Comparison between dose-responses of prolactin, thyroid stimulating hormone and growth hormone to two different histamine H-2 receptor antagonists in normal men

The effect of long-term cimetidine treatment on PRL and TSH response capacity to TRH in male patients with duodenal ulcer

The effect of long-term cimetidine treatment for 6 months on basal and thyrotropin-releasing hormone (TRH)-stimulated prolactin (PRL) and thyroid-stimulating hormone (TSH) secretion was studied in eight male patients with duodenal ulcer. They received 1,000 mg cimetidine orally per day until ulcer healing and thereafter 400 mg daily for the remaining period. TRH perturbation tests were performed before and after the 6 months of treatment. A significant reduction in the pituitary TSH response capacity was found. No significant changes in basal and TRH-stimulated PRL, basal TSH, thyroxine and triiodothyronine were found. It is uncertain if the reduction in pituitary TSH response capacity has any clinical implications in euthyroid patients.

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.

The cimetidine-induced increase in prolactin secretion in schizophrenia: effect of clozapine

There is considerable interest in the role of serotonin (5-HT) in the pathophysiology of schizophrenia and in the mechanism of action of clozapine, an atypical antipsychotic agent and a potent dopamine (DA), 5-HT2/5-HT1C and histamine (H) antagonist. Cimetidine, an H2 antagonist, produces robust, transient increase in plasma prolactin (PRL) levels in man following intravenous administration. This effect has been attributed, in part, to indirect central serotonergic mechanisms involving 5-HT2 receptors in the hypothalamus, but the evidence is inconclusive. This study investigated the effects of cimetidine on plasma PRL levels in unmedicated schizophrenic patients versus normal controls and the effect of chronic treatment with clozapine on the cimetidine-induced PRL response. The PRL response to cimetidine was significantly blunted in male but not female schizophrenic patients. The PRL response in male schizophrenic patients was inversely related to psychopathology. Chronic treatment with clozapine completely suppressed the plasma PRL response following cimetidine. These data are consistent with the hypothesis of an abnormality of serotonergic activity, including downregulation of 5-HT2 receptors, in male but not female schizophrenic patients. The role of antagonism of 5-HT2 receptors in the action of clozapine is discussed.

Plasma concentrations of pituitary and peripheral hormones during ranitidine treatment for two years in men with duodenal ulcer

The effects of treatment for 2 years with the histamine H2-receptor antagonist ranitidine (100 or 200 mg b.d. for 6 weeks followed by 100 or 200 mg daily) on plasma concentrations of pituitary and peripheral hormones in ten men with duodenal ulcer have been investigated. Stimulation tests with TRH 200 micrograms i.v. and LHRH 100 micrograms i.v. were performed before, during (6 and 24 months), and at least 6 months after treatment. Basal and TRH-stimulated prolactin (PRL) secretion was marginally reduced after treatment for 6 months, but not for 24 months. The LH response to LHRH was slightly increased after treatment for 6 months and 24 months and after the end of treatment. The plasma concentrations of TSH, FSH, cortisol, androgenic hormones, and thyroid hormones did not change significantly during treatment. No adverse effects were reported during the observation period. The few, minor changes in pituitary hormone concentrations were all within the reference range. They may be related to ranitidine treatment, but are more likely to be due to age-dependent alterations in hormone secretion. It is concluded that long-term treatment with ranitidine does not cause major changes in circulating hormone concentrations.

A pharmacokinetic profile of nizatidine in man

In this report, the pharmacokinetic, pharmacodynamic, and hormonal effects of nizatidine are reviewed in healthy volunteers and in patients with renal or hepatic impairment. The absolute oral bioavailability of nizatidine exceeded 90%; the half-life (t1/2), plasma clearance (Clp), and volume of distribution (Vd) of iv nizatidine were 1.3 h, 461/h, and 1.21/kg, respectively. Within 16 h of dosing volunteers with nizatidine, more than 90% of the administered dose was recovered in urine as parent drug and metabolites; unchanged nizatidine accounted for 65 and 75% of the recovered substances, after oral and intravenous administration, respectively. Renal impairment decreased the elimination of nizatidine and dosage reductions are recommended for patients with creatinine clearance (Clcr) less than 50 ml/min/m2. Nizatidine suppressed gastric acid secretion produced by sham meals, protein meals, or pentagastrin; its antisecretory activity was dose and concentration dependent. Nizatidine was three times more potent than cimetidine. Nizatidine, after oral or iv administration, did not alter hormone concentrations in plasma.

Adverse reactions and interactions with H2-receptor antagonists

Histamine H2-receptor antagonists have been used in the treatment of gastrointestinal diseases for more than a decade and during this period have become one of the most commonly prescribed groups of drugs in the world. The deserved popularity of the H2-receptor antagonists reflects, in part, their therapeutic efficacy, which has revolutionised the treatment of peptic ulcer disease. An equally, or more, important reason for the widespread use of H2-receptor antagonists is their remarkably low toxicity. We have attempted, in this review, to present a detailed account of the minor and more serious adverse reactions, while emphasising the low incidence of the former and the rarity of the latter. The toxicology of the H2-receptor antagonists is discussed under two main headings: adverse effects; and drug interactions. The latter category is potentially the more significant, since the frequent use of therapy with multiple drugs may give rise to drug interactions, some of which are serious and may even be lethal. These drug interactions occur especially in the gastrointestinal tract, the liver and the kidneys. Thus, the absorption of other drugs may be altered because the H2-receptor antagonists inhibit gastric secretion--an effect illustrated by ketoconazole, the absorption of which is reduced when given in combination with cimetidine. Very important drug interactions are caused by inhibition of the hepatic microsomal enzyme cytochrome P450 by some of the H2-receptor antagonists. This effect appears to be related to the chemical structure of the individual H2-receptor antagonists and is not attributable to histamine H2-receptor blockade. For example, cimetidine is a powerful inhibitor of cytochrome P450, while the interaction of ranitidine with this system is weaker. Consequently, cimetidine reduces the metabolism of many drugs which are normally degraded by phase I reactions, leading to potentially toxic plasma concentrations of therapeutic agents such as some oral anticoagulants, beta-blockers, anticonvulsants, benzodiazepines and xanthines. Some of the H2-receptor antagonists are actively secreted by the renal tubules and may thus compete with other drugs for cationic tubular transport mechanisms, resulting in reduced urinary excretion and hence potentially toxic plasma concentrations. This type of drug interaction has been reported after administration of both cimetidine and ranitidine with procainamide or quinidine.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of ranitidine on pituitary-thyroid function

Although several studies have examined the effects of cimetidine on pituitary-thyroid function, few have investigated ranitidine in this respect. We found no changes in thyroid-stimulating-hormone (TSH) or prolactin responses to TSH-releasing-hormone (TRH) in 10 patients with peptic ulcer disease given oral ranitidine. Serum total and free thyroxine (TT4 and FT4) concentrations declined slightly, whereas total and free triiodothyronine (TT3 and FT3) increased slightly following ranitidine. None of these changes achieved statistical significance. Both the ratio of TT4/TT3 and FT4/FT3, however, declined (P less than 0.05) following ranitidine. Thus ranitidine may have a minor influence on peripheral deiodination of thyroxine but has little effect on hormone production from the thyroid gland. The diagnostic value of biochemical tests of thyroid function is not seriously compromised in patients receiving ranitidine.

Ranitidine hydrochloride

Ranitidine is a selective, competitive histamine H2-receptor antagonist recently approved by the Food and Drug Administration for use in the short-term treatment of active duodenal ulcers and gastric hypersecretory conditions. Ranitidine is four to ten times more potent than cimetidine on a molar basis in inhibiting stimulated gastric acid secretion. Clinical studies have demonstrated that ranitidine is as effective as cimetidine and is similarly well tolerated. Based on available literature (approximately 700 publications), this article reviews the pharmacology, safety profile, and clinical efficacy of ranitidine in duodenal ulcers and gastric hypersecretory conditions.

Single nocturnal dose of an H2 receptor antagonist for the treatment of duodenal ulcer

Twenty four hour intragastric acidity and nocturnal acid output have been measured over five separate 24 hour periods in each of 12 patients with duodenal ulcer receiving either placebo, cimetidine 400 mg bd, cimetidine 300 mg nocte, ranitidine 150 mg bd, or ranitidine 300 mg nocte. In these doses ranitidine was significantly more effective at decreasing intragastric acidity and nocturnal acid output than cimetidine. There was no significant difference between twice daily ranitidine and night time ranitidine or between twice daily cimetidine and night time cimetidine in the reduction of intragastric acidity. Nocturnal acid output was controlled significantly better with ranitidine at night, twice daily dosage of ranitidine, and cimetidine at night, than by the twice daily dosage of cimetidine. It is suggested that a single nocturnal dose of cimetidine or ranitidine should be evaluated in a clinical trial.

Effect of meclastine, a selective H1 receptor antagonist, upon ACTH release

To elucidate further the role of histamine in the control of ACTH secretion we investigated the effect of the selective H1 receptor antagonist meclastine on the ACTH response to insulin hypoglycaemia and to metyrapone-induced hypocortisolaemia in normal subjects. Intravenous meclastine (4.8 mg/90 min) significantly inhibited the hypoglycaemia-induced ACTH and cortisol increase whereas serum GH and PRL concentrations were unaffected. Orally administered meclastine (3 X 2 mg) also reduced the ACTH feedback response to cortisol deficiency in a modified metyrapone test, compared to a placebo. Our findings support the concept of an excitatory influence of histamine upon ACTH secretion via H1 receptors, possibly by stimulation of CRF release.

Pharmacology and clinical efficacy of ranitidine, a new H2-receptor antagonist

Ranitidine is a new histamine H2-receptor antagonist that includes a furan ring structure, whereas other H2-receptor antagonists include an imidazole ring. It is more potent than cimetidine in inhibiting gastric acid secretion and lacks cimetidine's anti-androgenic and hepatic microsomal enzyme inhibiting effects. In the recommended dosage of 150 mg twice daily, ranitidine is as effective as cimetidine in healing duodenal and gastric ulcers and has the advantages of less frequent dosing and fewer side effects. Ranitidine appears to be the drug of choice in the treatment of the Zollinger-Ellison syndrome because of its increased potency and lesser effect on endocrine function compared to cimetidine.

The acute and long term effect of the H2-receptor antagonists cimetidine and ranitidine on the pituitary-gonadal axis in men

We have investigated the effect on the human pituitary-gonadal axis of the H2-receptor antagonists cimetidine 300 mg and ranitidine 50, 100, and 200 mg by i.v. bolus, or treatment for 6 months with either cimetidine (1000 mg/day for 1.5 months followed by 400 mg/day for 4.5 months) or ranitidine (200-400 mg/day for 1.5 months followed by 100-200 mg/day for 4.5 months). Administration of the H2-antagonists (i.v.) to normal men did not cause any release of LH, FSH, or testosterone. Long-term treatment with cimetidine of duodenal ulcer patients caused a significant rise in basal LH (6 weeks) and FSH secretion (11 weeks). Following reduction of the cimetidine dose LH and later FSH returned to pre-treatment values. However, despite reduction of the cimetidine dose, the LH and FSH responses to LHRH stimulation were still significantly higher after 6 months of treatment compared with pre-treatment responses. No changes were found in basal or in LHRH stimulated testosterone or dihydrotestosterone secretion. Treatment with the more potent H2-antagonist ranitidine did not cause any change in basal or in LHRH stimulated LH and FSH secretion. The effects on LH and FSH secretion observed during cimetidine treatment might therefore be caused by other mechanisms than blockade of H2-receptors. It is possible that cimetidine, having anti-androgen properties, blocks pituitary or hypothalamic androgen receptors.