Pharmacokinetics and dynamics of famotidine in patients with renal failure

A Rare Case of Famotidine-Induced Delirium in a Peritoneal Dialysis Patient

H2 receptor antagonists are commonly employed to manage gastro-esophageal reflux and peptic ulcer diseases with a very low incidence of side effects. Herein, we report an extremely rare incidence of famotidine-induced acute confusion in a patient with end-stage renal failure. We also discuss the pharmacokinetic properties of famotidine and its interplay with compromised renal function to result in neuropsychiatric manifestations, highlighting the importance of dosage adjustment in individuals with renal insufficiency.

Reduction in the rate of postoperative delirium by switching from famotidine to omeprazole in Japanese hepatectomized recipients

Background

Hepatectomy is a highly invasive procedure with a high probability of postoperative delirium. Treatment with antiulcer drugs is indispensable after hepatectomy for anastomotic ulcer management. The clinical pathway for hepatectomy was reviewed and the antiulcer drug used was switched from famotidine, a H₂-receptor antagonist, to omeprazole, a proton pump inhibitor, owing to the pharmacist’s intervention.

Methods

Hepatectomized recipients over 65 years of age, except in the cases of laparoscopic surgery and intensive care unit entry, were treated with famotidine injections (10 patients) or omeprazole injections (11 patients), and the incidence rates and severity of delirium were compared between the famotidine and omeprazole groups. The delirium after hepatectomy was assessed using the Japanese version of the NEECHAM confusion scale.

Results

The incidence rates of delirium were 90% in the famotidine group and 27.3% in the omeprazole group. Four out of 9 recipients in the famotidine group were injected with haloperidol to treat for delirium, but no recipients needed this treatment in the omeprazole group.

Conclusions

Compared with famotidine, the use of omeprazole was found to be effective in reducing the incidence rate and severity of postoperative delirium in patients undergoing hepatectomy. Pharmacists should actively strive to mitigate the risks of delirium.

The frequency of oral famotidine administration influences its effect on gastric pH in cats over time

Background

Famotidine is commonly administered to cats. Prolonged famotidine administration results in decreased efficacy in humans, dogs, and cows, but the long‐term effects in cats are unknown.

Objectives

To compare the effect of 2 oral administration frequencies of famotidine, twice daily (Group 1) and twice daily every second day (Group 2), on intragastric pH and serum gastrin concentrations in cats. We hypothesized a diminished effect on intragastric pH would be observed over time in Group 1 but not Group 2.

Animals

Sixteen healthy cats.

Methods

Randomized, 2‐factor repeated measures crossover design. Cats received 0.5‐1.24 mg/kg (median, 0.87 mg/kg) famotidine twice daily or twice daily every second day for 14 consecutive days. Intragastric pH monitoring was used to record intragastric pH on treatment days 1‐3 and 11‐13. Mean pH and mean percentage time (MPT) intragastric pH was ≥3 and 4 were compared between and within treatment groups by analysis of variance.

Results

Significant treatment group by time interactions were observed for mean intragastric pH, MPT intragastric pH ≥3 and 4 (P = .009, P = .02, P = .005, respectively). Interaction post hoc tests identified significant decreases in mean intragastric pH (P = .001), MPT ≥3 (P = .001), and MPT ≥4 (P = .001) on day 13 compared to day 1 in Group 1 but not in Group 2.

Conclusions and Clinical Importance

Oral famotidine administration results in a diminished effect on intragastric pH in healthy cats when given twice daily every day.

Renal Drug Dosage Adjustment According to Estimated Creatinine Clearance in Hospitalized Patients With Heart Failure

It is of clinical importance to determine creatinine clearance and adjust doses of prescribed drugs accordingly in patients with heart failure to prevent untoward effects. There is a scarcity of studies in the literature investigating this issue particularly in patients with heart failure, in whom many have impaired kidney function. The purpose of this study was to determine the degree of awareness of medication prescription as to creatinine clearance in patients hospitalized with heart failure. Patients hospitalized with a diagnosis of heart failure were retrospectively evaluated. Among screened charts, patients with left ventricular ejection fraction <40% and an estimated glomerular filtration rate (eGFR) of ≤50 mL/min were included in the analysis. The medications and respective doses prescribed at discharge were recorded. Medications requiring renal dose adjustment were determined and evaluated for appropriate dosing according to eGFR. A total of 388 patients with concomitant heart failure and renal dysfunction were included in the study. The total number of prescribed medications was 2808 and 48.3% (1357 medications) required renal dose adjustment. Of the 1357 medications, 12.6% (171 medications) were found to be inappropriately prescribed according to eGFR. The most common inappropriately prescribed medications were famotidine, metformin, perindopril, and ramipril. A significant portion of medications used in heart failure requires dose adjustment. Our results showed that in a typical cohort of patients with heart failure, many drugs are prescribed at inappropriately high doses according to creatinine clearance. Awareness should be increased among physicians caring for patients with heart failure to prevent adverse events related to medications.

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.

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).

Central nervous system reactions associated with famotidine: report of five cases

H2-receptor antagonists may cause various types of central nervous system reactions, particularly in patients with advanced age and/or impaired renal or liver function. These reactions have rarely been reported in association with famotidine. In five elderly patients, four of them with renal failure, central nervous system reactions developed shortly after initiation with famotidine therapy. These adverse reactions completely resolved after famotidine withdrawal. The authors' five cases and the other seven previously reported emphasize the need for dosage adjustment of famotidine in elderly patients and in those with renal failure, and that these patients should be carefully monitored for development of central nervous system reactions, which sometimes could be very serious.

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 roxatidine in patients with renal insufficiency

1. Roxatidine acetate, a new histamine H2-receptor antagonist, was administered in the evening (75 mg p.o.) to eight patients with renal insufficiency (CLCR 8-17 ml min-1) for 12 days and plasma drug concentrations were measured. 2. Ambulatory intragastric pH was monitored following the last dose and values were compared with those on day 1 when all patients received a placebo. 3. The terminal elimination half-life (mean +/- s.d.) of roxatidine was 10.8 +/- 2.4 h and its oral clearance was 178 +/- 43 ml min-1. 4. During roxatidine treatment gastrin levels increased slightly (median 189 vs 289 ng l-1) and the hyperparathyroid status of the patients was almost normalized (parathyroid hormone levels: median 199 vs 132 ng l-1). 5. The mean latency to a gastric pH of at least 4 was 4.3 +/- 1.4 h. The duration of action (intragastric pH > 4) was 10.6 +/- 3.9 h. 6. As in a pilot study with six patients (CLCR < or = 17 ml min-1) the recommended dosage regimen (75 mg 48 h-1) was unable to maintain gastric pH > 4 for more than 6 h, daily nocturnal intake of 75 mg roxatidine acetate appears appropriate to elevate gastric pH > 4 for a sufficient period of time.

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.

Drug dosage in patients during continuous renal replacement therapy. Pharmacokinetic and therapeutic considerations

The advantages of continuous haemofiltration and haemodialysis over intermittent haemodialysis for the treatment of acute renal failure are well recognised. In intensive care patients, 4 different continuous procedures, arteriovenous and venovenous haemofiltration (CAVH and CVVH) or haemodialysis (CAVHD and CVVHD), are employed. These effective detoxification treatments require knowledge of their influence on drug disposition. Data on kinetics of drugs during continuous treatment are scarce and limited almost exclusively to the oldest and least effective procedure (CAVH). Selected dialysis membranes may adsorb drugs, as in the case of aminoglycosides. In addition, elimination of substances with large molecular weights may vary depending on the pore size of the membrane, as in the case of vancomycin. Thus, even if drug dosages can be based on pharmacokinetic studies, selection of a dialysis membrane not studied may cause unpredictable drug concentrations. With these limitations in mind and considering the available literature on pharmacokinetics in patients with renal failure, general guidelines for drug dosage during continuous renal replacement therapy can be given. In haemofiltration, drug protein binding is the major factor determining sieving, i.e. the appearance of the drug in the ultrafiltrate. In haemodialysis, diffusion is added to ultrafiltration, and therefore the saturation of the combined dialysate and ultrafiltrate will decrease further with increasing dialysate flow rate. In continuous haemofiltration or haemodialysis the extracorporeal clearance can be calculated by multiplying the saturation value (estimated or, better, measured) with the ultrafiltrate and dialysate flow rate. Dividing the extracorporeal clearance by the total clearance (including the nonrenal clearance) gives the fraction of the dose removed due to extracorporeal elimination. Whether dosage recommendations available for anuric patients have to be modified or not can be decided on the basis of this value. In case of high nonrenal clearance, the degree of saturation is without clinical significance. Based on these considerations guidelines have been constructed for the effect of extracorporeal elimination on more than 120 different drugs commonly used in intensive care patients.

Hemofiltrability of histamine H2-receptor antagonist, nizatidine, and its metabolites in patients with renal failure

To study if an H2-receptor antagonist, nizatidine, and its metabolites [N-2-monodesmethylnizatidine (N-2-MDMN) and nizatidine sulfoxide (nizatidine S-Ox)] would be removed by an arteriovenous hemofiltration, the authors measured their plasma concentrations and amounts recovered in ultrafiltrate during 11 sessions of an intermittent hemofiltration performed in seven patients with renal failure who were given an oral administration of nizatidine (150 mg). The concentrations of the parent drug and its metabolites in plasma and ultrafiltrate were determined with a high-performance liquid chromatography with ultraviolet absorbance detection. The mean (+/- standard deviation [SD]) amounts of nizatidine removed by the procedure performed at the mean ultrafiltration rate of 18 (range, 11-25) mL/min over the mean duration of 179 (60 to 300) minutes accounted for 1.9 +/- 1.4% of the dose administered. The corresponding values for N-2-MDMN and nizatidine S-Ox were 0.3 +/- 0.2% and 0.2 +/- 0.2% of the molar dose of nizatidine, respectively. There was a significant correlation between the filtration rate and the hemofiltration clearance of nizatidine (r = .94, P < .001) or its active metabolite, N-2-MDMN (r = 0.83, P < .01), indicating that the sieving coefficient (Sc), an index of filtration efficiency, for these compounds is largely constant (0.59 and 0.67 for nizatidine and N-2-MDMN, respectively) under the current hemofiltration conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Pharmacology of gastric acid inhibition

Gastric acid secretion is precisely regulated by neural (acetylcholine), hormonal (gastrin), and paracrine (histamine; somatostatin) mechanisms. The stimulatory effect of acetylcholine and gastrin is mediated via increase in cytosolic calcium, whereas that of histamine is mediated via activation of adenylate cyclase and generation of cAMP. Potentiation between histamine and either gastrin or acetylcholine may reflect postreceptor interaction between the distinct pathways and/or the ability of gastrin and acetylcholine to release histamine from mucosal ECL cells. The prime inhibitor of acid secretion is somatostatin. Its inhibitory paracrine effect is mediated predominantly by receptors coupled via guanine nucleotide binding proteins to inhibition of adenylate cyclase activity. All the pathways converge on and modulate the activity of the luminal enzyme, H+,K(+)-ATPase, the proton pump of the parietal cell. Precise information on the mechanisms involved in gastric acid secretion and the identification of specific receptor subtypes has led to the development of potent drugs capable of inhibiting acid secretion. These include competitive antagonists that interact with stimulatory receptors (e.g. muscarinic M1-receptor antagonists and histamine H2-receptor antagonists) as well as non-competitive inhibitors of H+,K(+)-ATPase (e.g. omeprazole). The histamine H2-receptor antagonists (cimetidine, ranitidine, famotidine, nizatidine and roxatidine acetate) continue as first-line therapy for peptic ulcer disease and are effective in preventing relapse. Although they are generally well tolerated, histamine H2-receptor antagonists may cause untoward CNS, cardiac and endocrine effects, as well as interfering with the absorption, metabolism and elimination of various drugs. The dominance of the histamine H2-receptor antagonists is now being challenged by omeprazole. Omeprazole reaches the parietal cell via the bloodstream, diffuses through the cytoplasm and becomes activated and trapped as a sulfenamide in the acidic canaliculus of the parietal cell. Here, it covalently binds to H+,K(+)-ATPase, the hydrogen pump of the parietal cell, thereby irreversibly blocking acid secretion in response to all modes of stimulation. The main potential drawback to its use is its extreme potency which sometimes leads to virtual anacidity, gastrin cell hyperplasia, hypergastrinaemia and, in rats, to the development of carcinoid tumours. The cholinergic receptor on the parietal cell has recently been identified as an M3 subtype and that on postganglionic intramural neurones of the submucosal plexus as an M1 subtype.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Clinical pharmacokinetics of famotidine

Famotidine is a potent histamine H2-receptor antagonist widely used in the treatment and prevention of peptic ulcer disease. After intravenous administration the plasma famotidine concentration-time profile exhibits a biexponential decay, with a distribution half-life of about 0.18 to 0.5h and an elimination half-life of about 2 to 4h. The volume of distribution of the drug at steady-state ranges from 1.0 to 1.3 L/kg; plasma protein binding is low (15 to 22%). Famotidine is 70% eliminated unchanged into urine after intravenous administration. The total body and renal clearances of famotidine correlate significantly with creatinine clearance. Because its renal clearance (15 L/h) far exceeds the glomerular filtration rate, famotidine is considered to be eliminated not only via glomerular filtration but also via renal tubular secretion. Since its clearance is reduced in patients with renal insufficiency and in elderly patients, the maintenance dosage should be reduced in these patient groups. Removal of famotidine by any of the currently employed blood purification procedures (haemodialysis, peritoneal dialysis and haemofiltration) does not occur to a clinically significant degree. Liver cirrhosis does not appear to affect the disposition of famotidine unless severe renal insufficiency coexists. After oral administration, peak plasma concentrations are attained within 2 to 4h; the oral bioavailability ranges from 40 to 50%, due mainly to incomplete absorption. The oral absorption of the drug is dose-independent within a range of 5 to 40 mg. There are 3 formulations available (tablet, capsule and suspension), which appear to be bioequivalent. Coadministration of potent antacids reduces the oral absorption of famotidine by 20 to 30%. On a weight-to-weight basis, the antisecretory effect of famotidine is about 20 and 7.5 times more potent than those of cimetidine and ranitidine, respectively. Plasma famotidine concentrations correlate with its antisecretory effect: values of about 13 and 20 micrograms/L produce a 50% reduction in the gastrin-stimulated gastric acid secretion and a fasting intragastric pH of greater than 4, respectively. Available data suggest that famotidine interacts neither with the hepatic oxidative drug metabolism nor with the tubular secretion of other commonly used therapeutic agents. However, further studies are required to evaluate a full spectrum of its drug interaction potential.

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)

Famotidine. Pharmacokinetic properties and suppression of acid secretion in paediatric patients following cardiac surgery

The pharmacokinetic and pharmacodynamic properties of the H2-receptor antagonist famotidine have been well described in adult subjects. However, similar data for children are not available. Therefore, this study looked at the disposition of the drug (given to prevent aspiration following cardiac surgery) in 10 paediatric patients with normal kidney function (age range 2 to 7 years, bodyweight 14 to 25 kg) after a single intravenous dose of famotidine 0.3 mg/kg. Plasma concentrations of the drug and gastric pH values were both monitored for 20 hours by high performance liquid chromatography and aspiration of gastric juice, respectively. Plasma famotidine concentrations declined with an elimination half-life of 3.3 +/- 1.8 h (mean +/- SD) and the drug was effective in elevating the gastric pH above 3.5 for about 9 hours in 6 patients. The variable volume of distribution and total plasma clearance of famotidine averaged 1.4 +/- 1.0 L/kg and 0.3 +/- 0.17 L/h/kg, respectively. In 4 patients unchanged famotidine could also be measured in a 12-hour urine fraction. The amount excreted (21 to 79%) correlated with clearance (r = 0.97). All these data are comparable to those obtained in healthy adults, indicating that paediatric patients receiving intensive medical treatment after cardiac surgery can handle famotidine in a way very similar to healthy adult subjects. A dosage of 0.3 mg/kg every 8 hours appears to be advisable.

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.

Frequent non-response to histamine H2-receptor antagonists in cirrhotics

The effect of ranitidine 300 mg po given at 1800 h (famotidine 40 mg/cimetidine 800 mg) on the night time gastric pH was tested using longterm intragastric pH monitoring in 27 patients with and 32 patients without liver cirrhosis. A rise in the gastric pH above 4.0 for more than six hours between 1800 h and 0600 h was considered as sufficient effect (response) of the H2-receptor antagonists on gastric acidity. Among the patients with cirrhosis, there were significantly (p less than 0.005) more non-responders to ranitidine (16 of 27 patients) than in the control group (six of 32). When 13 of the 22 non-responders to ranitidine were subsequently treated with famotidine, only two showed a sufficient rise in their gastric pH. Of the 11 patients not responding to both H2-receptor antagonists, 10 were finally treated with cimetidine and eight did not respond. Plasma levels of all three drugs measured two and four hours after oral administration were not significantly different between cirrhotic and noncirrhotic patients as well as between responders and non-responders. In addition, in all patients plasma levels were far above the corresponding IC50 values. Therefore, differences in the absorption and plasma levels of these drugs cannot account for the frequent non-response in cirrhotics.

Newer H2-receptor antagonists. Clinical pharmacokinetics and drug interaction potential

Since H2-receptor antagonists are widely and successfully used in the treatment of peptic ulcer, several alternatives to the standard agents cimetidine and ranitidine have been developed. Promising 'new' candidates might be famotidine and nizatidine. For proper selection of the appropriate drug, its pharmacokinetic properties and interaction potential should be known. All 'old' and 'new' H2-receptor blockers are eliminated relatively rapidly (t 1/2 ranges from 1.5 to 4 hours), mainly by the renal route (glomerular filtration and tubular secretion). They exhibit a linear disposition and their distribution is similar. Absorption is most complete for nizatidine, whereas famotidine demonstrates the lowest effective plasma concentrations. Since etintidine shares the same imidazole ring structure as cimetidine, it can also impair oxidative drug metabolism in the liver. In this respect, the non-interacting famotidine and nizatidine (like ranitidine) offer a definite advantage. Based on their very similar pharmacokinetic and interaction profiles, these 2 H2-receptor antagonists might be regarded as alternatives to the older drugs in this group, and at least some economic benefits might result from the competition they will provide.

Pharmacokinetics of ranitidine in patients undergoing haemofiltration

The pharmacokinetics of ranitidine was investigated in 11 patients with acute or end stage renal failure during haemofiltration. Each patient received 50 mg ranitidine i.v. The mean distribution and elimination half lives were 0.13 and 2.57 h, respectively. The total body clearance (CL) and volume of distribution (Vz) were 298 ml.min-1 (5.19 ml.min-1.kg-1) and 1.08 l.kg-1, respectively. About 17.1% of the administered dose was removed by haemofiltration (in approximately 20 l filtrate). Five of the patients still had some urine output and they excreted 0.1 to 11.8% of the dose in urine in 24 h. The haemofiltration clearance was 66.9 ml.min-1 at a filtrate flow rate of 86 ml.min-1, corresponding to a mean sieving coefficient of 0.78 (n = 6). As plasma concentrations were still in an effective range after haemofiltration, dose supplementation is not recommended.