US3017324A

US3017324A - Antacid composition

Info

Publication number: US3017324A
Application number: US804414A
Authority: US
Inventors: Wart M Beekman
Original assignee: Reheis Co Inc
Current assignee: Reheis Co Inc
Priority date: 1959-04-06
Filing date: 1959-04-06
Publication date: 1962-01-16
Anticipated expiration: 1979-01-16

Description

Jan. 16, 1962 Filed April 6. 1959 s. M. BEEKMAN 3,017,324

ANTACID COMPOSITION 5 Sheets-Sheet 1 CODE 0 Q WEE.

TIME

FIG.

INVENTOR;

STEWART M. BEEKMAN 8 Maui-M ATTORNEYS Jan. 16, 1962 s, BEEKMAN 3,017,324

ANTACID COMPOSITION Filed April 6, 1959 5 Sheets-Sheet 2 EXAMPLE No. RAT O 3 use FIG. 2.

INVEN TOR. STEWART M. BEEKMAN BY W'MM*M A T TORNE Y5 Jan. 16, 1962 Filed April 6, 1959 s. M. BEEKMAN 3,017,324

O 20 4O 6O 80 I00 I20 TIME FIG. 3.

IN VEN TOR.

STEWART M. BEEKMAN BY 51. Mkimu A TTORNE Y5 Jan. 16, 1962 s. M. BEEKMAN 3,017,

ANTACID COMPOSITION Filed April 6, 1959 5 Sheets-Sheet 4 CODE Al O =MqO g mm m A 82 0 2o 40 so 80 I00 I20 TIME INVENTOR. STEWART M. BEEKMAN ATTORNEYS Jan. 16, 1962 s. M. BEEKMAN 3,017,324

ANTACID COMPOSITION Filed April 6, 1959 5 Sheets-Sheet 5 CODE Al O =MqO EXAMPLE No. w

0 2o 40 so 80 I00 I20 TIME FIGI 5o INVENTOR.

STEWART M. BEEKMAN BY QM ATTORNEYS lnited States Patent 3,017,324 ANTACID COMPOSITION wart M. Beekman, Berkeley Heights, N.J., assignor to ieheis Company, Inc., a corporation of New York Filed Apr. 6, 1959, Ser. No. 804,414 Claims. (Cl. 167-55) [his invention relates to an antacid composition, and re particularly to an antacid composition comprising minum hydroxy carbonate and magnesium silicate, and a process of preparing the same. Antacid preparations are now quite generally employed the treatment of peptic ulcers, gastric hyperacidity and spepsia. Gwilt, Livingstone and Robertson in the Jouri of Pharmacy and Pharmacology, X, No. 12, 770-775 958), describe the characteristics of an ideal antacid. iey point out that it should show its maximum neurlizing effect in the shortest possible time, that it should utralize an adequate amount of gastric hydrochloric id and maintain its action during the normal period of vstric digestion, that any excess however great beyond e amount required to neutralize free gastric acid should at cause alkalization, that it should raise the pH of the istric contents to a :level at which pepsin activity is relced significantly but not totally inhibited, that adequate 1d repeated doses should be palatable to the hyperacid itient, and that its use should not lead to laxative, conipating or other side effects such as gastric irritation. In ldition to these factors the antacid composition should 2 inexpensive and it should not deteriorate significantly l any respect on aging. These workers summarize the arious statements in the literature as to the pH ranges esirable for the ideal antacid, and conclude that a pH within the range from about 3.5 toabout 4.5 is apparntly the optimum to ensure adequate relief from hyperctidity, particularly if an ulcer site is present, and at the ame time permits sufficient residual pepsin activity to .void secondary digestive disturbances.

Edwards in The Chemist and Druggist, December 14, .957, page 647, also discusses the properties of an ideal intacid, and suggests that the nearest approach to the deal attained as of that date was wet activated alumina gel. Dr. Edwards views ot the proper-ties of the ideal antacid are in substantial agreement with those expressed 9y Gwilt et al.

Liquid aluminum hydroxide gel closely approaches the ideal for an antacid but its liquid form makes it inconvenient to use, especially in the case of ambulatory patients. The liquid gel is quite rapid in its action and gives a prolonged antacid effect in the optimum pH range. It is not significantly affected in its antacid properties by pepsin and it also does not significantly lose its antacid characteristics in aging. However, as Edwards and others have pointed out, it may have a mildly constipating effect which many have sought to remedy by combining it with other ingredients such as magnesium hydroxide or carbonate.

The advantages of the dried gel are obvious. However, the obvious material, dried aluminum hydroxide gel, is actually far from an ideal antacid. It exhibits a lag in its rate of reaction with stomach acids. It does not give a prolonged antacid in the optimum pH range and its antacid properties are severely affected by pepsin. Also, its antacid activity is less than that of the liquid ice igel, being decreased by the drying and the reduced activity decreases further with aging. These disadvantages have been noted by Gwilt et a1. and other workers in this field.

German Patent No. 941,864 describes an antacid composition composed of mixed coprecipitated aluminum and magnesium hydroxy silicates prepared from sodium silicate and sodium hydroxide by reaction with magnesium sulfate and aluminum sulfate. The product is described as having the formula AlMg Si O This preparation is shown by the patent graph to be superior to sodium bicarbonate, calcium carbonate, magnesium carbonate and magnesium trisilicate. However, according to the test used, the pH shortly following its administration rises to 6 or above, and remains above 4.5 for approximately minutes, which is too high for a satisfactory antacid preparation.

In accordance with the instant invention, there. is provided an antacid composition composed of a mixture of magnesium silicate and aluminum hydroxy carbonate in certain proportions. This composition is capable of maintaining a pH in the stomach within the range from 3 to 4.5 for two hours or longer, and is thus characterized by a remarkably constant pH in the optimum range for a sufliciently long time per dose to enable the patient to avoid irritation with a minimum of medication.

The proportions of aluminum hydroxy carbonate and magnesium silicate are quite critical in maintaining a fast antacid action within this pH range. The molecular ratio Al O :MgO of aluminum hydroxy carbonate calculated as A1 0 to magnesium silicate calculated as MgO should be within the range of from 1:2 to 32:2. At Al O :MgO ratios below this, the maximum pH following administration of the composition will rise to considerably in excess of 4.5, which is undesirable. Proportions of A1 0 in excess of 32:2 can be used without disadvantageously affecting pH, but with the detriment that the composition is greatly slowed in its antacidaction, so that the desired pH is not reached until a considerable time following administration, which also is undesirable. Thus, the stated range represents the optimum proportions of the essential ingredients for effective and prompt antacid action.

The composition can be prepared in any of several ways. The only prerequisite is that the aluminum hydroxy carbonate be in hydrous gelatinous form at the time of mixing with the magnesium silicate. The aluminum hydroxy carbonate must not have been dried prior to use, that is, it must be in moist, undried form. It must contain at least suflicient of the original gel water to make it moist. There are several magnesium silicates, with varying MgOzSiO ratios, but the trisilicate 2MgO:3SiO .,,H O is preferred The magnesium silicate can be in the form of a dry gel which is physically mixed with the moist aluminum hydroxy carbonate. It is usually more desirable, however, to blend the magnesium silicate in freshly precipitated moist gel form with the aluminum hydroxy carbonate, since the particles are then in a more finely-divided state. The magnesium silicate also may be coprecipitated with the aluminum hydroxy carbonate from a common reaction solution, if desired, containing silicate, hydroxyl,

carbonate, magnesium and aluminum ions, such as a mixture of sodium silicate, sodium carbonate, sodium hydroxide, magnesium sulfate and aluminum sulfate, in

proper stoichiometric proportions to give the desired precipitate. This procedure is somewhat more complicated, requiring more careful control of the precipitation conditions so as to obtain a good precipitate of both these salts, in the desired proportions, and therefore is less desirable than the others.

The resulting mixture prepared as above described is dried by any convenient method known to those skilled in the art, such as for example, spray or tray drying. The final composition is in the form of a dried gel which can be reduced to powdered form for convenience of packaging and marketing.

The following examples in the opinion of the inventor represent the best embodiments of his invention.

EXAMPLE 1 370 lbs. of precipitated magnesium trisilicate slurry (0.895% MgO, 2% SiO;, pH 9.7) was blended with 525 lbs. of freshly precipitated basic aluminum hydroxy carbonate slurry (1.6% A1 pH 5.3) in a 150 gallon Haveg cylindrical tank using a H.P. 425 r.p.m. portable type agitator employing two inch marine type propellers. After fifteen minutes of agitation the pH of the blend was measured and found to be 7.35. Agitation was continued for a total of one hour.

The resulting slurry, which had an alumina content of 0.939%, was filtered through a 12 inch Shriver filter press equipped with plastic plates and frames. Three cycles were required for filtering and washing the entire batch.

Each cycle required eighty minutes at 45 p.s.i.g. and eight 30 hours washing time. The white filter press cakes obtained had a total weight of 116.31 lbs.

The cakes were dried in a circulating air dryer in the pilot plant at 125 F. yielding 20.06 lbs. of dry product. The dried lumps were pulverized in a No. 1 Mikro pulverizer at 9600 r.p.m. using an 0.020 inch herringbone screen. The product analyzed as follows:

Al O :MgO ratio 2:2 A1 0 percent 28.6 MgO do 115 SiO- do 25.3 CO2 d0 Moisture (Dean & Starke) do 13.6 Sulfates (S0 do 0.03 Chlorides (Cl) do 0.03 1 pH (4% aqueous dispersed) 9.8 Apparent density (g./ml.) 0.16 Screen analysis:

Percent through 200 mesh 95.2

Percent through 325 mesh 83.3 Acid consuming capacity (ml. N/ HCl/g.) 205 The antacid characteristics were determined by the method of Holbert, Noble and Grote, Journal of the American Pharmaceutical Association, 36, 149 (1947), 37, 292 (1948), Murphey, 0d, a test sample of antacid is added to 150 ml. of pH 1.5 hydrochloric acid containing 2 g. of pepsin N.F. per liter (artificial gastric juice) at 37.5 C. ml. of the artificial gastric juice is withdrawn every ten minutes and replaced with an equal volume of fresh gastric juice. The test procedure used in the work reported in this and the following examples, however, was carried out by continuously introducing fresh artificial gastric juice and removing the antacid-gastric juice mixture by overflow at the rate of 2 ml. per minute. Theantacid effect is determined by measuring the pH of the artificial gastric juice during the test period, which was two hours 120 minutes).

The pH data taken in this test, carried out on a 1 gram sample, are reported below in Table I.

41, 361 (1952). In this methnate gel (303 g. A1 0 4 Table I ANTACID CHARACTERISTICS The data show that the composition was capable maintaining the pH within the range from 3.2 to 4 f two hours.

EXAMPLES 2 TO 6 A group of five compositions was prepared by intimat ly blending moist basic aluminum hydroxy carbonate g with aqueous gelatinous magnesium trisilicate, follows by drying and reduction to powder. The proportions aluminum hydroxy carbonate as A1 0 to magnesium tr silicate as MgO ranged from 8:2 to 1:4 (0.5:2).

The magnesium trisilicate gel employed in the:

35 preparations was prepared from magnesium sulfal MgSO -7H O and sodium silicate Na SiO (40 Baumr 9.13% Na O, 28.2% SiO 262.5 lbs. of magnesiur sulfate was dissolved in 232 lbs. of water. 4.935 lbs. 0 sodium hydroxide was dissolved in 20 lbs. of water, anl these were mixed in 37.25 lbs. of the sodium silicat solution, and 200 lbs. of water then added. The solu tions were mixed in a Haveg reactor with a marine typi propeller. The solution was allowed to age for one hou: after mixing had been completed, and the magnesium tri silicate separated by filtration; 44.5 lbs. of cake was ob tained.

(Example 2) was prepared from a blend of 5000 g. moist aluminum hydroxy carbonate gel g. A1 0 and 1210 g. of magnesium tri- 0 silicate gel (49.7 g. MgO). 2000 g. of deionized water was placed in a three gallon mixing tank, and the aluminum hydroxycarbonate was thoroughly dispersed therein using a 0.5 H.P. laboratory Dispersator. The magnesium trisilicate gel was added, and the slurry intimately blended at high speed for five minutes. The wet gel contained 5.79% A1 0 and 0.57% MgO. The particles were spread out on a tray and dried in an atmospheric tray dryer at F. for nine hours. The mixture was pulverized to a fine powder by one pass through a No. 1 Mikro Pulverizer at 5000 r.p.m. using a 0.020 inch herringbone screen.

The 2:2 product (Example 4) was prepared by the same procedure, using 3000 g. aluminum hydroxy carboand 2840 g. magnesium trisilicate gel (119.4 g. MgO). 1500 g. of water was used. The wet gel contained 4.13% A1 0 and 1.62% MgO.

The 1:2 product (Example 5) was prepared from 2000 g. aluminum hydroxy carbonate gel (202 g. A1 0 and 75 3790 g. magnesium trisilicate gel (159.5 g. MgO). 1000 g.

pared by hydroxy carbonate gel icate gel of. deionized water to tested for antacid activity Noble, and Grote test prole 7) was pre gh to blend. Agitation was Mole Ratio lailuminum A1 0 and 1.91 lbs. magnesium trisil 500 ml. fluid enou Apparent Density,

The gels were using the modified Holbert, cedure.

g0) with 2 the mixture followed by drying at 150 F. and pulverizing to pow- The 12:2 product (Examp adding 12 lbs. of 10.1

Screen Test, Percent Remaining dered form.

5 and additional (4.21% M render Carbonates as CO2,

Table II t percent carbonate gel (126.25 trisilicate (199 g. MgO) Acid 1 Consuming Cl Capacity percen droxy lyzed as follows:

Si O 2 duct (Example 6) was prepared blended at high speed d. The wet gel containe MgO, percent percent A12 percent later was used. The wet gel contained 2.97

2.35 MgO. he 0.5:2 (1:4) pro n 1250 g. aluminum by .1 0 and 4730 g. magnesium two gels were cr was not require 0, and 3.33% MgO. The dried products ana ample No.

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is the pH of the original gastric 5) represents the minimum desirable proportion of alu- The above data are EXAMPLES 7 To 9 70 It is apparent that eac ble of maintaining a p approximately For purposes of comparison, dried gel U.S.P. having a pH of pletely unsatisfactory.

EXAMPLES 10 TO 13 A group of antacid preparations were prepared by blending dried magnesium trisilicate U.S.P. with wet aluminum hydroxy carbonate gel in the Al O :MgO molecular ratios of 8:2, 4:2, 2:2 and 1:2, drying the mixtures in air at 150 F., pulverizing them to -a powder, and then determining the antacid characteristics using the in vitro test method of Holbert, Noble and Grote as set forth in Example 1. The magnesium trisilicate used contained 22% MgO, and the aluminum hydroxy carbona-te gel contained 10.1% A1 and 4.3% carbonates 3S In each case, 50 g. of magnesium trisilicate powder was thoroughly mixed and blended with the aluminum hydroxy carbonate gel. 1100 g. of the gel was used to make the 8:2 product (Example 10), 550 g. for the 4:2 product (Example 11), 775 g. for the 2:2 product (Example 12) and 137 g. for the 1:2 product (Example 13). 250 ml. of deionized Water was added to make the blend more fluid and to facilitate mixing. The mixtures were dried in an air circulating dryer at 140 F. until constant weight was reached, and the dried samples were finely pulverized in a Mikro pulverized sample mill.

The pH data obtained using 1 .gram samples by the Holbert, Noble and Grote test procedure are set forth in the table below.

Table V Example N0. M 10 11 12 13 The above data are Each of these compositions is capable of maintaingraphed in FIGURE 3.

ing the pH Within the two hours.

These results are to be contrasted with the results obtained when a dried aluminum hydroxide gel U.S.P. is mixed with the dried magnesium trisilicate U.S.P. to form a simple dry blend. Such blends were prepared using magnesium trisilicate U.S.P. (22% MgO) and dried aluminum hydroxide gel U.S.P. (53.7% A1 0 8:2 (blend A), 4:2 (blend B), 2:2 (blend C), 1:2 (blend D) and 0.5 :2 (1:4) (blend E) products were prepared using 9.32 g. dried aluminum hydroxy gel to furnish 5 g. A1 0 and 2.24 g., 4.50 g., 9 g., 17.95 g. and 35.95 g. magnesium trisilicate to furnish 0.494, 0.989, 1.975, 3.95 and 7.91 'g. MgO, respectively. The

range of 3 to 4.2 for approximately 8 blends were then tested by the Holibert, Noble Grote procedure as outlined in Example 1, using gram samples. The pH data obtained was as follows Table VI N Blend Blend Blend Blend Ble A B O D E 1. 5 l. 5 l. 5 1. 5 2. 0 2. O 2. O 2. O 2. 0 2. 0 2. 01 2. 04 i 2. 0 2. 0 2. 05 2. 13 2 2. 0 2. 00 2. 11 2. 22 2 2. 0 2. 02 2. l9 2. 34 2 2. O 2. O4 2. 25 2. 48 2 2. 05 2. 21 2. 60 3. 22 4 2. 12 2. 38 2. 99 3. 78 5 2. 12 2. 42 2. 3. 66 4 2. 08 2. 3S 2. 67 3. 20 4 2. 02 2. 30 2. 49 2. 88 3. 2. 02 2. 23 2. 35 2. 61 3. 2. 0 2. 16 2. 25 2. 45 2. 2. 0 2. 11 2. 17 2. 32 2. 2. 0 2. 08 2. 11 2. 21 2. 2. 0 2. 06 2. 08 2. l7 2. 2. 0 2. 02 2. O5 2. l0 2. 2. 0 2 00 2. 03 2. 06 2.

These data are graphed in FIGURE 4.

It is apparent from the above data that these compos tions are incapable of meeting the requirements for satisfactory antacid composition. Blends A to C di not even reach a pH of 3. Blend D maintained a pl above 3 only for thirty minutes and blend E maintaine this pH for only fifty minutes, while the maximum pl reached 5.2 well beyond the desirable upper limit of 4.5 Thus, the data show the significance of mixing the mag nesium trisilicate with a wet aluminum hydroxy carbonan gel.

EXAMPLES 14 TO 16 Three compositions were prepared having Al O :MgC molecular ratios of 8:2, 2:2 and 1:4. These compositions were prepared from aluminum sulfate and magnesium sulfate by reaction thereof in alkaline aqueous sodium silicate solution, followed by coprecipitation of the two substances.

The magnesium sulfate and aluminum sulfate were both dissolved in deionized water in a tank equipped With a Lightnin' portable agitator with a 2 inch at blade turbine. The sodium silicate (40 Baum 28.2% SiO and caustic soda pellets were dissolved separately in deionized water and the magnesium silicate-aluminum hydroxide gels coprecipitated by the addition of the sodium silicate solution to the mixed sulfate solution at about 26 ml. per minute at room temperature. The precipitated slurry was aged for sixteen hours and filtered through a 24 cm. Buchner funnel under 23 inches of vacuum. The filtered cake was washed with deionized water until the effluent was sulfate-free. The wet cake was dried for twenty-four hours at 176 F. in an atmospheric tray dryer and the dried material pulverized in a Mikro sample mill.

The 8:2 composition (Example 14) was prepared from 60.4 g. MgSO -7H O and 580 g. aluminum sulfate ironfree dissolved in 6500 ml. of deionized water, using as the precipitant 79 g. of the sodium silicate and 246 g. caustic soda pellets dissolved in 5868 g. of deionized water.

The 2:2 product was prepared from 121 g. MgSO -7H 0 in 580 g. of aluminum sulfate, iron-free, added to 6499.6 g. deionized water, using 316 g. sodium silicate and 278 g. sodium hydroxide pellets dissolved in 5602 g. deionized water.

The 1:4 product (Example 16) was prepared from 134 g. of magnesium sulfate and 79.0 g. of aluminum sulfate, iron-free, dissolved in 770 g. of deionized water, using as precipitant 170.5 g. of sodium silicate and 56 g. caustic da dissolved in 631 g. deionized water.

The antacid characteristics of these three materials were .termined by the Holbert, Noble and Grote procedure .ing 1 gram samples as set forth in Example 1 above. he pH data obtained was as follows:

Table VII Example 14 Example 15 Example 16 A120 hlgO A110 MgO Al O zNlgo Ratio, 8:? Ratio, 2:2 Ratio, 0.33:2

1. 5 l. 5 l. 5 2. 3. 8 3. 2 2. 3 3. 9 3. 6 3.0 3. 9 3. S 3. 6 4. 0 4.3 3. 7 4. 0 4. 6 3. 7 4. 0 4. 8 3. 7 4.0 5. 0 7 4. 0 5.1 3. 7 4.0 5. 2 3. 7 4. 0 5. 2 3. 7 4. 0 5. 3 3. 8 4.0 5. 3 3. 7 4. O 4. 6 3. 6 3. 9 4. 3 3. 3. 8 3. 9 3. 1 3.7 3. 6 3. 3 3. 7 3. 5 3. 2 3.6 3.3 3.0 3. 5 3. 2 2. 9 3. 4 3. 0 2. S 3. 2 2. 9 2. 6 3.1 2. 7 2. 5 2. 8 2. 6

These data are graphed in FIGURE 5.

These data show the criticality of the Al O :MgO ratio. Examples 14 and 15 are capable of maintaining the pH within the range from 3 to 4.5 for approximately two hours. The Example 16 composition with a 1:4

ratio could not maintain an upper pH limit at 4.5 or below. The pH was in excess of 4.5 for most of the first twenty minutes of the test procedure, which is undesirable. Thus, in this composition there was too little aluminum hydroxide.

As previously indicated, the compositions in accordance with the invention are useful in the treatment of internal conditions where excess acidity is to be encountered, such as gastric acidity in the stomach, in, for example, the treatment of gastric and peptic ulcers. For this purpose, the dry compositions are readily administered in the form of slurries, or as dry powders or tablets, with an excipient, if desired, which are suitably taken orally or added to a liquid carrier such as water.

It is usually most convenient to prepare the compositions in tablet form, and since the compositions are relatively inert and store well, tablets are easily prepared by conventional procedures. The composition can be tableted as such, or with an excipient mixture of conventional The quantity indicated is sufficient to prepare approximately 48,000 tablets, containing 10 grains each of the antacid composition.

Those skilled in the art will perceive other methods for the administration of the compositions, and it will be apparent that these are in no way critical but can be selected to meet any particular requirements.

I claim:

1. An antacid composition capable as determined by the Holbert, Noble and Grote test method of maintaining the pH of artificial gastric juice within the range from about 3 to about 4.5 for at least one hour, comprising the dried combination of hydrous gelatinous aluminum hydroxy carbonate and magnesium silicate, in a molecular weight ratio calculated as Al O :MgO within the range from about 1:2 to about 32:2.

2. An antacid composition in accordance with claim 1 in which the magnesium silicate is in the form of dry magnesium trisilicate gel.

3. An antacid composition in accordance with claim 1 in which the magnesium silicate is in the form of moist magnesium trisilicate gel.

4. A composition in accordance with claim 1 in which the aluminum hydroxy carbonate and the magnesium silicate are in the form of coprecipitated gels.

5. A composition in accordance with claim 1 in the form of a slurry of the gels in water.

6. An antacid tablet comprising a composition in accordance with claim 1 and an excipient.

7.. A process for preparing an antacid composition capable as determined by the Holbert, Noble and Grote test method of maintaining the pH of artificial gastric juice within the range from 3 to about 4.5 for at least one hour, which comprises mixing hydrous gelatinous aluminum hydroxy carbonate and magnesium silicate in a molecular weight ratio calculated as Al o zMgO within the range from about 1:2 to about 32:2, and drying the resulting mixture.

8. A process in accordance with claim 7 in which the aluminum hydroxy carbonate gel and magnesium silicate are formed in situ by coprecipitation from a common solution.

9. A process in accordance with claim 7 in which the magnesium silicate is a dry magnesium trisilicate gel.

10. A process in accordance with claim 7 in which the magnesium silicate is a moist magnesium trisilicate.

2,797,978 Beekman July 2, 1957 corrected below.

UNITED STATES- PATENT. OFFICE I CERTIFICATE 0F CORRECTION Patent No. 3,017,324 January 16 1962 Stewart M. Beekman above numbered patcertified that error appears in the should read as It is hereby tion and that the said Letters Patent ent requiring correc Column 5, line 41, Table 111, Example N0. 6, and opposite "1.0" for 2.9" read 4.0

d and sealed this 15th day of May 1962.

Signe (SEAL) Attest; h I

ERNEST W. SWIDER "DAVID LA-DD Attesting Officer Commissioner of Patents

Claims

1. AN ANTACID COMPOSITION CAPABLE AS DETERMINED BY THE HOLBERT, NOBLE AND GROTE TEST METHOD OF MAINTAINING THE PH OF ARTIFICIAL GASTRIC JUICE WITHIN THE RANGE FROM ABOUT 3 TO ABOUT 4.5 FOR AT LEAST ONE HOUR, COMPRISING THE DRIED COMBINATION OF HYDROUS GELATINOUS ALUMINUM HYDROXY CARBONATE AND MAGNESIUM SILICATE, IN A MOLECULAR WEIGHT RATIO CALCULATED AS AL2O3:MGO WITHIN THE RANGE FROM ABOUT 1:2 TO ABOUT 32:2.