Effects of H2-receptor antagonists on the central nervous system

Potential immunological consequences of pharmacological suppression of gastric acid production in patients with multiple sclerosis

Corticosteroids are standard treatment for patients with multiple sclerosis experiencing acute relapse. Because dyspeptic pain is a common side effect of this intervention, patients can be given a histamine receptor-2 antagonist, proton pump inhibitor or antacid to prevent or ameliorate this disturbance. Additionally, patients with multiple sclerosis may be taking these medications independent of corticosteroid treatment. Interventions for gastric disturbances can influence the activation state of the immune system, a principal mediator of pathology in multiple sclerosis. Although histamine release promotes inflammation, activation of the histamine receptor-2 can suppress a proinflammatory immune response, and blocking histamine receptor-2 with an antagonist could shift the balance more towards immune stimulation. Studies utilizing an animal model of multiple sclerosis indicate that histamine receptor-2 antagonists potentially augment disease activity in patients with multiple sclerosis. In contrast, proton pump inhibitors appear to favor immune suppression, but have not been studied in models of multiple sclerosis. Antacids, histamine receptor-2 antagonists and proton pump inhibitors also could alter the intestinal microflora, which may indirectly lead to immune stimulation. Additionally, elevated gastric pH can promote the vitamin B12 deficiency that patients with multiple sclerosis are at risk of developing. Here, we review possible roles of gastric acid inhibitors on immunopathogenic mechanisms associated with multiple sclerosis.

Pharmacology I: effects on sleep of commonly used ICU medications

Critically ill patients are almost universally administered medications to treat their acute illnesses and to maximize their comfort. The effects of many of these medications on their sleep, however, may be important. It is known that critically ill patients have severely disrupted sleep and that this disrupted sleep has a negative impact on ICU outcomes. This article reviews how some commonly used ICU medications may affect patients' sleep.

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.

Comparative effects of H2-receptor antagonists on subjective and objective assessments of sleep

BACKGROUND

Clinically, it is common for patients to experience drowsiness in association with consumption of H1-receptor antagonists. Reported side-effects with H2-receptor antagonists include insomnia and somnolence. The present study was designed to assess and compare the effects of three H2-receptor antagonists (cimetidine, famotidine, and ranitidine) on nocturnal and daytime sleepiness.

METHODS

This is a double-blind crossover study on 12 normal volunteers. Subjects were studied under conditions of placebo, cimetidine (400 mg b.d.), famotidine (20 mg b.d.), and ranitidine (150 mg b.d.) for one week. Sleep was assessed at the end of each one-week interval via polysomnographic evaluation conducted on nights 6 and 7 of drug administration. On the day between the two nights in the sleep laboratory, a multiple sleep latency test was conducted.

RESULTS

The results revealed a significant reduction in the sleep onset latency with famotidine administration, but since there were no effects of any of the medications in the multiple sleep latency test, this finding is of dubious clinical significance. Cimetidine revealed a small increase in subjective estimates of sleepiness. No effects on sleep-related respiratory parameters were noted.

CONCLUSIONS

This study demonstrates the lack of effect of peripheral administration of H2-receptor antagonists on sleep stages, while subjective or objective assessment of daytime alertness revealed small effects of famotidine and cimetidine.

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)

What do we miss with the traditional efficacy/safety evaluation?

The traditional efficacy/safety evaluation has mainly been based on objective clinical features, findings and tests. Subjective symptoms have often been taken into account and much efforts have been put into the methods of their measurement. The emotional, social and functional consequences of disease, however, seldom have received much attention. Little attention has also been paid to patients expectation and the true causes of why the patient has sought medical help. Important aspects of disease and consequences of intervention are therefore often missed when adhering only to the traditional methods of evaluation.

Ranitidine and depression

Three cases are described in which the cessation of the H2-antagonist ranitidine was followed by a rapid improvement in severe depressive symptoms. The literature concerning H2-receptor antagonists and depression is reviewed, and an alternative drug (omeprazole) for severe peptic ulceration is discussed.