Magnesium Trisilicate Mixture Research Articles

Correlation of the physical properties of some commercial brands of magnesium trisilicate mixture with their In-vitro antacid properties

Correlation of the physical properties of some commercial brands of magnesium trisilicate mixture with their <i>In-vitro</i> antacid properties

Solution calorimetry as a tool to study the neutralising capacity of magnesium trisilicate mixture BP and its components

Magnesium trisilicate mixture BP, a liquid antacid, contains three active components; magnesium trisilicate BP (MT) (5% (w/v)), light magnesium carbonate BP (LMC) (5% (w/v)) and sodium bicarbonate BP (SB) (5% (w/v)). The role of each component in the mixture is not well understood although each contributes to the overall acid neutralising capacity (ANC) of the product, the standard measure by which antacid performance is rated. Previous work has suggested that the inclusion of magnesium trisilicate BP in the mixture is unwarranted [Int. J. Pharm., 29 (1986) 253], because of its extremely slow reaction with hydrochloric acid. In light of these observations, there is a need to study the basic mechanisms of neutralisation of the components of the mixture. Since the heat change associated with simple mono-protic acid–base neutralisation is approximately −57 kJ mol −1 [Chemistry Data Book, John Murray, London, 1982], calorimetry may be used to study the reactions. In this work, the relative contributions to the ANC of the product of each component were measured using solution calorimetry. It was found that light magnesium carbonate BP contributed most to the overall ANC of the product, sodium bicarbonate BP the least. Magnesium trisilicate BP was found to neutralise acid over an extended time period, and contributed most to the duration of action of the dose. Moreover, it appears that light magnesium carbonate BP and magnesium trisilicate BP in combination exhibit a greater than expected ANC, showing positive synergy.

Acid aspiration prophylaxis in Australian obstetric hospitals--a survey.

During 1987 a confidential survey of all hospitals in Australia providing obstetric services was undertaken to determine the antacid medications used routinely as prophylaxis against acid aspiration pneumonitis. Of the 567 hospitals surveyed, 379 (67%) responded. Of these, 243 hospitals provide an obstetric service which includes caesarean section, and 67% of these perform less than 500 deliveries per annum. Aspiration prophylaxis during labour was used in 22.4% of responding hospitals. Prior to elective caesarean section, 11.5% used no prophylaxis, and 39.4% used particulate antacids such as magnesium trisilicate mixture (33.3%) or Mylanta (6.1%). Sodium citrate mixture was the most popular therapy (37%). Results were similar in the emergency caesarean section group. The use of cimetidine or ranitidine was uncommon in all groups. Results of this survey suggest marked differences in attitudes towards acid aspiration prophylaxis between Australian and British obstetric anaesthetic practices.

Hyperosmolality due to antacid treatment

Magnesium trisilicate mixture is an antacid used commonly in our Intensive Care Unit in the prevention and treatment of stress ulcers. In this case the administration of large doses over a period of time led to the development of massive hyperosmolality, cerebral dehydration and coma. Management with hypotonic fluid resulted in complete recovery.

The Effect of Cimetidine, Magnesium Tri-Silicate Mixture, and Metoclopramide on Gastric pH and Volume

Surgery patients are considered at risk for pulmonary acid aspiration if the gastric pH is 2.5 or less and/or the gastric aspirate volume is 25 ml or more. This study compares the effect of cimetidine, magnesium tri-silicate (MTS) and metoclopramide on the intragastric volume and pH in 120 elective surgery patients divided into four equal groups. Sixty to ninety minutes before anaesthesia, the cimetidine and metoclopramide groups received 300 and 10 mg i.m., respectively. One hundred twenty minutes before anaesthesia, the MTS group received 30 ml orally. Patients receiving MTS showed the highest gastric pH and intragastric volume. The cimetidine group had the lowest intragastric volume and a significant increase in pH. The metoclopramide group effectively reduced gastric volume but showed no significant effect on pH. We conclude that no single drug can be relied upon to reduce intragastric volume and neutralize gastric acid in all patients.

The neutralization capacity of magnesium trisilicate BP and magnesium trisilicate mixture BP

The in vitro neutralization properties of magnesium trisilicate mixture BP and its ingredients have been examined using the Rossett and Rice test. It is concluded that the inclusion of the principal component, magnesium trisilicate, in the mixture is unwarranted due to the failure to demonstrate a significant neutralizing action. This appears to be due to the extremely slow rate of reaction of this compound with hydrochloric acid.

Comparison of the Prophylactic Use of Magnesium Trisilicate Mixture B.P.C., Sodium Citrate Mixture or Cimetidine in Obstetrics

The effects of magnesium trisilicate mixture B.P.C., sodium citrate mixture or cimetidine on gastric pH and aspirated gastric volumes were compared in 78 obstetric patients during elective (a), or emergency (b) surgery. Magnesium trisilicate mixture B.P.C. was associated with the most alkaline values of gastric pH (mean (a) 7.9, (b) 7.3; range 2.9–9.1). Sodium citrate 0.3 mol litre-1 mixture resulted in the narrowest range of pH values of gastric contents (mean (a) 5.4, (b) 5.9; range 3.9–7.7). The ranges of aspirated gastric volumes were wide with both antacid regimens (magnesium trisilicate 12–172 ml, sodium citrate9–290ml). Cimetidine increased gastric pH to greater than 2.5 in 82% of patients (mean (a) 6.2, (b) 5.0; range 1.6–7.3), and was associated with significantly smaller volumes of aspirated gastric contents (range 0.5–44 ml). When gastric pH and volume were considered together, the groups of patients who received cimetidine were found to be closest to the defined safe limits, of pH ≥ 2.5 and volume ≤ 25 ml.

Magnesium Trisilicate Mixture BP—Its Physical Characteristics and Effectiveness as a Prophylactic

Magnesium Trisilicate Mixture BP—Its Physical Characteristics and Effectiveness as a Prophylactic

The assessment of gastric acidity and antacid effect in pregnant women by a non-invasive radiotelemetry technique.

Non-invasive radiotelemetry techniques were used for the in-vivo assessment of gastric acidity and the effect of antacids in non-pregnant women and women in the third trimester of pregnancy. A particulate (magnesium trisilicate mixture) and a non-particulate (sodium citrate) antacid were studied. There was no significant difference in basal gastric acidity and gut transit time between the pregnant and non-pregnant subjects. The median and range of values for the efficacy (defined as the integrated area under the pH/time curves) of sodium citrate was 138.3 pH.min (29.8-520.7) in the non-pregnant and 103.0 pH.min (54.3-375.6) in the pregnant subjects. The median and range of values for the duration of action of sodium citrate were 38.6 (18.1-147.4) min in the non-pregnant and 30.5 (20.0-119.1) min in the pregnant women. Magnesium trisilicate mixture resulted in a greater intragastric pH change and had a greater efficacy than sodium citrate, but the duration of action of the two antacids was similar.

Comparison of the Prophylactic Use of Magnesium Trisilicate Mixture B.P.C., Sodium Citrate Mixture or Cimetidine in Obstetrics

The effects of magnesium trisilicate mixture B.P.C., sodium citrate mixture or cimetidine on gastric pH and aspirated gastric volumes were compared in 78 obstetric patients during elective (a), or emergency (b) surgery. Magnesium trisilicate mixture B.P.C. was associated with the most alkaline values of gastric pH (mean (a) 7.9, (b) 7.3; range 2.9–9.1). Sodium citrate 0.3 mol litre-1 mixture resulted in the narrowest range of pH values of gastric contents (mean (a) 5.4, (b) 5.9; range 3.9–7.7). The ranges of aspirated gastric volumes were wide with both antacid regimens (magnesium trisilicate 12–172 ml, sodium citrate9–290ml). Cimetidine increased gastric pH to greater than 2.5 in 82% of patients (mean (a) 6.2, (b) 5.0; range 1.6–7.3), and was associated with significantly smaller volumes of aspirated gastric contents (range 0.5–44 ml). When gastric pH and volume were considered together, the groups of patients who received cimetidine were found to be closest to the defined safe limits, of pH ≥ 2.5 and volume ≤ 25 ml.

Magnesium trisilicate mixture BP. Its physical characteristics and effectiveness as a prophylactic.

Study of samples of magnesium trisilicate mixture BP obtained commercially has shown that redistribution of the mixture into a reasonably well-dispersed suspension becomes increasingly difficult the longer the mixture is stored. This process of compacting is hastened in response to an increase of environmental temperature. It is possibly for this reason that to administer the mixture at some time later than shortly after it has been prepared contravenes the recommendation of the British National Formulary, that 'it should be recently prepared.' These findings were reflected in the contrast between gastric aspirates obtained from anaesthetised patients who had received the commercially-obtained antacids and those whose antacid had been prepared by the hospital pharmacy. There was a higher incidence of patients 'at risk' because of aspirates with pH value less than 3.0 in the former group. Among the latter group of 131 patients, only one was found to have been 'at risk'. The importance of administering a final dose of antacid within the 15-minute period before induction of anaesthesia is emphasised. The results of assays of the magnesium concentration in the gastric aspirates varied widely, and bore no systematic relationship to the total dose of antacid administered, the time elapsing since the last dose was given, or the pH value of the same aspirate.

COMPARISON OF THE PROPHYLACTIC USE OF MAGNESIUM TRISILICATE MIXTURE B.P.C., SODIUM CITRATE MIXTURE OR CIMETIDINE IN OBSTETRICS

The effects of magnesium trisilicate mixture B.P.C., sodium citrate mixture or cimetidine on gastric pH and aspirated gastric volumes were compared in 78 obstetric patients during elective (a), or emergency (b) surgery. Magnesium trisilicate mixture B.P.C. was associated with the most alkaline values of gastric pH (mean (a) 7.9, (b) 7.3; range 2.9-9.1). Sodium citrate 0.3 mol litre-1 mixture resulted in the narrowest range of pH values of gastric contents (mean (a) 5.4, (b) 5.9; range 3.9-7.7). The ranges of aspirated gastric volumes were wide with both antacid regimens (magnesium trisilicate 12-172 ml, sodium citrate 9-290 ml). Cimetidine increased gastric pH to greater than 2.5 in 82% of patients (mean (a) 6.2, (b) 5.0; range 1.6-7.3), and was associated with significantly smaller volumes of aspirated gastric contents (range 0.5-44 ml). When gastric pH and volume were considered together, the groups of patients who received cimetidine were found to be closest to the defined "safe limits", of pH greater than 2.5 and volume less than 25 ml.

Comparison of the Prophylactic Use of Magnesium Trisilicate Mixture B.P.C., Sodium Citrate Mixture or Cimetidine in Obstetrics

Comparison of the Prophylactic Use of Magnesium Trisilicate Mixture B.P.C., Sodium Citrate Mixture or Cimetidine in Obstetrics

Mixing of antacids with stomach contents. Another approach to the prevention of the acid aspiration (Mendelson's) syndrome.

An investigation was carried out into the readiness with which magnesium trisilicate mixture BPC, Andursil suspension (Geigy) and 0.33 M aqueous sodium citrate mixed with gastric contents, to evaluate their suitability for use as an antacid before the induction of anaesthesia in obstetric patients. Laboratory investigations demonstrated that magnesium trisilicate and Andursil did not mix adequately with gastric contents, whereas sodium citrate mixed readily. A clinical investigation of sodium citrate revealed significant improvement in the mixing of gastric juice with the antacid if the patient was turned into the right lateral position following its administration (p < 0.05), but highly significant improvement followed a rotation through 360 degrees (p < 0.005). It was thought that these findings were caused by the division of the stomach into two sacs, a phenomenon confirmed by radiological studies and the use of a pig's stomach as a model of the human stomach.

The effectiveness and duration of preoperative antacid therapy.

The administration of 10 ml of magnesium trisilicate mixture to premedicated patients, maintains the pH of gastric contents below pH 2-5 during subsequent general anaesthesia. This effect was sustained for over seven hours--the longest anaesthetic time studied. No antacid supplementation is required to offer protection from acid aspiration during emergence and initial recovery from general anaesthesia.

LOSS OF CHLOROFORM FROM MAGNESIUM TRISILICATE MIXTURE UNDER SIMULATED IN-USE CONDITIONS

Summary Investigations were carried out under simulated in use conditions to determine the loss of chloroform from Magnesium Trisilicate Mixtures manufactured using Chloroform Water Double Strength, Chloroform Emulsion and Chloroform Spirit. Magnesium Trisilicate Mixture B.P.C. showed a loss of 33–40% of the initial chloroform content after 140 × 10 ml aliquots had been removed from a single container. Mixtures manufactured using Chloroform Spirit and Emulsion had higher initial values of chloroform content, also the chloroform remained in solution longer than in the B.P.C. mixtures. A survey of hospital manufactured Magnesium Trisilicate Mixtures showed that there are difficulties in manufacturing mixtures that contain the correct chloroform content. Mixtures from 22 hospitals were analysed of which three contained the expected concentration of chloroform.

Preoperative magnesium trisilicate in infants.

Three groups, each of forty children aged less than five years and prepared for elective surgery, had their gastric contents' volume and pH measured. The control group showed an incidence of 67-5 per cent with high acidity (pH equal to or less than 2-5). In the second and third groups magnesium trisilicate mixture was given within thirty minutes prior to induction of anaesthesia. The second group, sampled after induction of anaesthesia, showed a marked reduction in acidity, while the third group, sampled at the termination of anaesthesia and surgery, demonstrated that in most cases the neutralization of gastric acidity was still effective.

Pre-operative Neutralization of Gastric Acidity

The incidence of Mendelson's syndrome in the four major Auckland hospitals is reviewed. The frequency of this condition was reduced following the pre-operative administration of magnesium trisilicate mixture in two hospitals. A trial was conducted in a third hospital and this showed that a 52 per cent incidence of highly acid gastric juice (pH less than 2.5) in patients prepared for elective surgery was reduced by administration of magnesium trisilicate mixture at the time of premedication. When the magnesium trisilicate mixture was given within the 30 minutes prior to induction of anaesthesia, the number of patients with highly acid gastric content fell to one per cent.

TITRATION OF MAGNESIUM TRISILICATE MIXTURE AGAINST GASTRIC ACID SECRETION

Magnesium Trisilicate Mixture BPC has been titrated against a solution representing a high average gastric acid secretion. The results suggest that the 2-hourly administration of 10 ml of antacid is insufficient to maintain the intragastric pH above 3.0, but that 15 ml of the antacid given 2-hourly will ensure that the pH of the gastric contents will be kept above 3.0, and thus that, if such contents are aspirated, the acid-aspiration syndrome will not developed