Antacid drugs
Oral antacids neutralize gastric acid to water and a neutral salt. Common antacids are bases of aluminum, magnesium or calcium.
In addition to their acid-neutralizing ability, antacids decrease pepsin activity, bind to bile acids in the stomach and stimulate
local prostaglandin production. Antacids are effective as long as they remain within the stomach and consequently must be
given frequently. Antacids may interfere with the GI absorption of concurrently administered drugs and often cause constipation.
Many OTC antacids are available.
Sucralfate (carafate) is a nonabsorbable compound containing aluminum hydroxide and sucrose octasulfate. When given orally,
sucralfate forms a gel that has local effects on the gastrointestinal tract. It has a high affinity for ulcerated tissue,
and will selectively bind with connective tissue in the ulcer, exerting a local protective role. It will inactivate pepsin,
absorb bile acids, and the aluminum hydroxide portion has an acid-neutralizing effect. Studies have shown that this compound
has a cytoprotective role thought to be caused by stimulating local tissue prostaglandins.
A dose of 1/4 to 1 gram three to four times a day is suggested, depending on animal size. The timing when given with other
drugs has been a topic of debate, suggesting gastric acid is needed to dissolve the tablet, and that antacids should be given
following sucralfate. That has not been proven in vivo and probably is of little significance; however, more important is
the fact that sucralfate can bind to other drugs and inhibit their absorption. Sucralfate also is effective in treating esophagitis
when given as a liquid.
H2-receptor antagonists such as cimetidine, ranitidine, famotidine and nizatidine are effective in reducing acid production
by blocking the histamine receptor of the parietal cell. However, blocking only one of the three receptors on the parietal
cell does not maximally inhibit all acid secretion. Some studies also suggest the H2-receptor antagonists may have benefits
related to stimulation of local prostaglandin synthesis and thus a cytoprotective function.
The prophylactic value of H2-receptor antagonists to prevent gastric ulceration is at this time questionable, but they have
been shown to be effective in healing ulceration. Cimetidine is given at 5-10 mg/kg QID given IV, IM, or PO. Ranitidine is
more potent, has a longer half-life and is administered at 2 mg/kg TID and famotidine is dosed at 0.5 mg/kg BID or once daily.
Cimetidine will alter hepatic biotransformation of certain drugs, and should be used with care in dogs with liver disease.
Proton-pump inhibitors (PPIs) block all acid production by the parietal cell by irreversibly binding the proton-transporting
enzyme at the luminal surface of the cell. There is a delayed onset of action, but the duration of action is prolonged (24
hours or more) until new enzyme is produced. It is a potent acid blocker, effectively blocking all stimuli causing acid secretion
(histamine, gastrin and acetylcholine). Omeprazole (Prilosec) is given at a dose of 0.7 mg/kg PO once a day. This drug is
safe, with minimal side effects, but may compete with hepatic metabolism of some drugs. It is more effective in healing aspirin-induced
ulcers than the H2 antagonists and may also have some gastroprotective effects, preventing gastric ulcer formation.
Omeprazole is recommended in animals with severe ulceration or those that fail to respond to traditional ulcer therapy, such
as dogs with mastocytosis, gastrinomas or other causes of hypergastrinemias. PPIs are my choice when treating reflux esophagitis
because the esophagus is easily damaged by gastric acid, and PPIs block all gastric acid-formation.
Prostaglandin E has potent anti-secretory effects as well as cytoprotective effects. The synthetic PGE misoprostol (Cytotec)
is given at a dose of 2-5 mcg/kg QID. Misoprostol suppresses gastric acid secretion by inhibiting the activation of histamine-sensitive
adenylate cyclase. The cytoprotective effects arise from stimulation of bicarbonate and mucus secretion, increased mucosal
blood flow, decreased vascular permeability and increased epithelial cell renewal.
The main indication for misoprostol use is the prevention or treatment of gastric ulceration from NSAIDs. It is uncertain
if misoprostol will improve healing of established gastric ulcers and apparently does not have distinct advantages over other
antacids in treating ulcers not associated with NSAIDs. High doses cause diarrhea and abdominal cramping and should not be
used in pregnant animals because it can cause abortion.
Dr. Hoskins is owner of Docu-Tech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: jdhoskins@mindspring.com
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