Haematological adverse effects of histamine H2-receptor antagonists

Histamine receptor 2 blockade selectively impacts B and T cells in healthy subjects

Histamine receptor 2 (H2R) blockade is commonly used in patients with gastric, duodenal ulcers or gastroesophageal reflux disease. Beyond the gastrointestinal tract, H2R is expressed by multiple immune cells, yet little is known about the immunomodulatory effects of such treatment. Clinical reports have associated H2R blockade with leukopenia, neutropenia, and myelosuppression, and has been shown to provide clinical benefit in certain cancer settings. To systematically assess effects of H2R blockade on key immune parameters, a single-center, single-arm clinical study was conducted in 29 healthy subjects. Subjects received daily high dose ranitidine for 6 weeks. Peripheral blood immunophenotyping and mediator analysis were performed at baseline, 3 and 6 weeks into treatment, and 12 weeks after treatment cessation. Ranitidine was well-tolerated, and no drug related adverse events were observed. Ranitidine had no effect on number of neutrophils, basophils or eosinophils. However, ranitidine decreased numbers of B cells and IL-2Rα (CD25) expressing T cells that remained lower even after treatment cessation. Reduced serum levels of IL-2 were also observed and remained low after treatment. These observations highlight a previously unrecognised immunomodulatory sustained impact of H2R blockade. Therefore, the immune impacts of H2R blockade may require greater consideration in the context of vaccination and immunotherapy.

Idiosyncratic Drug-Induced Neutropenia and Agranulocytosis in Elderly Patients

Agranulocytosis is a rare, but serious and life-threatening hematologic disorder in elderly patients. Idiosyncratic drug-induced agranulocytosis (IDIA) has been classically defined by a neutrophil count below 0.5 × 10⁹/L. The annual incidence of IDIA in Europe is about 1.6–9.2 cases per million inhabitants. Increasing age and female sex have been considered as risk factors for the development of this condition. Besides, it is well known that older people take on average more drugs than younger people. This condition is most often associated with the intake of antibacterial agents, antiplatelets, antithyroids, antipsychotics, antiepileptics and nonsteroidal anti-inflammatory drugs (NSAIDs). Initially, agranulocytosis may present without symptoms, but may quickly progress to a severe infection and sepsis. The causative drug should be immediately stopped. In febrile patients, blood cultures and where indicated, site-specific cultures should be obtained and early treatment with empirical broad-spectrum antibiotics started. Even with adequate treatment, the mortality rate is higher in elderly patients reaching up to 20%. Hematopoietic growth factors have proven to be useful as they shorten the duration of neutropenia. However, data on neutropenia and agranulocytosis in the elderly meeting the criteria of evidence-based medicine are still poor in the literature. This review analyzes the results of our experience as well as other published studies of the universal literature.

Febrile Neutropenia in a Patient with Non-Small Cell Lung Cancer Treated with the Immune-Checkpoint Inhibitor Nivolumab

Patient: Male, 57-year-old

Final Diagnosis: Febrile neutropenia

Symptoms: Fever

Medication: Nivolumab

Clinical Procedure: Chemotherapy

Specialty: Oncology

Metformin and Micronutrient Status in Type 2 Diabetes: Does Polypharmacy Involving Acid-Suppressing Medications Affect Vitamin B12 Levels?

Metformin is the first-choice drug in uncomplicated type 2 diabetes (T2DM) and is effective in improving glycaemic control. It is the most widely prescribed oral antidiabetic medicine and has a good safety profile. However, there is an abundance of evidence that metformin use is associated with decreased Vitamin B12 status, though the clinical implications of this in terms of increased risk of diabetic peripheral neuropathy are debated. There is growing evidence that other B vitamins, vitamin D and magnesium may also be impacted by metformin use in addition to alterations to the composition of the microbiome, depending on the dose and duration of therapy. Patients using metformin for prolonged periods may, therefore, need initial screening with intermittent follow-up, particularly since vitamin B₁₂ deficiency has similar symptoms to diabetic neuropathy which itself affects 40-50% of patients with T2DM at some stage. Among patients with T2DM, 40% are reported to experience symptomatic gastroesophageal reflux disease (GORD), of whom 70% use oral antidiabetic medications. The most common medications used to treat GORD are proton pump inhibitors (PPIs) and antagonists of histamine selective H₂ receptors (H₂RAs), both of which independently affect vitamin B₁₂ and magnesium status. Research indicates that co-prescribing metformin with either PPIs or H₂RAs can have further deleterious effects on vitamin B₁₂ status. Vitamin B12 deficiency related to metformin and polypharmacy is likely to contribute to the symptoms of diabetic neuropathy which may frequently be under-recognised. This review explores current knowledge surrounding these issues and suggests treatment strategies such as supplementation.

Variables associated with stress ulcer prophylaxis misuse: a retrospective analysis

BACKGROUND

Stress ulcer prophylaxis (SUP) is commonly used in hospitals. Although its indications are better delineated for intensive care unit (ICU) patients, its use in non-ICU settings is somewhat arbitrary and based on judgment.

OBJECTIVE

We attempted to assess the extent of SUP overuse in our hospital. We also carefully collected and analyzed several variables to detect associations governing this flawed behavior and its financial burden on the hospital's budget.

MATERIALS AND METHODS

We retrospectively analyzed charts of patients admitted to the medical floor of a tertiary referral university hospital over a 1 year period. All adult patients admitted to the medical ward who received at least one dose of SUP were included and reviewed for a multitude of variables in addition to the appropriateness of acid suppression therapy (AST).

RESULTS

We included 320 charts and found that 92% of patients admitted during that period were not eligible for SUP. The total inappropriateness of SUP was noted to be 58% (p = 0.015). Increasing age and male gender were found to be significant variables in AST misuse (p = 0.045 and p = 0.010), much like duration of hospital stay (p = 0.008). Comorbidities was also found to be a defining variable for AST overuse (odds ratio [OR] = 3.27). Patients with two or more minor risk factors were also subjected more to SUP inappropriately (OR = 3.53), in addition to patients of certain specialties (Neurology, Infectious Diseases, etc.). Our calculated financial burden was more than $23,000 per year for the medical floor.

CONCLUSION

This retrospective study confirmed the growing suspicion that SUP misuse is evident on the medical floors. We also delineated several factors and variables associated with and affecting SUP overuse.

A review of stress-related mucosal disease

OBJECTIVE

To review and summarize the human and veterinary literature regarding stress-related mucosal disease (SRMD) pathogenesis, patient risk factors, and therapeutic options for prophylaxis and treatment.

ETIOLOGY

SRMD is a common sequela of critical illness in human patients. Development of SRMD results from splanchnic hypoperfusion, reperfusion injury, and exposure of the gastric mucosa to acid, pepsin, and bile acids following breakdown of the gastric mucosal defense system. Human patients with the highest risk of stress ulceration include those with respiratory failure necessitating mechanical ventilation greater than 48 h or coagulopathy. Currently, little is known about the incidence and pathophysiology of SRMD in critically ill veterinary patients.

DIAGNOSIS

A presumptive diagnosis can be made in high-risk patient populations following detection of occult or gross blood in nasogastric tube aspirates, hematemesis, or melena. Definitive diagnosis is achieved via esophagogastroduodenoscopy. Lesions are localized to the acid-producing portions of the stomach, the fundus, and body.

THERAPY

Therapy is aimed at optimization of tissue perfusion and oxygenation. Pharmacologic interventions are instituted to increase intraluminal pH and augment natural gastric defenses. Histamine(2)-receptor antagonists, proton pump inhibitors, and sucralfate are the mainstays of therapy. In people, clinically significant bleeding may necessitate additional interventions (eg, packed red blood cell transfusions, endoscopic, or surgical hemostasis).

PROGNOSIS

Mortality is increased in people with clinically significant bleeding compared to those patients who do not bleed. Institution of prophylaxis is recommended in high-risk patients. However, no consensus exists regarding initiation of prophylaxis, preference of frontline drug class, or indication for discontinuation of therapy. The prognosis of veterinary patients with SRMD remains unknown at this time.

Deep Vein Thrombosis and Stress Ulcer Prophylaxis in the Intensive Care Unit

Deep vein thrombosis (DVT) and stress gastric ulcers can be serious complications in patients admitted to the intensive care unit. This review discusses the risk factors associated with the development of DVT and stress-related mucosal disease (SRMD), evaluates the available literature on current options for DVT and stress ulcer prophylaxis, and examines the associated adverse effects and optimal duration of therapy.

Pica associated with iron deficiency or depletion: clinical and laboratory correlates in 262 non-pregnant adult outpatients

BACKGROUND

There are many descriptions of the association of pica with iron deficiency in adults, but there are few reports in which observations available at diagnosis of iron deficiency were analyzed using multivariable techniques to identify significant predictors of pica. We sought to identify clinical and laboratory correlates of pica in adults with iron deficiency or depletion using univariable and stepwise forward logistic regression analyses.

METHODS

We reviewed charts of 262 non-pregnant adult outpatients (ages ≥18 y) who required treatment with intravenous iron dextran. We tabulated their sex, age, race/ethnicity, body mass index, symptoms and causes of iron deficiency or depletion, serum iron and complete blood count measures, and other conditions at diagnosis before intravenous iron dextran was administered. We excluded patients with serum creatinine >133 μmol/L or disorders that could affect erythrocyte or iron measures. Iron deficiency was defined as both SF <45 pmol/L and TS <10%. Iron depletion was defined as serum ferritin (SF) <112 pmol/L. We performed univariable comparisons and stepwise forward logistic regression analyses to identify significant correlates of pica.

RESULTS

There were 230 women (184 white, 46 black; ages 19-91 y) and 32 men (31 white, 1 black; ages 24-81 y). 118 patients (45.0%) reported pica; of these, 87.3% reported ice pica (pagophagia). In univariable analyses, patients with pica had lower mean age, black race/ethnicity, and higher prevalences of cardiopulmonary and epithelial manifestations. The prevalence of iron deficiency, with or without anemia, did not differ significantly between patients with and without pica reports. Mean hemoglobin and mean corpuscular volume (MCV) were lower and mean red blood cell distribution width (RDW) and platelet count were higher in patients with pica. Thrombocytosis occurred only in women and was more prevalent in those with pica (20.4% vs. 8.3%; p = 0.0050). Mean total iron-binding capacity was higher and mean serum ferritin was lower in patients with pica. Nineteen patients developed a second episode of iron deficiency or depletion; concordance of recurrent pica (or absence of pica) was 95%. Predictors of pica in logistic regression analyses were age and MCV (negative associations; p = 0.0250 and 0.0018, respectively) and RDW and platelet count (positive associations; p = 0.0009 and 0.02215, respectively); the odds ratios of these predictors were low.

CONCLUSIONS

In non-pregnant adult patients with iron deficiency or depletion, lower age is a significant predictor of pica. Patients with pica have lower MCV, higher RDW, and higher platelet counts than patients without pica.

Safety issues relating to long-term treatment with histamine H2-receptor antagonists

H2-receptor antagonist therapy is associated with a low incidence of adverse reactions. Adverse events reported in clinical trials of ranitidine in daily doses of up to 1200 mg include headache, tiredness and mild gastrointestinal disturbances, but the incidence is similar to or less than that for placebo. High doses of cimetidine (> 5 g/day) can cause reversible impotence or gynaecomastia. While ranitidine exhibits no clinically significant drug-drug interactions, cimetidine interacts with many drugs metabolized by cytochrome P450. In contrast to ranitidine and cimetidine, where safety data are available for up to 10 years of continuous therapy, experience with famotidine and nizatidine is limited. The safety of long-term H2-receptor antagonist therapy needs to be considered in relation to the potential consequences of prolonged acid suppression, including the risk of proliferation of gastric flora and the risk of developing enterochromaffin-like cell hyperplasia, which could in turn, theoretically, lead to gastric malignancy. Such problems have not been observed in patients during long-term therapy at low or full doses of H2-receptor antagonists. Standard doses of currently available H2-receptor antagonists permit acid secretion in response to food and other stimuli, and this daily acid tide prevents persistent bacterial colonization.

Safety profile of long-term H2-antagonist therapy

The safety profile of low-dose maintenance therapy with H2-antagonists for duodenal ulcer disease suggests that these agents can be given safely for several years and probably much longer. Because information regarding the use of these compounds for more than 10 years in large numbers of patients is lacking, the safety of these drugs should continue to be monitored. The safety profiles of famotidine and nizatidine will require several additional years of postmarking surveillance data to match the depth of our knowledge regarding cimetidine and ranitidine. Compared to a surgical approach to ulcer disease, continuous H2-blocker maintenance therapy is cost-effective and is associated with significantly less morbidity. Patients with a history of bleeding or other ulcer complication should be encouraged to remain on maintenance therapy if they do not undergo surgery. The need for extended maintenance therapy also applied to individuals with frequent symptomatic ulcer relapses, reflux oesophagitis, and a range of less common disorders. Currently, H2-blockers and sucralfate are the only agents approved by the Food and Drug Administration for maintenance therapy of duodenal ulcer disease. Experience with omeprazole is still limited, and its long-term safety profile must await the completion of controlled trials of maintenance therapy. Given the apparent long-term safety of the H2-blockers for maintenance therapy, any new agent must prove to be equally safe in the clinical arena, a task that may be indeed formidable.

Drug eruption caused by ranitidine hydrochloride (Zantac) which showed a strong reaction in a drug-induced lymphocyte stimulation test

An 80-year-old male who developed a generalized papular erythema-type drug eruption after being treated with ranitidine hydrochloride is herein reported. The duration from the intake of the medicine to the onset of the eruption was 3 days, and the eruption remained unchanged for a week after withdrawal of the medicine and even after the eruption itself was treated. A diagnosis of drug eruption by ranitidine hydrochloride was confirmed based on a strongly-positive reaction of a drug-induced lymphocyte stimulation test (DLST).

Long-term effects of nitrous oxide anaesthesia on laboratory and clinical parameters in elderly Omani patients: a randomized double-blind study

AIMS

This study examined the long-term effects of nitrous oxide anaesthesia on serum levels of cobalamin and folate, red cell folate levels and haematological parameters, and neurological status in elderly Omani patients.

METHODS

Sixty-nine consecutive patients undergoing ophthalmic surgery were randomly and double-blind assigned to nitrous oxide or propofol anaesthesia. They met the following entry criteria: age 55 years or above, no major organ failure, no clinical signs or symptoms of cobalamin or folate deficiency, mean cell volume (MCV) </= 96 fl, haematocrit (Hct) higher than 0.3 and no cobalamin and/or folate substitution therapy during the preceding months. Serum levels of cobalamin and folate, red cell folate levels, and haematological parameters were measured prior to anaesthesia and 3-5 weeks later. At that time, the patients also underwent thorough neurological examination.

RESULTS

Data of 51 patients were complete and considered for analysis. In both nitrous oxide and propofol group, the range of exposure time was comparable (+/-1 h). In the nitrous oxide group, a slight but significant decrease in haemoglobin, Hct, and red blood cell count (RBC) (P < 0.001) was observed, whereas there was a mild increase in mean cell haemoglobin (MCH) and mean cell volume (P < 0.05). In addition, there was a significant decrease in serum folate levels (P < 0.05). Hct and RBC decreased slightly in the propofol group (P < 0. 05), whereas there was a small increase in MCH. There was no difference between the two anaesthetics with regard to serum cobalamin and red cell folate levels, but there was a significant decrease in serum folate levels in the nitrous oxide group compared to those in the propofol group. Three patients with pre-existing low red cell folate levels, who were randomized to nitrous oxide anaesthesia, developed clinical symptoms of folate deficiency.

CONCLUSION

This study showed that short-term (40-80 min) nitrous oxide anaesthesia did not affect cobalamin levels but reduced serum folate levels in this elderly population. Although this reduction was clinically irrelevant, some patients with pre-existing asymptomatic folate deficiency developed nitrous oxide-induced folate deficiency.

Drug interaction studies with repaglinide: repaglinide on digoxin or theophylline pharmacokinetics and cimetidine on repaglinide pharmacokinetics

Drug interaction studies were carried out to ensure that hypoglycemia due to inhibition of repaglinide elimination or chronic hyperglycemia due to inhibition of repaglinide absorption was avoided. Conversely, the effects of repaglinide on the pharmacokinetics of drugs with only a narrow margin between effective and toxic concentrations, such as digoxin or theophylline, were determined. The studies reported here compared monotherapy with combined therapies in healthy volunteers. There were no significant differences between the pharmacokinetic parameters of repaglinide when given as monotherapy and when administered concurrently with cimetidine. Similarly, the coadministration of repaglinide and digoxin did not influence the pharmacokinetics of digoxin administered alone. When repaglinide was coadministered with theophylline, the only pharmacokinetic change was that the peak plasma theophylline concentration was slightly reduced. No direct drug-drug interactions were found in these studies, suggesting that repaglinide may be coprescribed with cimetidine, digoxin, or theophylline at the dosage used for monotherapy.

Gastrointestinal diseases in women

Gastrointestinal disorders are among the most common disorders for which women seek medical attention. Most gastrointestinal diseases in women are not inherently different from those that occur in men. There are several disorders, however, that occur more frequently or manifest themselves differently in women. This article reviews common gastrointestinal disorders affecting women. The pathophysiology, clinical manifestations, management, and gender-specific issues of gastroesophageal reflux disease, peptic ulcer disease, irritable bowel syndrome (IBS), and inflammatory bowel disease (IBD) are discussed.

The safety of ranitidine in over a decade of use

BACKGROUND

Ranitidine hydrochloride (Zantac) is one of the most extensively studied and widely used drugs of all time. This has provided an excellent opportunity to define its safety profile.

METHODS

Data from 189 controlled clinical trials in which more than 26,000 patients received daily doses of ranitidine for 4 weeks or more were reviewed. More than 80% of patients were treated with up to 300 mg ranitidine daily; the remaining patients received doses of up to 1200 mg daily. Eighty-seven trials were placebo controlled. Analyses of post-marketing surveillance and a database of all spontaneously reported adverse events were also evaluated.

RESULTS

Overall in the clinical trial programme adverse events were reported by 20% of those receiving ranitidine compared with 27% of those receiving placebo. The pattern of events was similar in all treatment groups with no evidence of dose-related toxicity in regimens encompassing an eightfold range of therapeutic doses. Similarly in a programme of studies designed to evaluate a dose of ranitidine of 75 mg for non-prescription (over-the-counter) use in the treatment of heartburn, ranitidine was not associated with an adverse event profile distinct from that of placebo. Analysis of spontaneously reported adverse event data allowed identification of rare idiosyncratic events.

CONCLUSIONS

Review of data from a large population of controlled clinical trials with analyses of postmarketing surveillance studies and spontaneously reported adverse events confirmed the excellent safety profile of ranitidine.

Thrombocytopenia in intensive care patients: a comprehensive analysis of risk factors in 314 patients

OBJECTIVE

To define the incidence and severity of thrombocytopenia in a mixed medical-surgical population of critically ill patients and to examine factors that may be related to the development of thrombocytopenia.

DESIGN

Retrospective chart review of 314 critically ill patients requiring at least 3 days of critical care.

SETTING

A 17-bed combined medical-surgical intensive care unit (ICU) in a 560-bed tertiary care community hospital.

PATIENTS

Medical and surgical patients admitted to the ICU.

INTERVENTIONS

All medical records over the duration of the ICU stay were reviewed. All scheduled medications, including dosage and start/stop dates, were recorded. All platelet counts, placement of pulmonary artery catheters, liver function test results, and admission serum creatinine concentrations were collected.

MEASUREMENT AND MAIN RESULTS

Thrombocytopenia (platelet count less than 200 x 10(9)/L) was observed frequently, but rarely reached a severe stage (7 patients). No single diagnostic category was significantly associated with thrombocytopenia alone, although the combination of sepsis syndrome/septic shock and respiratory failure was strongly correlated (p < 0.0001) with thrombocytopenia. Liver function abnormalities were correlated strongly with thrombocytopenia, and the majority of patients (5 of 7) with severe thrombocytopenia (less than 20 x 10(9)/L) were found to have concurrent severe alterations in liver function test results. Pulmonary artery catheter placement and heparin exposure were associated strongly with thrombocytopenia (p < 0.0001). Drug therapies that were correlated with thrombocytopenia included heparin and vancomycin (p < 0.05). Hemodynamic instability was correlated strongly with the presence and severity of thrombocytopenia. In a stepwise linear regression model, the admission platelet count accounted for the largest proportion of the variance (43%), followed by hemodynamic instability (8%) and the requirement for inotropic agents (2%).

CONCLUSIONS

Thrombocytopenia in the critically ill occurs frequently, rarely reaches severely depressed concentrations, and primarily represents a manifestation of disease processes initiated prior to admission. Hemodynamic instability and/or heparin exposure appear to be the strongest identifiable correlates with thrombocytopenia. Although these may cause infrequent isolated cases, other specific drug causes of thrombocytopenia are not responsible for the majority of cases of thrombocytopenia in the critically ill.

Is cimetidine associated with neutropenia?

BACKGROUND

Cimetidine is perceived as sufficiently safe that it is being considered for over-the-counter use. However, because of residual concerns about cimetidine-induced neutropenia, a study was conducted to evaluate this association.

METHODS

A population-based, case-control study was undertaken using a large database with Medicaid data from six states. Cases were defined as patients hospitalized with a discharge diagnosis of neutropenia. Medical records were sought to validate the diagnoses of neutropenia and to characterize the severity of disease. Four controls were randomly selected for each case, matched for age, sex, state, and year of diagnosis. The frequency of exposures to cimetidine in the 30 days prior to hospital admission in the cases was compared to that in the identical time periods in the controls.

RESULTS

When investigators simultaneously controlled for multiple, potentially confounding variables by using conditional logistic regression, the odds ratio associated with the use of cimetidine was 1.2 (P = 0.33), with a one-sided upper 95% confidence limit of 2.6 for all patients over 20 years of age, and 0.6 (P = 0.30) with a one-sided upper 95% confidence limit of 3.1 for validated cases over 12 years of age. Neither a dose-response relationship was evident (P = 0.899 and P = 0.716, respectively, when excluding the nonusers, or P = 0.245 and P = 0.215, respectively, when including the nonusers). From these data, one can exclude the occurrence of hospitalization with neutropenia or agranulocytosis due to cimetidine occurring more often than once in every 116,000 patients and once in every 573,000 patients receiving a 6-week course of the drug, respectively.

CONCLUSION

If there is an association between cimetidine and neutropenia, it appears to be very small.

Safety of acid-suppressing drugs

There is an extensive literature on the adverse effects of drugs that inhibit gastric acid secretion. This study presents a critical examination of interactions between antisecretory drugs and other compounds, the frequency of serious adverse effects relating to various body systems, the safety of antisecretory drugs in pregnancy, and longer-term safety data from postmarketing surveillance studies. While interactions with some other drugs, alcohol, and certain carcinogens are of potential concern, in practice clinically significant reactions appear to be rare if they occur at all. A small number of major side-effects have been documented, but they occur rarely, and postmarketing surveillance has not detected other longer-term sequelae. Safety of these drugs in pregnancy is not established, as data are so few. It is concluded that antisecretory agents, by comparison with most other classes of drugs, are remarkably well tolerated.

Ranitidine-associated autoimmune hemolytic anemia in a health maintenance organization population

Reversible hematologic abnormalities including hemolytic anemia [1] with a positive direct Coombs' test have been associated with ranitidine. In addition to the case report cited above, the U.S. Food and Drug Administration had received five other cases of hemolysis associated with recent intake of ranitidine as of February 1991. To investigate the possible association of ranitidine with autoimmune hemolytic anemia, a study was conducted to determine how often diagnoses of hemolytic anemia or abnormal Coombs' test results followed dispensing of ranitidine using the automated medical and pharmacy records of a large health maintenance organization. No occurrences of hemolytic anemia were identified among 12,054 individuals following 38,686 prescriptions for this medication. The 95% upper confidence bound was 3.1 cases/10,000 exposed persons. One abnormal direct Coombs' test with mild anemia was discovered during routine prenatal testing of an asymptomatic patient who was dispensed ranitidine two and a half months previously. Hemolysis, however, was not demonstrated and an association with prior ranitidine use could not be confirmed. Additional analyses indicate that in only 30% of ranitidine courses was a blood count obtained. In those courses with hematocrits below 40%, less than 1% had a Coombs' test performed. Chart review suggests that the majority of individuals with severe anemia have alternative explanations other than autoimmune hemolysis for their anemia. This analysis indicates that ranitidine is unlikely to be a common cause of clinically recognized autoimmune hemolytic anemia and demonstrates the utility of large automated medical and pharmacy data bases to conduct post-marketing studies of spontaneously reported drug effects.

The pharmacokinetics of naproxen, its metabolite O-desmethylnaproxen, and their acyl glucuronides in humans. Effect of cimetidine

1. The pharmacokinetics of 500 mg naproxen given orally were described in 10 subjects using a direct h.p.l.c. analysis of the acyl glucuronide conjugates of naproxen and its metabolite O-desmethylnaproxen. 2. The mean elimination half-life of naproxen was 24.7 +/- 6.4 h (range 7 to 36 h). 3. Naproxen acyl glucuronide accounted for 50.8 +/- 7.3% of the dose recovered in the urine, its isomerised conjugate isoglucuronide for 6.5 +/- 2.0%, O-desmethylnaproxen acyl glucuronide for 14.3 +/- 3.4%, and its isoglucuronide for 5.5 +/- 1.3%. Naproxen and O-desmethylnaproxen were excreted in negligible amounts (< 1%). 4. Even though the urine pH of the subjects was kept acid in order to stabilize the acyl glucuronides, isomerisation took place in blood. 5. The extents of plasma binding of the unconjugated compounds were 98% (naproxen) and 100% (O-desmethylnaproxen), while naproxen acyl glucuronide binding was 92%; that of its isomer isoglucuronide 66%. O-desmethylnaproxen acyl glucuronide was 72% bound and its isoglucuronide was 42% bound. 6. Cimetidine (400 mg twice daily) decreased the t1/2 of naproxen by 39-60% (mean 47.3 +/- 11.5%; P = 0.0014) from 24.7 +/- 6.4 h to 13.2 +/- 1.0 h. It increased (10%) the urinary recovery of naproxen acyl glucuronide (P = 0.0492). The urinary recoveries of naproxen isoglucuronide and O-desmethylnaproxen acyl glucuronide remained unchanged.

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)

Adverse reactions to H2-receptor antagonists in Denmark before and after transfer of cimetidine and ranitidine to over-the-counter status

The H2-receptor antagonists cimetidine and ranitidine were transferred from prescription only to over-the-counter (OTC) status in Denmark on March 27, 1989. Reports to the Danish Committee on Adverse Drug Reactions, a voluntary reporting system, have been evaluated to detect possible changes in frequency and pattern of adverse drug reactions (ADRs) caused by the altered delivery status. From the introduction of cimetidine in 1977 and until March 31, 1990, the Committee received 494 reports of 612 suspected adverse reactions to anti-ulcer drugs. The H2-receptor antagonists (mainly cimetidine and ranitidine) were responsible for 548 (90%) of the ADRs. The study, which presents experience with these drugs from more than a decade and a total consumption corresponding to 65 million treatment days, confirms their excellent safety record. Serious reactions were rare, and when they occurred, reversible. During the first year with cimetidine and ranitidine available OTC no changes were seen in reporting frequency or ADR pattern which could be ascribed to OTC transfer. Only one ADR report concerning OTC cimetidine was received. This may be caused by several factors: the safety of these drugs, the fact that only very little was actually sold OTC, and a relatively low sensitivity of the voluntary reporting system.

Side effects of ranitidine

Ranitidine was first marketed in 1981; since then many patients have been treated such that much experience has been accumulated on the safety of this histamine H2-receptor antagonist in the treatment of gastroduodenal disease. A wide array of ranitidine-associated side effects has been described, but infrequently. As so much information is now available, the aim of this review is to assess the weight of evidence for a causal link between ranitidine and the reported side effects. Overall, ranitidine is well tolerated. The incidence of general side effects at less than 2% is very similar to placebo. Headaches, tiredness, dizziness and mild gastrointestinal disturbance (e.g. diarrhoea, constipation and nausea) are among the most frequent complaints, but have very seldom resulted in stopping treatment. Cardiovascular side effects are extremely rare and unpredictable with the usual doses of oral ranitidine (at most 1 in 1 million patients). They mostly comprise sinusal bradycardia and atrioventricular blockade, especially after rapid intravenous administration, receding after cessation of the drug. Clinical studies, however, have not shown a significant pharmacological effect of ranitidine on the cardiovascular system via H2-receptors, even though individual sensitivities cannot be ruled out in a few isolated reports. Ranitidine is unlikely to be directly hepatotoxic: a transient change in liver function tests has been noted in only 1 in 100 to 1 in 1000 patients. Several cases of mixed hepatitis have been reported, but very few were fully documented. The incidence of ranitidine-associated acute hepatitis has been estimated to be less than 1 in 100,000 patients. Neuropsychiatric complications may be less common and clinically quite similar to those reported with cimetidine, i.e. confusion, disorientation, hallucinations, delirium. These side effects have occurred especially in critically ill and multiple-therapy patients, or patients with chronic renal or hepatic failure, so that the direct causal link with ranitidine treatment was often difficult to ascertain. Even though an H2-receptor-mediated effect is an attractive hypothesis (since similar complications were noted with other H2-receptor antagonists), other mechanisms have been suggested to play a role, e.g. cholinergic or histaminic effects. The overall incidence of neuropsychiatric complications is probably markedly less than 1%. White cell injury (i.e. agranulocytosis) appears to be the most frequent haematological complication, even though case reports are very few and poorly documented.(ABSTRACT TRUNCATED AT 400 WORDS)