Pharmacokinetics of famotidine, a new H2-receptor antagonist, in relation to renal function

Famotidine use and quantitative symptom tracking for COVID-19 in non-hospitalised patients: a case series

OBJECTIVE

Treatment options for non-hospitalised patients with coronavirus disease 2019 (COVID-19) to reduce morbidity, mortality and spread of the disease are an urgent global need. The over-the-counter histamine-2 receptor antagonist famotidine is a putative therapy for COVID-19. We quantitively assessed longitudinal changes in patient reported outcome measures in non-hospitalised patients with COVID-19 who self-administered high-dose famotidine orally.

DESIGN

Patients were enrolled consecutively after signing written informed consent. Data on demographics, COVID-19 diagnosis, famotidine use, drug-related side effects, temperature measurements, oxygen saturations and symptom scores were obtained using questionnaires and telephone interviews. Based on a National Institute of Health (NIH)-endorsed Protocol to research Patient Experience of COVID-19, we collected longitudinal severity scores of five symptoms (cough, shortness of breath, fatigue, headaches and anosmia) and general unwellness on a four-point ordinal scale modelled on performance status scoring. All data are reported at the patient level. Longitudinal combined normalised symptom scores were statistically compared.

RESULTS

Ten consecutive patients with COVID-19 who self-administered high-dose oral famotidine were identified. The most frequently used famotidine regimen was 80 mg three times daily (n=6) for a median of 11 days (range: 5-21 days). Famotidine was well tolerated. All patients reported marked improvements of disease related symptoms after starting famotidine. The combined symptom score improved significantly within 24 hours of starting famotidine and peripheral oxygen saturation (n=2) and device recorded activity (n=1) increased.

CONCLUSIONS

The results of this case series suggest that high-dose oral famotidine is well tolerated and associated with improved patient-reported outcomes in non-hospitalised patients with COVID-19.

Identification and Quantitative Assessment of Uremic Solutes as Inhibitors of Renal Organic Anion Transporters, OAT1 and OAT3

One of the characteristics of chronic kidney disease (CKD) is the accumulation of uremic solutes in the plasma. Less is known about the effects of uremic solutes on transporters that may play critical roles in pharmacokinetics. We evaluated the effect of 72 uremic solutes on organic anion transporter 1 and 3 (OAT1 and OAT3) using a fluorescent probe substrate, 6-carboxyfluorescein. A total of 12 and 13 solutes were identified as inhibitors of OAT1 and OAT3, respectively. Several of them inhibited OAT1 or OAT3 at clinically relevant concentrations and reduced the transport of other OAT1/3 substrates in vitro. Review of clinical studies showed that the active secretion of most drugs that are known substrates of OAT1/3 deteriorated faster than the renal filtration in CKD. Collectively, these data suggest that through inhibition of OAT1 and OAT3, uremic solutes contribute to the decline in renal drug clearance in patients with CKD.

Mechanistic Approaches to Volume of Distribution Predictions: Understanding the Processes

PURPOSE

To use recently developed mechanistic equations to predict tissue-to-plasma water partition coefficients (Kpus), apply these predictions to whole body unbound volume of distribution at steady state (Vu(ss)) determinations, and explain the differences in the extent of drug distribution both within and across the various compound classes.

MATERIALS AND METHODS

Vu(ss) values were predicted for 92 structurally diverse compounds in rats and 140 in humans by two approaches. The first approach incorporated Kpu values predicted for 13 tissues whereas the second was restricted to muscle.

RESULTS

The prediction accuracy was good for both approaches in rats and humans, with 64-78% and 82-92% of the predicted Vu(ss) values agreeing with in vivo data to within factors of +/-2 and 3, respectively.

CONCLUSIONS

Generic distribution processes were identified as lipid partitioning and dissolution where the former is higher for lipophilic unionised drugs. In addition, electrostatic interactions with acidic phospholipids can predominate for ionised bases when affinities (reflected by binding to constituents within blood) are high. For acidic drugs albumin binding dominates when plasma protein binding is high. This ability to explain drug distribution and link it to physicochemical properties can help guide the compound selection process.

A structure–activity relationship study of compounds with antihistamine activity

A structure-activity relationship (SAR) analysis of H(1)-, H(2)- and H(3)-antihistamine activity was carried out and chromatographic data of 2-[2-(phenylamino)thiazol-4-yl]ethanamine, 2-(2-benzyl-4-thiazolyl)ethanamine, 2-(2-benzhydrylthiazol4-yl)ethanamine, 2-(1-piperazinyl- and 2-(hexahydro-1H-1,4-diazepin-1-yl)benzothiazole, 2-(1-piperazinyl)benzothiazole, 2-[4-(1-alkyl)piperidinyl]benzothiazole, 2-(N,N',N'-dimethylalkyl-1,2-ethanediamino)benzothiazole, 2[1-(4-aminopiperidinyl)]benzothiazole, 2-[2-phenyl-4-thiazolyl]ethanamine derivatives and selected H(1)- and H(2)-antihistamine drugs were obtained. NP TLC and RP2 TLC plates (silica gel NP 60F(254) and silica gel RP2 60F(254) silanized precoated), impregnated with a solution of aspartic acid (L-Asp) and a solution of an analogue of aspartic acid (propionic acid), were used in two developing solvents as H(1)-, H(2)- and H(3)-antihistaminic interaction models. The lipophilicity data of the examined compounds were obtained and used in the SAR assay. Biochromatographic tests using TLC plates impregnated with solutions of asparic acid or propionic acid were found to be a source of useful data for the qualitative analysis of compounds with different structures, demonstrating activity to histamine H(1)-, H(2)- and H(3)-receptors. The four presented discriminant models based on biochromatographic studies are an efficient tool in the SAR analysis for initial prediction of compound activity direction within histamine receptors.

Dose-reducing H2 receptor antagonists in the presence of low glomerular filtration rate: a systematic review of the evidence

BACKGROUND

While it is recommended that H2 receptor antagonists (H2RAs) be dose reduced in the presence of low glomerular filtration rate (GFR), in practice such adjustments often do not occur. We reviewed the evidence for this recommendation.

METHODS

We searched multiple medical reference databases for relevant cohort studies and randomized clinical trials. Studies that enrolled five or more participants with low GFR who also received at least one unadjusted dose of an H2RA, and who were compared with controls were included. Data were abstracted on study and participant characteristics and drug-related adverse effects. Pharmacokinetic measures were pooled using meta-analysis.

RESULTS

A total of 22 articles were included, comprising 19 unique cohort studies. With declining GFR, there was a significant increase in the area under the curve (AUC) and elimination half-life (t(1/2)) of the serum drug concentration of H2RAs (P < 0.001). Compared with a GFR >80 ml/min/1.73 m2, drug AUC increased by 200% when the GFR was 30 ml/min/1.73 m2, and by 300% when the GFR was 20 ml/min/1.73 m2. In hospitalized patients with low GFR, reducing the interval dose of intravenous H2RA was associated with fewer adverse reactions. The gastro-protective effects of H2RAs were similar with reduced and unadjusted doses.

CONCLUSIONS

Reducing the dose of H2RAs in persons with low GFR will decrease drug expenditure and may prevent adverse events, without a change in efficacy. Quality assurance programmes, which improve deficiencies in H2RAs prescribing, appear justified.

Use of Famotidine in Adult Patients with End-Stage Renal Disease: Assessment of Dosing and Mental Status Changes

BACKGROUND

Famotidine dosage adjustment is required in patients with chronic kidney disease. Since recommendations on the degree of famotidine dose reduction vary between references, a chart review was conducted to evaluate the tolerability of varying famotidine doses in adults with end-stage renal disease (ESRD).

METHODS

An assessment was made of famotidine doses prescribed to patients with ESRD over a 7-year period in a university hospital. Patient medical records were reviewed for evidence of mental status changes associated with famotidine.

RESULTS

In 38 patients who met study criteria, 35 had no evidence of mental status change while receiving famotidine therapy. Among these 35 patients, the mean dose of famotidine was 24 mg/daily for 5.5 days. Three patients had mental status changes possibly associated with famotidine therapy.

CONCLUSIONS

In this study, most ESRD patients seemed to tolerate famotidine 20 mg daily well, but larger prospective studies need to be done before final recommendations can be made. A small percentage of patients may require further dose reduction to minimize risk of mental status change.

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.

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).

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.

Determination of famotidine in human plasma and urine by high-performance liquid chromatography

An improved, rapid and specific high-performance liquid chromatographic assay was developed for the determination of famotidine in human plasma and urine. Plasma samples were alkalinized and the analyte and internal standard (cimetidine) extracted with water-saturated ethyl acetate. The extracts were reconstituted in mobile phase, and injected onto a C18 reversed-phase column; UV detection was set at 267 nm. Urine samples were diluted with nine volumes of a mobile phase-internal standard mixture prior to injection. The lower limits of quantification in plasma and urine were 75 ng/ml and 1.0 microg/ml, respectively; intra- and inter-day coefficients of variation were < or =10.5%. This method is currently being used to support renal function studies assessing the use of intravenously administered famotidine to characterize cationic tubular secretion in man.

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.

Oral famotidine: a potential treatment for children with autism

Famotidine (Pepcid, a histamine-2 receptor blocker, is marketed for the treatment of peptic ulcer disease, gastroesophageal reflux, and the treatment of pathological hypersecretory conditions, including the Zollinger-Ellison syndrome. Recent reports indicate that it is also effective in relieving the deficit (or withdrawal) symptoms of adults with schizophrenia. Autism, a neuropsychiatric disorder which presents within the first few years of life, is defined by deficient social interaction, communication, language, play, and a markedly restricted repertoire of activities and interests. Similarities between the deficit symptoms of schizophrenia and the social deficit symptoms of autism suggest the hypothesis that famotidine may be useful in treating children with autism. Histamine serves as a neurotransmitter and neuromodulator in the brain. H2-receptors in the brain predominantly transmit inhibitory signals; when these receptors are stimulated in animals, spontaneous activity and exploratory behavior decrease; blockade of H2-receptors would therefore be expected to reverse this inhibition.

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.

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.

Pharmacokinetic optimisation of the treatment of peptic ulcer in patients with renal failure

The pathogenesis of peptic ulceration is not yet clear. It could be due to an imbalance between acid secretion and mucosal defensive and/or protective mechanisms, but the association between Helicobacter pylori and peptic ulceration has questioned this hypothesis. Therefore, drugs inhibiting acid secretion and/or eradicating H. pylori are of major interest. Peptic ulcer disease is often associated with renal failure. For the selection of the proper dosage of these agents their pharmacokinetic properties and alterations in pharmacokinetics in various disease states, including renal failure, should be known. As histamine H2-receptor antagonists and pirenzepine are mainly eliminated by the renal route their elimination is dependent on creatinine clearance. Consequently, their elimination will be impaired in patients with renal insufficiency, which makes dosage reduction mandatory in these patients. No dosage supplementation is necessary after any type of dialysis because the drugs are removed in insignificant amounts by the various blood purification procedures. Misoprostol and proton pump inhibitors, such as omeprazole, lansoprazole and pantoprazole, are primarily eliminated by nonrenal routes. Therefore no dosage adjustments are necessary in patients with renal insufficiency. Bismuth salts, sucralfate and antacids should be avoided in patients with renal failure because of the accumulation of their cations and the associated risk of toxic reactions. For most agents more long term experience from comparative and double-blinded studies is needed to define better their clinical efficacy and tolerability in patients with renal failure.

Pharmacokinetics and pharmacodynamics of H2-receptor antagonists in patients with renal insufficiency

H2-receptor antagonists are frequently used in patients with renal insufficiency to treat hyperacidity and resultant peptic ulceration. All H2-antagonists are mainly eliminated by the renal route (glomerular filtration and tubular secretion). Since it is dependent on creatinine clearance (CLCR), elimination will be impaired in renal insufficiency. Protein binding and volumes of distribution (Vd) of H2-antagonists are not significantly altered in patients with renal impairment. Bioavailability (F) is similar in patients with and without renal insufficiency, except for nizatidine, which has an F that is lower in uraemic patients. When given in similar doses, mean peak concentrations (Cmax) and area under the concentration-time curve (AUC) are higher in patients with renal insufficiency than in those with normal renal function. Thus, maintenance doses of H2-antagonists should be reduced in line with reductions in CLCR. The time to reach Cmax is similar for all drugs except ranitidine, which has a delayed Cmax. Due to the decreased renal clearance (CLR), elimination half-life (t1/2) is prolonged 3- to 8-fold depending upon the degree of renal failure and the particular drug. H2-antagonists are removed by various dialysis procedures in insignificant amounts. Thus, no dosage supplementation is necessary after any type of dialysis therapy. By means of intragastric long term pH-metry it has been shown that inhibition of gastric acid secretion is prolonged in patients with renal insufficiency.

Pharmacokinetics of famotidine in patients with cirrhosis and ascites

The pharmacokinetics of famotidine has been investigated in ascitic cirrhotic patients. 10 decompensated cirrhotic patients were studied (9m, 1f), who had normal renal function, and six healthy control subjects (4m, 2f), matched for age, sex and weight. Each subject received on two occasions, at least four days apart, a single oral (40 mg) or intravenous dose (20 mg) of famotidine, at 21.00 h in a randomised manner. Serial blood samples were collected and famotidine in plasma was determined by a HPLC/UV method. Plasma data were subjected to non compartmental pharmacokinetic analysis. There were no statistically significant differences in pharmacokinetic parameters between the two groups after either the intravenous or oral administration of famotidine. The findings suggest that the dose of famotidine may not require any adjustment in ascitic patients without renal failure.

Renal effects of peptic ulcer therapy

Drugs used in the treatment of peptic ulcer disease may interact with the renal system in a variety of ways. Since many agents are eliminated by renal excretion, clearance of these agents may be reduced and half-life extended in the presence of renal insufficiency. The histamine H2-receptor antagonists may interfere with renal tubular excretion of creatinine and cationic drugs, resulting in elevated serum concentrations and reduced renal clearance. The prostaglandin E1 analogue misoprostol is used as a cytoprotective agent but has renal effects. The renal effects differ between systems studied. In the rat, misoprostol reduces cyclosporin-induced renal tubular toxicity, whereas in humans it has been shown to attenuate renal allograft rejection. Sucralfate is the aluminium salt of sucrose octasulfate. It permits the absorption of aluminium in amounts similar to aluminium-containing antacids, and toxicity has been demonstrated in the presence of renal insufficiency. Bismuth compounds are used increasingly to treat peptic ulcer disease, and bismuth toxicity has been described in association with renal insufficiency. Aluminium-, calcium- and magnesium-containing antacids are used as oral phosphate binders in patients with renal insufficiency in addition to their usual indications. Cation absorption and accumulation with all of these antacid preparations has been described and may lead to toxicity.

Sensitive high-performance liquid chromatographic determination of famotidine in plasma. Application to pharmacokinetic study

A sensitive high-performance liquid chromatographic (HPLC) method for the quantitation of famotidine in human plasma is described. Clopamide was used as the internal standard. Plasma samples were extracted with diethyl ether to eliminate endogenous interferences. Plasma samples were then extracted at alkaline pH with ethyl acetate. Famotidine and the internal standard were readily extracted into the organic solvent. After evaporation of ethyl acetate, the residue was analysed by HPLC. The chromatographic separation was accomplished with an isocratic mobile phase consisting of acetonitrile-water (12:88, v/v) containing 20 mM disodium hydrogenphosphate and 50 mM sodium dodecyl sulphate, adjusted to pH 3. The HPLC microbore column was packed with 5 microns ODS Hypersil. Using ultraviolet detection at 267 nm, the detection limit for plasma famotidine was 5 ng/ml. The calibration curve was linear over the concentration range 5-500 ng/ml. The inter- and intra-assay coefficients of variation were found to be less than 10%. Applicability of the method was demonstrated by a bioavailability/pharmacokinetic study in normal volunteers who received 80 mg famotidine orally.

Pharmacokinetics of newer drugs in patients with renal impairment (Part I)

Many drugs are eliminated via the renal route and the usual dose must be modified in patients with severe renal impairment. This review is an attempt to supply physicians with the more recent data on pharmacokinetic studies of new drugs administered in uraemic patients. The review is in 2 parts: the first indicates the results of studies on the pharmacokinetics of antibiotic agents, antifungal, antiviral and antiulcer drugs, and nonsteroidal anti-inflammatory drugs. Special mention is made of epoetin (recombinant human erythropoietin). It was not possible to give all the information collected from the recent literature: since mild renal failure has little effect on the fate of a drug, pharmacokinetic data obtained in patients with a creatinine clearance (CLCR) of more than 50 ml/min has been omitted. Both the text and tables give recommendations for treating patients with moderate renal insufficiency (CLCR of about 50 ml/min), more severe renal impairment (CLCR between 10 and 50 ml/min) and end-stage renal failure with a very low creatinine clearance (below 10 ml/min). It was not possible to give uniform recommendations (i.e. reducing the dose while maintaining the same interval, or giving the same dose and prolonging the interval). This article follows the recommendations of the authors, which may vary for drugs in similar classes.

Hemofiltrability of H2-receptor antagonist, famotidine, in renal failure patients

To determine if a new H2-receptor antagonist, famotidine, would be significantly removed by arteriovenous hemofiltration, we measured plasma concentrations and amounts of the drug recovered in ultrafiltrate during 18 sessions of an intermittent hemofiltration performed in five patients with renal failure receiving the repeated intravenous dosings of the drug (5-20 mg/day). Plasma and ultrafiltrate drug concentrations were determined by using a high performance liquid chromatography with fluorescent detection. The mean (+/- SD) amount of the drug removed by the procedure, which was performed at the mean ultrafiltration rate of 19.0 +/- 6.0 ml/min over the mean duration of 212 +/- 168 min, corresponded to 4.1 +/- 2.2% of the daily maintenance doses. There was a significant (r = 0.90, P less than .01) linear relationship between the hemofiltration clearance and the ultrafiltration rate, indicating that the sieving coefficient, an index filtration efficiency, for the drug was largely constant (i.e., 0.73 +/- 0.10) over the ranging filtration rates (i.e., 3.9-29.5 mL/min) employed in the present study. When the mean filtration efficiency of 0.73 obtained from the study is extrapolated into a 24-hour continuous arteriovenous hemofiltration performed at commonly used filtration rates (i.e., 6-12 ml/min), the 24-hour hemofiltration clearances are estimated to range from 4 to 9 ml/min. These clearance values are found to correspond to only 10 to 25% of the mean total body clearance (about 35 ml/min) reported from anuric patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the Parenteral histamine2-receptor antagonists

The chemical structure, pharmacokinetic properties, and drug-drug interaction profiles of the parenterally available histamine2 (H2)-receptor antagonists were compared. Famotidine is a guanidinothiazole derivative, ranitidine contains an aminomethylfuran ring, and cimetidine has an imidazole ring. Data from the literature indicate that because of its chemical structure famotidine has a much greater potency and affinity for the H2-receptor and a notable lack of drug-drug interactions when compared with ranitidine and cimetidine. As a result, famotidine should be considered the H2-receptor antagonist of choice for critically ill patients who require gastric-acid suppression and at the same time are being treated with other drugs that depend on the cytochrome P-450 mixed-function oxidase system for their metabolism and/or on renal tubular mechanisms for their excretion.

Famotidine. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in peptic ulcer disease and other allied diseases

Famotidine is a highly selective histamine H2-receptor antagonist. In healthy volunteers and patients with acid hypersecretory disease it is approximately 20 to 50 times more potent at inhibiting gastric acid secretion than cimetidine and 8 times more potent than ranitidine on a weight basis. As shown in placebo-controlled trials, famotidine is effective in healing both duodenal and gastric ulcers. Famotidine 20mg twice daily or 40mg at bedtime achieves healing rates and symptom relief similar or superior to those achieved by cimetidine 800mg daily or ranitidine 300mg daily in patients with peptic ulcer disease. Results of 1 placebo-controlled study suggest that famotidine prevents recurrence of duodenal ulcer, but comparative trials are needed to establish its relative efficacy in maintenance therapy. The few non-comparative trials conducted to date also suggest that famotidine 10 to 20mg twice daily may be effective in the treatment of gastritis and reflux gastro-oesophagitis. In comparative trials, famotidine was similar in efficacy to cimetidine in the treatment of upper gastrointestinal bleeding and to ranitidine in the prevention of pulmonary aspiration of acid. In patients with Zollinger-Ellison syndrome, the potency and long duration of action of famotidine may confer an advantage over other H2-receptor antagonists--in individualised doses (mean 0.33 g/day) famotidine successfully controlled acid secretion for up to 72 months in 1 study of such patients. Accumulated clinical evidence confirms that famotidine is very well tolerated and is free of the antiandrogenic effects infrequently reported with cimetidine. Moreover, famotidine is not associated with altered hepatic metabolism of drugs. Thus, famotidine is an effective, well-tolerated alternative to cimetidine and ranitidine. Famotidine is also promising as maintenance therapy for preventing recurrence of duodenal ulcer and as initial or maintenance treatment of gastric hypersecretory disorders, but further clinical experience, particularly in the long term, is needed to define the relative efficacy and tolerability of famotidine in these indications.

Pharmacokinetics of famotidine in elderly patients with and without renal insufficiency and in healthy young volunteers

The pharmacokinetics of the H2-receptor antagonist famotidine, after oral administration of a 20 mg tablet, has been studied in 10 elderly patients with normal renal function (CLCR greater than or equal to 59 ml.min-1, Mean = 80 ml.min-1), 5 elderly patients with renal insufficiency (CLCR less than or equal to 38 ml.min-1, Mean = 15 ml.min-1), and 6 healthy young volunteers. Elimination half-life in the elderly patients with renal insufficiency was significantly prolonged compared to the elderly patients with normal renal function and the young volunteers. The correlation coefficient between creatinine clearance and the elimination rate constant of famotidine was 0.672. Mean urinary recovery of unchanged drug up to 24 h in the young volunteers was 44%. The mean renal clearance of famotidine in the young volunteers (270 ml.min-1) was substantially greater than the creatinine clearance, 128 ml.min-1, which suggests the possibility of tubular secretion of famotidine.

Famotidine-associated mental confusion in elderly patients

Central nervous system effects, such as mental confusion and hallucinations, have been reported with both cimetidine and ranitidine. Elderly patients with renal or hepatic dysfunction are more susceptible to these adverse reactions. We report two cases of reversible mental confusion in elderly patients with mild renal insufficiency following intravenous famotidine therapy, possibly explained by an increased permeability of the blood-brain barrier in patients with decreased renal function.

Haematological adverse effects of histamine H2-receptor antagonists

Histamine H2-receptor antagonists are widely used in the treatment of gastrointestinal diseases related to gastric acid hypersecretion. Cimetidine was introduced into medical practice in 1976 and ranitidine, famotidine and nizatidine in 1981, 1985 and 1987, respectively. Haematological adverse effects are relatively uncommon and most have been reported in cases of cimetidine administration. These adverse effects are reviewed under 4 main headings: (a) blood cytopenias and leucocytosis; (b) coagulation disorders related to drug interactions with oral anticoagulants; (c) reduction of dietary iron absorption; and (d) reduction of dietary cobalamin absorption. 85 reported cases of blood cytopenias attributed to these drugs are reviewed, of which 75 (88%) were associated with cimetidine therapy. In postmarketing surveillance studies, the incidence of cimetidine-associated blood cytopenia has been evaluated at about 2.3 per 100,000 patients. Neutropenia and agranulocytosis are by far the most frequently encountered. Whatever the drug or the type of cytopenia, this adverse effect is almost always rapidly reversible when treatment is stopped. Moreover, in several cases other factors such as underlying diseases or additional drugs could have been responsible, at least partly, for the cytopenia. The pathophysiological basis of these adverse effects remains poorly explained. Various mechanisms have been proposed, which in some cases are probably associated: (a) direct toxicity for haemopoietic stem cells; (b) drug-induced immune reactions leading to blood or bone marrow cell damage, and (c) drug interactions, with increased and prolonged action of potentially haematotoxic drugs. Mechanisms (a) and (c) appear to be of particular clinical importance in cases of impaired renal elimination of H2-receptor antagonists. Cimetidine and probably to a lesser extent ranitidine potentiate the action of oral anticoagulants of both coumarin and indanedione structure. This may result in haemorrhagic complications. Such action is a consequence of the reduced hepatic metabolism of oral anticoagulants through a dose-dependent, reversible inhibition of cytochrome P450. Malabsorption of dietary iron and cobalamin appears to result from inhibition of gastric secretion by the H2-receptor antagonists. This is of no clinical importance in short term treatment, but long term use of H2-receptor antagonists may theoretically contribute to the occurrence of iron or cobalamin deficiency anaemia.

Pharmacokinetics of mifentidine after single and multiple oral administration to healthy volunteers

1. The pharmacokinetics of mifentidine, a new long acting histamine H2-receptor antagonist, were studied using two protocols. 2. In one study, on 5 different days six normal male subjects were given 2.5, 5, 10, or 20 mg mifentidine or placebo orally 60 min before starting a 3 h continuous gastric aspiration during which time blood samples were taken for measurement of mifentidine concentration. 3. The area under the curves of mifentidine plasma levels (AUC) vs time for the four doses was linearly related to the dose for each individual subject (r = 0.972, P less than 0.001). After doses of 2.5, 5, 10 and 20 mg, mifentidine reduced hydrogen ion output by respectively 36, 37, 60 and 75% and secretory volume by 1, 17, 40, and 47%. The effects at the two highest doses were statistically significant. AUC was correlated positively with the percentage reduction in hydrogen ion output (r = 0.802, P less than 0.001) and volume (r = 0.834, P less than 0.001) over a 3 h period. 4. In the second study, the pharmacokinetics were evaluated after once-daily treatment for 14 days in seven subjects given 10 mg and in seven others subjects given 20 mg. 5. After multiple dosing, renal clearance was similar for the two doses (11.6 +/- 2.11 l h-1 for the low dose and 17.0 +/- 2.0 l h-1 for the high dose). Plasma half-life (t1/2 lambda 2) was 16.0 +/- 3.0 h after the 10 mg dose and 11.9 +/- 1.2 h after 20 mg.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and dynamics of famotidine in patients with renal failure

1. Famotidine, a new histamine H2-receptor antagonist was administered intravenously (20 mg) to 22 patients with end stage renal disease during a dialysis free interval (n = 6) and during different blood purification processes including haemodialysis (HD; n = 4), intermittent haemofiltration (HF; n = 4), continuous haemofiltration (CHF; n = 4) and continuous ambulatory peritoneal dialysis (CAPD; n = 4). The plasma, the dialysate/filtrate and the urine concentrations of famotidine were analysed by h.p.l.c. 2. In addition, intra-gastric pH was measured by a long-term-pH probe in seven patients with renal failure and in six patients with normal renal function (control group) following 20 mg famotidine. 3. A 7 to 10 fold prolongation of famotidine's elimination half-life (27.2 +/- 8.5 h; mean +/- s.d.) was observed in patients with renal failure as compared with the half-life (2.6-3.6 h) in subjects with normal renal function. 4. Total body clearance (CL) and volume of distribution (V) were found to be 33.5 +/- 10.1 ml min-1 and 1.3 +/- 0.7 l kg-1, respectively in patients with end-stage renal failure. 5. Blood purification processes have shown considerable variation in clearing famotidine from the body: 16.4 +/- 8.9 and 6.0 +/- 2.9% of the administered dose in HD with polysulphone and cuprophan membranes respectively, 7.7 +/- 5.2% in HF with a polyacrylonitrile membrane (each for 5 h), 4.5 +/- 1.1% in CAPD and 16.2 +/- 4.9% in CHF with a polysulphone membrane within 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of histamine (H2)-receptor antagonists, including roxatidine, in chronic renal failure

In this paper the effects of chronic renal failure on the pharmacokinetics of H2-antagonists are reviewed and the results obtained with roxatidine presented. In normal renal function renal clearance is around 60-80% of total plasma clearance of all H2-antagonists. Consequently, prolongation of serum half-life, mainly due to a decrease in urinary excretion, is noted in patients with decreasing glomerular filtration rate. In chronic renal failure, a dose reduction is therefore necessary with all H2-antagonists, including roxatidine. It appears that neither haemodialysis nor peritoneal dialysis substantially influences the pharmacokinetics of these drugs. Therefore, the same dosage schedule as in uraemia may be applied in patients with dialysis. Finally, in the elderly the dosage of all H2-antagonists should be adapted to the expected decrease in renal function.

Safety and pharmacokinetics of mifentidine after increasing oral doses in healthy subjects

Eight healthy men were each given single oral doses of mifentidine 20, 40 and 80 mg, a new H2-receptor antagonist, in a four-way, double-blind, placebo-controlled, cross-over, dose-proportionality study. No significant objective or subjective effects were noted. Mifentidine showed unusual pharmacokinetic behaviour, producing a significant secondary peak in the drug concentration profile. The plasma AUC of mifentidine increased linearly with dose (r = 0.983). The apparent plasma clearance was 38.1 l.h-1, 31.0 l.h-1, and 47.4 l.h-1 for the 20, 40 and 80 mg doses, respectively, and the corresponding terminal plasma half-lives were 10.3 h, 12.0 h, and 8.6 h. About 20% of the parent drug was excreted in urine over 24 h. The renal clearance (9.41 l/h for 20 mg, 9.5 l/h for 40 mg, and 12.8 l/h for 80 mg mifentidine) indicates that some of the drug was excreted by active tubular secretion. The results indicate that mifentidine is safe after single oral doses up to 80 mg. The pharmacokinetics of the 20 and 40 mg doses were similar, but after 80 mg the total body and renal clearances were significantly greater than after the two lower doses. As the terminal plasma half-life of mifentidine is longer than of other available H2-receptor antagonists, it may have clinical implications for once-a-day therapy of peptic ulcer diseases.

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

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

Disposition of famotidine in renal insufficiency

The disposition of famotidine was evaluated in 18 patients; Group 1, mild renal insufficiency, [creatinine clearance (CLCR): 30-60 mL/min]; Group 2, moderate to severe renal insufficiency (CLCR: 10-30 mL/min); Group 3, end-stage renal disease requiring maintenance hemodialysis (anuric). Blood and urine samples were obtained over a 72-hour period. Plasma concentration-time data demonstrated biexponential decay. The terminal elimination half-life was prolonged in Group 3 (18.6 +/- 5.7 hr) compared with Groups 1 (9.3 +/- 2.3 hr) and 2 (9.7 +/- 1.7 hr), P less than .05. Steady-state volume of distribution ranged from 0.80 to 1.26 L/kg but did not differ among the groups. Total body clearance (CLp) and renal clearance were significantly lower in Groups 2 and 3 patients compared with Group 1 patients. Nonrenal clearance was not related to CLCR. The CLp correlated well with CLCR (CLp = 1.59 CLCR + 33.8, r = 0.830, P less than .05). These data indicate that dosage adjustment may be necessary in patients who have renal insufficiency.

The effect of famotidine on renal function in patients with renal insufficiency

The effect of famotidine, a new histamine H2-receptor antagonist, on renal tubular creatinine secretion was evaluated in twelve patients with reduced renal function (creatinine clearance 10-60 ml min-1). Creatinine and inulin clearances were determined at baseline and for 4 h after a 10 mg intravenous dose of famotidine. Famotidine renal clearance exceeded inulin clearance by an average of 152%, indicating that renal tubular secretion of famotidine occurred. No significant changes in the clearances of creatinine or inulin, or the fractional clearance of creatinine were observed after famotidine administration. These data suggest that famotidine, unlike cimetidine, does not inhibit renal tubular secretion of creatinine. Thus, famotidine does not affect creatinine-dependent measurements of renal function and is unlikely to alter the renal elimination of basic drugs.

Treatment of active duodenal ulcers with famotidine. A double-blind comparison with ranitidine

In a double-blind multicenter trial, 100 patients with active duodenal ulcer were treated with a single nocturnal dose of famotidine 40 mg or ranitidine 300 mg. Antacid tablets were allowed as additional treatment if needed for pain relief. Endoscopy was repeated after two weeks, and again after four weeks if the ulcer had not healed earlier. Two patients in the famotidine group were withdrawn from the study because of non-compliance with the protocol. After two weeks, ulcers in 64 percent of the patients receiving famotidine and 46 percent of the patients receiving ranitidine were healed (p = 0.072). After four weeks, healing rates were 94 percent (famotidine) and 90 percent (ranitidine). Pain relief was rapid in either treatment group, with a tendency for better response during the day in the famotidine group. Mean antacid consumption during the first week was 3.0 tablets (34.5 mmol) in the famotidine group and 4.1 tablets (47.2 mmol) in the ranitidine group. Famotidine provides excellent healing and relief of symptoms in patients with duodenal ulcer disease.

Pharmacokinetics of TZU-0460, a new H2-receptor antagonist, in patients with impaired renal function

We have studied pharmacokinetics of a new H2-receptor antagonist, TZU-0460, in patients with varying degrees of renal impairment. The apparent volume of distribution at steady-state was 1.70 l/kg, and the plasma protein binding of TZU-0460 or its active metabolite, desacetyl TZU-0460 was less than 10% in normal subjects. These variables were not altered with renal impairment. Sixty percent of TZU-0460 given orally was excreted via the kidney, mainly by tubular secretion. The half-time of elimination was 3.94 h in normal subjects, and was prolonged to 12.13 h in severe renal failure (creatinine clearance below 30 ml/min/1.48 m2). Dosage adjustment of TZU-0460 is necessary in renal failure.

Famotidine, a new H2-receptor antagonist, does not affect hepatic elimination of diazepam or tubular secretion of procainamide

In 8 healthy male volunteers the pharmacodynamic responses to a single dose of diazepam and a single dose of procainamide were assessed before and after pre-treatment with the H2-receptor antagonist famotidine in a randomized crossover study. The pharmacokinetics of diazepam and procainamide were also studied, and the binding of famotidine to human liver microsomes was also measured. Cimetidine induced binding changes with a spectral dissociation constant (Ks) of 0.87 mM, whereas famotidine produced no measurable spectral alteration in concentrations up to 4 mM. The elimination half-life (t1/2: 45.6 h) and total plasma clearance (CL: 0.28 ml/min/kg) of diazepam were not significantly altered by famotidine (t1/2 = 39.0 +/- 11.4 h; CL = 0.31 +/- 0.08 ml/min/kg). Similarly, there was no enhancement of the sedative effect of diazepam by famotidine. The pharmacodynamics and pharmacokinetics of procainamide and N-acetylprocainamide (NAPA), too, were not significantly changed by famotidine: procainamide t1/2 2.9 vs 3.0 h under famotidine and renal clearance (CLR) 436 vs 443 ml/min; and NAPA CLR 195 vs 212 ml/min under famotidine. The data suggest that famotidine, in contrast to cimetidine, does not affect the pharmacokinetics of diazepam (hepatic elimination) or procainamide (tubular secretion). This new H2-receptor antagonist appears to be devoid of an interaction potential for either type of drug elimination.