Antacids

Explaination about antacids

2. MEANING ?
These are the drugs which are usually alkaline
substances and used for neutralising excess acid
in the stomach of patients Suffering from hyper-
chlorhydria (hyperacidity).

3. IDEAL REQUIREMENTS
The ideal requirements of an antacid are as follows:
1.It should be insoluble in water and has fine particle form.
2.It should not be absorbable or cause systemic alkalosis.
3.It should be able to exert its effect gradually and over a long period of time.
4.It should not be a laxative or cause constipation.
5.It should not cause any side effects.
6.It should be stable and readily available.
7.The reaction between antacid and gastric hydrochloric acid should not
produce large volume of gas.
8.The antacid should buffer in the pH range 4 to 6.
9.The antacid should probably inhibit pepsin, the proteolytic enzyme.

4. COMBINATION OF ANTACIDS
Itiswellknownthatnoantacidisavailableinthemarketwhichsatisfiesthe
requirementanidealantacid.
However,manypreparationswhicharehavingcombinationofantacidsare
beingmarketed.
Theideabehindsuchcombinationistocounteracttheconstipationactionof
calciumandaluminiumcontainingantacidswithlaxativeeffectofmagnesium
containingantacid.

5. Sometimesthecombinationantacidpreparationishavingonewithrapidonset
ofactionwithanantacidwithalongerdurationofaction.
Inanothertype,theantacidsarecombinedwithsimethiconetypeofcompounds
whicharehavinganti-flatulent(agentsusedforpreventionofexcessive
intestinalgas)actionastheyareantifoamingagentsandcausedispersionof
gases.
FewsuchcombinationsarereportedtobeofficialinB.P.

6. COMBINATIONPREPARATIONS
(1)Compoundmagnesiumtrisilicateoralpowder:Itishavingmagnesium
trisilicate,chalkpowder,sodiumbicarbonateandheavymagnesium
carbonateeach250mg.
(2)Magnesiumtrisilicatemixture:Itisasuspensionhaving5percentw/wof
eachofmagnesiumtrisilicate,lightmagnesiumcarbonateandsodium
carbonateinasuitablevehiclewithapeppermintflavour
(3)Compoundmagnesiumtrisilicatetablets: Itishavingineach250mgof
magnesiumtrisilicateand120mgofdriedaluminiumhydroxidegel.
Peppermintisaddedasaflavour.

7. SODIUM BICARBONATE
Formula :NaHCO
3 Molecular Weight : 58.82 g/mol
It contains or less than 99 per cent and not more than the equivalent of 100.5 per cent
NaHCO
3
Preparation:On a small scale, it is prepared by passing CO
2, gas through a solution of
sodium hydroxide. The solution is concentrated to get the product
2NAOH + CO
2→ Na
2CO
3+ H
2O
Na
2CO
3+ H
20 + CO
2 2NaHCO
3

8. Onanindustrialscale,itisobtainedbytheSolvayProcess.
Brinesolution(NaCl)issaturatedwithammoniatoremovetracesof
impuritieslikeMgandFe.
Thesolutionisnowfilteredandpassedthroughthecarbonatingtower.
InthisitisallowedtocomeincontactwithacurrentofCO
2andthetoweris
cooledtoenhanceprecipitation(sodiumbicarbonateislesssolubleinwater
below15°).
Theprecipitateisfilteredoutanddried.
H
2O + CO
2 H
2CO
3
NH
3+ H
2CO
3 NH
4HCO
3
NaCl + NH
4HCO
3 NaHCO
3+ NH
4Cl

9. Properties:Itoccursinwhitecrystallineoramorphouspowderhavinga
salinetaste.
Itisfreelysolubleinwaterbutpracticallyinsolubleinalcohol.
Assay: 1gmisweighedaccurately&dissolvedin20mlofwater.
Itisthantitratedwith0.5NSulphuricacidusingmethylorangeasindicator.
Eachmlof0.5NH
2SO
4=0.042gmofNaHCO
3
Uses:Acidneutralizingsubstance.
Itisaantacid.
UsedinPreparationofBuffersolutions.

10. ALUMINIUM HYDROXIDE GEL
Itisanaqueouswhiteviscoussuspensionofhydratedaluminiumoxidehaving
varyingamountsofbasicaluminiumcarbonate.
Thepreparationcontainsnotlessthan3.5percentandnotmorethan4.4per
centw/wofaluminiumoxide(Al
3O
3).
Thepreparationmaybesometimeshavingmethyloil,peppermintoil,glycerine,
sucrose,saccharinetcasflavouringandsweeteningagentsandupto0.05per
centsodiumbenzoate,asapreservative.

11. Preparation:Itispreparedbyaddingahotsolutionofpotashalumslowlywithconstantstirringtoahot
solutionofsodiumcarbonate.
Aftercompleteremovalofcarbondioxidecarbondioxidetheprecipitatedaluminiumhydroxideisfiltered.
It is washed thoroughly with hot water until hot water until it becomes free from sulphate ion and the
precipitate is suspended in distilled water.
3Na
2CO
3+ 2 KAI (SO
4)
2+ 3H
20 3Na
2SO
4 + K
2SO
4+ 2Al(OH)
3+ 3CO
2
Intheabovepreparation,themainprecautiontobekeptinmindisthatthealumsolutionaddedtothe
solutionofsodiumcarbonateandnotviceversabecausethatwouldyieldprecipitatehavingalkalisulphate
whichwouldbedifficulttowash.
InwashingtheprecipitateofAl(OH)
3,hotwaterbutnotboilingwatershouldbeusedasthelattertendsto
decomposethealuminiumhydroxide. Itistoberememberedthatahydroxideisformedinsteadofa
carbonate. Thereasonisthataluminiumcarbonateisunstableandimmediatelygetshydrolysedtoyield
aluminiumhydroxideandcarbondioxide.

12. Properties: Itisawhiteviscoussuspension. Aclearliquidgets
separatedwhenitiskeptstandingforsometime.
Aluminiumhydroxidegelgivesastringentaluminiumchloride
whenitreactswithgastrichydrochloricacid. Thisresultsinto
nausea,vomitingandconstipation.
Use:goodslowactingantacid.
Usedintreatmentofhyperchlorhydria.

13. MAGNESIUM HYDROXIDE
Formula :Mg(OH)
2 Mol. Wt.: 58.32 g/mol
Preparation:It is also prepared by treating sea water or other natural brines with
sufficient calcium hydroxide to precipitate magnesium as magnesium hydroxide,
then washing and drying the precipitate.
MgO + H
20 Mg(OH)
2
MgSO
4+ 2NaOH Mg(OH)
2 + Na
2SO
4

14. Properties:Itisawhitefineamorphouspowder.Itisalmostinsolublein
wateryieldingasolutionwhichisslightlyalkaline.
Itdissolvesindilutemineralacids.
Itslowlyabsorbscarbondioxidefromatmosphere.
Assay:An accurately weighed amount of sample is taken in a flask. To it 25
ml of 1 N H
2SO
4 is added. Now the excess of acid is back titrated with 1 N
NaOH using methyl red as an indicator.
Each ml of 1 N H
2SO
4= 0.02917 g of Mg(OH)
2
Uses:It is used as an antacid.