Effects of age and chronic renal failure on the urinary excretion kinetics of famotidine in man

Predicting the Effect of Renal Function on Systemic Clearance: Is a simple scaling method sufficient?

PURPOSE

To employ a simple scaling method to predict systemic or oral clearance for drugs that are primarily renally cleared knowing the fraction eliminated in urine (f_e) and a patient's renal function relative to healthy controls (S_GFR).

METHODS

Observations evaluating drug clearance as a function of creatinine clearance for renally cleared drugs (f_e >0.3) were obtained from literature sources. The analysis comprised of 82 unique drugs from 124 studies including 31 drugs with replicate studies. A simple scaler for renal function was employed and compared to the linear regression of available data. For drugs in which replicate studies were available, the ability of the linear regression (Cl vs Cl_CR) from one pharmacokinetic study was used to predict observations from an assigned replicate and compared to the scaling approach.

RESULTS

For patients categorized as severe kidney disease (Cl_CR fixed at 20 ml/min), the scalar tended to over predict some observations, but 92% of the predictions were within 50 - 200% of the observed data. For drugs with available replicates, the scalar was as good or better in predicting the influence of Cl_CR on systemic clearance from a separate study when comparing against the linear regression approach.

CONCLUSION

A scaling approach to account for alterations in drug clearance appears to have its advantages and represents a simple and generalizable method for guiding dose adjustments in patients with decreased renal function for drugs that are renally cleared (f_e >0.3). In addition to its use in clinical practice, validation of this approach may have implications in facilitating more efficient drug development processes for designing dose-adjusted pharmacokinetic studies in patients with renal disease.

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.

Feline CKD

Practical relevance:

Treatment of feline chronic kidney disease (CKD) tends to focus on minimising the adverse effects of reduced renal function, rather than addressing an underlying cause. Despite this, and the progressive nature of CKD, treatment can improve quality of life and enable many cats to have long survival times.

Evidence base:

Strong evidence supports the provision of renal diets, which are protein and phosphorus restricted; compliance is improved by gradual dietary transition. Additional phosphorus restriction is achieved by the use of phosphate binding agents, although it is unknown if these yield similar survival benefits to those provided by renal diets. Interventions to control hypokalaemia and hypertension in affected cats are important to prevent serious complications. Administration of benazepril to cats with proteinuric kidney disease has been shown to significantly improve their appetite but not their survival. As CKD progresses, many cats will benefit from treatment to control clinical signs of uraemic gastroenteritis and anaemia.

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.

Evaluation of a novel method to estimate absolute bioavailability of drugs from oral data

The goal of this investigation was to evaluate the performance of a novel method allowing estimation of absolute bioavailability from oral data only. In contrast to the traditional method, which compares areas under the drug concentration time curves after oral and intravenous administration in subjects with normal renal function, the novel method uses total and renal clearance values following oral administration from subjects with varying renal functions to estimate bioavailability. The novel method can also provide estimates for nonrenal clearance.Published data on total clearance and renal clearance of drugs obtained from subjects with variable renal functions were collected, the novel method applied, estimates of bioavailability and nonrenal clearance obtained and compared with reported estimates by the traditional methods. In addition computations were performed to assess various factors that could possibly affect the reliability of the novel method. The results indicated that the novel method provides accurate estimates for bioavailability of drugs meeting the prerequisites: linear kinetics, predominant renal excretion in normals, absence of metabolic polymorphism and independence of bioavailability and nonrenal clearance from renal function. The average (standard deviation) of the prediction error and bias of the bioavailability estimates by the novel method was 7.8 (6.0) and -1.4 (9.8)%, respectively. The estimates for nonrenal clearance by the novel method were less accurate. The computations confirmed that the estimates by the novel method are sensitive to renal-function dependent changes in nonrenal clearance and bioavailability and also depend on the extent of renal excretion of a drug. In conclusion, the novel method's main use is to diagnose absence or presence of changes in bioavailability and non-renal clearance of drugs in populations with varying renal function.

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).

Alternative high-performance liquid chromatographic assay for p-aminohippuric acid (PAH): effect of aging on PAH excretion in the isolated perfused rat kidney

Para-aminohippuric acid (PAH), an indicator of renal plasma flow, is a commonly used marker of organic anion transport by the kidney. An analytical method for PAH using HPLC was developed. The method is simple, fast and requires a minimum amount of organic solvent. Sample preparation involved protein precipitation with zinc sulfate. Para-amino benzoic acid was utilized as an internal standard (IS). Chromatography was performed using a reversed-phase phenyl column with UV detection at a wavelength of 254 nm. Mobile phase consisted of 0.1 M acetic acid and acetonitrile (99:1) at a flow rate of 1 ml/min. The assay was validated over a standard concentration range from 1 to 25 microg/ml. Accuracy, precision, reproducibility and specificity of the method was established with coefficients of variation <10%. The method was sensitive and showed linear response in peak height ratio (analyte:IS) over the concentration range studied (r(2)>0.99). The assay was used to study the effect of aging on PAH excretion in the isolated perfused rat kidney model. Experiments were conducted in kidneys from young (2-3 months, n=6), adult (6-9 months, n=5) and aged (12-16 months, n=3) male Sprague-Dawley rats at an initial drug concentration of 20 microg/ml. Significant differences in kidney function (e.g. glomerular filtration rate and glucose reabsorption) were observed in aged kidneys. Despite a 5-fold reduction in glomerular filtration rate, PAH renal clearance (kidney weight-corrected) decreased by only 2-fold in aged (2.2+/-0.42 ml/min per gram) compared to young (4.6+/-0.70 ml/min per gram, P<0.05) rats. Furthermore, renal excretion ratio was significantly higher in aged rats (27+/-8.0 vs. 15+/-5.0, P<0.05). These preliminary findings challenge the 'Whole Nephron Hypothesis' that assumes parallel reductions in renal filtration and secretory capacity secondary to disease or aging.

Delirium following a switch from cimetidine to famotidine

OBJECTIVE

To describe a patient who developed delirium when switched from cimetidine to famotidine.

CASE SUMMARY

An 84-year-old Taiwanese woman was hospitalized for tarry stools. Her past medical history revealed only a decrease in renal function. She tolerated both oral and intravenous cimetidine therapy with a daily dose of 400-900 mg intermittently for 20 years. On hospital days 1-3, cimetidine 300 mg was injected intravenously every eight hours without difficulty. Considering the possible existence of a cimetidine-resistant bleeding ulcer, famotidine 20 mg was given twice daily orally on hospital days 4-7 and then injected intravenously. Six days after being switched from cimetidine to famotidine, the woman's mental status deteriorated. A series of clinical tests revealed no apparent causative factors. Famotidine was then suspected as a probable cause of her delirium. Discontinuation of the drug resulted in rapid resolution of the patient's delirious status. DICUSSION: Famotidine crosses the blood-brain barrier less easily than cimetidine and was taken for a much shorter period in this patient. Thus, we propose that the occurrence of delirium in this patient was associated with famotidine, but not cimetidine, and was idiosyncratic rather than dose related. Furthermore, this case involved an elderly patient with compromised renal function who developed delirium in response to intravenous, but not oral, administration of famotidine. These factors seem to increase the risk for, famotidine-induced delirium.

CONCLUSIONS

Clinicians should be aware of the possible occurrence of delirium following a switch from one histamine2-receptor antagonist to another. In rare instances, patients switched to famotidine from cimetidine may experience delirium, particularly elderly patients with poor renal function who receive intravenous famotidine.

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.

Dose-dependent pharmacokinetics: experimental observations and theoretical considerations

Clinically, absorption and elimination of most drugs follow linear kinetics, and pharmacokinetic parameters describing absorption and elimination of a drug do not change over the therapeutic dose range. However, dose-dependent pharmacokinetics have been reported more frequently in preclinical studies, particularly in toxicity studies, where high doses are often employed. This review highlights the major types of dose-dependent pharmacokinetics with unique examples. Before setting out on a pivotal subchronic and chronic toxicity study of a new drug, a pilot study is often performed to establish a dose range in which a reasonable relationship between plasma AUC and dosage exists to ensure sufficient exposure of animals to the drug. Theoretical bases and possible causes of dose-AUC disproportionality are discussed. Factors affecting the distribution and elimination of drugs and causes of dose-dependent tissue distribution and elimination are also discussed. Often, the non-linear kinetics complicate the design of dosage regimens and prediction of efficacy and toxicity. Thus, an understanding of the influence of dose on the pharmacokinetics is important in the evaluation of the efficacy and toxicity of new drugs.

Risk for adverse events among patients receiving intravenous histamine2-receptor antagonists

OBJECTIVE

To identify risk factors for adverse drug reactions (ADRs) in patients receiving intravenous histamine2-receptor antagonists (H2-RAs).

DESIGN

The study hypothesis was evaluated by performing a logistic regression procedure with a backward elimination of the explanatory variables associated with ADRs.

MAIN OUTCOME MEASURES

ADRs temporally associated with the use of intravenous H2-RAs served as the dependent variable. Background information about the patients and drug use evaluation criteria in three general areas were entered into the regression analysis.

SETTING

Hospitals were selected from the southeastern US, based on their willingness to participate and their characteristics. Participating hospitals exhibited a variety of sizes and ownership arrangements.

PATIENTS

1200 adult patients who were receiving intravenous H2-RAs.

RESULTS

Seven percent of patients experienced a presumed ADR (PADR) to intravenous H2-RAs. The only risk factor for ranitidine was for patients who did not have their dosage corrected for renal function ("overdose"); these patients were twice as likely to experience a PADR compared with patients who received the correct dosage as determined by their renal function. Two risk factors for cimetidine were identified: (1) patients taking cimetidine with another medication known to cause a drug interaction; and (2) patient age. No risk factors were identified for famotidine.

CONCLUSIONS

The two risk factors for ADRs identified in this study are preventable. Healthcare providers should strive to prevent ADRs by adjusting patients' dosages based on their renal function and by monitoring patients receiving cimetidine with another medication known to interact with cimetidine.

Prescribing policy for antiulcer treatment in the elderly

In the short and long term treatment of peptic ulcer in the elderly some problems have yet to be resolved, mainly concerning the physiology and pathophysiology of the aging stomach, the pharmacokinetic and pharmacodynamic properties of antiulcer drugs, and the presence of different risk factors compared with young patients. The available data from controlled trials of peptic ulcer in the general population and from the limited experience in geriatrics, show that the clinical efficacy and tolerability of the anti-secretory drugs (e.g. cimetidine, ranitidine and famotidine) and of cytoprotective compounds are similar to that observed in younger patients. However, more data are necessary concerning the optimal dosage in relation to physiological age-related changes of liver and kidney function, the duration of prophylactic treatment, and importantly, the assurance of adequate patient compliance.

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 molsidomine and of its active metabolite, SIN-1 (or linsidomine), in the elderly

The pharmacokinetics of molsidomine were investigated in six young (25.5 +/- 0.6 years) and in six elderly healthy volunteers (81.1 +/- 3.1 years). After a 2 mg oral administration, molsidomine elimination half-life was prolonged in elderly subjects (1.9 +/- 0.2 h versus 1.2 +/- 0.1 h, P less than 0.05) because of a decrease in its plasma clearance (15.1 +/- 3.2 l.h-1 versus 41.8 +/- 2.5 l.h-1 (P less than 0.01) in young volunteers). The elimination half-life of the active metabolite, SIN-1 or linsidomine was also prolonged in elderly subjects (1.8 +/- 0.2 h versus 1.0 +/- 0.08 h, P less than 0.05). AUCs of both molsidomine and SIN-1 were increased in the elderly subjects, but the increase in the former was greater (x 3.4) than the increase in the latter (x 1.6). These results suggest that pharmacokinetics and metabolism of molsidomine are impaired in elderly subjects.

Prediction of the renal clearance of cimetidine using endogenous N-1-methylnicotinamide

We investigated the influence of the type rather than the degree of renal insufficiency on the renal clearance of drugs. Different models of site specific experimental renal failure (ERF) have been developed in the rat; proximal tubular necrosis, induced by cisplatin; papillary necrosis, induced by 2-bromoethylamine, and glomerulonephritis, induced by sodium aurothiomalate or by antiglomerular basement membrane antibody. Several parameters of kidney function were assessed: the clearance of inulin, PAH, and endogenous N-1-methylnicotinamide (NMN). Plasma BUN and creatinine concentrations, and the presence of proteinuria and glucosuria were also measured. Our results showed a nonparallel decrease in glomerular filtration rate (GFR) and tubular secretion as measured by the secretory clearance of endogenous NMN or by the secretory clearance of p-aminohippuric acid (PAH), that is incompatible with the "intact nephron hypothesis." As a result, the renal clearance of cimetidine, a drug eliminated mainly by renal secretion, correlated better with the renal clearance of endogenous NMN than with the GFR. We conclude that (i) our models of ERF demonstrated the existence of glomerulo-tubular imbalance that is contrary to expectations based on the intact nephron hypothesis; (ii) the type of the renal disease has a direct influence on the renal clearance of cimetidine; (iii) the clearance of endogenous NMN may be a valuable noninvasive test for assessing renal tubular secretion which could be useful in predicting the clearance of drugs eliminated predominantly by tubular secretion.

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.

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.

Clinical pharmacokinetic considerations in the elderly. An update

There are numerous studies of drug handling in the elderly, but it is difficult to assess the significance of changes seen in vitro, or after single-dose administration, because they are often compensated by other mechanisms at steady-state. However, a knowledge of these studies is important as the results alert the investigator to possible treatment problems. The high incidence of adverse drug reaction in the elderly population leaves no doubt that improvements in therapy are needed. Research has been directed at seeking patterns of abnormality in the elderly on which to base recommendations for alterations in dosage regimens. The major shortcoming of this approach has been the failure to distinguish between the effect of chronological age on drug pharmacokinetics, and drug kinetics in elderly people with multiple pathology. The latter concern appreciates the variety of factors involved and the importance of treating each patient as an individual: presentation of mean data is confusing and misleading. The objective of drug treatment in any age group, but particularly in the elderly, is to administer the smallest possible dose which gives adequate therapeutic benefit throughout the entire dosage interval with the minimum of side effects. For most drugs the safe starting dose in the elderly is one-third to half that recommended in the young. Vigilance for potential side effects with plasma concentration monitoring, if available, should help keep toxicity to a minimum. When other medications are added or changed, the possibility of interaction should be anticipated. Methods for individualisation of dosage regimens and the use of sustained-release formulations in the elderly are discussed. Dosage alteration in the elderly in terms of reduced dose frequency, rather than dose size, may help improve compliance. A knowledge of the pharmacokinetics of a drug helps determine which approach will be most beneficial.

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.