Elevated Gastric pH Research Articles

Sodium bicarbonate as a single dose antacid in obstetric anaesthesia

Gastric pH and volumes were measured in 84 women who had general anaesthesia for emergency Caesarean section. Forty-eight received only 20 ml 8.4% sodium bicarbonate immediately before induction of anaesthesia and 36 ranitidine 150 mg 6-hourly during labour in combination with NaHCO3. Gastric pH was less than 2.5 in four women who received only bicarbonate. All aspirates from the ranitidine plus bicarbonate group had a pH greater than 2.5. Mean volumes of gastric content aspirated were 87 (SD 87.4) and 60 (SD 46.3) ml for the bicarbonate alone and bicarbonate plus ranitidine series respectively. These differences were not significant. Twenty millilitres of 8.4% NaHCO3 cannot be recommended as a single dose antacid for emergency Caesarean section. Ranitidine plus bicarbonate is considered a reliable antacid regimen to ensure elevation of gastric pH to safe levels.

Comparison of the effects of famotidine and ranitidine on gastric secretion in patients undergoing elective surgery

A randomised double-blind comparison of oral famotidine and ranitidine given 2 hours before induction, on gastric secretion (volume and pH) was carried out on 93 patients undergoing elective surgery. Gastric contents were aspirated immediately after tracheal intubation. Famotidine significantly reduced the gastric volume, compared with the other groups, including ranitidine. Both famotidine and ranitidine significantly elevated gastric pH towards neutral, compared with the other groups. There was no significant difference between ranitidine and famotidine in respect of the pH. The patients premedicated with famotidine and ranitidine were well protected against Mendelson's syndrome, whereas 38% of patients from the other groups remained at risk.

Ibuprofen Release is Sustained Following Gastric pH Elevation

Ibuprofen Release is Sustained Following Gastric pH Elevation

Investigation on N-nitroso compounds in patients with chronic gastritis

By GC-TEA and HPLC-TEA methods, NNO analysis in fasting gastric juice of 152 patients with chronic gastritis in high- and low-risk areas of stomach cancer was carried out. The only volatile N-nitrosamine detected in these samples was NDMA. Besides, a photolabile unknown non-volatile N-nitrosamine which responded only on HPLC-TEA was detected directly. Its concentration (geometric mean) was 9.4 times higher than that of NDMA. The total positive rate of these two NNOs was positively correlated with the adjusted mortality rate of stomach cancer in males in studied areas, and the highest concentration of “total” NNO was observed in the pH range of 1.5–2.5 and showed a significant negative correlation with the intragastric nitrite. The combined positive rate of NDMA and unknown nonvolatile N-nitrosamine in the superficial gastritis was significantly higher than that in atrophic. The phenomenon that NNO content increases with the elevation of gastric pH and nitrite in patients with atrophic gastritis was not seen.

Effect of pH on the In Vitro Dissolution and In Vivo Absorption of Controlled-Release Theophylline in Dogs

Dogs were used to examine the effect of elevated gastric pH on the absorption of controlled-released theophylline dosage forms with pH-dependent dissolution. In vitro studies showed that a controlled-release theophylline tablet dissolved more rapidly if it was initially exposed to an acidic media. In contrast, a controlled-release theophylline beaded capsule was slightly more rapidly dissolved in the absence of an initial exposure to an acidic media. Gastric pH was increased from 0.5-2.5 to 4.5-7.0 in four dogs by using 150-mg ranitidine HCI tablets, administered every 3 h, to induce an achlorhydric condition. Gastric pH was monitored using a Heidelberg capsule. Ranitidine was shown to have no apparent effect on the absorption or clearance of theophylline administered to the dogs as an oral liquid. The mean area under the concentration-time curve to infinity (AUCinf) for the controlled-release theophylline tablet was 21% greater (p < 0.05) when administered to the four dogs without ranitidine treatment, compared with that following dosing with ranitidine. In contrast, the controlled-release beaded capsule exhibited a 10% greater AUCinf when ranitidine was given concomitantly. In general, ranitidine-induced changes in the in vivo absorption rate parameters for both dosage forms were opposite to those predicted from the in vitro dissolution rates. The results of this study demonstrated that the extent of theophylline absorption from controlled-release dosage forms, in control dogs and dogs with ranitidine-induced achlorhydria, corresponds to the pH-dependent in vitro dissolution properties of the products.

Comparative efficacy of parenteral histamine (H 2)-antagonists in acid suppression for the prevention of stress ulceration

Stress-related mucosal damage is related to a high intraluminal hydrogen ion concentration, a low intramural pH value, and a breakdown of the gastric mucosal barrier. Because the presence of gastric acid is required for stress-related mucosal damage to occur, therapy aimed at increasing intraluminal pH values has often been used as prophylaxis against complications. The amount of acid suppression required for adequate prophylaxis of gastrointestinal bleeding from stress-related mucosal damage has not been determined, but many investigators use a target gastric pH level of 3.5 to 4.0. When intravenous histamine (H 2)-receptor antagonists are given in bolus dosing regimens to critically ill patients, fluctuations in gastric pH values are often observed, as might be expected. However, recent studies with primed continuous infusion of cimetidine in critically ill patients have demonstrated that consistent elevation of gastric pH to 4.0 may be attained with this regimen. Studies with continuous infusions of ranitidine are less conclusive; little information is available on famotidine.

Elevation of gastric pH heals peptic oesophagitis ‐ A role for omeprazole

AbstractThe aim of this study was to investigate the hypothesis that the prolonged and substantial elevation of gastric pH which can be achieved with the antisecretory agent omeprazole will result in healing of peptic oesophagitis. Eight patients with erosive or ulcerative peptic oesophagitis were treated with omeprazole (30 mg daily) for 8 weeks. Complete healing occurred in seven patients after 8 weeks of omeprazole therapy. Only a small area of residual ulceration persisted in one unhealed patient. Heartburn resolved within the first 2 weeks of therapy in all but one patient. Specific food intolerances also were eliminated in most cases. Post‐prandial oesophageal pH monitoring during omeprazole administration showed abolition of acid reflux episodes (pH &lt; 4). This effect appeared to be due solely to the antisecretory effect of omeprazole, since motility measurements demonstrated a continued high frequency of reflux while concurrent gastric pH monitoring showed sustained elevation of gastric pH above 4. These results support the hypothesis that a prolonged and potent inhibition of gastric acid secretion renders refluxed gastric juice sufficiently innocuous to allow healing of severe peptic oesophagitis.

Oral Ranitidine in Labor

Comment: These reviewers question the wisdom of prophylactic antacids or H2 blockers to all women in labor. We do not question the increased risk of the parturient to the catastrophe of pulmonary aspiration of both acid and particulate material. However the danger of particulate aspiration may be increased by the use of oral antacid in suspension and is not decreased by H2 blockers which also interfere with hepatic metabolism and slow breakdown of amide type local anesthetics.1 The vast majority of women in labor today do not require general anesthesia and need not have consciousness and upper airway reflexes sufficiently obtunded by narcotics and sedatives that prevent protection of the airway should vomiting occur. Properly administered conduction analgesia, in which hypotension and local anesthetic toxicity are avoided, do not depress the protective upper airway reflexes. In an emergency procedure requiring general anesthesia, rapid alkalinization of gastric contents is reliably achieved by oral administration of 30 ml 0.3 M sodium citrate or similar soluble antacids (e.g., Bicitra, Alka Seltzer, Gold). Why then do many insist on increasing the workload of labor floor nurses and making mothers uncomfortable by giving them unpleasant and often nauseating mixtures of particulate antacids that, if aspirated, may increase pulmonary problems.2 The administration of expensive systemic H2 blockers that have rare but potential serious side effects is also questionable. Should not the above preparations be reserved for obstetric patients undergoing elective general anesthesia or having symptoms of gastric reflux? Would it not be more prudent to invest the time and money spent on these questionable prophylactic methods in the assurance that the parturient has adequate monitoring throughout labor and delivery and in providing methods of pain relief that do not compromise the upper airway reflexes? H2 blockers may have a role in prophylaxis or treatment when elective general anesthesia is to be used, or if the patient suffers gastric reflux. In the rare incidence when emergency general anesthesia is required, the use of a soluble antacid and an H2 blocker will be effective in immediately elevating and maintaining the gastric pH above the critical level of 2.5 to 3.0. We suggest that the limited benefits derived from routine prophylactic elevation of gastric pH are more than offset by their costs in money, time, maternal discomfort, and maternal risk.

Effect of antacids on oral absorption of rifampicin

A study has been carried out on the effect of concomitant administration of aluminium hydroxide gel (15 ml), magnesium trisilicate (2 g) and sodium bicarbonate (2 g) on the bioavailability of rifampicin in healthy male volunteers. The antibiotic bioavailability, as measured by a urinary excretion method over a period of 24 h, was significantly reduced by the 3 antacids following the sequence: magnesium trisilicate > aluminium hydroxide > sodium bicarbonate. Doubling the dose of either magnesium trisilicate or aluminium hydroxide gel produced no further reduction. The results obtained are interpreted in the light of the effect of gastric pH elevation on the solubility and dissolution rate of rifampicin, chelation of the drug with aluminium ions and binding by magnesium trisilicate.

Tetracycline absorption in elderly patients with achlorhydria.

Five elderly achlorhydric patients and five controls took 250 mg tetracycline as a capsule or as an oral solution. Venous blood samples drawn during the 12-hr period following administration and urine collected for 72 hr post-dosing were assayed fluorometrically for tetracycline. There were no differences between the two groups in either rate or extent of tetracycline absorption. The mean apparent first-order rate constant (ka) for absorption of drug from capsules was 0.58 +/- 0.17 hr-1 for patients and 0.65 +/- 0.21 hr-1 for controls. The mean extent of absorption for capsule dosage forms relative to an oral solution was 1.0 +/- 0.20 for patients and 1.0 +/- 0.24 for controls. Concurrent administration of 2 gm of sodium bicarbonate to 2 of the normal subjects resulted in no impairment of either the rate or extent of tetracycline absorption from capsules, suggesting that the effect of elevated gastric pH on tetracycline bioavailability may relate to formulation.

Changes in the oral absorption characteristics in man of dipotassium clorazepate at normal and elevated gastric pH.

The in vivorate of biodegradation of dipotassium clorazepate to N-desmethyldiazepam in humans was shown to decrease with an increase in gastric pH. When gastric pH was maintained above 6 for 2 hr with sodium bicarbonate, the bioavailability of intact clorazepate, as determined by evaluating its conversion and absorption as N-desmethyldiazepam, was reduced from 5% to 75% when compared in the same subject with gastric pH less than 3. The corresponding N-desmethyldiazepam blood level maxima occurred later in time and were only 14–46% of the levels achieved from an acidic stomach. These findings indicate that the pH of the stomach can influence the absorption of dipotassium clorazepate.

Observations on the stomach pH in pigs following massive infections with Hyostrongylus rubidus larvae

Clinical symptoms of inappetence and vomiting were observed in minimal disease (M.D.) growing pigs infected with 500 000 infective larvae of Hyostrongylus rubidus. Elevated gastric pH values, a mean of pH 6 compared with a mean control value of pH 4·5 in one experiment and a maximum pH value of 7·5, compared with a maximum preinfection value of 5 in a second experiment, were observed in the infected pigs when clinical signs were evident. Radiotelemetry capsules which were successfully used to monitor gastric pH in pigs, provide a continuous record of gastric pH and in this respect are superior to the methods currently used to measure gastric pH since wide variations from hour to hour are normally seen and the pH recorded therefore depends on the time at which samples are withdrawn.

Effects of Buffered and Unbuffered Acetylsalicylic Acid upon the Gastric Acidity of Normal Human Subjects

Acetylsalicylic acid in tablet form, in buffered tablets, and effervescent buffered solution, has been compared with regard to the effect upon gastric acidity and pH. Aspirin and buffered aspirin have little or no effect as compared to controls, whereas the effervescent preparation reduces free acidity and raises gastric pH significantly for 30 minutes. This elevation of gastric pH correlates well with the more rapid absorption and reduced gastric irritation which has been reported for various soluble and buffered forms of salicylates.

A New Highly Reactive Aluminum Hydroxide Complex for Gastric Hyperacidity II : In Vitro Buffering Range and Duration of Action

A new, highly reactive polymeric aluminum hydroxide hexitol complex has been developed and incorporated into an antacid tablet. When tested in comparison with a liquid aluminum hydroxide gel of proved clinical effectiveness, the new Creamalin tablet has an almost identical duration of action and buffering range. When tested in comparison with ten leading aluminum hydroxide tablets using an in vitro method recognized as having good correlation with in vivo experience, the new Creamalin tablet exerts its buffering activity in the optimal range for much longer periods than the others. Effective antacid therapy has been defined as the elevation of gastric pH to between 3.0 and 5.0 with the optimum being 3.5 to 4.5. The new Creamalin tablet should provide a highly effective and convenient antacid for poising gastric hyperacidity within this optimal range.