Gynaecomastia with cimetidine

Omeprazole-induced galactorrhea in kidney transplant patients-a case report

BACKGROUND

Omeprazole belongs to the pharmacological classifications of proton pump inhibitors and is a widely used medicine. All proton pump inhibitors have a common mechanism of action and are prodrugs that require activation in an acidic environment. Omeprazole is extensively metabolized in the liver by cytochrome 2C19 and cytochrome 3A4, which are responsible for drug interactions. Omeprazole-induced galactorrhea is a rare adverse event of drug metabolism and is often underreported.

CASE PRESENTATION

This is a case of a 26-year-old unmarried Asian (Bhutanese) female who underwent kidney transplant and was administered standard antirejection medication (tacrolimus, prednisolone, and leflunomide) along with an antihypertensive agent. She came to the emergency department with complaints of nausea, vomiting, abdominal pain, chronic gastritis, anemia, hypertension, and loss of appetite. The tacrolimus trough level was in the subtherapeutic range at admission. The tacrolimus dose was adjusted, and oral omeprazole was administered. After 3 days, she experienced milk production from her left breast, which according to the patient was her second incidence after omeprazole ingestion.

CONCLUSION

Causality assessment using Naranjo's algorithm and recovering from galactorrhea after stopping omeprazole and omeprazole rechallenge with the reappearance of galactorrhea confirmed omeprazole as the causative agent. Tacrolimus interferes with omeprazole metabolism and increases tacrolimus levels in the blood. Caution needs to be taken when omeprazole is administered with other drugs that interfere with metabolizing enzymes.

A Prospective Review of Cimetidine use

A prospective-drug-use analysis was conducted on the first 60 patients receiving cimetidine in a general hospital. Only 18 percent had FDA-approved cimetidine indications, although another 62 percent received the drug for reasons supported by the medical literature. Other than a few cases of use for inappropriate reasons, the major limitation was that almost all patients received intensive antacid therapy along with cimetidine before being given an adequate trial with either drug alone. Thus, an assessment of cimetidine's efficacy was impossible.

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.

Drugs and prolactin

Medications commonly cause hyperprolactinemia and their use must be differentiated from pathologic causes. The most common medications to cause hyperprolactinemia are the antipsychotic agents, although some of the newer atypical antipsychotics do not do so. Other medications causing hyperprolactinemia include antidepressants, antihypertensive agents, and drugs which increase bowel motility. Often, the medication-induced hyperprolactinemia is symptomatic, causing galactorrhea, menstrual disturbance, and erectile dysfunction. In the individual patient, it is important differentiate hyperprolactinemia due to a medication from a structural lesion in the hypothalamic-pituitary area. This can be done by stopping the medication temporarily to determine if the prolactin (PRL) levels return to normal, switching to another medication in the same class which does not cause hyperprolactinemia (in consultation with the patient's physician and/or psychiatrist), or by performing an MRI or CT scan. If the hyperprolactinemia is symptomatic, management strategies include switching to an alternative medication which does not cause hyperprolactinemia, using estrogen/testosterone replacement, or cautiously adding a dopamine agonist.

Correction of gynecomastia through a single puncture incision

In men, the development of feminized breasts may cause significant emotional distress and embarrassment, particularly in young men and adolescents. Unfortunately, gynecomastia responds poorly to diet and exercise, and conventional corrective surgery may produce large stigmatizing areolar or chest scars and a flattened or concave chest. In 2004, board-certified plastic surgeons performed 16,275 corrective procedures, and in 2005 there was a 17% increase, according to The American Society of Plastic Surgeons (ASPS) procedural statistics. This report describes a surgical approach for removal of both glandular and adipose tissue using a small 3-mm areolar stab wound incision and a piecemeal glandular resection to correct gynecomastia with minimal and imperceptible external scarring. Pectoral etching of the chest and suction lipectomy are performed simultaneously to enhance and define the thoracic musculature and further virilize the upper thorax. Excellent results have been obtained with minimal complications. The authors present their experience with more than 200 consecutive cases over the past 4 years. They are very optimistic with these results because they have obtained a high degree of patient satisfaction.

Medication-induced hyperprolactinemia

Medication use is a common cause of hyperprolactinemia, and it is important to differentiate this cause from pathologic causes, such as prolactinomas. To ascertain the frequency of this clinical problem and to develop treatment guidelines, the medical literature was searched by using PubMed and the reference lists of other articles dealing with hyperprolactinemia due to specific types of medications. The medications that most commonly cause hyperprolactinemia are antipsychotic agents; however, some newer atypical antipsychotics do not cause this condition. Other classes of medications that cause hyperprolactinemia include antidepressants, antihypertensive agents, and drugs that increase bowel motility. Hyperprolactinemia caused by medications is commonly symptomatic, causing galactorrhea, menstrual disturbance, and impotence. It is Important to ensure that hyperprolactinemia in an Individual patient is due to medication and not to a structural lesion in the hypothalamic/pituitary area; this can be accomplished by (1) stopping the medication temporarily to determine whether prolactin levels return to normal, (2) switching to a medication that does not cause hyperprolactinemia (in consultation with the patient's psychiatrist for psychoactive medications), or (3) performing magnetic resonance imaging or computed tomography of the hypothalamic/pituitary area. If the patient's hyperprolactinemia is symptomatic, treatment strategies include switching to an alternative medication that does not cause hyperprolactinemia, using estrogen or testosterone replacement, or, rarely, cautiously adding a dopamine agonist.

Risk of gynaecomastia associated with cimetidine, omeprazole, and other antiulcer drugs

OBJECTIVE

To study the risk of gynaecomastia associated with cimetidine, misoprostol, omeprazole and ranitidine.

DESIGN

Open cohort study with nested case-control analysis.

SETTING

General practices in United Kingdom that had computerised offices, 1989-92.

SUBJECTS

81,535 men aged 25-84 years who received at least one prescription for cimetidine, misoprostol, omeprazole, or ranitidine during the study period.

MAIN OUTCOME MEASURES

New occurrences of idiopathic gynaecomastia diagnosed by general practitioner.

RESULTS

The relative risk of gynaecomastia for current users of cimetidine compared with non-users was 7.2 (95% confidence interval 4.5 to 11.3). Relative risks for misoprostol, omeprazole, and ranitidine were 2.0 (0.1 to 10.7), 0.6 (0.1 to 3.3), and 1.5 (0.8 to 2.6), respectively. Current users of cimetidine on a daily dose > or = 1000 mg had more than 40 times the risk of developing gynaecomastia than non-users. The period of highest risk was seven to 12 months after starting cimetidine treatment. Spironolactone (relative risk 9.3 (3.3 to 26.1)) and verapamil (9.7 (2.6 to 36.0)) were associated with a relative risk of gynaecomastia comparable to one for cimetidine.

CONCLUSIONS

Use of cimetidine, but not the three other antiulcer drugs, is associated with a substantially greater risk of gynaecomastia in men. A strong dose-response relation was present among cimetidine users.

Premature thelarche: a possible adverse effect of cimetidine treatment

An 18-month-old girl is reported in whom marked unilateral breast enlargement occurred after 4 weeks of cimetidine therapy. After withdrawal of the drug the enlargement rapidly disappeared. This observation points to cimetidine as a possible cause of premature thelarche. Cimetidine, a selective H2 receptor blocking agent, is known to cause gynaecomastia in males. This effect seems related to elevated plasma oestrogens, gonadotropins, or to binding of the drug to androgen receptors. Ranitidine, a much more potent selective H2 receptor blocker, does not cause gynaecomastia and seems therefore preferable to cimetidine.

Cimetidine and adverse reactions: a meta-analysis of randomized clinical trials of short-term therapy

PURPOSE

We pooled data from randomized, double-blind, placebo-controlled trials to determine the frequency of adverse reactions among patients treated with cimetidine for acute acid-peptic disorders.

METHODS

Meta-analysis was used to analyze data obtained from a search of English language reports of trials of cimetidine in the ambulatory treatment of acute acid-peptic disorders that were published between January 1982 and April 1987.

RESULTS

Of 161 trials of cimetidine that we identified, 84 provided complete reporting of data on adverse reactions and, of these, 24 employed a randomized, double-blind, placebo-controlled design. Across these 24 trials, the overall rate of reported adverse reactions among 622 patients randomly assigned to receive cimetidine was 10.9%; the corresponding rate among 516 patients randomly assigned to receive placebo was 10.1%. This difference was not statistically significant (p greater than 0.10), nor were any significant differences noted in the frequencies of reported central nervous system or gastrointestinal adverse reactions (p greater than 0.10). Rates of adverse reactions also did not differ by dosage or trial duration. The overall rate of adverse reactions reported in the 60 trials that did not utilize a randomized, double-blind, placebo-controlled design was similar to the rate reported in those that did.

CONCLUSIONS

Our findings suggest that the frequency of adverse reactions among patients receiving cimetidine for acute acid-peptic disorders is not significantly different from that of patients receiving placebo.

Plasma prolactin, sex steroids and gastrin in human volunteers treated for 2 weeks with therapeutic doses of cimetidine or the new histamine H2-receptor antagonist ramixotidine (CM 57755A)

Three groups of eight healthy male volunteers received placebo for 2 days, then daily morning doses either of cimetidine 800 mg, ramixotidine 750 mg (CM 57755A), or placebo, for 14 days, and then were all returned to placebo for one more day. Plasma levels of prolactin, testosterone and 17 beta-estradiol were measured on Days 2, 3, 16 and 17 in blood samples taken 30 and 15 min before and 0, 60, 120, 180, 240 and 300 min after treatment. Gastrin was assayed in blood collected on the same days 180 min after treatment. Mean pre- and post-treatment areas under the time-concentration curves of the first three hormones were not significantly different in the three groups on any test day, or within the same group throughout the four test days. Mean plasma gastrin levels ranged between 27 and 42 pg/ml, respectively, in the placebo and cimetidine treated groups on test day 3, and intermediate values were found in the group receiving CM 57755A. There was no statistically significant difference in gastrin level between the groups on any test day or within the same group throughout the four test days. No subjective side-effects attributable to the treatments were reported, and there were no abnormalities in blood pressure, heart rate or standard laboratory tests.

Behavioural effects of histamine and its antagonists: a review

This review focuses on the behavioural effects of histamine and drugs which affect histaminergic function, particularly the H1- and H2-receptors antagonists. Research in this area has assumed considerable importance with increasing interest in the role of brain histamine, the clinical use of both H1 and H2 antagonists and evidence of nonmedical use of H1 antagonists. Results from a number of studies show that H1 and H2 antagonists have clear, but distinct subjective effects and that H1 antagonists have discriminative effects in animals. While H1 antagonists are reinforcers in certain conditions, histamine itself is a punisher. Moderate doses of H1 antagonists affect psychomotor performance in some situations, but the results are variable. The exceptions are terfenadine and astemizole, which do not seem to penetrate the blood-brain barrier readily. In studies of schedule-controlled behaviour, marked changes in response rate have been observed following administration of H1 antagonists, with the magnitude and direction dependent on the dose and the baseline behaviour. Histamine reduces avoidance responding, an effect mediated via H1-receptors. Changes in drinking and aggressive behaviour have also been observed following histamine administration and distinct roles for H1- and H2-receptors have been delineated. Separate H1- and H2-receptor mechanisms have also been suggested to account for changes in activity level. While the H2 antagonists do not always have strong behavioural effects when administered peripherally, there is evidence that cimetidine has a depressant effect on sexual function. These and other findings reveal an important role for histaminergic systems in a wide range of behaviour.

Some effects of cimetidine on the reproductive organs of rats

The development of genital organs of rats chronically treated with cimetidine showed that the drug may present anti-androgenic activity. This treatment did not alter the sensitivity of vas deferens to noradrenaline, but increased their sensitivity to BaCl2. In the male reproductive system, cimetidine must have peripheral actions apart from the central ones observed after chronic treatment.

Influence of cimetidine, ranitidine and imidazole on the behavioral effects of (+/-) N-n-propylnorapomorphine in male rats

Cimetidine injected IP 15 min before (+/-) N-n-propylnorapomorphine (NPA) antagonized in dose-dependent fashion the penile erections (PE) and stretching and yawning (SY) induced by this typical dopaminergic agonist in male rats. Ranitidine, which acts on H2 histamine receptors in much the same way as cimetidine despite its lack of an imidazole ring, failed to produce the same effect. On the other hand, imidazole itself was similar to cimetidine in antagonizing PE and SY induced by (+/-) NPA, whether injected IP or ICV. Neither imidazole nor cimetidine antagonized the stereotyped behaviour (SB) induced by (+/-) NPA. Indeed, imidazole reduced the latency of this response. A mechanism which may underly these effects is discussed, as well as the possible preclinical use of this test in animals.

Long-term follow-up study of cimetidine

In a 5-year follow-up study of 8553 recipients of cimetidine at Group Health Cooperative of Puget Sound, we examined the frequency of uncommon serious illness requiring hospitalization that may have been drug induced. With the possible exception of one patient with probable drug-induced liver disease, we did not find any instances of serious illness requiring hospitalization that could be attributed with reasonable certainty to cimetidine. This large study provides reassurance that cimetidine is a relatively safe medication.

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.

Histamine and the hypothalamus

The chemical tools that could be used to examine the function of histamine in the brain are considered together with the evidence linking histamine specifically with the hypothalamus. The distribution of histamine and the enzymes responsible for its synthesis and metabolism is consistent with there being both mast cells and histaminergic nerve terminals within the hypothalamus. Iontophoresis, mepyramine binding and histamine-stimulated adenylate cyclase studies suggest that both histamine H1- and H2- receptors are present in the hypothalamus. In addition, intracerebroventricularly injected histamine receptor agonists and antagonists affect many functions associated with the hypothalamus such as cardiovascular control, food intake, body temperature control, and pituitary hormones whose release is mediated via the hypothalamus, such as corticotropin, growth hormone, thyroid stimulating hormone, prolactin, gonadotropins and vasopressin. However, only in the case of thyroliberin release, prolactin release, body fluid control and blood pressure control is there evidence yet that such effects are mediated via histamine receptors actually in the hypothalamus. The effects of enzyme inhibitors suggest endogenous histamine may be involved in the physiological control of thyroid stimulating hormone, growth hormone and blood pressure, and the effects of receptor antagonists support a role for endogenous histamine in prolactin control. Otherwise, there is little evidence for a physiological role for endogenous, as against exogenous, histamine whether it be from histaminergic terminals or mast cells. In addition, few studies have tried to distinguish possible effects on presynaptic receptors, postsynaptic receptors, hypothalamic blood vessels or the hypophyseal portal blood vessels. It is concluded that although there is good evidence now linking histamine and the hypothalamus more specific studies are required, for instance using microinjection or in vitro techniques and the more specific chemical tools now available, to enable a clearer understanding of the physiological role of histamine in the hypothalamus.

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.

Cimetidine effect of dopaminergic modulation of prolactin release in healthy women

The aim of the present study was to test whether cimetidine (Cim) influences PIF (prolactin inhibitory factor), and thereby indirectly affects the release of prolactin (PRL) from the pituitary lactotrophs. For that purpose 10 mg metoclopramide (Met), known for its dopamine-receptor blocking properties, were first given orally to 6 subjects. This raised the PRL level from 13 +/- 2 to 97 +/- 12 ng/ml in 60 min (p less than 0.001). PRL tended to plateau at this level until 120 min. An additional 7 subjects were then injected iv with 400 mg Cim, 90 min after oral administration of placebo. Placebo did not change the basal PRL level, but the subsequent Cim injection raised the PRL level from 14 +/- 4 to 66 +/- 9 ng/ml (p less than 0.01). When, in the same subjects, an oral dose of Met was given (10 mg) PRL increased from 19 +/- 4 to 112 +/- 10 ng/ml (p less than 0.001). A subsequent Cim injection, given on top of the PRL plateau, 90 min after the Met ingestion, however, failed to induce any further increase in PRL. To exclude that this failure was not merely a reflection of a Met-induced depletion of the PRL stores, 25 micrograms thyrotropin-releasing hormone (TRH) were given iv to an additional 6 subjects, 90 min after ingestion of either placebo or Met. Also in these subjects placebo left basal PRL unaffected. The subsequent TRH injection, however, raised PRL from 10 +/- 2 to 55 +/- 6 ng/ml (p less than 0.001). Met increased PRL from 17 +/- 4 to 133 +/- 19 ng/ml (p less than 0.01) in these subjects, and TRH, subsequently injected, induced a further PRL increase to 174 +/- 18 ng/ml (p less than 0.01). The observation that Cim fails to elicit an increase in PRL after priming with Met thus indicates that Cim, under normal conditions, stimulates the PRL release via a reduced dopaminergic inhibition of the lactotrophs.

Ranitidine: a review of its pharmacology and therapeutic use in peptic ulcer disease and other allied diseases

Ranitidine is a new histamine H2-receptor antagonist which, unlike cimetidine, does not contain an imidazole group. On a weight basis, ranitidine is 4 to 10 times more potent than cimetidine in inhibiting stimulated gastric acid secretion in humans. Therapeutic trials comparing ranitidine and cimetidine have demonstrated that ranitidine 150 mg twice daily is an effective alternative to cimetidine 1000 mg daily in 4 divided doses in increasing the rate of healing of duodenal and gastric ulcers over a period of 4 to 6 weeks. Ranitidine, given as a single 150 mg dose at night, decreases the incidence of ulcer recurrence. Preliminary studies in the Zollinger-Ellison syndrome and in patients intolerant of, or unresponsive to cimetidine, indicate that ranitidine controls the gastric hyperacidity and heals most ulcers, including those which failed to respond to months of treatment with cimetidine 1 to 1.6 g daily. Ranitidine, unlike cimetidine, has no antiandrogenic effects and does not alter hepatic metabolism of drugs. Ranitidine is well tolerated. Preliminary reports of the resolution of cimetidine-induced adverse effects following substitution of ranitidine, suggest that ranitidine may be of value in patients intolerant of cimetidine. However, wider clinical experience with ranitidine is needed to determine the clinical relevance of these reports.

Effect of cimetidine on gonadal function in man

1 To study the effect of cimetidine on gonadal function in man, eleven male subjects with chronic duodenal ulcer were given cimetidine orally at a dosage of 1000 mg per day 3 months and 400 mg nocte for the subsequent 3 months. 2 Testosterone levels were found to be elevated during therapy when compared to pre- and post-treatment periods. Serum LH remained unchanged but FSH was increased during therapy. In five out of eleven subjects serum PRL levels were increased. Mean sperm count was lower during cimetidine therapy when compared with that after drug withdrawal. The motility and morphology of the spermatozoa were not affected.

Effect of cimetidine o endocrine functions--prolactin

Effects of cimetidine on the endocrine function were examined in 16 human subjects, i.e. 6 healthy adult volunteers, and each 5 male and female gastro-duodenal ulcer patients. They were all subjected to the examination on the fluctuation of prolactin (PRL) after one-shot intravenous injection of cimetidine. The peptic ulcer patients were orally given 800 mg/day of cimetidine for further 4 weeks. PRL, gonadotropins and sex hormones were determined in the male patients, and only PRL in the females patients. TRH-load test was carried out in all the ulcer patients before and after the administration of cimetidine. The results are shown below: 1) After one-shot intravenous administration of cimetidine 200 mg, serum-PRL significantly increased, the peak level, however, being within normal value range. The increase in PRL was transient, and recovered to the pretreatment value in 60-180 minutes after the administration. 2) During and after the repeated oral administration of 800 mg/day of cimetidine for the consecutive 28 days, serum PRL level did not significantly change. Neither was noted any influence on gonadotropin (LH, FSH) nor sex hormones (estradiol, testosterone) secretion. 3) PRL secretory functions at 500 microgram TRH loading were similar before and after oral administration of cimetidine, without difference in the reactivity.

Pharmacosexology: the effects of drugs on sexual function a review

The literature on the sexual side effects of drugs and chemicals has been reviewed. There are many substances which alter the human sociosexual response cycle either negatively, positively or both. Many of the drugs used therapeutically have been reported to have adverse effects on sexuality, and this must be taken into account when these drugs are used clinically. Many substances which are used for recreational purposes (or sometimes abused) also have profound effects on sexual response. Many of these substances are used in such a way that they can correct underlying sexual problems. Treatment of a drug abuser may well prove unsuccessful without consideration of preexistent sociosexual problems and concerns. From the dawn of recorded history, many substances have been used for the purpose of sexual enhancement. Some of these have known success and their reputations have been passed down through the millenia. The chapter has not yet been closed on aphrodisiacs, even though none have survived the rigors of scientific scrutiny. As long as humans place value on optimal sexual functioning, there will be a demand for sex-enhancing drugs. In order for the scientific and medical community to successfully meet these challenges, more effective and relevant study designs will have to be utilized in order to separate fact from fancy. The study of pharmacosexology is in its infancy, and in order for it to grow and contribute to the world body of knowledge, more researchers and clinicians must be trained in both pharmacology and sexology.

Some in vitro and in vivo actions of the new histamine H2-receptor antagonist, ranitidine

1 Ranitidine has been investigated as an antagonist of the H2-receptor-mediated responses to histamine of guniea-pig atrium and rat uterus in vitro and as an inhibitor of gastric acid secretion in the rat. 2 Ranitidine competitively antagonized histamine-induced increases in contraction frequency of the guinea-pig isolated rat atrium. Ranitidine had a pA2 of 7.2 and was 7.9 and 4.5 times more potent than metiamide and cimetidine respectively. 3 Ranitidine competitively antagonized histamine-induced relaxations of the rat isolated uterine horn. Ranitidine had a pA2 of 6.95 and was 3.6 and 5.9 times more potent than metiamide and cimetidine respectively. 4 Ranitidine, even at high concentrations, did not affect responses of the guinea-pig isolated atrium or rat isolated uterus to (-)-isoprenaline. Similarly it was without effect on either histamine or bethanechol-induced contractions of guinea-pig isolated ileum. 5 Ranitidine inhibited histamine- and pentagastrin-induced gastric acid secretion in the perfused stomach preparation of the anaesthetized rat. Ranitidine was 5.2 and 7.0 times more potent on a molar basis than metiamide and cimetidine respectively, as an inhibitor of histamine-induced gastric acid secretion. 6 It is concluded that ranitidine is a potent, competitive and selective antagonist of histamine at H2-receptor sites and and effective inhibitor of gastric acid secretion in vivo.

Effect of ranitidine, a new H2-antagonist, on gastric and pancreatic secretion in duodenal ulcer patients

The effects of a new H2-receptor blocker, ranitidine, given intravenously (for comparison with cimetidine) or orally an gastric and pancreatic secretion have been studied in duodenal ulcer patients. Ranitidine appears to be several times more potent and a longer-acting inhibitor of gastric secretion than cimetidine. This H2 blocker does not affect pancreatic bicarbonate and enzyme secretion.

The effect of oral cimetidine on the basal and stimulated values of prolactin, thyroid stimulating hormone, follicle stimulating hormone and luteinizing hormone

The effect of cimetidine on the basal values of PRL, TSH, FSH and LH and on the TRH/LHRH-stimulated values of these hormones was investigated in patients with peptic ulcer. No difference was found between the values before, during or after cimetidine maintenance treatment. To evaluate whether a rise in PRL occurs during the early phase of cimetidine treatment, daily estimations were made of basal PRL values during the first week of cimetidine adminstration in volunteers. No significant difference was found. It is concluded that oral cimetidine treatment has no influence on the basal and stimulated values of PRL, TSH, FSH and LH.

Hypothalamic-pituitary-gonadal dysfunction in men using cimetidine

We studied the effect of cimetidine therapy (1200 mg per day by mouth for nine weeks) on the hypothalamic-pituitary-gonadal axis of seven men. There was a 43 per cent mean reduction in sperm count after therapy. The luteinizing hormone response to luteinizing hormone releasing factor was also reduced, and a statistically significnat rise in plasma testosterone occurred, although it was less than that before therapy. Gonadotropin responses to provocative clomiphene stimulation were inadequate when compared with those of controls. Cimetidine did not affect the responses of thyroid-stimulating hormone, prolactin, growth hormone and thyroxine to thyrotropin releasing factor. Caution is advisable in administration of cimetidine for prolonged periods to young men.

Effects of the H2 receptor antagonist cimetidine on pituitary hormones in man

The effects of the histamine (H2) receptor antagonist cimetidine on serum levels of prolactin (PRL), growth hormone (GH), thyroid stimulating hormone (TSH), luteinizing hormone (LH), follicle stimulating hormone (FSH) and cortisol were studied in five normal males. Cimetidine, when given by infusion at the dose of 100 mg/h for 5 h, did not alter adenohypophyseal secretion either basally or after pituitary stimulation with LHRH and TRH. However, 400 mg cimetidine given intravenously as a bolus injection significantly stimulated PRL release in all subjects, without affecting any other measured hormone. A dose-reponse relationship existed, and 200 mg cimetidine seems to be the minimum PRL-releasing dose when given as an intravenous bolus injection. These results suggest that cimetidine releases PRL and that this effect is dose-related, but only when large intravenous injections are given.

Inhibition of cimetidine-induced hyperprolactinaemia by pretreatment with levodopa or bromocriptine

A single i.v. administration of cimetidine, an histamine receptor antagonist, produced a significant increase in serum prolactin (PRL) levels in fifteen normal men. This effect was suppressed by pretreatment with levodopa or bromocriptine.