Effect of cimetidine on circulating parathyroid hormone in primary hyperparathyroidism

Hypocalcemic tetany associated with simultaneous administration of cimetidine and nifedipine: a case report

BACKGROUND

Acute hypocalcemia is generally caused by a sudden drop in serum calcium ion and presents with a mild or severe form of tetany. Even though the occurrence of hypocalcemia is well documented with certain drugs such as calcium chelators, bisphosphonates, and cisplatin, it is a very unusual and poorly documented adverse event with cimetidine and nifedipine. Here, we present a case of severe hypocalcemic tetany during simultaneous administration of cimetidine and nifedipine in a hypertensive patient with dyspepsia.

CASE PRESENTATION

A 46-year-old known human immunodeficiency virus patient from Ethiopia on antiretroviral therapy over the past 14 years presented to the emergency department with acute exacerbation of dyspepsia and hypertensive urgency. She was given intravenous cimetidine (400 mg) and oral nifedipine (30 mg) simultaneously. One hour after the administration of these two drugs, she developed severe hypocalcemic tetany with carpopedal spasm, involuntary plantar flexion, and muscle spasms. She also had severe retrosternal chest pain and shortness of breath. Her blood pressure was 160/110 mmHg during the attack and she had no skin changes, such as urticaria. She was immediately given 1 g of calcium gluconate intravenously over 30 minutes. The carpopedal spasm progressively decreased during calcium gluconate administration. An hour later, she completely regained voluntary movement of her fingers and feet. The chest pain persisted, but resolved over the next 12 hours. The patient was discharged home after 2 days of observation. This is an unusual adverse effect that needs caution during concomitant administration of these drugs.

CONCLUSIONS

Severe hypocalcemic tetany can occur with concomitant administration of cimetidine and nifedipine. Immediate treatment with calcium gluconate quickly reverses this adverse event. Concomitant administration of these drugs should be done with caution or be avoided if possible.

Dissociation between changes in immunoreactive parathormone and its biological indices induced by cimetidine in primary hyperparathyroidism

In three out of four patients with primary hyperparathyroidism, 2 000 mg of cimetidine daily caused a reduction of immunoreactive parathormone (iPTH) when measured at 8.30 and 11.30 on days 16 and 17 on treatment. Serum Ca, PO4 and maximal tubular reabsorption of PO4 remained unchanged. Excretion of cAMP/100 ml GFR remained elevated to at least the same extent as before treatment. Two patients, in whom cimetidine treatment was continued for an additional 4 weeks, did not show further hormonal or biochemical changes compared with the evaluation on days 16 and 17. We conclude that reduction of iPTH is not accompanied by any change in biological activity of this hormone. The reason for this discrepancy remains unclear.

Effects of secretin on parathyroid hormone and calcium in normal subjects, patients with hyperparathyroidism and patients with gastrinoma

In vitro studies have demonstrated that secretin can stimulate the release of parathyroid hormone (PTH), but reports concerning its effects on PTH and calcium in vivo are contradictory. To examine this question further, a bolus injection of secretin (75 IU) was given to 12 normal subjects and 10 patients with primary hyperparathyroidism (HPT). Six of the patients had multiple endocrine neoplasia and five had endocrine pancreatic tumours (EPT). Three normocalcaemic patients with EPT were also included in the study. The mean serum gastrin level rose significantly (from 19 to 40 pmol/l, p less than 0.01) within 15 min of secretin injection in the normal subjects. HPT patients without EPT had a somewhat higher mean basal level of gastrin (39 pmol/l, p less than 0.05 compared with controls), but it did not increase significantly after the secretin bolus. In six EPT patients the gastrin concentrations rose by more than 300 pmol/l. Although secretin had a biological capacity to release gastrin, it had no discernible effects on either serum PTH or serum calcium in any of the groups studied. Nor were any changes in PTH or calcium observed when secretin was given as a continuous infusion (3 IU/kg/h) over 90 min. Thus, our data do not support the concept that secretin, in vivo, is a secretagogue of PTH.

Morphological and histochemical characteristics of mast cells and the content of in-tissue histamine in various pathological parathyroids: do mast cells participate in hormone secretion in human parathyroids?

The possibility of the participation of mast cells in human parathyroid hormone secretion was studied with regard to the frequency, distribution, and sub-types of mast cells and the content of in-tissue histamine, a chemical mediator in mast-cell granules, in human parathyroids with various pathological conditions. The above factors were compared between those of a 'normal' parathyroid group and those of 'pathological' parathyroids associated with adenoma and hyperplasia. Specimens were scanned for the mean value of the mast cell number per field of microscopic view and for the ratio of the mast cell number in glandular parenchymal tissue to that in interstitial tissue. The activated state of the mast cells was examined through classifying the mast cells into two sub-types, mucosal mast cells and connective-tissue mast cells. The high-performance liquid chromatography (HPLC) method was used for assay of in-tissue histamine. The frequency of mast cells showed no difference between the groups, whereas the distribution of mast cells, showed a distinct difference. The occurrence rate of mast cells in glandular parenchymal tissue in the 'pathological' group presented an increase as compared with that in the 'normal' group. Furthermore, the occurrence rate of mucosal mast cells in an activated state also showed an increase. This suggests that mast cells are likely to participate in parathyroid hormone secretion. The histamine-content in the 'normal' group was significantly larger than that in the 'pathological' group, which was a different outcome from that observed in mast cells from the results of light microscopy. This may require taking into consideration the difference in the histamine content of the mast cells themselves between that of mucosal mast cells and connective-tissue mast cells.

Histamine receptors and bioeffects on clonal parathyroid endothelial cells

Using a clonal line of bovine parathyroid endothelial cells (BPE-1) we defined the presence on these cells of a histamine H2 receptor and characterized its pharmacological properties. Interaction of histamine with its receptor induced an increase of cAMP accumulation in a dose- and time-dependent fashion. This effect appears unique for parathyroid endothelial cells, in fact, clonal parathyroid epithelial cells did not exhibit a similar response. No effect of histamine was observed on BPE-1 cell proliferation.

Pharmacokinetics and pharmacodynamics of roxatidine in patients with renal insufficiency

1. Roxatidine acetate, a new histamine H2-receptor antagonist, was administered in the evening (75 mg p.o.) to eight patients with renal insufficiency (CLCR 8-17 ml min-1) for 12 days and plasma drug concentrations were measured. 2. Ambulatory intragastric pH was monitored following the last dose and values were compared with those on day 1 when all patients received a placebo. 3. The terminal elimination half-life (mean +/- s.d.) of roxatidine was 10.8 +/- 2.4 h and its oral clearance was 178 +/- 43 ml min-1. 4. During roxatidine treatment gastrin levels increased slightly (median 189 vs 289 ng l-1) and the hyperparathyroid status of the patients was almost normalized (parathyroid hormone levels: median 199 vs 132 ng l-1). 5. The mean latency to a gastric pH of at least 4 was 4.3 +/- 1.4 h. The duration of action (intragastric pH > 4) was 10.6 +/- 3.9 h. 6. As in a pilot study with six patients (CLCR < or = 17 ml min-1) the recommended dosage regimen (75 mg 48 h-1) was unable to maintain gastric pH > 4 for more than 6 h, daily nocturnal intake of 75 mg roxatidine acetate appears appropriate to elevate gastric pH > 4 for a sufficient period of time.

Hypocalcemic emergencies

Chronic hypocalcemia occurs frequently, although emergent hypocalcemia does not. When hypocalcemia is suspected, verification of ionized hypocalcemia is required and an etiopathologic search warranted. Etiology-specific therapy is suggested, although at times emergent intravenous calcium is indicated. Long-term nonspecific therapy includes oral calcium and vitamin D supplementation.

Medical management of asymptomatic primary hyperparathyroidism

Patients with mild asymptomatic primary hyperparathyroidism who do not meet currently accepted guidelines for surgery may be followed medically. General medical management of these individuals should be directed toward maintaining adequate hydration, therapy of hypertension, and avoiding immobilization. Diuretics should be used only with caution. Moderate dietary calcium intake (500-800 mg/day) should be encouraged. Propranolol and cimetidine are not useful in the therapy of primary hyperparathyroidism. Oral phosphate is efficacious in lowering serum and urinary calcium. However, because of concerns related to ectopic calcification, phosphate is usually reserved for those patients who meet surgical guidelines but who are not to undergo surgery. Bisphosphonates, potent inhibitors of osteoclast-mediated bone resorption, have been shown to lower serum and urinary calcium in patients with primary hyperparathyroidism. However, long-term data on their efficacy in this disorder are not yet available. The use of bisphosphonates at the present time is generally restricted to the research setting. More potent bisphosphonates as well as the design of newer agents that interfere with parathyroid hormone secretion may become very useful in future approaches to the medical management of primary hyperparathyroidism.

The effect of cimetidine on parathyroid function and histopathology in primary hyperparathyroidism

Recent evidence suggests that cimetidine given pre-operatively in primary hyperparathyroidism (1 degree HPT) might cause structural changes in parathyroid glands, while its suppressive effects on the disease are disputable. To determine these possible changes we studied 38 patients with 1 degree HPT who underwent parathyroidectomy. In 14 of these (group I) cimetidine was given pre-operatively (1000 mg orally daily for 4 weeks). The remaining 24 patients (group II) did not take any drug. Parathyroid function was estimated by nephrogenous cAMP (NcAMP) and serum immunoreactive parathyroid hormone (iPTH) measurements. Histological examination of the parathyroids was made by conventional techniques. In group I at the end of cimetidine treatment, the only change observed was a small but significant (p less than 0.05) decrease of plasma calcium (-0.77 mg/dl). Histologically, the glands of group I--compared with those of group II--showed the following findings: increased gland mass: mean increase 1050 mg (adenomas) and 700 mg (hyperplasias); central oedema in all the cases of group I only; increased (about 50 per cent) cellular size and intranuclear 'inclusions' in 10 out of 14 cases of group I only. It is concluded that treatment with cimetidine in 1 degree HPT is followed by histopathologic alterations leading to increased size of the diseased parathyroids.

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)

Assessment of calcium homeostasis in the critically ill surgical patient. The diagnostic pitfalls of the McLean-Hastings nomogram

Hypocalcemia is a common problem in critically ill surgical patients. We prospectively evaluated whether measurement of the total serum calcium (Ca) concentration or calculation of the serum ionized Ca level (by the McLean-Hastings nomogram) accurately reflects the measured serum ionized Ca level. Although 71% and 58% of 156 predominantly surgical intensive care unit (ICU) patients were hypocalcemic by the total serum Ca or calculated ionized Ca level, respectively, only 12% were hypocalcemic by directly measured serum ionized Ca measurement. The total serum Ca and calculated ionized Ca concentrations were sensitive (95% and 89%, respectively) but lacked specificity (32% and 46%, respectively) in predicting ionized hypocalcemia. Analyses of Ca binding to albumin in the serum of surgical ICU patients and normal subjects suggested that there is a circulating factor in critically ill patients that increases the binding of Ca to albumin. These observations may explain why the McLean-Hastings nomogram underestimates the protein-induced changes in serum Ca in critically ill surgical subjects. We conclude that: total serum Ca and calculated ionized Ca concentrations are poor indicators of the true serum ionized Ca status in critically ill surgical patients, and we recommend direct measurement of serum ionized Ca levels in these patients; and variability in the affinity of Ca for binding proteins in critical illness may explain the poor correlation between serum total and ionized Ca measurements.

Long-term effects of histamine H2-receptor antagonists on serum parathyroid hormone in chronic renal failure

We assessed the effects of ranitidine and cimetidine (histamine H2-receptor antagonists) on the serum concentrations of parathyroid hormone (PTH) in 22 patients with end-stage chronic renal failure. Treatment for 3 months induced a significant decrease in serum concentrations of PTH determined by radioimmunoassay directed at the mid portion of the PTH molecule. In contrast, significant increases were noted using an assay directed at the amino-terminal portion, whereas no change was noted with a carboxy-terminal assay. No significant changes in serum calcium, phosphate and alkaline phosphatase were noted after treatment with either agent, but serum concentrations of osteocalcin increased significantly. We conclude the H2-receptor antagonists do not favourably influence the natural history of hyperparathyroid bone disease in patients with end-stage chronic renal failure.

Cellular immune functions in patients with primary hyperparathyroidism: effects of histamine and cimetidine

The possibility of a link between parathyroid hyperfunction and cellular immune functions was studied in primary hyperparathyroid (1 degree HP) patients. The effect of cimetidine on lymphocyte functions in 1 degree HP patients and control subjects was also investigated. Histamine-induced suppressor activity of lymphocytes from 1 degree HP patients was significantly greater than that of controls. Cimetidine addition to both normal and 1 degree HP lymphocyte cultures abolished histamine-induced suppression. In vivo administration of cimetidine, while ineffective towards normal lymphocytes, depressed phytohemagglutinin stimulation of 1 degree HP lymphocytes, indicating possible immunological damage caused by this drug, which is frequently used in the treatment of patients with 1 degree HP.

Effect of combination therapy with cimetidine and pirenzepine on plasma parathyroid hormone and calcitonin levels in hemodialyzed patients

In this study we evaluated the effects of an oral combination therapy with cimetidine and pirenzepine on plasma parathyroidhormone (PTH) and calcitonin (CT) levels in 24 patients on maintenance hemodialysis (mean age: 50 years; mean duration of dialysis treatment: 23 months). As compared to the pre-treatment plasma levels of PTH and CT, there were no significant changes of their plasma concentrations during a 4-week administration of 800 mg cimetidine or 100 mg pirenzepine daily, and the concentrations also did not change significantly during the following 4 weeks of combination therapy with cimetidine and pirenzepine in the above mentioned dosage. Serum concentrations of calcium and phosphate and the activity of the alkaline phosphatase showed no significant changes either. Therefore, we suggest that this therapeutic approach cannot be considered for the treatment of uremic hyperparathyroidism.

Multiple endocrine neoplasia syndromes

The multiple endocrine neoplasia (MEN) syndromes are characterized by autosomal dominant inheritance with a high degree of penetrance but varying expression. This review gives a classification of these syndromes and a short summary of the historical background. The pathogenesis of the disease and its possible origin in the APUD cell system are discussed together with the mechanisms underlying normal and ectopic hormone production by MEN tumors on the basis of recent findings in molecular endocrinology. The natural history and the clinical manifestations of the different syndromes are described. The sensitivity and discriminative capacity of the tests used to detect the syndromes in an early stage are compared. The choice of therapy and criteria for the timing and extensiveness of treatment are also considered. Lastly, problems associated with the ethical and legal aspects of screening, central registration, and monitoring of relatives at risk are described.

Cimetidine does not correct circulating calcium and parathyroid hormone in primary hyperparathyroidism

Thirteen patients with primary hyperparathyroidism were treated for 4-8 weeks with the H2-blocker cimetidine at a daily dose of 1 g. The drug had no effect on the serum concentrations of calcium or parathyroid hormone, nor did any of the patients improve clinically during the period of treatment. The recently reported efficacy of cimetidine in primary hyperparathyroidism is strongly questioned by the present results.

Drug treatment of primary hyperparathyroidism: use of clodronate disodium

Clodronate disodium (dichloromethylene diphosphonate), a specific inhibitor of bone resorption, was given by mouth (1.0-3.2 g daily) to nine patients with primary hyperparathyroidism for two to 32 weeks so that its clinical and metabolic effects could be evaluated. Bone resorption decreased in all patients as judged by a fall in the fasting urinary calcium to creatinine and hydroxyproline to creatinine ratios. Serum calcium concentration was increased in all patients before treatment and fell in response to treatment to values near the upper end of the normal range. Hypercalcaemia and hypercalciuria recurred when treatment was stopped. In three patients treated for longer than 19 weeks clodronate failed to sustain the reduction in serum calcium concentration but the concentration remained below pretreatment values. These results suggest that clodronate may be of use in the medical management of primary hyperparathyroidism, particularly in patients in whom suppression of bone disease is desirable before surgery or in whom surgery is contraindicated.

Treatment of hypercalcemia

The indications, effectiveness, and adverse effects of the numerous treatment modalities for hypercalcemia are presented. Results of a retrospective chart review of 72 admissions (53 patients) for hypercalcemia-related diseases are presented to emphasize the therapeutic principles that should be applied in the management of these patients. Hydration, forced diuresis, oral phosphates, and glucocorticosteroid drugs are common therapeutic approaches. Combination therapy with glucocorticosteroid drugs, oral phosphates, and forced diuresis is utilized to take advantage of multiple mechanisms of action. Outpatient therapy for hypercalcemia consists primarily of glucocorticosteroid agents and oral phosphates. Most patients are treated if the serum calcium level is greater than or equal to 12 mg/dL. An algorithm is presented to assist the clinician in selecting the most efficacious treatment plan.

The effects of cimetidine on serum calcium and parathyroid hormone levels in primary hyperparathyroidism

1 Cimetidine has been reported to reduce serum calcium and parathyroid hormone (PTH) levels in primary hyperparathyroidism, but some studies have reported negative findings. 2 A double-blind, controlled trial of cimetidine in this condition was, therefore, conducted. Eight patients were given cimetidine and placebo for 2 months each, in random order. Only one patient showed a significant fall in serum calcium on cimetidine and no patient showed a fall in PTH levels. 3 In addition, eight patients were studied during a 48 h continuous intravenous infusion of cimetidine. The first five patients exhibited no effect of the drug on either calcium of PTH levels, but in the sixth there appeared to be a dose-dependent suppression of PTH. The seventh and eighth patients were, therefore, given a higher dose of the drug but it failed to suppress calcium or PTH values. 4 It is concluded that cimetidine is not of value in primary hyperparathyroidism.

The effect of histamine2 and muscarine receptor antagonists on plasma levels of parathyroid hormone and calcitonin

Long-term administration of cimetidine, a histamine2 receptor antagonist, has been reported to normalize elevated parathyroid hormone (PTH) concentrations in patients with secondary [1] and primary hyperparathyroidism [2] and even to improve the clinical symptoms. We have compared the effect of cimetidine and pirenzepine on PTH and calcitonin (CT) plasma levels in a short-term trial on patients with secondary hyperparathyroidism. After cimetidine a significant effect on PTH was seen within 30 min lasting 30 min and after pirenzepine, within 60 min and lasting 60 min. The effect on CT was only significant after cimetidine.

Cimetidine inhibits the pentagastrin-induced release of calcitonin in normocalcaemic man

Pentagastrin stimulates the release of calcitonin from normal C-cells in the human thyroid. In the present investigation the effect of cimetidine on the liberation of calcitonin in response to intraarterial pentagastrin (0.6 micrograms . kg-1) was studied in 14 normocalcaemic patients undergoing surgery for thyroid adenomas. Cimetidine was administered as a bolus injection of 200 mg followed by an intravenous infusion of 1.5 mg . kg-1 . h-1. In seven patients not given cimetidine, mean calcitonin concentration in the thyroid vein rose from 419 +/- 58 to 2787 +/- 645 pM in response to pentagastrin. In seven patients given cimetidine, mean calcitonin concentration only increased from 107 +/- 33 to 166 +/- 51 pM after pentagastrin. The difference between the two groups was statistically significant both during basal conditions (P less than 0.001) and in response to pentagastrin (P less than 0.01). The results suggest that pentagastrin affects normal C-cells via release of histamine and that cimetidine markedly interferes with this mechanism.

Failure of cimetidine to suppress immunoreactive parathyroid hormone and hypercalcaemia in primary hyperparathyroidism

Cimetidine has been reported as suppressing the excess parathyroid hormone secretion and hypercalcaemia seen in hyperparathyroidism. A case of primary hyperparathyroidism is described, in which the level of circulating parathyroid hormone and hypercalcaemia remain entirely unaffected by cimetidine. The drug is implicated in the management of primary hyperparathyroidism unsuitable for surgery, but present evidence, as reviewed, is insufficient to recommend the use of cimetidine in this way.

Dialysis pruritus: effect of cimetidine

The effect of oral Cimetidine compared to a classic antihistaminic and to a placebo was evaluated, under the double hypothesis of its anti-PTH and anti-pruritus action, in a population of patients recently included in Hemodialysis that were asked about the incidence and intensity of pruritus according to a scored questionnaire made for this purpose. No different efficacy of Cimetidine versus the antihistaminic classic and the placebo was observed in our study.