chemistry of antacids
DESCRIPTION
Chemistry of antacids. Chia Jia YanU062203H Lee Dang NiU051984H Lim Chai YingU062410N Lim Ren Hann U062774H. Content. Introduction Types of antacids Usage and treatment Mode of action & reaction Side effects Combination Drugs Conclusion . Introduction. - PowerPoint PPT PresentationTRANSCRIPT
CHEMISTRY OF ANTACIDS
Chia Jia Yan U062203HLee Dang Ni U051984HLim Chai Ying U062410NLim Ren Hann U062774H
Content Introduction Types of antacids Usage and treatment Mode of action & reaction Side effects Combination Drugs Conclusion
Introduction Stomach contains gastric acid of pH of 2 to
3.
Gastric acid contains HCl, KCl and NaCl.
Excess acid can cause pH to fall below 2 which can cause problems such as abdominal pain and heartburn etc.
Gastric juice activates pepsin, an enzyme that carries out proteolysis – break down proteins by breaking bonds that links amino acids
Gastric Juice
Parietal cell produce gastric acid using proton pump H+/K+ ATPase, an enzyme.
As a proton pump, it transport 1 H+ in exchange of 1 K+ from stomach against concentration gradient with ATP providing the energy.
Epithelial cells
Picture taken from My Optum Health. http://www.myoptumhealth.com/portal/DiseasesandConditions/item/Gastroesophageal+reflux+disease+and+hea?section=2 (accessed on 8 April 2009)
Antacids Alkaline salt or buffer
substances used to neutralize stomach acid and bring its pH back to 2 to 3
Treat indigestion or relieve any discomfort caused by acidity of stomach acid
Reduces acid concentration within the lumen of the esophagus which increase the intra-esophageal pH and decrease pepsin activity In forms of tablet, liquid suspension , lonzenges, chewing gum, dissolving tablet
Liquid relief symptoms faster
Types of Antacids Active ingredient: Basic metal salt
Cations used are highlighted in Red Anions used: OH-, O2-, CO3
2-, HCO3-, HPO3
-, Trisilicate (Mg), amino acetate (Al)
Types of Antacids Commonly used: Al(OH)3, MgOH, CaCO3
By mixing and matching cations and anions, combiningdifferent types of antacids, unique attributes, properties
andpotency of antacids are created.
Either Mixture or Complex antacids
Other common ingredient: Simethicone – relieve gas by breaking down
bubbles Alginic acid – foaming agent that floats on top
of stomach content
Calcium Carbonate
Magnesium Salts
Aluminium Salts (usually
hydroxide) Most potent
antacid ingredient; acts rapidly with more prolonged action than sodium bicarbonate
Fast acting and long lasting effect
Good when patient suffers from calcium deficiency
Can use hydroxide, phosphate and trisilicate (common in Singapore)
Less potent that Ca hydroxide has the
highest potency Slow acting Magnesium
antacids are generally NOT absorbed. Any small amounts are cleared renally
Most stable form of aluminium salts under normal conditions
May be dehydrated to form powder that readily dissolves in acids
Mild and slow acting antacid, last longer
Insoluble in water and forms a suspension/gel that coats and protects the stomach lining
Most appropriate if patient suffers from renal failure
3 Common Antacids
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
Brand Names & AOB
Usage and Treatments Antacids needs to be in hydrated form for
better neutralizing effect
Aluminium Antacids Aluminium based antacids preferred for kidney
failure patient as it can be used to remove excess phosphate ions
Other usage:Magnesium used as a laxative for constipated patient
Reactions Strength of an antacid to neutralize acid in the stomach is
determined using the antacid’s neutralizing capacity (ANC)
ANC is expressed as milliequivalents (mEq) of the amount of 1N HCl that can be neutralized
FDA: all antacids must have a neutralizing capacity of at least 5 mEq per dose.
The commonly used antacids are ranked in this order with respect to ANC, from strongest to weakest
CaCO3 > NaHCO3 > Mg(OH)2 > Al(OH)3
Reactions - Ca CaCO3 + 2 HCl CaCl2 + H2O + CO2
1g will neutralize 20mEq of acid CaCl2 + CO3
2- CaCO3 + Cl- (higher pH in intestine)
Some unchange calcium is absorbed by the gut, which can raise the pH of the blood causing alkalosis – can affect proteins
Reactions - Mg Magnesium oxides, hydroxides and carbonates
are poorly soluble, only Chloride are soluble.
Mg(OH)2 + 2HCl MgCl2 + 2H2O1 g can neutralize 2.7 mEq of acid
MgCl + HCO3- MgCO3 +
Although non-absorbable, 5% - 10% of Mg enter systemic circulation which then rapidly removed by kidney
Reactions - Al Al(OH)3 + 3HCl AlCl3 + 3H2O Al(H2O)6
3+
1 g can neutralize 0.4 – 1.8 mEq of acid
Solubility of Al increases as pH decrease
Reaction- complex antacids Complex antacids can be used. E.g. Magaldrate [Mg(OH)Al2(OH)10]4-.2H2O
Side Effect – Al(OH)3 Causes constipation Relaxation of the gastrointestinal smooth muscle
delay in stomach emptying constipation Form insoluble complex of aluminum phosphate
(AlPO4), which is excreted in the feces. May lead to lowered serum phosphate concentrations and phosphorus mobilization from the bone. If phosphate depletion is already present, osteomalacia, osteoporosis, and fracture may result
BUT it reduce phosphates in the urine and prevent formation of phosphatic (struvite) urinary stones
Side Effect – Mg Salt Causes diarrhea: 1. Mg2+ draw water from the surrounding
body tissues into the intestinal tract by osmosis.2. Higher quantity of water in the intestinal tract softens and increases the volume of feces, stimulating nerves in the intestines.3. Mg2+ also play a role in releasing the peptide hormone cholecystokinin, causing accumulation of water and electrolytes in the intestine and triggering intestinal motility.
Side Effect – Mg Salt Magnesium salts may cause central nervous
depression in the presence of renal insufficiency
Causes hypermagnesaemia in patients with severe renal function impairment
BUT Magnesium hydroxide inhibits the precipitation of calcium oxalate and calcium phosphate, thus preventing the formation of calcium stones
Side Effect – CaCO3 Release of CO2 cause belching, nausea, abdominal distention, and flatulence.
Calcium may induce rebound acid secretion.
Calcium stone (kidney stone) can be formed.
Excess Ca2+ cause hypercalcemia. Not a problem in normal patients. But 3 - 4 g of CaCO3 per day can be problematic in patients with uremia.
Antacids may affect drugs by altering gastric and urinary pH, (e.g., thyroid hormones)
Al3+ and Mg2+ antacids are notable for their propensity to chelate other drugs present in the GI tract, forming insoluble complexes that pass through the GI tract without absorption
Most interactions can be avoided by taking antacids 2 hours before or after ingestion of other drugs
Antacids-Drugs Interaction
Require large neutralizing capacity single dose (156 meq) antacid 1 hr after meal neutralize gastric acid for 2 hr2nd dose 3 hr after eating maintains effect for > 4 hr
Tablet antacids generally weaker large number required
Very inconvenient to adminster
Limitation
Reference Pictures: http://www.specialtyminerals.com/
specialty-applications/specialty-markets-for-minerals/pharmaceuticals/antacids/
NiDDK Image Library, http://www.catalog.niddk.nih.gov/imagelibrary/detail.cfm?id=124