No detectable concentrations of oxmetidine but measurable concentrations of cimetidine in cerebrospinal fluid (CSF) during multiple dose treatment

Randomized, double-blind study comparing postoperative effects of treatment timing with histamine H-receptor antagonist cimetidine

BACKGROUND

The purpose of this study was to evaluate the effect of timing of preoperative, postoperative, and placebo administration of the H(2)-antagonist cimetidine on postoperative pain management and the incidence of side-effects.

METHODS

One hundred and twenty ASA I to II patients, undergoing major gynaecological abdominal surgery, were randomly divided into three groups, and received a standardized general anaesthesia. The patients in the preoperative ('Pre') group received an intravenous infusion of cimetidine 4 mg kg(-1) prior to anaesthesia induction; the postoperative ('Post') group received the same volume of normal saline. Postoperatively, the patients in the Post group received an intravenous infusion of cimetidine 4 mg kg(-1); the patients in the Pre group received the same volume of normal saline. The Control group received the same volume of normal saline prior to anaesthesia induction and after the end of operation. Postoperatively, all patients were treated with a patient-controlled intravenous analgesia system, which was programmed to deliver 1 mg of morphine on demand for three consecutive days.

RESULTS

Pain intensity, morphine consumption, sedation score, and side-effects were recorded and evaluated. We found no difference among the three groups with respect to pain intensities, morphine usage, sedation scores, and the incidence of nausea, vomiting, pruritus, or dizziness.

CONCLUSIONS

Our results suggested that neither preoperative nor postoperative administration of cimetidine 4 mg kg(-1) provided a pre-emptive or preventive analgesic advantage for postoperative pain or morphine consumption, and that the use of cimetidine failed to reduce the incidence of nausea or vomiting.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The fate of cimetidine sulphoxide in the guinea pig

1. An oral dose of cimetidine given to guinea pigs was totally excreted in 3 days, divided equally between urine and faeces. 2. Only 40% of an oral dose of cimetidine sulphoxide was voided in 3 days, the remainder being found in the mesentery and omental tissues. 3. In contrast, 90% of an i.v. dose of cimetidine sulphoxide was excreted in urine in 24 h. 4. Approx. 20% of an oral dose of both cimetidine (17.2%) and cimetidine sulphoxide (24.9%) was secreted in bile during the first day. 5. The major metabolic routes encountered were sulphoxidation and sulphoxide reduction.

Cimetidine elimination from the cerebrospinal fluid of the rat

The major goal of this study was to develop a small animal model that could be used to assess quantitatively the clearance of cimetidine from the cerebrospinal fluid (CSF) under relatively physiologic conditions. In addition, we addressed questions related to the pathways involved in the elimination of cimetidine from the CSF. We administered high and low bolus doses of cimetidine together with inulin, as a marker of bulk flow, into the lateral ventricle of anesthetized rats and sampled CSF from the cisterna magna. Principles of linear pharmacokinetic systems were applied to the data to obtain clearances from the CSF. The clearance of inulin was 2.02 +/- 0.22 microliters/min, which is in excellent agreement with the CSF production rate of 2.2 microliters/min in anesthetized rats. The clearance of cimetidine from the CSF following the administration of a low dose was 11.8 +/- 3.1 microliters/min, which is in good agreement with the cimetidine CSF clearance in the rat obtained previously in studies using the technique of ventriculocisternal perfusion. A 32% decrease in the CSF clearance of cimetidine (P less than 0.05) was observed when the high dose was administered, suggesting that CSF elimination is saturable. The clearance of inulin was unaffected by the high dose of cimetidine. This study demonstrates that the technique of lateral ventricle injection and sampling from the cisterna magna is useful in quantitatively assessing the elimination of compounds from the CSF in the rat under relatively physiologic conditions.

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.

Recent advances in pharmaceutical chemistry--review II. Histamine H2-receptor antagonists

The concept of histamine receptors is outlined and the rationale for the synthesis of H2-antagonists presented. Structure-activity relationships among these compounds are described and aspects of absorption, distribution and elimination discussed with particular reference to cimetidine and ranitidine. Oxmetidine, lupitidine and loxtidine are also considered. Methods for the analysis of these drugs in body fluids are presented followed by a discussion of their toxicology. Volunteer and patient studies are also surveyed.