Prophylaxis of stress ulcers: antacid titration vs. histamine2-receptor blockade

The Influence of pH Control on the Prevention and Management of Gastrointestinal Bleeding

Gastrointestinal bleeding from stress-related mucosal damage (SRMD) is caused by a breakdown in the pro cesses that normally protect the gastric mucosa from the corrosive effects of gastric acid and the proteolytic enzyme pepsin. Prostaglandins stimulate some of these protective factors, which include mucus secretion, bi carbonate secretion, rapid cellular repair and rapid blood flow. Acid and pepsin inhibit blood clotting in the stomach by inhibiting platelet aggregation and the func tion of all of the blood clotting factors. The inhibition of blood clotting in the stomach exacerbates bleeding caused by ulcers in the stomach and duodenum. Hence, treatment that will raise intragastric pH (lower acid con centration) should be effective in preventing gastric bleeding from SRMD. Patients in intensive care units are at high risk of developing upper gastrointestinal bleed ing from SRMD. It is easier to prevent SRMD bleeding than to treat it once it starts. Hence, patients in intensive care units should be treated prophylactically to prevent bleeding. Controlled trials and clinical experience indi cate that both antacids and H2 blockers in doses high enough to raise the intragastric pH above 4 are effective forms of prophylaxis. Intravenously administered H2 blockers are more convenient to administer and have fewer side effects than the large doses of antacid re quired to maintain the intragastric pH above 4.

Pharmacological Approach to the Prevention and Treatment of Stress Ulcers

The mortality associated with bleeding stress ulcers in patients in intensive care units exceeds 50%. Iden tification of patients at risk and use of early and effec tive prophylaxis are necessary in the management of patients in intensive care units. The use of antacids is inconvenient, expensive, and associated with electro lyte disturbances and erratic pH control. H2-receptor antagonists are the preferred agents for stress ulcer pro phylaxis because of their proven efficacy, safety, and ease of administration. Adjunct therapy with cyto protective agents may be useful in patients with com promised mucosal defences.

Stress-related mucosal disease: risk factors and prophylactic therapy

BACKGROUND

The term stress-related mucosal disease (SRMD) represents a continuum of conditions ranging from stress-related injury (superficial mucosal damage) to stress ulcers (focal deep mucosal damage). Caused by mucosal ischemia, SRMD is most commonly seen in critically ill patients in the intensive care unit (ICU). Prophylaxis of stress ulcers may reduce major bleeding but has not yet been shown to improve survival.

OBJECTIVES

This article reviews currently available agents for the prophylaxis of SRMD and discusses their uses and potential adverse effects.

METHODS

Relevant articles in the English-language literature were identified through a MEDLINE search (1968-2003) using the key words stress-related mucosal disease, stress-related injury, ulcer, prophylaxis, intensive care unit, and upper gastrointestinal bleeding.

RESULTS

The most widely used drugs for stress-related injury are the intravenous histamine(2)-receptor antagonists. These drugs raise gastric pH but are associated with the development of tolerance and possible drug interactions and neurologic manifestations. Sucralfate, which can be administered by the nasogastric route, can protect the gastric mucosa without raising pH, but may decrease the absorption of concomitantly administered oral medications. The prostaglandin misoprostol has not been shown to be of benefit in the prophylaxis of SRMD. Antacids lower the risk of gastrointestinal bleeding, but large volumes of antacids are required and treatment is labor intensive. Proton pump inhibitors (PPIs) are the most potent acid-suppressive pharmacologic agents available. Esomeprazole, lansoprazole, omeprazole, pantoprazole, and rabeprazole substantially raise gastric pH for up to 24 hours after a single dose. The availability of an intravenous formulation of pantoprazole may help improve the treatment of SRMD in ICU patients, particularly those receiving mechanical ventilation. Tolerance does not develop, and few adverse effects have been reported.

CONCLUSIONS

Recent studies of PPIs have shown promising results in high-risk patients, making this class of drugs an option for the prophylaxis of SRMD.

Evidence-based analysis: postoperative gastric bleeding: etiology and prevention

Although the incidence of stomach hemorrhage is declining, stress-related gastric bleeding remains an important source of morbidity and mortality in cancer patients undergoing major surgical procedures to remove tumor. Prevention of stress-related bleeding is desirable; however, the optimal use of drugs to prevent gastric bleeding is unclear. Prophylaxis is recommended for surgical patients who require prolonged mechanical ventilation or have a coaguloathy. Histamine-2 receptor antagonists and sucralfate will reduce the likelihood of clinically important gastric-bleeding. Sucralfate appears to be less effective than H-2 blockers, but it is associated with fewer side effects such as nosocomial pneumonia. Preliminary studies show that proton pump inhibitors are most effective, have few side effects, but are most expensive. Intravenous proton pump inhibitors may be the drugs of choice for stress ulcer prophylaxis (SUP) in high-risk patients.

Acute gastrointestinal bleeding in the intensive care unit. The gastroenterologist's perspective

Although SRES-associated hemorrhage previously constituted a significant cause of bleeding in the ICU, improvements in ICU management and the institution of prophylactic measures in high-risk patients have significantly reduced SRES-associated hemorrhage since the 1980s. Antacids, H2-receptor antagonists, and sucralfate have been shown to be effective in preventing clinically significant bleeding resulting from SRES, particularly when the intragastric pH is maintained at greater than 4. A selective approach should be adopted in SRES prophylaxis: Patients on mechanical ventilation, with coagulopathy, or with two of the other known risk factors should receive prophylaxis. Although the drug of choice depends to some extent on local preferences, an H2-receptor antagonist by continuous intravenous infusion may represent the best option. No pharmacologic therapy is of proven value once hemorrhage begins, but the current interventional techniques are effective in controlling hemorrhage. Gastrointestinal bleeding from NOMV has become less common with improvements in the hemodynamic monitoring of critically ill patients, but this disease must always be considered when lower gastrointestinal bleeding occurs in the context of relative hypoperfusion. For SRES and NOMV, treatment of the underlying disease or diseases is the optimal route to prevention.

Comparison of the effect of intermittent administration and continuous infusion of famotidine on gastric pH in critically ill patients: results of a prospective, randomized, crossover study

OBJECTIVES

To compare the effects of intermittent intravenous administration and continuous intravenous infusion of famotidine on gastric pH in critically ill patients.

DESIGN

A prospective, randomized, crossover study of continuous infusion and bolus administration of famotidine in critically ill patients.

SETTING

A 14-bed medical intensive care unit (ICU) of a 500-bed county hospital.

PATIENTS

Medical ICU patients requiring stress ulcer prophylaxis.

INTERVENTIONS

Patients were randomized to receive an equivalent dose of famotidine by continuous infusion or intravenous bolus for 24 hrs, and then were crossed over to the other arm of the study.

MEASUREMENTS AND MAIN RESULTS

Critically ill patients who met the inclusion criteria were randomly assigned to receive famotidine 20 mg i.v. over 10 mins, every 12 hrs or a continuous infusion of 1.7 mg/hr for 24 hrs. After a 16-hr washout period, patients crossed over to the other arm of the study. Gastric pH was monitored continuously for 24 hrs. A total of 710 gastric pH measurements were obtained for each phase of the study. The mean area under the pH-time curve for a 24-hr period was higher for continuous infusion than bolus administration (p = .05). Continuous infusion of famotidine maintained a gastric pH of > or = 4 over a longer time period than bolus administration (20.8 hrs vs. 12.6 hrs, respectively; p < .01). Onset of therapeutic gastric pH for continuous infusion was slightly delayed as compared with bolus administration.

CONCLUSIONS

Continuous infusion of famotidine is more effective than an equivalent dose given by intermittent bolus in maintaining the appropriate gastric pH necessary for prevention of stress ulceration. Delayed onset of effect may warrant a priming dose when famotidine is given by continuous infusion.

Assessment of 24-hour gastric pH measurements in trauma patients receiving intravenous famotidine by intermittent bolus versus continuous infusion administration

OBJECTIVE

To compare the effects of intermittent bolus versus continuous infusion intravenous famotidine on gastric pH in critically ill trauma patients.

DESIGN

Twenty patients were randomized to receive famotidine by intermittent bolus or continuous infusion for 24 hours. Patients fasted during the study period. Hourly gastric pH measurements were made using an indwelling sensor/sump tube.

SETTING

The study was conducted in a university teaching hospital.

PARTICIPANTS

Adult patients admitted to the neurosurgical or surgical/trauma intensive care unit within 72 hours of traumatic injury were enrolled in the study if they had two consecutive hourly gastric pH readings of < 4 without receiving antacids, sucralfate, or histamine2-antagonists.

MAIN OUTCOME MEASURES

Groups were compared with regard to (1) total dose of famotidine received/24 hours, and (2) number of dosage changes required to maintain a gastric pH value of > or = 4.

RESULTS

The median dose of famotidine required to maintain a gastric pH > or = 4 was 50 mg/24 h (25th-75th percentiles = 40-55 mg) in the intermittent bolus group compared with 42 mg/24 h (25th-75th percentiles = 42-52 mg) in the continuous infusion group (p = 0.9577). A dosage increase was required by 5 of 8 patients (62 percent) receiving intermittent bolus therapy, whereas only 2 of 8 patients (25 percent) in the continuous infusion group required a dosage adjustment (p = 0.315, power = 0.318).

CONCLUSIONS

Intravenous famotidine (40-50 mg/d) effectively controlled gastric pH in critically ill trauma patients. Patients treated with intermittent bolus therapy required slightly more drug and more frequent dosage adjustments to achieve a gastric pH > or = 4. These differences did not reach statistical significance.

Stability of famotidine in minibags refrigerated and/or frozen in total parenteral nutrition solutions

The use of histamine2-receptor antagonists could be beneficial in critically ill patients for protection against stress-induced gastrointestinal bleeding. Famotidine, similar to cimetidine and ranitidine, is stable when mixed in dextrose 5% injection and NaC1 0.9% injection at a concentration of 200 micrograms/mL and stored in polyvinyl chloride bags at 4 degrees C for 14 days or when frozen for 28 days and subsequently refrigerated for 14 days. Furthermore, famotidine, also like cimetidine and ranitidine, is stable when added to most common total parenteral nutrition (TPN) solutions. Famotidine in concentrations of 20 mg/L and 40 mg/L is stable in crystalline amino acid solutions (20 g/L and 42.5 g/L) when refrigerated for 24 hours, then held at room temperature for 24 hours, at room temperature for 48 hours, or refrigerated for seven days. The concentration of amino acids in the TPN solutions containing 42.5 g/L also is not affected by the addition of famotidine 40 mg/L when stored under conditions similar to those stated above for 48 hours. TPN solutions remain clear and free of turbidity.