AntacidsAntacids

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DigestionDigestion

DigestionDigestion involves the break down of foods, involves the break down of foods, particularly carbohydrates, lipids, and particularly carbohydrates, lipids, and proteins into forms that can be metabolized proteins into forms that can be metabolized in the cells.in the cells.

Amylase Amylase found in saliva begins the found in saliva begins the breakdown of starches.breakdown of starches.

The breakdown of proteins occurs primarily The breakdown of proteins occurs primarily in the stomach in the stomach Hydrochloric acidHydrochloric acid through the through the action of the enzyme action of the enzyme pepsinpepsin

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The StomachThe Stomach

The walls of the The walls of the stomach are lined stomach are lined with cells that with cells that secrete mucus, secrete mucus, pepsinogenpepsinogen and and hydrochloric acid.hydrochloric acid.

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The StomachThe StomachThe hydrochloric The hydrochloric acid concentration acid concentration of the stomach of the stomach ranges from 0.03 M ranges from 0.03 M to 0.003 M which to 0.003 M which corresponds to a pH corresponds to a pH range of about 1.5 range of about 1.5 to 2.5to 2.5

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The StomachThe Stomach

The mucus lining of The mucus lining of the stomach the stomach protects the protects the stomach walls from stomach walls from the action of the action of stomach acidstomach acid

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Acid Indigestion and Acid Indigestion and “Heartburn”“Heartburn”

When excess acid is When excess acid is produced a condition produced a condition known as acid indigestion known as acid indigestion results.results.If excess acid is forced If excess acid is forced into the esophagus acid into the esophagus acid reflux or “heart burn” reflux or “heart burn” results.results.High acid concentrations High acid concentrations can damage the stomach can damage the stomach lining resulting in ulcers.lining resulting in ulcers.

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Causes of Acid IndigestionCauses of Acid Indigestion

Excess stomach acid results in a state of Excess stomach acid results in a state of discomfort known as acid indigestiondiscomfort known as acid indigestion

Acid indigestion may result form a variety of Acid indigestion may result form a variety of factors including:factors including:

– OvereatingOvereating– Alcohol consumptionAlcohol consumption– Eating certain foodsEating certain foods– AnxietyAnxiety– SmokingSmoking– Certain Drugs, i.e. AspirinCertain Drugs, i.e. Aspirin

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Antacid CompoundsAntacid Compounds

Antacids are weak bases that are used to Antacids are weak bases that are used to neutralize excess stomach acidneutralize excess stomach acidMost antacids are weak inorganic Most antacids are weak inorganic basesbasesCommon examples includeCommon examples include

–CaCOCaCO33

–NaHCONaHCO33

–Al(OH)Al(OH)33

–Mg(OH)Mg(OH)22

–MgO and Mg(OH)MgO and Mg(OH)22 (Milk of Magnesia) (Milk of Magnesia)

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Types of AntacidsTypes of AntacidsActive ingredient: Basic metal saltActive ingredient: Basic metal salt

Cations used are highlighted in RedCations used are highlighted in Red

Anions used: OHAnions used: OH--, O, O2-2-, CO, CO332-2-, HCO, HCO33

--, HPO, HPO33--, Trisilicate , Trisilicate

(Mg), amino (Mg), amino acetate (Al)acetate (Al)

Calcium Carbonate

Magnesium Salts

Aluminium Salts (usually

hydroxide) Alka-mints tablets Childrens’ Mylanta

Tablet Chooz Gum Alcalak Titralac

Milk of Magnesia Philips Tablets Philips Oral

Suspension

Maalox Mylanta ALternaGEL

Most potent antacid ingredient; acts rapidly with more prolonged action than sodium bicarbonate

• Less potent that Ca

• Slow acting• Can use

hydroxide, phosphate & trisilicate (common in Singapore)

Mild and slow acting antacid, last longer

Most stable form of aluminium salts under normal conditions

3 Common Antacids3 Common Antacids

Antacid ReactionsAntacid Reactions

Antacids react with HCl in the stomachAntacids react with HCl in the stomach

Some common antacid reactions include:Some common antacid reactions include:CaCOCaCO33 + 2 HCl + 2 HCl CaCl CaCl22 + H + H22O + COO + CO22

Mg(OH)Mg(OH)2 2 + 2 HCl + 2 HCl MgCl MgCl22 + 2 H + 2 H22OO

MgO + 2 HCl MgO + 2 HCl MgCl MgCl22 + H + H22OO

NaHCONaHCO33 + HCl + HCl NaCl NaCl + H + H22O + COO + CO22

Al(OH)Al(OH)3 3 + 3 HCl + 3 HCl AlCl AlCl33 + 3 H + 3 H22OO

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Reactions - CaReactions - CaCaCOCaCO33 + 2 HCl + 2 HCl CaCl CaCl22 + H + H22O + COO + CO22

CaClCaCl22 + CO + CO332-2- CaCO CaCO33 + Cl + Cl-- (higher pH in (higher pH in

intestine)intestine)

Some unchange calcium is absorbed by the Some unchange calcium is absorbed by the gut, which can raise the pH of the blood gut, which can raise the pH of the blood causing alkalosis – can affect proteinscausing alkalosis – can affect proteins

Calcium is then removed through the renal Calcium is then removed through the renal systemsystem

Reactions - MgReactions - Mg

Magnesium oxides, hydroxides and Magnesium oxides, hydroxides and carbonates are poorly soluble, only carbonates are poorly soluble, only Chloride are soluble.Chloride are soluble.

Mg(OH)Mg(OH)22 + 2HCl + 2HCl MgCl MgCl22 + 2H + 2H22OO

Although non-absorbable, 5% - 10% of Mg Although non-absorbable, 5% - 10% of Mg enter systemic circulation which is then enter systemic circulation which is then rapidly removed by kidney rapidly removed by kidney

Effect of AntacidsEffect of Antacids

In addition to neutralizing excess stomach acid they In addition to neutralizing excess stomach acid they may be helpful in preventing inflammation, relieving may be helpful in preventing inflammation, relieving pain and discomfort, and allowing the mucus layer in pain and discomfort, and allowing the mucus layer in the stomach lining to heal.the stomach lining to heal.

They are often used to treat ulcers by preventing the They are often used to treat ulcers by preventing the stomach acids from attacking the stomach lining stomach acids from attacking the stomach lining allowing it to heal.allowing it to heal.

Mucus Lining

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Reactions - AlReactions - AlAl(OH)Al(OH)33 + 3HCl + 3HCl AlCl AlCl33 + 3H + 3H22O Al(HO Al(H22O)O)66

3+3+

Solubility of Al increases as pH decrease, above ph>5 Solubility of Al increases as pH decrease, above ph>5 neutralizing effect will stopneutralizing effect will stop

AlAl3+3+ + PO + PO443-3- AlPO AlPO4 4 (insoluble)(insoluble)

Inadequate amount of phosphate ions will cause AlInadequate amount of phosphate ions will cause Al3+ 3+ to to be absorbedbe absorbed

It will rebind back at soft tissue or bones where It will rebind back at soft tissue or bones where phosphates are foundphosphates are found

Antacid Side EffectsAntacid Side Effects

Antacids Antacids are relatively harmless but they can have are relatively harmless but they can have minor contraindicationsminor contraindications

Magnesium CompoundsMagnesium Compounds may cause diarrheamay cause diarrhea

Aluminum CompoundsAluminum Compounds may cause constipation may cause constipation and they also may interfere with the adsorption of and they also may interfere with the adsorption of phosphates in the formation of bones. This is more likely phosphates in the formation of bones. This is more likely to be true if these compounds are taken for an extended to be true if these compounds are taken for an extended period of time.period of time.

CarbonatesCarbonates may generate carbon dioxide leading to may generate carbon dioxide leading to

bloating and flatulencebloating and flatulence..

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Alginates and Antifoaming Alginates and Antifoaming AgentsAgents

Antacids are often combined with Antacids are often combined with alginatesalginates and and anti-foaming agentsanti-foaming agents..AliginatesAliginates float on the stomach contents float on the stomach contents to form a neutralizing layer preventing to form a neutralizing layer preventing reflux of stomach acids up into the reflux of stomach acids up into the esophagus. Hence they help to prevent esophagus. Hence they help to prevent acid reflux or heart burn.acid reflux or heart burn.Anti-foaming agentsAnti-foaming agents such as such as simethiconesimethicone (dimethicone) prevent the formation of (dimethicone) prevent the formation of gases and reduce flatulence.gases and reduce flatulence.

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H2 BlockersH2 Blockers

H2 blockersH2 blockers impede acid production in the impede acid production in the stomach by blocking the actions of stomach by blocking the actions of histamine, a substance produced by the histamine, a substance produced by the body that encourages acid secretion in the body that encourages acid secretion in the stomach. stomach. These drugs cannot cure ulcers, but in These drugs cannot cure ulcers, but in certain cases they are useful in reducing certain cases they are useful in reducing inflamation allowing the stomach to heal inflamation allowing the stomach to heal H2 blockers are effective only for duodenal H2 blockers are effective only for duodenal ulcers, however, and have little effect on ulcers, however, and have little effect on stomach (gastric) ulcers. stomach (gastric) ulcers.

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H2 BlockersH2 BlockersFour H2 blockers are currently Four H2 blockers are currently available as over the counter drugs in available as over the counter drugs in the US: the US:

– Famotidine (Pepcid AC) Famotidine (Pepcid AC)

– Cimetidine (Tagamet)Cimetidine (Tagamet)

– Ranitidine (Zantac)Ranitidine (Zantac)

– Nizatidine (Axid). Nizatidine (Axid).

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Structures of common Structures of common H2 BlockersH2 Blockers

Note the similarities in structure of these H2 blockersNote the similarities in structure of these H2 blockers20

Proton Pump InhibitorsProton Pump Inhibitors Proton Pump InhibitorsProton Pump Inhibitors reduce the production of reduce the production of acid by blocking the enzyme in the wall of the acid by blocking the enzyme in the wall of the stomach that produces acid. stomach that produces acid.

InhibitorsInhibitors do not neutralize excess acid but do not neutralize excess acid but inhibit the initial production of hydrochloric acidinhibit the initial production of hydrochloric acid

The reduction of acid prevents ulcers and allows The reduction of acid prevents ulcers and allows any ulcers that exist in the esophagus, stomach any ulcers that exist in the esophagus, stomach and duodenum to heal. and duodenum to heal.

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Proton Pump InhibitorsProton Pump Inhibitors

Proton Pump Inhibitors are generally available Proton Pump Inhibitors are generally available only by prescription but low doses of some only by prescription but low doses of some products are now approved for over the counter products are now approved for over the counter useuse

Commonly prescribed Proton Pump inhibitors Commonly prescribed Proton Pump inhibitors includeinclude

– Rabeprazole (Aciphex)Rabeprazole (Aciphex)– Lansoprazole (Prevacid)Lansoprazole (Prevacid)– Omeprazole (Prilosec)Omeprazole (Prilosec)– Esomeprazole (Nexium)Esomeprazole (Nexium)

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Proton Pump InhibitorsProton Pump Inhibitors

RabeprazoleRabeprazole (Aciphex)(Aciphex)

Lansoprazole Lansoprazole (Prevacid)(Prevacid)

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Proton Pump InhibitorsProton Pump InhibitorsOmeprazoleOmeprazole (Prilosec)(Prilosec)

This is a racemic This is a racemic mixturemixture

EsomeprazoleEsomeprazole (Nexium) (Nexium)

Same structure Same structure as Omeprazole as Omeprazole but only the S but only the S isomer is isomer is includedincluded

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Summary of Antacid ProductsSummary of Antacid ProductsCommonly Commonly used antacid used antacid productsproducts

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