Chapter 50 Acid-controlling drugs Flashcards
Antacids are basic compounds used to neutralize stomach acid. Most commonly they are?
nonprescription salts of aluminum, magnesium, calcium, and/or sodium.
Many antacid preparations contain the antiflatulent drug?
simethicone, which reduces gas and bloating
Many aluminum- and calcium-based formulations also
include?
magnesium, which not only contributes to the acid neutralizing capacity, but also counteracts the constipating effects of aluminum and calcium.
Antacids (Calcium carbonate [tums], magnesium hydroxide [milk of magnesia]) MOA
neutralizing gastric acidity. They do not prevent the overproduction of acid but instead help to neutralize acid secretions. It is also believed that antacids promote gastric mucosal defensive mechanisms, especially at lower dosages.
- They do this by stimulating secretion of mucus, prostaglandins, and bicarbonate from cells inside gastric glands
- mucus serves a protective barrier against destructive actions of hydrochloric acid
- bicarbonate helps buffer acidity of hydrochloric acid
- prostaglandins prevent histamine from binding to its corresponding parietal cell receptors, which inhibits production of adenylate cyclase. W/out adenlyate cyclase, no cAMP can be formed and no second messenger is available to activate proton pum
The primary drug effect of antacids is?
reduction of the symptoms associated with various acid-related disorders, such as pain and reflux “heartburn”
-Antacid pain reduction is thought to be a result of base-mediated inhibition of the protein-digesting ability of pepsin, increase in the resistance of the stomach lining to irritation, and increase in the tone of the cardiac sphincter, which reduces reflux from the stomach
Antacids indications
indicated for the acute relief of symptoms associated with peptic ulcer, gastritis, gastric hyperacidity, and heartburn
Antacids contraindications
- known allergy to specific drug product
- severe renal failure or electrolyte disturbances (because of the potential toxic accumulation of electrolytes in the antacids themselves)
- GI obstruction (magnesium antacids may be contraindicated for pt’s with small bowel obstruction because of the laxative effect)
Antacids adverse effects
Adverse effects are limited
- Magnesium preparations, such as milk of magnesia, can cause diarrhea.
- Aluminum- and calcium-containing formulations can cause constipation
- Calcium products can cause kidney stones; rebound hyperacidity, or acid rebound, when antacid use is discontinued; chronic use of high-dose calcium containing antacids or use in renal failure can cause a syndrome known as milk-alkali syndrome (HA, nausea, alkalosis, hypercalcemia)
- excessive use of any antacid can result in systemic alkalosis; more common with sodium bicarbonate
long term self medication with antacids may?
mask symptoms of serious underlying disease such as bleeding ulcer or malignancy
Antacids interactions
Many drug interactions occur with the acid-controlling drugs due to alteration of oral dosage forms, and so other medications are to be avoided within 1 to 2 hours of taking an antacid. Antacids are sometimes to be avoided when other acid-controlling drugs are taken.
Combination products containing both magnesium and aluminum may have fewer adverse effects than either type of antacid by itself. The net effect is a?
balancing of both adverse effects and fewer problems with altered bowel patterns.
Cautious use of antacids high in sodium is recommended in patients who have?
heart failure, hypertension, or other cardiac diseases or who require sodium restriction.
Many drug interactions occur with the acid-controlling drugs due to alteration of oral dosage forms, and so other medications are to be avoided within?
1 to 2 hours of taking an antacid. Antacids are sometimes to be avoided when other acid-controlling drugs are taken.
Four basic mechanisms by which antacids cause interactions include:
(1) adsorption of other drugs to antacids, which reduces the ability of the other drug to be absorbed into the body (2) chelation, which is the chemical inactivation of other drugs that produces insoluble complexes
(3) increased stomach pH, which increases the absorption of basic drugs and decreases the absorption of acidic drugs
(4) increased urinary pH, which increases the excretion of acidic drugs and decreases the excretion of basic drugs.
Examples of drugs whose effects may be chemically enhanced by the presence of antacids (due to pH effects) are?
- Benzodiazepines
- Sulfonylureas
- Sympathomimetics
- Valprioic acid
Presence of antacids reduces the efficacy of interacting drugs by?
Interfering with their GI absorption
-such drugs include: allopurinol, tetracycline, thyroid hormones, captopril, corticosteroids, digoxin, histamine antagonists, phenytoin, isoniazid, nitrofurantoin, phenothiazines, salicylates, and quinolone antibiotics
Significant patient harm may ensue when the quinolone antibiotics (ciprofloxacin, levofloxacin, and moxifloxacin) are given with?
antacids
-these antibiotics are administered orally to treat serious infections. Antacids can reduce their absorption by more than 50%. Thus, antacids must be given either 2 hours before or 2 hours after the dose of a quinolone antibiotic
Antacids are generally excreted quickly through the?
GI tract and/or the electrolyte homeostatic mechanisms of the kidneys
Antacids are considered safe for use during pregnancy if?
Prolonged administration and high dosages are avoided
Aluminum and sodium based antacids recommended for?
Patients with renal compromise because they are more easily excreted than antacids in other categories
Calcium-containing antacids can be used as an extra?
Source of calcium
Calcium carbonate neutralization will produce?
Gas and possibly belching
-for this reason it is combined w/an antiflatulent drug such as simethicone
Magnesium-containing antacids commonly have a?
Laxative effect, and frequent administration of these antacids alone often cannot be tolerated
Both calcium and magnesium antacids are more likely to accumulate?
To toxic levels in pt’s with renal disease and are often avoided in this patient group
Some of the more serious concerns with antacids include?
acid rebound, hypercalcemia, milk-alkali syndrome, and metabolic alkalosis.
H2 receptor antagonists, also known as H2RAs and H2 receptor blockers, are the prototypical acid-secretion antagonists. They are H2 blockers that bind to and block?
histamine receptors located on parietal cells. This blockade renders these cells less responsive to stimuli and thus decreases their acid secretion. Up to 90% inhibition of acid secretion can be achieved.
-they competively block the H2 receptor of acid-producing parietal cells. This makes the parietal cell less responsive not only to histamine but also to the stimulation of ACh and gastrin
H2 receptor antagonist drugs
Cimetidine (Tagamet)
Ranitidine (Zantac)
Famotidine (Pepcid)
The effects of H2 receptor antagonists is
reduced hydrogen ion secretion from the parietal cells results in an increase in the stomach pH and relief of symptoms associated with hyperacidity-related conditions.
H2 receptor antagonists indications
used for GERD, peptic ulcer disease, and erosive esophagitis; adjunct therapy in the control of upper GI tract bleeding; and treatment of pathologic gastric hypersecretory conditions such as Zollinger-Ellison syndrome.
H2 receptor antagonists contraindications
- known drug allergy
- liver and/or kidney dysfunction are relative contraindications that my warrant dosage adjustment
H2 receptor antagonists Adverse effects
- CNS AEs occur less than 1% of pt’s but sometimes seen in older adults (confusion & disorientation)
- Cimetidine (Tagamet) may induce impotence and gynecomastia (result of the drugs inhibition of estradiol metabolism and displacement of dihydrotestosterone from peripheral androgen-binding sites)
- all 4 drugs may increase secretion of prolactin from the anterior pituitary gland
- Thrombocytopenia has been reported with Ranitidine and Famotidine
H2 receptor antagonists interactions
- Cimetidine carries a higher risk of drug interactions than ranitidine, famotidine, and nizatidine, especially in elderly. Cimetidine binds enzymes of the hepatic cytochrome P-450 microsomal oxidase system. By inhibiting the metabolism of drugs metabolized via this pathway, it may raise the blood concentrations of certain drugs.
- Ranitidine has 10-20% of the binding action of cimetidine on the P-450 enzyme system, and famotidine has essentially no effect
- significant interactions more likely to arise with medications having a narrow therapeutic range, such as theophylline, warfarin, lidocaine, and phenytoin
- All 4 drugs may inhibit absorption of certain drugs, such as ketoconazole, that require an acidic GI environment for gastric absorption
- smoking decreases effectiveness of H2 antagonists
- they are taken 1-2 hours BEFORE antacids
H2 Receptor Antagonist: Cimetidine (Tagamet)
- Because of potential to cause drug interactions, its use has been replaced by ranitidine and famotidine
- still used to treat certain allergic reactions
H2 Receptor Antagonist: Ranitidine (Zantac)
- does not carry concerns over drug interactions that cimetidine has and has become most widely used
- oral and IV
- dosing different for different forms
- oral ranitidine is dosed as 150mg twice a day or 300 mg at bedtime
- IV dosed at 50 mg every 8 hours
