Antacid
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| Antacid |
ANTACIDS
These are basic substances which neutralize gastric acid and raise the pH of
gastric contents.
Peptic activity is indirectly reduced if the pH rises above 4, because
pepsin is
secreted as a complex with an inhibitory terminal moiety that
dissociates below pH 5: optimum peptic activity is exerted between
pH 2 to 4.
Antacids do not decrease acid production;
rather, agents that raise the antral pH to > 4
evoke reflex gastrin release → more acid is
secreted, especially in patients with hyperacidity
and duodenal ulcer; “acid rebound” occurs and
gastric motility is increased.
The potency of an antacid is generally expressed in terms of its
acid neutralizing
capacity (ANC), which is defined as the number of
mEq of 1N HCl that is brought to a pH of 3.5 in 15
min (or 60 min in some tests) by a unit dose of
the antacid preparation. This takes into consideration
the rate at which the antacid dissolves and
reacts with HCl. This is important because a
a single dose of any antacid taken in empty
the stomach acts for 30–60 min only, since in this
the time any gastric content is passed into the duodenum.
Taken with meals antacids may act for at the most 2–3 hr.
Antacid classification
(a) Systemic: Sodium bicarbonate, Sod. citrate
(b) Nonsystemic: Magnesium hydroxide, Mag. trisilicate,
Aluminum hydroxide
gel, Magaldrate, Calcium carbonate
Systemic Antacids
Sodium bicarbonate It is water-soluble, acts instantaneously,
but the duration of action is short. It is a potent
neutralizer (1 g → 12 mEq HCl), pH may rise above 7. However,
it has several demerits:
(a) Absorbed systemically: large doses will induce alkalosis.
(b) Produces CO2 in stomach → distention, discomfort,
belching, risk of ulcer perforation.
(c) Acid rebound occurs but is usually short-lasting.
(d) Increases Na+ load: may worsen edema and CHF.
Use of sod. bicarbonate is restricted to the casual treatment
of heartburn. It provides quick symptomatic relief. Other uses
are to alkalinize urine and to treat acidosis.
Sodium citrate Properties similar to sod. bicarbonate;
1 g neutralizes 10 mEq HCl; CO2 is not evolved.
Nonsystemic Antacids
These are insoluble and poorly absorbed basic compounds;
react in the stomach to form the corresponding chloride salt. The
chloride salt again reacts with the intestinal bicarbonate so
that HCO3
¯ is not spared for absorption—no acid-base disturbance
occurs. However, small amounts that are absorbed
have the same alkalinizing effect as NaHCO3
Antacid combinations |Antacid syrup|Antacid tablet
A combination of two or more antacids is frequently used.
These may be superior to any single agent on the following accounts:
(a) Fast (Mag. hydroxy.) and slow (Alum. hydroxy.)
acting components yield prompt as well as sustained effect.
(b) Mag. salts are laxative, while alum. salts are
constipating: combination may annul each other’s
action and bowel movement may be least
affected.
(c) Gastric emptying is least affected; while
alum. salts tend to delay it, mag./cal. salts tend to hasten it.
(d) Dose of individual components is reduced;
systemic toxicity (dependent on fractional absorption) is minimized.
What are the examples of antacids? Antacid medicine
Some available antacid combinations are: What is the best antacid?
ACIDIN: Mag. carb. 165 mg, dried alum. hydrox. gel 232 mg,
cal. carb. 165 mg, sod. bicarb. 82 mg, with kaolin 105 mg and
belladonna herb 30 μg per tab.
ALMACARB: Dried alum. hydrox. gel 325 mg, mag. carb. 50
mg, methyl polysilox. 40 mg, deglycyrrhizinated liquorice 380
mg per tab.
ALLUJEL-DF: Dried alum. hydrox. gel 400 mg, mag. hydrox.
400 mg, methyl polysilox. 30 mg per 10 ml susp.
DIGENE: Dried alum. hydrox. gel 300 mg, mag. alum. silicate
50 mg, mag. hydrox. 25 mg, methylpolysilox. 10 mg per tab.
DIGENE GEL: Mag. hydrox. 185 mg, alum. hydrox. gel 830 mg,
sod. carboxymethyl cellulose 100 mg, methylpolysilox. 25 mg
per 10 ml susp.
GELUSIL: Dried alum. hydrox. gel 250 mg, mag. trisilicate 500
mg per tab.
GELUSIL LIQUID: Mag. trisilicate 625 mg, alum. hydrox. gel
312 mg per 5 ml susp.
MUCAINE: Alum. hydrox. 290 mg, mag. hydrox. 98 mg,
oxethazaine 10 mg per 5 ml susp.
Drug interactions of Antacid
By raising gastric pH and
by forming complexes, the non-absorbable
antacids decrease the absorption of many drugs,
especially tetracyclines, iron salts, fluoroquinolones,
ketoconazole, H2 blockers, diazepam, phenothiazines,
indomethacin, phenytoin, isoniazid,
ethambutol and nitrofurantoin. Stagger their
administration by 2 hours. The efficacy of
nitrofurantoin is also reduced by alkalinization
of urine.
Uses of Antacid: What is an antacid used for?
Antacids are no longer used for healing
peptic ulcer, because they are needed in large
and frequent doses, are inconvenient, can cause
acid rebound and bowel upset, afford little
nocturnal protection and have poor patient
acceptability. Antacids are now employed only
for intercurrent pain relief and acidity, mostly
self-prescribed by the patients as over the
counter preparations. They continue to be used
for non-ulcer dyspepsia and minor episodes of
heartburn.
Gastroesophageal reflux Antacids afford
faster symptom relief than drugs which inhibit
acid secretion, but do not provide sustained
benefit. May be used off and on for acid
eructation and heartburn.
Is milk an antacid?
No, Milk is not an antacid.
