). Famotidine renal clearance (Clr) was found to be significantly different between the mild and severe groups (p < 0.05). A linear relationship was observed between Clcr and Clp (p < 0.0001; R2 = 0.70). No significant differences in nonrenal clearance (Clnr) were found between groups; however, Clnr as a percentage of Clp was significantly different in the severe group (92.9% +/- 7.3% Clnr) compared to the combined mild and moderate groups (21.9% +/- 45.6% Clnr) (p < 0.05). It was concluded that the pharmacokinetics of famotidine are significantly altered in children with chronic renal insufficiency; accordingly, dosing should be based on glomerular filtration rate (i.e., Clcr).

Improved selectivity in detection of polar basic drugs by liquid chromatography-electrospray ionization mass spectrometry. Illustration using an assay method for the determination of famotidine in human plasma

It is well to assume that bioanalytical chromatographic methods for the determination of polar basic drugs are developed and optimised according to a standardised procedure which involves two alternatives: (a) modifications in the sample preparation procedures, and (b) changes in the stationary phase of the chromatographic system. In this paper, a simple and rapid chromatographic procedure using a specific analytical detection method (ESI tandem mass spectrophotometric detection) in combination with a fast and efficient sample work-up procedure, protein precipitation, is presented. A demonstration of the entire chromatographic procedure is given for an HPLC method for the determination of famotidine in human plasma, a basic polar drug with poor solubility in organic solvents. In order to optimize the mass detection of famotidine, several parameters such as ionization mode, fragmentor voltage, m/z ratios of ions monitored, type of organic modifier and eluent additive, were investigated. Each analysis required 5 min. The calibration curve of famotidine in the range 1-200 ng/ml was linear with a correlation coefficient of 0.9992 (n = 6), and a detection limit a signal-to-noise ratio of 3 was approximately 0.2 ng/ml. The within- and between-day variations in the famotidine analysis were 5.2 (n = 6) and 6.7% (n = 18), respectively. The applicability of this method was also demonstrated for the analysis of plasma samples in a Phase-I human pharmacokinetic study.

Determination of famotidine in low-volume human plasma by normal-phase liquid chromatography/tandem mass spectrometry

A rapid, sensitive and robust assay procedure using liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) for the determination of famotidine in human plasma and urine is described. Famotidine and the internal standard were isolated from plasma samples by cation-exchange solid-phase extraction with benzenesulfonic acid (SCX) cartridges. The urine assay used direct injection of a diluted urine sample. The chromatographic separation was accomplished by using a BDS Hypersil silica column with a mobile phase of acetonitrile-water containing trifluoroacetic acid. The MS/MS detection of the analytes was set in the positive ionization mode using electrospray ionization for sample introduction. The analyte and internal standard precursor-product ion combinations were monitored in the multiple-reaction monitoring mode. Assay calibration curves were linear in the concentration range 0.5--500 ng ml(-1) and 0.05--50 microg ml(-1) in plasma and urine, respectively. For the plasma assay, a 100 microl sample aliquot was subjected to extraction. To perform the urine assay, a 50 microl sample aliquot was used. The intra-day relative standard deviations at all concentration levels were <10%. The inter-day consistency was assessed by running quality control samples during each daily run. The limit of quantification was 0.5 ng ml(-1) in plasma and 0.05 microg ml(-1) in urine. The methods were utilized to support clinical pharmacokinetic studies in infants aged 0-12 months.

Characterization of tubular functional capacity in humans using para-aminohippurate and famotidine

BACKGROUND

Renal drug excretion by glomerular filtration and active tubular secretion may be altered by factors such as acute and chronic renal disease, nephrotoxins, and drug interactions. Thus, accurate and reproducible methods for quantitation of glomerular filtration rate (GFR) and tubular functional capacity are critical.

METHODS

We utilized a four-step sequential infusion method to characterize anionic [para-aminohippurate (PAH)] and cationic (famotidine) tubular functional capacity in healthy volunteers. Filtration and secretion rates were quantitated from renal clearance and iothalamate-derived GFR determinations.

RESULTS

Concentration-dependent renal clearance of PAH was observed at plasma concentrations> 100 mg/L; renal clearances were 442 +/- 131 (mean +/- SD), 423 +/- 94, 233 +/- 45, and 152 +/- 18 mL/min/1.73 m2 at plasma concentrations of 18 +/- 2, 92 +/- 5, 291 +/- 47 and 789 +/- 28 mg/L, respectively. The apparent affinity (Km) and maximum secretory capacity (TmPAH) were 141 +/- 70 mg/L and 71 +/- 16 mg/min/1.73 m2, respectively. The unbound renal clearance and tubular secretory clearance of famotidine were 384 +/- 70 and 329 +/- 78 mL/min/1.73 m2, respectively, and were not significantly correlated with the unbound plasma concentrations, which ranged from 126 to 2659 ng/mL. The rate of tubular secretion was linear at unbound plasma concentrations up to 2659 ng/mL.

CONCLUSIONS

These data indicate that a sequential infusion method using PAH may be used to characterize the anionic secretory component of proximal tubular function. The tubular clearance of famotidine may be a suitable index of the cationic secretory capacity of the proximal tubule in humans. Saturation of the cationic secretory pathway was not observed, and further investigation into parallel pathways of cationic secretion, such as p-glycoprotein, may be warranted.

Saturable transport of H2-antagonists ranitidine and famotidine across Caco-2 cell monolayers

The purpose of this study was to investigate the mechanism by which the H2-antagonists ranitidine and famotidine interacted with the paracellular space during their transport across Caco-2 cell monolayers. Transport experiments with ranitidine and famotidine across Caco-2 cell monolayers were performed to determine the apical-to-basolateral flux at various concentrations. Kinetic analysis of the transport data showed that ranitidine and famotidine were transported by both saturable and nonsaturable processes. Na+, K+-ATPase inhibitor ouabain and metabolic inhibitors sodium azide + 2-deoxy-D-glucose did not affect ranitidine transport, suggesting that the active transport was not involved. Famotidine and some other guanidine-containing compounds, e.g., guanethidine, Arg-Gly, L-arginine methyl ester, and L-argininamide, inhibited the transport of ranitidine, whereas other guanidine-containing compounds with an additional negative charge, e.g., L-arginine, did not. 2,4, 6-Triaminopyrimidine (TAP), an inhibitor of paracelluar cationic conductance, also inhibited the transport of both ranitidine and famotidine. On the basis of these results, it is proposed that the saturable transport of ranitidine and famotidine across Caco-2 cell monolayers appears to be via a facilitated diffusion process mediated by the paracellular anionic sites. This mechanism is consistent with the observation that ranitidine and famotidine caused a concentration-dependent increase in transepithelial electrical resistance (TEER) across Caco-2 cell monolayers, presumably by blocking the paracellular anionic sites and thus inhibiting the flux of cations (e.g., Na+).

Pharmacokinetics and pharmacodynamics of famotidine in infants

The pharmacokinetics and pharmacodynamics of intravenous famotidine were evaluated in 10 infants ranging from 5 to 19 days of age who had a therapeutic indication for the prophylactic treatment of stress ulceration. After a 0.5-mg/kg infusion of famotidine, timed serum (n = 6), urine (24-hour collection), and repeated measurements of gastric pH were obtained. The mean +/- standard deviation maximum plasma concentration (Cmax) was 640.66 +/- 250.66 ng/mL, the elimination half-life (t1/2 beta) was 10.51 +/- 5.43 hours, and the apparent volume of distribution at steady state (Vdss) was 0.82 +/- 0.29 L/kg. Plasma clearance (Cl) and renal clearance (ClR) were 0.132 +/- 0.061 L/hr/kg and 0.093 +/- 0.056 L/hr/kg, respectively. No significant correlations were found between t1/2 beta, Vdss, Cl, and ClR and age. Six of the nine infants who had intragastric pH monitoring maintained a gastric pH > 4 until the final 24-hour sampling point. In this study, the t1/2 beta of famotidine was prolonged and the Vdss, Cl, ClR were reduced compared with corresponding parameters in previously reported studies of children older than one year of age and adults.

Pharmacokinetics of famotidine in patients with cystic fibrosis

Famotidine pharmacokinetics were studied in 13 patients with severe cystic fibrosis (CF) ranging from 10 to 47 years of age and 25 to 72 kg in weight. Patients were randomized to first receive famotidine either 20 mg intravenously or 40 mg orally. Twelve patients were crossed over to the alternate treatment. Repeated blood samples were obtained over 12 hours after intravenous and oral administration and urine was collected over 24 hours for quantitation of famotidine by means of high-performance liquid chromatography (HPLC). A compartment model-dependent approach was used to characterize the disposition of famotidine. From the intravenous data, the mean +/- standard deviation elimination half-life (t1/2) was 2.11 +/- 0.75 hours, the total clearance (Cl) was 0.79 +/- 0.41 L/kg/hr, the renal clearance was 0.57 +/- 0.26 L/kg/hr, the fraction eliminated unchanged in the urine was 83% +/- 16%, and the apparent volume of distribution (Vdss) was 1.33 +/- 0.53 L/kg. The bioavailability determined from comparison of intravenous and oral area under the curve data was 71% +/- 27%. Results of this study support an initial famotidine dose of 20 mg intravenously or 40 mg orally every 12 hours in patients with CF who are older than 9 years of age.

Low-dose famotidine and effervescent cimetidine in healthy subjects: a placebo-controlled overnight pH study

BACKGROUND

Amongst the low-dose H2-receptor antagonists available for the self-medication of dyspepsia, both famotidine 10 mg and cimetidine 200 mg have been shown to raise intragastric pH, but there is a delay after ingestion before significant effects can be demonstrated. A new effervescent preparation of cimetidine 200 mg releases an acid buffer which has a more rapid effect on intragastric pH.

AIM

To investigate the relative abilities of low-dose famotidine and effervescent cimetidine to raise intragastric pH after a single postprandial evening dose.

METHODS

Twenty-four healthy subjects (12 men, 12 women, median age 32 years) completed a three-period crossover trial of famotidine 10 mg, effervescent cimetidine 200 mg and placebo. After a standard meal was given at 18.30 h to subjects fasted for 5.5 h, drug or placebo was given at 19.30 h. Intragastric pH was recorded with combined glass electrodes from 18.00 to 07.30 h by digital recorders.

RESULTS

Over the 12 h post-dose period the mean area under the pH/time curve (AUC) after famotidine 10 mg was 3.73, after cimetidine 200 mg effervescent 2.79, and after placebo 2.07. Over the same period the median pH and percentage of time that recordings were above pH 3 were 3.45 and 52.5 after famotidine 10 mg, 2.40 and 33.8 after cimetidine 200 mg effervescent, and 1.68 and 15.9 after placebo. Both active treatments were significantly different from placebo by each measure (P < 0.001), and famotidine 10 mg was significantly more effective than cimetidine 200 mg effervescent by each measure over the 0-12 h period (P < 0.001). Comparisons of mean AUCs for each 15 min period after dosing showed that decrease in acidity was significantly greater after cimetidine 200 mg effervescent than after famotidine 10 mg for the first 60 min. In the later post-dose period only famotidine 10 mg raised pH for all time points to 12 h, whilst the effect of effervescent cimetidine 200 mg was detectable to = 8 h.

CONCLUSIONS

Inhibition of gastric acidity over the 12 h post-dose period was significantly greater and endured longer after famotidine 10 mg than after effervescent cimetidine 200 mg, but for the 60 min period immediately after dosing the effect on intragastric pH was significant following effervescent cimetidine 200 mg but not famotidine 10 mg. This suggests effervescent formulations of H2-receptor antagonists with an acid buffer have a more rapid effect on intragastric pH than film-coated tablets.

Determination of famotidine in human plasma by high performance liquid chromatography with column switching

A rapid, sensitive and robust reverse-phase high performance liquid chromatographic (HPLC) method with column switching and an internal standard for the quantitative determination of famotidine in human plasma is described. Famotidine and the internal standard were isolated from plasma samples by cation exchange solid phase extraction with SCX cartridges. The chromatographic separation was accomplished by an Inertsil C4 column with a mobile phase of acetonitrile/phosphate aqueous solution, connected by a switching valve to a BDS Hypersil C8 column with a mobile phase of acetonitrile/sodium dodecyl sulfate and phosphate aqueous solution. UV detection was set at 267 nm. The standard curve was linear in the concentration range of 1-100 ng ml-1. The intraday coefficients of variation at all concentration levels were less than 10%. The interday consistency was assessed by running QC samples during each daily run. The limit of quantification for famotidine in human plasma was 1 ng ml-1. The method has been utilized to support clinical pharmacokinetic studies in healthy volunteers who received famotidine 10 mg orally.

Saturable urinary excretion kinetics of famotidine in the dog

An important elimination route of the histamine H2 antagonist famotidine is active tubular secretion via the renal organic cation transport system. To characterize the excretion kinetics of famotidine in-vivo, the relationship between plasma concentration and urinary excretion rate was investigated in the beagle dog over a wide concentration range. The maximum transport capacity and the apparent Michaelis-Menten constant of tubular secretion were estimated. Concentration-dependent renal clearance was determined either after intravenous infusion of high doses of famotidine for a short time or during continuous infusion. From individual experiments only indications of saturation were observed; these could not be quantified. A tubular titration curve, in which the active tubular famotidine secretion was plotted against the plasma concentration, was constructed from the data from all the experiments. Active tubular secretion was calculated for each experiment separately by subtracting the famotidine filtration rate from the total excretion rate. A tubular transport maximum of 2400 +/- 220 micrograms min-1 and an apparent Michaelis-Menten constant for tubular secretion of 26 +/- 4 micrograms mL-1 (76 +/- 12 microM) were estimated from the curve. To the best of our knowledge, this is the first time that saturation of famotidine renal clearance has been fully quantified in-vivo. Considering the low therapeutic plasma concentrations of famotidine (< 0.1 microgram mL-1), these results suggest that clinically the drug has a low interactive potential.

Pharmacokinetic optimisation in the treatment of gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GORD) is a very common disorder of upper gastro-intestinal motility, differing widely in severity and prognosis. Medical therapy of GORD has involved antacids, alginates, prokinetic agents and antisecretory compounds, primarily H2 receptor antagonists and proton pump inhibitors. Knowledge of the pharmacokinetics of these compounds is important, to optimise the therapeutic benefit in each patient. GORD patients are often elderly and pharmacokinetics are move variable in this group. Furthermore, they often suffer from other diseases needing medical therapy and may need a combination of drugs to heal reflux oesophagitis and relieve reflux symptoms. The ideal therapy for GORD will have linear pharmacokinetics, a relatively long plasma half-life (t1/2), a duration of action allowing once daily administration, and a stable effect independent of interactions with food, antacids and other drugs. Over-the-counter antacids and alginates are widely used, buy may affect absorption of H2 receptor antagonists like cimetidine and ranitidine. Aluminium-containing antacids may, over time, cause toxicity in patients with renal insufficiency. In the treatment of GORD, cisapride presents important advantages over earlier prokinetic compounds, with a longer plasma t1/2, low penetration of the blood-brain barrier and fewer adverse effects. The group of H2 receptor antagonists is still the most frequently use therapy for GORD. Linear pharmacokinetics make dose adjustments easy and safe. In individual patients, suppression of gastric secretion is related to the area under the plasma concentration-time curve (AUC), but there is wide interindividual variation in the effect of the same oral dose. Only with frequent administration and high doses will acid suppression approximate that of proton pump inhibitors. Tolerance, with loss of effect over time, however, is most pronounced in this situation. H2 receptor antagonists seem well suited for on-demand treatment of reflux symptoms, due to the rapid onset of effect and a decrease likelihood of the development of tolerance. Effervescent formulations provide more rapid absorption and almost immediate clinical effect. Cimetidine, however, causes interference with the metabolism of several other drugs in common use. In elderly patients elimination is delayed and in patients with renal insufficiency, dose reductions of all H2 receptor antagonists are recommended. The most effective medical therapy for any severity of GORD, particularly in severe oesophagitis, are the proton pump inhibitors. The substituted benzimidazoles (omeprazole, lansoprazole and pantoprazole), are prodrugs which once trapped and activated in the acid milieu of the gastric glands potently suppress gastric secretion of acid and pepsin. Their long duration of action, more related to the slow turnover of parietal cell H(+)-K+ ATPase molecules, allows once daily administration in most patients. Interindividual variation in bioavailability sometimes calls for higher doses or twice daily administration. Acid suppression is closely related to the AUC. Omeprazole is prone to interaction with the metabolism of other drugs, some of which may e be clinically important. Lansoprazole seems to have an earlier onset of action than omeprazole, ascribed to higher bioavailability during the first days of treatment. Proton pump inhibitors have a slow onset of action, which makes them unsuited for on-demand therapy. Clinical practice in GORD calls for the use of not one but several substances, according to the severity and symptom pattern of the patient. Pharmacokinetic optimisation in the treatment of GORD is a question of selecting the most suitable substances and administration schemes within each group. Cisapride is superior to other prokinetics in terms of longer plasma t1/2 and less toxicity. Amongst H2 receptor antagonists, the more long-acting compounds, ranitidine and famotidine, will improve acidity control througho

Pharmacokinetics and pharmacodynamics of famotidine in paediatric patients

Famotidine, an H2 receptor antagonist, has several potential advantages over cimetidine and ranitidine. These advantages include its potency, relatively longer elimination half-life, and lack of interaction with the cytochrome P450 isoforms. Eight studies addressing the use of famotidine in paediatric patients have been published. Data from these studies demonstrate that the pharmacokinetics and pharmacodynamics of intravenous famotidine appear to be similar in both children over the age of 1 year and adults. These data support a starting paediatric dosage for intravenous famotidine of 0.5 mg/kg every 8 to 12 hours. In addition, the safety and efficacy of famotidine in the treatment of peptic ulcer disease and esophagitis in paediatric patients is supported by these studies involving over 150 children. Future studies with famotidine in paediatrics should address its disposition in children under the age of 1 year and in children with compromised renal function, as well as the bioavailability of the oral formulation.

Famotidine-associated delirium. A series of six cases

Famotidine is a histamine H2-receptor antagonist used in inpatient settings for prevention of stress ulcers and is showing increasing popularity because of its low cost. Although all of the currently available H2-receptor antagonists have shown the propensity to cause delirium, only two previously reported cases have been associated with famotidine. The authors report on six cases of famotidine-associated delirium in hospitalized patients who cleared completely upon removal of famotidine. The pharmacokinetics of famotidine are reviewed, with no change in its metabolism in the elderly population seen. The implications of using famotidine in elderly persons are discussed.

Ferrous sulfate does not reduce serum levels of famotidine or cimetidine after concurrent ingestion

A series of randomized crossover studies were performed to determine whether there was a reduction in serum levels of cimetidine and famotidine when coingested with ferrous sulfate (300 mg). Coingestion of a ferrous sulfate tablet with cimetidine (300 mg) was associated with little reduction in serum cimetidine area under the curve (AUC) (mean versus mean, 20.8 versus 23.4 mumol.hr/L; mean percentage difference, -11%; 95% confidence interval [CI] of percentage difference, -26% to 4.2%) or peak concentration (Cmax) (mean versus mean, 5.1 versus 6.1 mumol/L; mean percentage difference, -16%; CI of percentage difference, -36% to 4%). Similarly, ferrous sulfate solution coingested with cimetidine caused little change in cimetidine AUC (mean versus mean, 19.9 versus 23.0 mumol.hr/L; mean percentage difference, -13%; CI of percentage difference, -34% to 7%) or Cmax (mean versus mean, 5.0 versus 5.0 mumol/L; mean percentage difference, 1%; CI of percentage difference, -18% to 20%). Concurrent ingestion of famotidine (40 mg) with a ferrous sulfate tablet did not result in significant reductions in serum famotidine AUC (mean versus mean, 1.78 versus 1.99 mumol.hr/L; mean percentage difference, -10%; CI of percentage difference, -34% to 13%) or Cmax (mean versus mean, 0.31 versus 0.32 mumol/L; mean percentage difference, -3%; CI of percentage difference, -27% to 22%). The formation of famotidine:iron(III) complexes was shown in methanol but was not observed in an aqueous buffer at pH 6.5. Ranitidine did not bind iron in an aqueous buffer and only weakly bound iron in methanol. Coingestion of ferrous sulfate with either cimetidine or famotidine does not cause a clinically relevant reduction in serum histamine H2-receptor blocker levels and, on the basis of in vitro binding experiments, iron is unlikely to interact with ranitidine.

Pharmacokinetics and pharmacodynamics of famotidine in children

The pharmacokinetics and pharmacodynamics of intravenous famotidine were studied in 12 children (1.1-12.9 years of age; mean weight +/- standard deviation = 27.6 +/- 21.2 kg) who were given the drug for prophylactic management of stress ulceration. After a 0.5-mg/kg infusion of famotidine, timed blood (n = 10) and urine (n = 6) samples and repeated evaluations of intragastric pH (n = 13) were obtained from each subject. Pharmacokinetic parameters were determined from curve fitting of serum concentration data. The mean (+/- SD) maximum serum concentration (Cmax) was 527.6 +/- 281.2 ng/mL, the elimination half-life (t1/2) was 3.2 +/- 3.0 hours, and the apparent steady-state volume of distribution (Vdss) was 2.4 +/- 1.7 L/kg. Plasma clearance (Cl) and renal clearance (ClR) were 0.70 +/- 0.34 L/hr/kg and 0.43 +/- 0.24 L/hr/kg, respectively. Over 24 hours, 73.0 +/- 27.3% of the dose was excreted unchanged in the urine (Fel). Pharmacodynamic analysis of gastric pH data using the sigmoid Emax model predicted that 50% of the maximal effect of famotidine (EC50) occurs at a serum concentration of 26.0 +/- 13.2 ng/mL. Children who did not have an initial intragastric pH < or = 4 did not have a significant response in pH after receiving famotidine. Although Vdss and Cl were higher in these children than those seen in adults, statistically significant relationships between these parameters and age were not observed in the study population. The pharmacodynamics and pharmacokinetics of famotidine in children older than one year of age appear to be similar to those noted in adults.

Isothermal and nonisothermal decomposition of famotidine in aqueous solution

The kinetics of hydrolysis of famotidine in aqueous solution was studied by isothermal and nonisothermal method over the pH range of 1.71 to 10.0. Nonisothermal kinetics was studied with the purpose of determining its use in the establishment of the expiration date of pharmaceutical preparations, particularly drugs in solutions and for assessment of stability characteristics of pharmaceutical formulations during the development stage. A comparison of isothermal (55, 70 and 85 degrees C) and nonisothermal kinetics was performed. Aqueous solutions of famotidine were buffered at pH 1.71, 2.24, 2.66, 4.0, 8.5, 9.0 and 10.0 were used. In the nonisothermal studies, the temperature rate of the reaction was continuously varied throughout the experiment. The energies of activation were found to be in close agreement for isothermal and nonisothermal studies, indicating that nonisothermal studies may save considerable amount of time in the early stages of drug development and stability testing. Logk-pH profiles were constructed for 55, 70 and 85 degrees C from the first-order rate constants obtained from isothermal studies at pH values ranging from 1.71 to 10.00. The pH-rate profile indicated that famotidine undergoes specific acid catalysis in the acidic region and general base catalysis in the alkaline region. Hydrolysis in the acidic and alkaline media resulted in the formation of four and five degradation products, respectively. A possible degradation pathway for the acidic and alkaline hydrolysis was discussed.

[Famotidine in the treatment of gastroduodenal ulcer]

In the treatment of gastroduodenal ulceration both the reduction of gastric acidity and the defence of mucosal membrane have an important role. The development of H2-receptor antagonist has brought a significant change in the decrease of acid secretion in the last two decades. After the development and clinical application of cimetidine and ranitidine, a newly developed H2-receptor blocker, the famotidine has been introduced. Both the pharmacological and clinical investigations demonstrated the efficacy of this drug either in gastric or in duodenal ulcerations. The clinical pharmacological studies expressed mainly the advantageous character, that in the achievement of therapeutic effect smaller quantity is required than that of the other H2-receptor blocker. In the dosage of 40 mg (bedtime once, or daily twice) significantly decreases the basal and the stimulated gastric acid secretion as well as the daily and the nocturnal pains of the patients. Experience for several years have demonstrated efficacy in a 20 mg dosage of this drug in defence of ulceration relapses. It can be very well tolerated without significant side effects. Its long term applications is safety and economically advantageous.

Pharmacokinetics and pharmacodynamics of famotidine in children with gastroduodenal ulcers

We treated 14 boys, six with gastric ulcers and eight with duodenal ulcers, to determine famotidine pharmacokinetics and its inhibition of gastric acid secretion (pharmacodynamics). Famotidine (1 mg/kg/day) was administered either intravenously or orally at a dose of 0.5 mg/kg twice a day (maximum: 40 mg/day). Blood samples were collected from all subjects and the intragastric pH monitored in eight. Pharmacokinetic parameters were calculated assuming a one-compartment model. Volume of distribution, elimination half-life, and area under the serum concentration-time curve were 1.52 +/- 0.37 l/kg, 2.29 +/- 0.38 h, and 1.14 +/- 0.32 ng.h/ml, respectively. The mean oral bioavailability of famotidine was 50.6%. Both intravenously and orally administered famotidine neutralized gastric acidity during sleep but failed to continuously maintain the intragastric pH > 5.0. All subjects' ulcers healed within 8 weeks. There were no side effects noted during famotidine treatment. Twice daily administration of 0.5 mg/kg famotidine for 8 weeks appears to be a tolerated and effective treatment of children with gastroduodenal ulcers.

Intestinal clearance of H2-antagonists

Jejunal perfusion of cimetidine resulted in the appearance of lumenal cimetidine sulfoxide in both rats and humans. In the rat, ileal perfusion yielded negligible sulfoxide metabolite as compared with that of the jejunum. Jejunal co-perfusion of an anionic-exchange inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, blocked the appearance of drug sulfoxide, and methionine co-perfusion yielded concentration-dependent inhibition of lumenal cimetidine sulfoxide. Intravenous injection of high concentrations of cimetidine sulfoxide did not produce detectable lumenal metabolite levels during jejunal perfusion of drug-free buffer, providing in situ evidence that lumenal metabolite is generated by the small intestine. The extent of the appearance of lumenal sulfoxide was significantly greater for cimetidine than for the other three marketed H2-antagonists in rat jejunum. Variable intestinal clearance of this extensively prescribed class of therapeutic agents may contribute to their absorption variability.

Short report: a comparative study of the interaction between antacid and H2-receptor antagonists

The influence of concomitant antacid administration on the relative bioavailability of the H2-receptor antagonists cimetidine, famotidine, nizatidine and ranitidine, was investigated in a panel of 21 healthy, adult male volunteers in an eight-way crossover trial. Administration with antacid reduced the bioavailability of all agents tested. The reduction in area under the serum concentration-time curve (AUC) was greatest for cimetidine (23%) and ranitidine (26%) and least for nizatidine (12%) and famotidine (19%). Reductions in peak serum concentration (Cmax) followed a similar pattern. The times of peak serum concentrations were not affected by antacid. Comparison of the relative bioavailability among all drugs tested showed no statistically significant differences in the effect of antacid administration on these agents. However, a high degree of intersubject variability was observed.

Renal excretion of famotidine and role of adenosine in renal failure induced by bacterial lipopolysaccharide in rats

Our previous studies have reported that bacterial lipopolysaccharide (LPS) dramatically changes the ability of the active tubular anion secretory system in rats. The present study has investigated the effects of LPS on the pharmacokinetics and renal handling of famotidine, an organic cation drug excreted primarily by an active tubular secretion mechanism in rats. The role of adenosine in the LPS-induced renal failure was also investigated using theophylline, an adenosine antagonist. Pretreatment with LPS (250 micrograms/kg) significantly decreased the steady-state volume of distribution, systemic clearance, and renal clearance (CLr) of famotidine, but not nonrenal clearance. No significant differences in total urinary recovery of unchanged famotidine were observed between treatments. Pretreatment with LPS significantly decreased the glomerular filtration rate (GFR), estimated as inulin clearance. LPS increased the clearance ratio of famotidine (CLr/GFR), but not the net tubular secretion, indicating that LPS has little or no effect on the active tubular cation secretory system. Theophylline (10 mg/kg) improved LPS-induced decrease in GFR without causing any changes in the pharmacokinetic parameters of famotidine. These findings provide further evidence that LPS produces different effects on the distribution and the active tubular secretory systems of anion and cation drugs, and that adenosine may play an important role in the induction of renal failure by LPS.

Drug interactions of H2-receptor antagonists

Three drug interactions of nizatidine and of other antisecretory agents were studied comparatively. First, the effects of nizatidine, cimetidine and ranitidine on the dispositional kinetics of theophylline were evaluated in chronic obstructive pulmonary disease (COPD) patients. Second, the effect of magnesium/aluminium hydroxide on the relative bioavailability of nizatidine, famotidine, cimetidine and ranitidine was evaluated in healthy volunteers. Finally, the effects of nizatidine and omeprazole on the dispositional kinetics of phenytoin were evaluated in healthy volunteers. Only cimetidine altered the steady-state kinetics of oral theophylline, slowing theophylline clearance by 25%. Each of the H2-receptor antagonists exhibited a modest decline in relative bioavailability when ingested with antacid. Antacid ingestion decreased the bioavailability of famotidine, ranitidine and cimetidine by 20-25%, and the bioavailability of nizatidine by 12%. Each of these effects was statistically significant. Finally, it was found that neither omeprazole nor nizatidine affected the single dose kinetics of phenytoin.

A controlled comparison of continuous ranitidine and intermittent famotidine infusions on gastric pH

Continuous infusions of any given H2-blocking drug have uniformly been found to be superior to intermittent infusions of the same H2-blocking drug in sustaining elevations in gastric pH. Comparisons of intermittent and continuous infusions among different H2-blocking drugs have heretofore not been made. Owing to its greater potency and longer half-life, the authors were interested in determining whether intermittent infusions of famotidine might be as effective as continuous infusions of ranitidine in sustaining elevations of gastric pH. The effectiveness of a continuous intravenous infusion of ranitidine (6.25 mg/hr) was compared with the effectiveness of intermittent intravenous infusions of famotidine (20 mg every 12 hours) in sustaining gastric pH above 4.0 in 18 young, healthy adult male subjects using a randomized two-way cross-over design. Gastric pH was continuously monitored for 24 hours. The intermittent famotidine regimen was determined to be as effective as the continuous ranitidine regimen with respect to the following parameters: (1) the percentage of the 24-hour dosing period during which gastric pH exceeded 4.0; (2) the area under the pH > or = 4 versus time curve; and (3) median gastric pH.

Pharmacokinetics and pharmacodynamics of famotidine in patients with reflux oesophagitis

The pharmacokinetics, pharmacodynamic effect and clinical efficacy of famotidine were studied in 10 patients with reflux oesophagitis Grades I and II. For the pharmacokinetic studies the patients received 20 mg famotidine i.v. The half-life of famotidine was 3.8 h, the total plasma clearance was 297 ml.min-1, and a steady state volume of distribution of 1.2 l.kg-1 was found. For pharmacodynamic assessment, intraoesophageal pH-metry was performed without and after acute treatment with famotidine 20 mg i.v. and following 3 weeks of oral famotidine 80 mg b.d. The resultant percentage total acid exposure time (pH < 4 within 24 h) were 23.9%, 19.0% and 19.2% (median), respectively (NS). At the end of 6 weeks of oral therapy, symptomatic and endoscopic improvement had occurred in 9 and 5 patients, respectively. Our study shows that the pharmacokinetics of famotidine in patients with reflux oesophagitis is comparable to that in healthy volunteers and peptic ulcer patients. The clinical response to the treatment appeared comparable to that found after other H2-receptor antagonists.

[Pharmacokinetics and pharmacodynamics of two morphologically homogenous forms of famotidine per os in Chinese healthy volunteers]

The lg C of famotidine (Fam) A and B forms in plasma vs time curve following a single oral dose of 40 mg showed an one-compartment open model in 5 healthy volunteers. The T1/2Ke of Fam A and B forms = 3.06 and 3.48 h, Tmax = 2.96 and 2.68 h, The Cmax = 115 and 145 ng.ml-1, AUC = 811 and 1190 h.ng.ml-1, respectively. No significant difference was found in the pharmacokinetic and pharmacodynamic properties between Fam A and B forms. The mathematical model describing the whole course of blood concentration of Fam A and B forms in relation to inhibiting effects on gastric acid were: E (A) = 100.C2.04/(C2.04 + 15.0(2.04)) and E (B) = 100.C1.67/(C1.67 + 14.0(1.67)). Predication of blood drug concentration from pharmacodynamics or vice versa became possible using the mathematical equations.

Famotidine and theophylline pharmacokinetics. An unexpected cimetidine-like interaction in patients with chronic obstructive pulmonary disease

The results of research studies conducted to date in vitro and in healthy volunteers are practically all concordant in demonstrating the lack of any kind of interference between famotidine and microsomal oxidative metabolism. The pharmacokinetics (elimination half-life, area under the plasma concentration-time curve, clearance and volume of distribution) of theophylline 3.4 mg/kg as an intravenous infusion over 5 min (a dosage previously used to test drug interactions with cimetidine and ranitidine) were evaluated in 7 patients with chronic obstructive pulmonary disease (COPD) and peptic ulcer disease before and after 8 days' treatment with famotidine 40mg at night. The results indicate that famotidine can induce substantial and statistically significant slowing of theophylline elimination with a cimetidine-like interaction profile.