Comparison Histamine-2 Receptor Antagonist & Antacid

Histamine-2 Receptor Antagonist

• Their onset is slower than that of antacids, but their duration is longer.
• In large heartburn studies the earliest onset of symptom relief occurs around 30 minutes  and peak effects are 1-1.5 hours after treatment.
• The anti-secretory effect, even with low doses, is prolonged and lasts for around 10-12 hours. This means dosing frequency compared to antacids can be reduced and many subjects require only one dose per day.

Antacid

• Acid in the oesophagus and stomach may be partly or completely neutralised for rapid relief of symptoms but further gastric acid production will occur and may be stimulated via a gastrin-mediated response to a rise in gastric pH. 
• The consumption of further food will contribute to the termination of activity as gastric acid production is stimulated.
• By virtue of their mode of action, antacids cannot be used to prevent symptoms associated with ‘trigger’ foods.
• For these reasons antacids require regular re-dosing as symptoms return.

	HISTAMINE-2 RECEPTOR ANTAGONISTS (Ranitidine)	ANTACIDS (Magnesium Trisilicate)
Mechanism of Action	Inhibit acid secretion by blocking H2 receptors on the parietal cell	Antacids can neutralize gastric acid and reduce acid delivery to the duodenum. They may also stimulate the defensive systems in the stomach by increasing bicarbonate and mucus secretion.
Side Effects	Side effects of H2RAs are rare A common side effect associated with ranitidine is headache, occurring in about 3% of people who take it.  Confusion: Rare cases of reversible confusion have been associated with ranitidine; usually elderly or severely ill patients, or in patients with renal or hepatic impairment. Hepatic effects: Elevation in ALT levels has occurred with higher doses (≥100 mg) or prolonged IV therapy (≥5 days); monitor ALT levels daily for the remainder of treatment. Vitamin B12 deficiency: Prolonged treatment (≥2 years) may lead to vitamin B12 malabsorption and subsequent vitamin B12 deficiency Rebound acid hypersecretion has been reported after discontinuation of therapy.	Antacid side effects depend upon the quantity consumed and the duration of therapy. Magnesium-containing antacids cause diarrhea and hypermagnesemia; the latter only becomes important in patients with renal insufficiency. Long-term, excessive use has been associated with the development of silica-based renal calculi.
Special Precautions	Relief of symptoms does not preclude the presence of a gastric malignancy. Use with caution in patients with hepatic impairment (ranitidine undergoes hepatic metabolism). Ranitidine is primarily excreted renally; dosage adjustment is recommended in patients with renal impairment.	May alter absorption of other drugs, therefore antacids, tetracyclines or iron salts should be given 1-2 hours apart. At high dosage, magnesium salts not only cause diarrhoea but also possible CNS depression. Magnesium trisilicate mixture has a sodium content of 6.4 mmol equivalent to 73.4 mg/5 ml or 147mg/10 ml dose. This must be taken into consideration for patients on a controlled sodium diet. Used with caution in patients with fluid retention There is a risk of metabolic alkalosis when oral magnesium salts are given with polystyrene sulphonate resins.
Effectiveness	Hotz et al, 1994 With ranitidine, acid-related as well as general dyspeptic symptoms disappeared in a significantly higher percentage after two and four weeks compared with antacid.  Complete disappearance of symptoms was documented with ranitidine after two weeks in 37% and after four weeks in 66% compared with antacid in 13% and 30% respectively (p < 0.005). Patients with severe symptoms, history of ulcer and long-term dyspepsia and slight endoscopic changes in the upper gastrointestinal tract showed a significant faster and more distinct response. Both kinds of treatment were well tolerated

References 

1. https://www.uptodate.com.
2. http://www.kck.usm.my/husm/pharmacy/formulary/5.htm#5a
3. https://www.uspharmacist.com/article/updates-in-nonprescription-therapy-for-heartburn-and-gerd
4. https://www.ncbi.nlm.nih.gov/pubmed/8164599
5. http://selfcarejournal.com/article/self-care-of-heartburn/
6. https://www.drugs.com/ppa/ranitidine.htm
7. https://www.medicines.org.uk/emc/medicine/25289
8. http://www.nytimes.com/health/guides/disease/gastroesophageal-reflux-disease/medications.html