Hypotension after intravenous cimetidine

Acute cardiovascular effects of intravenous cimetidine

To assess the acute cardiovascular effects of cimetidine--a widely used histamine-H(2)-receptor antagonist--cuff arterial blood pressure, M-mode echocardiogram of the left ventricle and systolic time intervals were recorded in 10 healthy volunteers before and after 200 mg of cimetidine or isotonic saline given intravenously in a double-blind cross-over manner. Neither echocardiograms nor systolic time intervals revealed any significant effects of cimetidine on the left ventricular performance. However, cimetidine decreased slightly the systolic arterial pressure. The maximal effect of cimetidine (7 +/- 1 mmHg, mean +/- SEM) differed significantly from that of saline (3 +/- 1 mmHg, p less than 0.02). When compared with the pre-injection level, the calculated total peripheral resistance decreased significantly after cimetidine (p less than 0.01), whereas saline induced no such change. We conclude that a bolus injection of cimetidine does not impair cardiac performance but may induce transient hypotension due to reduction of the total peripheral resistance. This reduction can explain the hypotensive effect of i.v. cimetidine reported in acutely ill patients.

Histologic evaluation of preventive measures for scald injury on the peritoneo-serosal surface due to intraoperative hyperthermic chemoperfusion for patients with gastric cancer and peritoneal metastasis

To histologically assess the preventive efficacy of cimetidine against scald injury on the peritoneo-serosal surface during intraperitoneal hyperthermic chemoperfusion (IHCP) for advanced gastric cancer, a randomized histologic study using cimetidine, a histamine H2-receptor antagonist, was performed for 20 patients with advanced or recurrent gastric cancer and peritoneal metastasis. Cimetidine 50 mg/kg was administered intravenously to 10 patients just prior to the IHCP (cimetidine group), and the remaining 10 patients underwent the IHCP without cimetidine (control group). The background factors and IHCP treatments of these two groups were nearly the same. Although the antitumour efficacy of the IHCP was not histologically different between the two groups, the histological analysis revealed that the peritoneo-serosal surface in the cimetidine group was protected against scald injury, compared with the control group. This finding suggests that pre-IHCP cimetidine is of great benefit for protecting the peritoneo-serosal surface from scald injury due to IHCP.

Survival time and prevention of side effects of intraperitoneal hyperthermic perfusion with mitomycin C combined with surgery for patients with advanced gastric cancer

In an attempt to prevent postoperative intraperitoneal recurrence in patients with advanced gastric cancer and consequently to improve survival time, we treated patients with intraperitoneal hyperthermic perfusion (IPHP) using mitomycin C (MMC) combined with surgery. There were 60 patients with advanced gastric cancer who were treated with IPHP (long-term study) group, and the survival of this group was compared with the outcome in 52 patients with advanced gastric cancer treated with surgery alone (control group). To avoid or diminish side effects derived from scald injury of the peritoneal surface due to IPHP, 50 mg/kg of cimetidine was given intravenously just before administration of IPHP. For prophylaxis of anastomotic leakage, duodenostomy using a Foley catheter was performed. The 60 patients who were treated with IPHP lived longer than the 52 patients in the control group (p = 0.000610). The 3 year survival rate was 45 percent for the former compared with 16 percent for the latter. The intravenous administration of cimetidine just prior to IPHP protected the peritoneoserosal surface from scald injury, even though the heated perfusate exposure was at 44.3-46.3 degrees C for 2 hours. Because the intraabdominal pressure within the duodenum and jejunum was decompressed postoperatively through catheter duodenostomy and the peritoneoserosal surface was protected from scald injury caused by IPHP, anastomotic leakage in the study group was nil. Therefore, IPHP treatment plus aggressive surgery combined with pre-IPHP cimetidine administration are indicated for patients with advanced gastric cancer. The side effects of IPHP and postoperative morbidity can thus be reduced and a favorable outcome obtained.

Metabolic changes in cimetidine treatment for scald injury on the peritoneo-serosal surface in far-advanced gastric cancer patients treated by intraperitoneal hyperthermic perfusion

Since pretreatment with cimetidine results in the prevention of scald injury on the peritoneo-serosal surface caused by intraperitoneal hyperthermic perfusion (IPHP) for advanced gastric cancer, the diverse influence of IPHP on patients who were either given or not given cimetidine was studied both during and after IPHP treatment. Cimetidine 50 mg/kg was injected intravenously into 12 patients immediately prior to IPHP. There were no statistical background differences between the cimetidine and control groups (those not given cimetidine). The inflow and outflow temperatures of the hyperthermic perfusate in the control and cimetidine groups were 46.1 +/- 0.1 degree C and 44.1 +/- 0.1 degree C and 46.3 +/- 0.1 degree C and 44.2 +/- 0.04 degree C, respectively. Either the pre-IPHP hypothermia or IPHP in the control group resulted in a considerable increase in serum noradrenaline and adrenaline. The intravenous administration of cimetidine led to a stransient but moderate drop in the mean blood pressure as well as a delayed appearance of high concentrations of noradrenaline and adrenaline, induced by high concentrations of circulating histamine released with cimetidine. These results suggest that the sympathetic nervous responses were activated either by hypothermia or hyperthermia. The transient hypotension and delayed increases of both serum catecholamines were attributed to a marked increase in circulating histamine, released with the intravenous cimetidine.

Hemodynamic status during famotidine infusion

Histamine H2 antagonists, which reduce gastric acid secretion, are often used in the intensive care setting for the prophylaxis of stress ulcers. This double-blind, placebo-controlled study evaluated hemodynamic parameters in 11 stable, critically ill patients receiving famotidine. Repeated-measures ANOVA demonstrated that famotidine had no significant effect on baseline hemodynamic measurements and that there was no significant difference in hemodynamic values following the famotidine infusion as compared with NaCl 0.9% placebo (p greater than 0.05).

Haemodynamic effects of famotidine and cimetidine in critically ill patients

To compare the cardiovascular effects of the histamine H2 receptor antagonists, famotidine and cimetidine, in critically ill patients, seven ICU patients were given 20 mg of famotidine or 200 mg of cimetidine intravenously in a randomized fashion. Each patient was studied on 2 separate days. In a random fashion, they received famotidine on one of the days and cimetidine on the other. Mean systemic arterial pressure (MAP) was maximally decreased 2 min after intravenous cimetidine from 103 +/- 10 (13.7 +/- 1.3 kPa) (mean +/- s.d.) to 83 +/- 15 mmHg (11.1 +/- 2.0 kPa) (P less than 0.05). MAP returned to control values 8 min after administration of the drug. Systemic vascular resistance (SVR) was significantly decreased during the 8-min observation period (P less than 0.01). In contrast, famotidine produced little haemodynamic effect over the 8-min period. Therefore, we suggest that famotidine may be a better H2 antagonist than cimetidine in critically ill patients requiring vasoconstrictor drug support, since it avoids the significant decrease in systemic blood pressure and peripheral vasodilation seen after cimetidine.

A comparative study of the actions of histamine H2 receptor antagonists on transmission in the isolated superior cervical ganglion of the rat

Ganglionic effects of the histamine H2 receptor antagonists cimetidine, ranitidine and 1-nitro-2-(2-propynylamino)-2-(2-[dimethylaminomethyl-2-furanyl) methylthiol]-ethylamino)ethylene (ORF 17578) were compared in the isolated superior cervical ganglion of the rat. Extracellular recording of compound action potentials showed that the drugs caused concentration-dependent inhibition of ganglionic transmission, as indicated by depression of the postganglionic compound action potential. Cimetidine-induced inhibition of ganglionic transmission was stimulus frequency-dependent. Increasing the Ca2+ from 2.2 to 4.4 mM in the bathing solution did not significantly affect the inhibitory actions of these agents. In the series with ranitidine, pretreatment with DFP to inhibit acetylcholinesterase similarly had no significant effect on the depression of the compound action potential by ranitidine. All three agents had little or no effect on nerve conduction in isolated vagi of the rat. The results indicate that all three histamine H2 receptor blockers inhibited ganglionic transmission, but only in large concentrations. The results also suggest that the blocking effect of these drugs was unrelated to their reported anticholinesterase action or to blockade of histamine H2 receptors, which are believed to exist on the presynaptic membrane. It is suggested that the ganglion effect may be due to the action of these agents on the acetylcholine receptor-ion channel complex in the postsynaptic membrane.

Blockade of histamine-stimulated alterations in cerebrovascular permeability by the H2-receptor antagonist cimetidine

Histamine has been shown previously to cause dose-dependent systemic hypotension and concurrent alterations in the permeability of the blood-brain barrier of rats. The purpose of the present study was to determine whether histamine-induced changes in cerebrovascular permeability were mediated by the histamine H2-receptor. Wistar-Kyoto (control) and spontaneously hypertensive rats were pretreated with the histamine H2-receptor antagonist cimetidine (10 mg/kg), followed by saline or histamine (1.25, 2.5 or 5.0 micrograms/kg). Premedication with cimetidine did not block histamine-induced systemic hypotension. The permeability of the blood-brain barrier was measured with 131I-labelled serum albumin (RISA) or with 99mTc-sodium pertechnetate (TcO4-). In both control and spontaneously hypertensive animals, cimetidine prevented histamine-induced changes in the permeability of the blood-brain barrier to either tracer. These findings suggest that the H2-receptor is the prime mediator of histamine-stimulated alterations in cerebrovascular permeability.

Ranitidine-induced chest pain

A 45-year-old woman with no history of heart disease twice experienced chest pain after consuming a dose of ranitidine. The chest pain, which lasted about one hour, was substernal, left of midline, dull, and pounding. H2-receptors are present in cardiovascular tissues. Although several studies have not noted an effect of ranitidine on cardiac indices there have been case reports indicating a cardiac effect. There are no reports of chest pain associated with H2-blocker ingestion; however, both bradycardia and hypotension (reported effects) might cause chest pain. A discussion of the possible mechanisms is presented.

Prophylaxis for pulmonary acid aspiration

Pulmonary acid aspiration in the perioperative period was first noted as a medical concern more than 40 years ago. Despite this awareness, identification of the patient at risk is by no means certain, and the true incidence of this condition is not known. Various therapeutic interventions have been proposed and tried. Physical therapies, such as pressure on the cricoid, have been successful, as has the administration of clear antacids prior to surgery. The histamine (H2)-receptor antagonists cimetidine and ranitidine have also been used successfully as prophylactic therapy when enough time is available prior to operation to make preoperative dosing practical. Metoclopramide, which can be given intravenously, may be useful in emergency surgery. When the degree of risk is high, concurrent use of physical and pharmaceutical interventions is recommended.

Pharmacodynamics and pharmacokinetics of parenteral histamine (H2)-receptor antagonists

Parenteral histamine (H2)-receptor antagonists are frequently used to prevent upper gastrointestinal bleeding caused by stress-induced gastric mucosal damage in critically ill patients. It is generally agreed that the goal of therapy in this syndrome is the consistent elevation of gastric pH levels above a certain value, often set at 4, in order to prevent the underlying mucosal damage from progressing to bleeding. The three H2-receptor antagonists currently available in a parenteral form and suitable for this mode of prophylaxis are cimetidine, ranitidine, and famotidine. The pharmacodynamic and pharmacokinetic properties of these agents, as they relate to their use in prevention of stress ulceration bleeding, are discussed here. These agents are more noted for their pharmacodynamic and pharmacokinetic similarities in acid suppression, elimination, and metabolism than for their differences. Ranitidine and famotidine are more potent than cimetidine, and famotidine has a slightly longer half-life than do cimetidine and ranitidine, but current dosing recommendations take these differences into account so that the agents have equivalent efficacy. Cimetidine and ranitidine have been widely used in this application. Less experience has been obtained, to date, with famotidine. Recent studies with primed, continuous infusions of cimetidine indicate that dosing schedule may be the key to obtaining better efficacy in prophylaxis of stress-related mucosal damage. Similar studies with ranitidine have not yielded results as promising as those with cimetidine, however, and few data are available on famotidine.

Clinically important adverse effects and drug interactions with H2-receptor antagonists: an update

The H2-receptor antagonists cimetidine, ranitidine, and famotidine are well tolerated, with a low frequency and similar spectrum of adverse effects. The occasional problematic effects that have been associated with these agents include central nervous system symptoms (mental confusion, headache, and depression), rare cases of thrombocytopenia, and cardiovascular events related to the rate of intravenous infusion. Severe renal and hepatic impairment appear to be associated with a higher occurrence of central nervous system effects. Because the H2-receptor antagonists elevate gastric pH, bind to and inhibit the hepatic cytochrome P-450 enzyme system, and undergo renal tubular secretion, competition with other drugs sharing these pathways has resulted in a number of drug interactions, most of which are not clinically significant. The interaction that occurs with theophylline and warfarin when the cytochrome P-450 enzyme system is inhibited by cimetidine and ranitidine requires monitoring. Recent data suggest that administering cimetidine 800 mg at bedtime has less effect on the serum concentrations of warfarin and theophylline than other dosing regimens. Evidence to date indicates that famotidine does not bind to cytochrome P-450 to a significant extent, and interactions with drugs metabolized by this system have not been reported; however, clinical experience with this agent is very limited.

Effect of clonidine on haemodynamic responses to endotracheal intubation and on gastric acidity

Sixty-three patients (ASA 1-2), scheduled for elective surgery under general anaesthesia, were randomly given either oral clonidine (225-375 micrograms) + diazepam (5 15 mg), cimetidine (300 mg the night before and 300 mg in the morning) + diazepam or only diazepam for premedication. Anaesthesia was induced with thiopentone and maintained with N2O + O2 (70:30), enflurane and fentanyl. Vecuronium bromide was used as a muscle relaxant. The sleep dose of thiopentone was significantly smaller in the patients pretreated with clonidine than in the other groups. The mean maximal increase in heart rate was lowest in the clonidine-pretreated patients, but there were no significant differences in the mean arterial pressure changes associated with intubation. Before and just after intubation and in the recovery room, the arterial pressures were lowest in the patients pretreated with clonidine. During anaesthesia, marked bradycardia (less than or equal to 45 beats min-1) did not occur more often when clonidine was used, but in the recovery room there were statistically significantly more patients with bradycardia in the clonidine group than in the other groups. On the electrocardiogram (ECG) during the endotracheal intubation, the incidence of bigeminy was higher in the diazepam patients (5/20) than in the cimetidine patients (2/20) and the clonidine patients (0/23). There were significantly more gastric content samples with a pH above 2.5 in the cimetidine group than in the other groups, and clonidine patients did not differ from diazepam patients in this respect. The high incidence of bradycardia with the concomitant hypotension may limit use of this drug to highly selected patients.

Actions of cimetidine and ranitidine at some cholinergic sites: implications in toxicology and anesthesia

Cimetidine and ranitidine are specific and potent H2-receptor antagonists widely used in the effective therapy of peptic ulcer disease. The drugs also possess other pharmacological properties unrelated to H2-receptor antagonism. More recently large experimental doses of cimetidine or ranitidine were found to have anticholinesterase, ganglion blocking and neuromuscular blocking activities. Actions of the drugs at such cholinergic sites may account for some of their clinically documented adverse effects. The toxicological implications of these findings including the potential for drug interactions to occur, especially during some anesthetic procedures, are discussed.

Ganglion blocking activity of cimetidine in the anaesthetized cat

Cimetidine produced a dose-dependent and reversible inhibition of contractions of the nictitating membrane elicited through stimulation of the preganglionic nerve supplying the superior cervical ganglion in the anaesthetized cat. Postganglionic nerve stimulation resulted in only a slight and variable inhibition of the contractions. Both hexamethonium and cimetidine also produced a dose-dependent and reversible fall in arterial blood pressure. The ganglion blocking activity of cimetidine was much weaker than that of hexamethonium; the ED50 ratio (cimetidine:hexamethonium) calculated from the cumulative log dose-response curves for the two drugs was 64. The possible mechanism(s) of ganglion blockade produced by cimetidine is discussed including a possible action at nicotinic receptors, either directly or indirectly (via its anticholinesterase activity), and ion channel blockade. The clinical implications of cimetidine-induced ganglionic blockade are also discussed, especially with respect to sexual impotence associated with the use of cimetidine.

Usefulness and safety of cimetidine in patients receiving mexiletine for ventricular arrhythmia

Cimetidine, a commonly used H2 receptor antagonist, was found to adversely interact with many drugs metabolized by the liver, including class I antiarrhythmic agents, lidocaine and quinidine. Mexiletine is a new class I antiarrhythmic agent similar to lidocaine which when used orally may have significant gastric side effects. Since some patients with peptic ulcer disease or gastric hyperacidity on mexiletine may benefit from the addition of cimetidine, it was important to rule out any significant adverse interaction between the two drugs in such patients. Eleven patients currently receiving long-term oral mexiletine for the treatment of complex ventricular arrhythmia underwent a double-blind crossover trial where they were maintained on their usual dose of mexiletine, and cimetidine, 300 mg orally every 6 hours, or placebo were added for a 1-week period each. Peak and trough mexiletine blood levels were not significantly altered by cimetidine. Similarly, there was no significant change in the frequency and severity of ventricular arrhythmia when cimetidine was added to mexiletine. Cimetidine reduced gastric side effects of mexiletine in 50% of patients who had complained of such symptoms on mexiletine alone or on mexiletine and placebo. We conclude that cimetidine can effectively reduce gastric side effects of mexiletine in many patients without adversely affecting the plasma concentration or the efficacy of the drug.

Hemodynamic studies on cimetidine and ranitidine in anesthetized dogs

The cardiovascular effects of the H2-receptor-antagonists cimetidine and ranitidine have been compared in a randomized double-blind crossover study. The experiments were performed in seven anesthetized mongrel dogs. Cimetidine (200 mg) and ranitidine (50 mg) were infused i.v. for 2 min. The time interval between cimetidine and ranitidine application was always 3 h. The direct comparison of the drug effects on blood pressure shows a significant difference between cimetidine and ranitidine (P less than 0.001). Apart from the sequence of application, cimetidine causes a significant decrease (P less than 0.01) in total peripheral resistance (-271 +/- 50 dyn . s . cm-5) resulting in a decrease in mean blood pressure (-9 +/- 1.1 mmHg). In contrast to cimetidine, none of the recorded parameters are altered significantly by ranitidine. Heart rate, left ventricular end-diastolic pressure, myocardial contractility (dP/dtmaxLV), mean right atrial pressure, mean pulmonary artery pressure, and cardiac output are not affected significantly by either drug. Due to our results it might be concluded that the cimetidine-induced hypotension is mediated by peripheral vasodilation.

Pharmacokinetics of cimetidine in critically ill patients

Cimetidine disposition was studied after rapid (1 min) intravenous infusion in eight critically ill patients aged between 20 years and 77 years; one patient was studied on two occasions. Cimetidine dose was 300 mg in seven patients and 400 mg in the remaining patient. Arterial plasma cimetidine concentrations at the end of the infusion were very high and ranged from approximately 15-35 mg/l. Pharmacokinetic parameters displayed wide interpatient variability (coefficients of variation of 30-50%) and significant relationships emerged between some of these parameters and certain patient characteristics. Most notable, total systemic plasma clearance of cimetidine was directly related to estimated creatinine clearance (p less than 0.01). This relationship might prove to be a useful method of individualizing cimetidine dosage in critically ill patients.

Intravenous ranitidine has no hemodynamic effects in subjects with normal lung function and patients with chronic obstructive airway disease

Ten patients with Chronic Obstructive Airway Disease (COAD) and five subjects with duodenal ulcers and normal lung function were given 50 mg ranitidine as a single intravenous bolus injection. Hemodynamic responses were continuously monitored. There were no significant alterations in systemic and pulmonary pressures, systemic and total pulmonary vascular resistances or cardiac output. Continuous ECG recordings did not reveal arrhythmias. Ranitidine does not appear to cause any significant disturbance of hemodynamic function in COAD patients. This contrasts with alterations in hemodynamics previously observed following administration of cimetidine.

Hypotension following cimetidine administration during cardiopulmonary bypass

Intravenous administration of cimetidine may occasionally cause profound hypotension. Cimetidine 200 mg was administered as a bolus injection to patients whilst on cardiopulmonary bypass and subsequent changes in systemic arterial pressure were recorded. A statistically significant fall in arterial pressure was observed (p less than 0.001), which was attributable to a fall in systemic vascular resistance.

Cimetidine, vasopressin and chronotropic incompetence

A 59-year-old man with severe variceal bleeding received therapy with intravenously administered vasopressin and cimetidine. Inappropriate bradycardia, sinoatrial and atrioventricular blocks, and terminal bradycardia leading to asystole, occurred during bleeding, with the greatest number of rhythm abnormalities occurring during combined cimetidine and vasopressin therapy. The results of post-mortem examination showed only mild coronary artery disease. The hazards of combined vasopressin and cimetidine therapy are reviewed.

Effects of histamine type 2 receptor stimulation on myocardial function in normal subjects

Myocardial histamine(H)2 receptor stimulation has been studied in six normal men. Since histamine is a potent vasodilator, the haemodynamic effects of histamine infusion were compared with those of nitroprusside at equihypotensive doses, to identify changes in myocardial contractility attributable to vasodilatation. After H1 receptor blockade with mepyramine, subjects received, in single blind crossover fashion, either histamine alone and with the H2 receptor antagonist cimetidine, or nitroprusside alone and with cimetidine. Echocardiographic left ventricular dimensions, plasma catecholamines, blood pressure, and heart rate were measured. The rise in catecholamines suggested similar baroreflex activation by both histamine and nitroprusside. Echo ejection phase indices did not alter significantly after nitroprusside, but histamine caused an increase in percentage fractional shortening from 38.2 +/- 4.1 to 53.5 +/- 3-6% and in mean fibre shortening velocity from 1.31 +/- 0.19 to 1.99 +/- 0.22 cm/s. These changes were both greatly reduced by cimetidine and suggest that H2 receptor stimulation in man causes a direct positive inotropic response.

The metabolism of [14C]cimetidine in man

1. The excretion and metabolism of [2-(14)C]cimetidine (500 mg orally) was studied in five male volunteers. 2. Over 70% of the 14C was excreted in the urine after 24 h by all individuals with 5% in the faeces; 97% being recovered in total after three days. 3. Unchanged cimetidine was the largest urinary component (63%), followed by a polar conjugate tentatively identified as cimetidine N'-glucuronide (24%). Smaller amounts of the oxidized metabolites, cimetidine sulphoxide and 5-hydroxymethylcimetidine, together with the hydrolysis products, cimetidine guanylurea and cimetidine guanidine, were also observed. 4. Cimetidine and its sulphoxide were identified in faecal samples. Anaerobic incubations of cimetidine or cimetidine sulphoxide with faecal homogenates showed that reduction was the predominant reaction under these conditions. 5. Studies in one individual over a wide dose range (0.5 mg to 1.5 g orally) showed little variation in excretory profile or metabolic spectrum.

Sodium citrate: an alternative antacid for prophylaxis against aspiration pneumonitis

In a double-blind study, 107 patients undergoing elective and emergency surgical procedures were given 15 ml of either sodium citrate 0.3 M or placebo 10 minutes before induction of anaesthesia. Gastric contents were sampled immediately after induction and the pH was measured. The mean pH of the Gastric contents of patients given sodium citrate was 5.67, whereas for those given the placebo it was 3.21 (p less than 0.001). Of patients given sodium citrate 92% had a gastric pH above 3.0 compared with only 37% in the placebo group (p less than 0.001). At the end of surgery gastric contents were emptied as completely as possible and the volume and pH measured. There was no significant difference in the mean volume of gastric contents in the two groups. In neither group was the mean pH at the end of surgery significantly different from that after induction.

Peripheral hypotensive and central hypertensive effects of cimetidine

Rapid intravenous (i.v.) injections of high doses (16-128 mumol/kg) of cimetidine induced a short-lasting (5-15 min) hypotension in anaesthetized rats. Diastolic pressure was reduced more than systolic pressure, suggesting vasodilatation. Heart rate was not affected. Diphenhydramine pretreatment (100 mumol/kg i.v.) did not antagonize the hypotensive effect of cimetidine. However, in the presence of diphenhydramine, cimetidine induced bradycardia. Intracerebroventricular administration of cimetidine or metiamide (2 mumol/rat) increased the blood pressure and heart rate. It is concluded that the hypotension after i.v. cimetidine is mediated by peripheral mechanisms. Since diphenhydramine pretreatment had no antagonistic effect cimetidine-induced hypotension could not be due to indirect H1-receptor stimulation caused by histamine liberation.

[Control of gastric acidity with cimetidine given as premedication before general anesthesia: efficacy and tolerance]

Cimetidine 400 mg was administered intramuscularly 60 minutes before the beginning of general anaesthesia. The double blind experiment was conducted on 84 patients divided in two groups: cimetidine and control. There was no difference in gastric fluid volume between the two groups during general anaesthesia, but acid secretion decreased significantly in the cimetidine group. Values of pH lower than 2.5 were observed in 33.3 per cent at induction and 34 per cent at recovery in the control group against 14.6 per cent and 0 per cent in the cimetidine group. Clinical tolerance to cimetidine was studied in 100 patients during operation. Cimetidine did not alter pharmacological action of usual anaesthetics. There were no significant changes in cardiovascular and electrocardiographic data.

Haemodynamic responses to intravenous cimetidine in subjects with normal lung function and in subjects with chronic airway obstruction

1 The haemodynamic responses to a bolus intravenous injection of 400 mg cimetidine were studied in eight subjects with normal lung function and sixteen with chronic obstructive airway disease (COAD), under continuous systemic and pulmonary arterial monitoring. In all subjects there were significant immediate but transient (less than 10 min) drops in the systemic and pulmonary arterial pressures (both systolic and diastolic), the systemic vascular resistance and total pulmonary resistance. The percentage drops were significant more marked in the COAD group in the following: systemic arterial pressures (systolic and diastolic), systemic vascular resistance and total pulmonary resistance. The cardiac output showed no significant change in the group with normal lung function but rose significantly in the COAD group. None of the subjects had any symptoms associated with the haemodynamic changes. 2 These results can be explained by a generalized vasodilatory effect of cimetidine, but the relationship to its H2-receptor blocking effect is undetermined. Hypoxia and/or hypercapnia may sensitize an individual to the vasodilatory effect of cimetidine.