Mental status, the intensive care unit, and cimetidine

Commonly used gastrointestinal drugs

This chapter reviews the spectrum and mechanisms of neurologic adverse effects of commonly used gastrointestinal drugs including antiemetics, promotility drugs, laxatives, antimotility drugs, and drugs for acid-related disorders. The commonly used gastrointestinal drugs as a group are considered safe and are widely used. A range of neurologic complications are reported following use of various gastrointestinal drugs. Acute neurotoxicities, including transient akathisias, oculogyric crisis, delirium, seizures, and strokes, can develop after use of certain gastrointestinal medications, while disabling and pervasive tardive syndromes are described following long-term and often unsupervised use of phenothiazines, metoclopramide, and other drugs. In rare instances, some of the antiemetics can precipitate life-threatening extrapyramidal reactions, neuroleptic malignant syndrome, or serotonin syndrome. In contrast, concerns about the cardiovascular toxicity of drugs such as cisapride and tegaserod have been grave enough to lead to their withdrawal from many world markets. Awareness and recognition of the neurotoxicity of gastrointestinal drugs is essential to help weigh the benefit of their use against possible adverse effects, even if uncommon. Furthermore, as far as possible, drugs such as metoclopramide and others that can lead to tardive dyskinesias should be used for as short time as possible, with close clinical monitoring and patient education.

Stress Ulcer Prophylaxis in the New Millennium!

Clinical trials conducted in the latter part of the past millennium suggested that bleeding from gastric stress ulceration was an important cause of morbidity and mortality in intensive care unit (ICU) patients and that treatment with acid-suppressive therapy reduced the risk of clinically significant bleeding. Stress ulcer prophylaxis therefore became regarded as the standard of care in all ICU patients. However, more recent clinical trials have demonstrated that the risk of clinically significant bleeding is extremely low (about 1%) and not altered by the use of acid-suppressive therapy. Furthermore, a critical review of the “historical” clinical trials, as well as the data from experimental and more recent clinical trials, suggests that enteral feeding (gastric) is at least as effective as acid-suppressive therapy in the prevention of gastric stress ulceration and is the prophylactic measure of choice in most ICU patients.

Dose-reducing H2 receptor antagonists in the presence of low glomerular filtration rate: a systematic review of the evidence

BACKGROUND

While it is recommended that H2 receptor antagonists (H2RAs) be dose reduced in the presence of low glomerular filtration rate (GFR), in practice such adjustments often do not occur. We reviewed the evidence for this recommendation.

METHODS

We searched multiple medical reference databases for relevant cohort studies and randomized clinical trials. Studies that enrolled five or more participants with low GFR who also received at least one unadjusted dose of an H2RA, and who were compared with controls were included. Data were abstracted on study and participant characteristics and drug-related adverse effects. Pharmacokinetic measures were pooled using meta-analysis.

RESULTS

A total of 22 articles were included, comprising 19 unique cohort studies. With declining GFR, there was a significant increase in the area under the curve (AUC) and elimination half-life (t(1/2)) of the serum drug concentration of H2RAs (P < 0.001). Compared with a GFR >80 ml/min/1.73 m2, drug AUC increased by 200% when the GFR was 30 ml/min/1.73 m2, and by 300% when the GFR was 20 ml/min/1.73 m2. In hospitalized patients with low GFR, reducing the interval dose of intravenous H2RA was associated with fewer adverse reactions. The gastro-protective effects of H2RAs were similar with reduced and unadjusted doses.

CONCLUSIONS

Reducing the dose of H2RAs in persons with low GFR will decrease drug expenditure and may prevent adverse events, without a change in efficacy. Quality assurance programmes, which improve deficiencies in H2RAs prescribing, appear justified.

Acid suppression in critically ill patients: what does the evidence support?

Stress-related mucosal disease is a frequent complication in critically ill patients. A wealth of evidence suggests that hypoperfusion to the upper gastrointestinal tract can lead to ulceration and is associated with increased morbidity. Management of stress ulcers depends on aggressive therapy that includes acid-suppressive agents. Proton pump inhibitors (PPIs) have gained recognition as a potentially important therapy for treatment and prevention of upper gastrointestinal bleeding in critically ill patients. Patients who present to the hospital with acute gastrointestinal bleeding benefit from potent acid inhibition. Whereas histamine2-receptor antagonists have questionable efficacy in preventing ulcer rebleeding in this patient population, PPIs are highly effective. They should be considered first-line therapy for patients undergoing endoscopic hemostasis and for those with stigmata of upper gastrointestinal bleeding.

Gastrointestinal disease control after histamine2-receptor antagonist dose modification for renal impairment in frail chronically ill elderly patients

OBJECTIVES

To determine whether histamine2-receptor antagonist (H2RA) dose modified for renal impairment affects gastrointestinal (GI) disease control.

DESIGN

Concurrent medical record review.

SETTING

One hundred forty-six nursing facilities throughout the United States.

PARTICIPANTS

Three hundred thirty-six patients aged 65 and older receiving H2RAs for GI disorders.

INTERVENTION

H2RA dose modified for renal impairment or no dose change.

MEASUREMENTS

Disease control (no H2RA dose increase for 6 months or longer, additional GI medication, hospitalizations, emergency room visits, and unscheduled physician visits for GI symptoms) was evaluated using chart review at 3, 6, 9, and 12 months in nursing home patients aged 65 and older with H2RA dose modified for decreased creatinine clearance (ClCr) according to manufacturer.

RESULTS

Three hundred thirty-six patients, mean age +/- standard deviation 85.9 +/- 7.9, with mean ClCr of 33.6 +/- 10.4 mL/min, were recommended to receive lower H2RA doses based upon estimated renal function. Patients were analyzed in two groups: H2RA dose reduced (Group 1) and dose reduction not adopted or implemented (Group 2). There was no difference in baseline characteristics (age, weight, ClCr, or starting H2RA dose and indication) between the two groups. One hundred ninety-eight patients in Group 1 were taking 195.5 +/- 71.0 mg per day of nizatidine or equivalent, compared with 183.7 +/- 66.6 mg for 138 patients in Group 2. For patients with 90 days of follow-up, the mean H2RA dose in Group 1 was 100.2 +/- 44.3 mg, compared with 187.8 +/- 69.9 for Group 2 (P <.0001) The mean decrease in daily dose for Groups 1 and 2 after 365 days were 98.9 +/- 72.9 mg and 22.2 +/- 68.2 mg, respectively (P <.0001). Except for more physician visits in Group 2, disease control was similar for all groups. Major and minor GI bleeding events were similar across both groups and over time. The 12-month mortality rate was 12.1% and 21.7% for Groups 1 and 2, respectively. This difference was statistically significant (P =.02).

CONCLUSION

The findings suggest that the dose of H2RAs may be decreased based upon renal function in frail elderly patients without compromising GI disease control.

Drug-induced cognition disorders in the elderly: incidence, prevention and management

The aetiology of cognitive impairment is multifactorial; however, drugs are an important cause of delirium and dementia. Several factors may increase the risk of drug-induced cognition disorders in the elderly including imbalances in neurotransmitters (e.g. acetylcholine), age-related alterations in pharmacokinetics and pharmacodynamics, and high levels of medication use. Nearly any drug can cause cognitive impairment in susceptible individuals; however, certain classes are more commonly implicated. Benzodiazepines, opioids, anticholinergics, and tricyclic antidepressants are probably the worst offenders. Older antihypertensive agents (reserpine, clonidine) have negative effects on cognition; however, large clinical trials in the elderly indicate that commonly used agents [e.g. thiazide diuretics, calcium antagonists (amiodipine, diltiazem), ACE inhibitors (captopril, enalapril) and beta-blockers (atenolol)] have minimal effects on cognition. Newer antidepressants such as selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors (SSRIs) and reversible inhibitors of monoamine oxidase A have not been shown to have negative effects on cognition. Although some drugs have shown low risk for causing cognition disorders in research studies, risk may be increased in frail older adults taking several medications and each case should be reviewed carefully. Identification of drug-induced cognitive impairment is crucial to early detection and resolution of symptoms. Preventive strategies directed at avoiding high risk medications when possible, appropriately adjusting doses based on age-related changes and close follow-up may prevent these conditions.

Drug-induced cognitive impairment in the elderly

Elderly people are more likely than younger patients to develop cognitive impairment as a result of taking medications. This reflects age- and disease-associated changes in brain neurochemistry and drug handling. Delirium (acute confusional state) is the cognitive disturbance most clearly associated with drug toxicity, but dementia has also been reported. The aetiology of cognitive impairment is commonly multifactorial, and it may be difficult to firmly establish a causal role for an individual medication. In studies of elderly hospital patients, drugs have been reported as the cause of delirium in 11 to 30% of cases. Medication toxicity occurs in 2 to 12% of patients presenting with suspected dementia. In some cases CNS toxicity occurs in a dose-dependent manner, often as a result of interference with neurotransmitter function. Drug-induced delirium can also occur as an idiosyncratic complication. Finally, delirium may occur secondary to iatrogenic complications of drug use. Almost any drug can cause delirium, especially in a vulnerable patient. Impaired cholinergic neurotransmission has been implicated in the pathogenesis of delirium and of Alzheimer's disease. Anticholinergic medications are important causes of acute and chronic confusional states. Nevertheless, polypharmacy with anticholinergic compounds is common, especially in nursing home residents. Recent studies have suggested that the total burden of anticholinergic drugs may determine development of delirium rather than any single agent. Also, anticholinergic effects have been identified in many drugs other than those classically thought of as having major anticholinergic effects. Psychoactive drugs are important causes of delirium. Narcotic agents are among the most important causes of delirium in postoperative patients. Long-acting benzodiazepines are the commonest drugs to cause or exacerbate dementia. Delirium was a major complication of treatment with tricyclic antidepressants but seems less common with newer agents. Anticonvulsants can cause delirium and dementia. Drug-induced confusion with nonpsychoactive drugs is often idiosyncratic in nature, and the diagnosis is easily missed unless clinicians maintain a high index of suspicion. Histamine H2 receptor antagonists, cardiac medications such as digoxin and beta-blockers, corticosteroids, non-steroidal anti-inflammatory agents and antibiotics can all cause acute, and, less commonly, chronic confusion. Drug-induced confusion can be prevented by avoiding polypharmacy and adhering to the saying 'start low and go slow'. Special care is needed when prescribing for people with cognitive impairment. Early diagnosis of drug-induced confusion, and withdrawal of the offending agent or agents is essential.

Effect of renal or hepatic dysfunction on neurotoxic convulsion induced by ranitidine in mice

We investigated the effect of acute renal and hepatic dysfunction on the neurotoxicity of ranitidine, a histamine H2 receptor antagonist. Experimental acute hepatic and renal dysfunction in mice were produced by i.p. injection of uranyl nitrate (UN) and carbon tetrachloride (CT), respectively. Ranitidine was then constantly infused into the tail vein until the onset of clonic convulsion. When compared to control mice, UN treated mice had a significantly shorter onset time to clonic convulsion, lower total dose and higher plasma concentration at initiation of clonic convulsion. In contrast, the convulsive threshold concentration in the brain of UN treated mice was not significantly different from that of control mice. In CT treated mice, all pharmacokinetic and pharmacodynamic data described above were not significantly different from those of the control mice. No significant difference in the brain/plasma concentration ratio was observed between both disease models and the corresponding control mice. Finally, the effect of UN and CT treatment on the convulsive potency after intracerebral (i.c.) administration of ranitidine was investigated in mice. Potentiation of the intrinsic neurotoxic sensitivity to ranitidine could not be demonstrated for mice with renal or hepatic dysfunction. From these findings, we conclude that renal dysfunction is a risk factor for ranitidine neurotoxicity, and this increased risk results from increase in the drug concentration in plasma and brain as a result of impaired renal excretion. No apparent effect of acute hepatic dysfunction was observed on both the pharmacokinetic and pharmacodynamic behavior of the drug.

The relationship between comprehensive functional assessment and optimal pharmacotherapy in the older patient

Older patients hospitalized for treatment of an acute medical illness will have improved outcomes when approached in a comprehensive fashion focusing on the physical, social, and emotional aspects of life. When used by an interdisciplinary team, comprehensive functional assessment can address social, biomedical, nutrition, continence, mobility, pharmacotherapy, and psychological issues to enhance patient care. Although the appropriate use of medications is often cited as an important part of medical care for the older person, it has not been defined for this group of patients. This article outlines steps pharmacists can take to achieve optimal pharmacotherapy in older patients. Prior to attending a team conference, the pharmacist should interview the patient and review the chart. During the team conference, a comprehensive patient database will be generated that allows medications to be linked to diagnoses. To aid in selecting appropriate medications, the potential for drug-induced functional impairment of mobility, continence, and mental state is reviewed. Recommendations for therapy and establishment of therapeutic endpoints will conclude the patient conference. The pharmacist can contribute much in the process of comprehensive functional assessment and to the goal of achieving optimal pharmacotherapy in older patients.

[Digestive stress hemorrhage. Physiopathology and prevention]

Lesions of the gastroduodenal mucosa are seen very early on in virtually 100% of patients suffering from organ failure. Bleeding, even if it is only occult, defines acute stress-induced gastrointestinal tract bleeding (SGIB). The rates of SGIB vary according to the inclusion criteria: 13 to 100% microscopic SGIB, 2.3 to 9.5% haemorrhage with blood transfusion and/or shock. Gastrointestinal bleeding does not really influence the death rate of patients with SGIB (0 to 5% increase). Damage to the gastric mucosa may be due to an intraluminal aggression, and/or decreased mucosal and mural defence mechanisms. H+ ions and bile salts are mostly responsible for the former. Physiological quantities of H+ ions may be sufficient, as their abnormal diffusion into the gastric mucosa will reduce the mucosal pH (pHm), which is itself sensitive to microcirculatory modifications and systemic acidosis. There is a good correlation between bleeding and pHm. Bile salts are involved because of the usual increase in frequency and volume of gastric biliary reflux due to stress. Surfactant, mucosal alkaline layer and the microcirculation are all involved in gastric protection. The PGE2 synthetized by the gastric mucosa have a favourable influence on these 3 mechanisms. Changes in microcirculation and hypoxia are the predominant factors involved in stress-induced mucosal damage. The prevention of SGIB relies on the treatment of risk factors, a reduction of intraluminal aggression, and the support and/or stimulation of gastric defence mechanisms. Antacids and anti-H2 drugs aim to neutralize most of the H+ ions, being more efficient than placebo in increasing gastric pH greater than 4, although anti-H2 agents are responsible of a greater number of failures. The non-homogenous character of the patient groups studied and the diagnostic methods, as well as the increasing lack of placebo groups in the published studies make the interpretation of the results rather risky. Antacids and anti-H2 drugs are more efficient than placebo, and equally efficient, in preventing overt SGIB. Efficiency is increased by giving anti-H2 drugs continuously, and antacids hourly. Other agents are thought to protect mucosal cells, probably increasing mucosal defences. Amongst them are the prostaglandins, the most interesting of which are still being investigated, and sucralfate. The latter molecule is as efficient as antacids and anti-H2 drugs, and does not alter gastric pH, so reducing the number of nosocomial pneumonias. Its reduced cost and easy administration make it, at the present time, the treatment of choice of SGIB. The few rare contraindications of sucralfate will justify the infusion of anti-H2 drugs in those patients at risk.

Penetration of roxatidine into the cerebrospinal fluid

Central nervous system side effects are occasionally associated with the administration of H2-receptor antagonists. There seems to be a direct correlation between the occurrence of side effects such as mental confusion and the drug concentration in the cerebrospinal fluid. In animal experiments the new H2-blocker roxatidine did not cross the blood-brain barrier. We therefore investigated the penetration of roxatidine into human cerebrospinal fluid (CSF). Nine healthy subjects scheduled for elective spinal anesthesia were premedicated with 150 mg roxatidine orally. Blood samples were taken at 30-min intervals for up to 6 h. A 2-ml CSF sample was taken from each patient at the time of spinal puncture. Small amounts of roxatidine were detectable in the CSF, the CSF to plasma ratio ranging from 0 to 0.89.

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.

A clinical pharmacy-oriented drug surveillance network: I. Program description

The limitations of the new drug development process, particularly in regard to the evaluation of drug safety, have resulted in a need for monitoring drug experience in the postmarketing period. Although a number of systems have evolved to perform postmarketing surveillance, each has important limitations, suggesting the need for an alternative, innovative approach that would permit rapid identification of potential problems and support studies of multiple drugs and/or disease states in patient populations large enough to permit identification of uncommon, but significant adverse drug reactions. This has led to the organization of a nationwide network of clinical pharmacists with an active role in patient-care monitoring to collect information regarding the safety and effectiveness of drugs. At the present time there are 383 clinical pharmacists from all 50 states participating in the network. These individuals collectively monitor more than 150,000 inpatient hospital beds, more than 40,000 nursing home beds, and more than 800,000 ambulatory care visits per year. Participating clinical pharmacists, using standardized data collection forms, perform concurrent monitoring of drug-therapy outcome in targeted patient populations. Careful analysis and interpretation of this information will yield clinically relevant information regarding the outcome of drug therapy under actual clinical conditions.

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)

Acute stress ulceration

Stress ulceration is usually considered a mucosal abnormality of the oesophagus, stomach or duodenum in the critically ill. It is found to a varying degree in all such patients. Only about one-quarter of lesions are associated with blood loss and less than 5% need resuscitation and treatment. However, because treatment of established bleeding is unsatisfactory, and associated with a high mortality, prophylactic measures are usually employed. These include optimising gastric mucosal blood flow and oxygen delivery, correcting coagulation abnormalities and treating underlying infection. Enteral feeding should also be employed whenever possible. Other prophylactic measures currently used involve raising gastric pH above 4, with either antacids or H2 receptor antagonists. This is best achieved by measuring the gastric pH hourly and titrating it against an appropriate dose of either type of drug or a combination of both. Newer drugs, such as omeprazole, sucralfate and prostaglandins, are proving very successful in the treatment and prevention of gastric and duodenal ulcers and may prove even more effective than currently available agents.

The pharmacokinetics of cimetidine and metabolites in a neonate

Limited pharmacokinetic data have been reported concerning the use of cimetidine in the neonate for the management of gastrointestinal hemorrhage. After receiving cimetidine at a dose of 10 mg/kg/d in a full-term infant, the steady-state peak and four-hour concentrations were 3.5 and 1.8 micrograms/ml, respectively. A mean half-life of 3.6 h for cimetidine and 2.2 h for cimetidine sulfoxide were determined. The cimetidine half-life was prolonged, and the total body clearance decreased as compared with values reported in critically ill children and adults.

The intensive care unit syndrome: causes, treatment, and prevention

The psychological assessment and management of the critically ill patient is often overlooked as a part of the patient care plan. The intensive care unit (ICU) syndrome is a type of organic brain syndrome manifested by a variety of psychological reactions, including fear, anxiety, depression, hallucinations, and delirium. Causes, treatment modalities, and a multidisciplinary approach to preventing the ICU syndrome are presented. Causative factors that should be assessed in the psychological evaluation of ICU patients include: (1) preadmission history; (2) past ability to adapt to stress; (3) past and current medications; (4) current clinical status; and (5) environmental factors. The treatment of the ICU syndrome includes: (1) the correction or elimination of causative factors; (2) the appropriate choice, dose, and route of administration of anxiolytic and antipsychotic agents; (3) reduction or elimination of sources of environmental stress; and (4) frequent patient and family communication. Finally, the prevention of the ICU syndrome through the involvement of physicians, nurses, and pharmacists is stressed.

Prospective evaluation of the risk of upper gastrointestinal bleeding after admission to a medical intensive care unit

One hundred seventy-four patients (179 admissions) were prospectively evaluated for the subsequent occurrence of upper gastrointestinal ("stress") bleeding after admission to a medical/respiratory intensive care unit. Evidence for either overt or occult gastrointestinal bleeding developed in 25 (14 percent). The group of bleeders had a higher mortality (64 percent versus 9 percent), duration of intensive care unit stay (median 14.2 versus 4.2 days), number of patients requiring mechanical ventilatory support (84 percent versus 26 percent), and duration of such support for those who required it (median 9.5 versus 4.2 days) than the group who did not bleed. In three patients, death was related to bleeding. Upon patients' admission to the intensive care unit, diagnoses of an acute respiratory illness (but not specifically chronic obstructive pulmonary disease), a malignancy, or sepsis were more common among those who subsequently bled. Of factors tested, a coagulopathy and the need for mechanical ventilation were most strongly associated with the risk of bleeding. Other factors did not add to the risk once these two were taken into account. Among patients receiving mechanical ventilation, the risk of overt bleeding was particularly low for those who required such support for less than five days (only 3 percent). It is concluded that (1) significant upper gastrointestinal bleeding occurring after medical intensive care unit admission is an uncommon event, and (2) prolonged mechanical ventilation and/or the presence of a coagulopathy are the most potent risk factors. Medical patients with either of the latter conditions are most likely to benefit from prophylaxis regimens against "stress"-induced upper gastrointestinal bleeding.

[Severe confusion following a theophylline-cimetidine combination]

Cimetidine and theophylline were given together to a 67 year old chronic bronchitic post-operatively: the patient became very confused, shook of all his limbs, vomited, and presented a tachycardia. The greater than normal blood levels of theophylline (27.8 mg . 1(-1) confirmed its involvement in this clinical state. But, as there was no real overdose, the simultaneous administration of cimetidine was probably responsible for inducing this state. Three days after stopping this treatment, the disorder had completely disappeared.