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Histamine H2 - Receptor Inhibitor

Cimetidine is a specific competitive histamine H2receptor antagonist which effectively inhibits gastric acid secretion. It is advocated for the treatment of conditions where the inhibition of gastric acid secretion is likely to be beneficial. It competitively inhibits the action of histamine at the histamine H2-receptors of the parietal cells and , thus, represents a new class of pharmacological agent, the histamine H2-receptor antagonist. Administered orally or i.v., cimetidine inhibits both daytime and nocturnal basal (non-stimulated) gastric acid secretion. Cimetidine significantly reduces gastric acid secretion stimulated by solid or liquid meals as well as that stimulated by histamine, pentagastrin, caffeine, or insulin infusion. It is generally much less effective in inhibiting carbachol (Carbarryl-choline chloride) stimulated acid secretion. The extent of inhibition is dose-related. A 50% reduction in gastric acid secretion is obtained by doses of cimetidine giving a blood concentration of 1 to 2 umol/L (0.25 to 5 ug/mL). Cimetidine reduces both hydrogen ion concentration and volume of gastric secretion. Addition of an anticholinergic agent to cimetidine at dosages greater than 400mg does not significantly enhance inhibition of acid output. Pepsin output is decreased by cimetidine, largely due to reduced volume, but to a lesser extent than acid output in the same patients. Cimetidine does not consistently alter gastric emptying or lower esophageal sphincter pressure. Pancreatic secretion of bicarbonate and enzymes is not influenced by cimetidine. Cimetidine is readily absorbed after oral administration; bio availability is about 70%. The plasma half-life is approximately 2 hours, and most of a dose of cimetidine is recovered in the urine within 24 hours.

For the treatment of duodenal ulcer therapy and prophylaxis of recurrent duodenal ulcer; non-malignant gastric ulcer; gastroesophageal reflux disease; management of upper gastrointestinal hemorrhage; control of gastric hypersecretion and peptic ulceration in the Zollinger-Ellison syndrome; and prophylaxis of stress ulceration.

Contraindications: None known.

Exclude the presence of malignant gastrointestinal neoplasm before treating symptoms of peptic ulceration with cimetidine. Because cimetidine is excreted in the urine, reduced dose is usually necessary in patients with impaired renal function. Cimetidine is removed by hemodialysis.

Pregnancy and Lactation: Give cimetidine to pregnant women only when, in the judgment of the physician, potential benefits outweigh possible risks. Give cimetidine with caution to nursing mothers; it is excreted in the milk.

Children: Clinical experience is limited; therefore, cimetidine therapy cannot be recommended for children unless anticipated benefits outweigh the potential risks. In very limited experience, 20 to 40 mg/kg/day has been administered in divided doses by mouth or i.v

Drug Interactions:
In therapeutic trials, cimetidine has been administered concomitantly with sedatives, analgesics. thiazide diuretics, bronchodilators, digoxin and propranolol without evidence of significant drug interaction. In patients on coumarin-type anticoagulants, however, further prolongation of prothrombin time has been observed with concomitant cimetidine administration. For this reason, monitor closely and adjust the anticoagulant dose as necessary when administering these drugs concurrently. Cimetidine impairs microsomal oxidative drug metabolism in a dose-dependent manner in a rat model. The inhibition was cimetidine inhibits microsomal drug metabolism.

Adverse Effects:
Mild and transient diarrhea, muscular pain, dizziness and rash have been reported in a small number of patients during treatment with cimetidine. A few cases of reversible confusional states have been reported, usually in elderly, severely ill patients, such as those with renal insufficiency or organic brain syndrome. Overdosage may have played a role in some cases. These confusional states generally cleared within 24 hours of drug withdrawal. There have been reports that a few patients have developed mild nonprogressive gynecomastia during prolonged treatment. No evidence of induced endocrine dysfunction was found, and the condition remained unchanged with continuing treatment. Rare cases of fever, hepatitis, pancreatitis, and interstitial nephritis which cleared on drug withdrawal have been reported. Some increased in plasma creatinine and serum transaminase have been reported. Decreased white blood cell counts including rare cases of agranulocytosis have been reported. These patients generally had serious concomitant illness and were receiving drugs and/or treatment known to produce neutropenia.

Hematologic Toxicity: Recently, cimetidine has been implicated in the development of cases of agranulocytosis, pancytopenia and thrombocytopenia. However, three patients recovering from metiamideinduced agranulocytosis, continued to improve after beginning treatment with cimetidine. Of the reports of bone-marrow depression reviewed, cimetidine cannot definitely by implicated in any instance.

Symptoms: In cases reported to date, involving oral ingestion of up to 12g of cimetidine per day for 5 days, no untoward effects were noted; recovery was uneventful.

Treatment: Employ the usual measures to remove unabsorbed material from the gastrointestinal tract, including clinical monitoring and supportive therapy. Studies in animals indicate that assisted respiration maybe of value and that any tachycardia may be controlled by administration of a B-blocker

Dosage: In clinical studies, cimetidine has been used in divided doses of up to 2400 mg/day in adults. Experience with cimetidine in children is limited and has not been evaluated in clinical studies (see Precautions)

Duodenal ulcer: Adults: 300mg 4 times a day, with meals and at bedtime. There has been considerable experience with a 200mg dose. A regimen of 200mg three times daily taken with meals and 400mg at bedtime is effective in treating benign gastric and duodenal ulceration. Although healing with cimetidine often occurs during the first week or two, continue treatment for at least 4 to 6 weeks, unless healing has been demonstrated by endoscopic examination. Use daily maintenance therapy for patients who will benefit from a reduction of gastric acid secretion, as well as for patients known to suffer frequent recurrence of duodenal ulcers. Following healing, initiate maintenance therapy for periods of 6 to 12 months at a reduced dosage with the last daily dose taken at bedtime. Reassess patients periodically after this period of maintenance preferably by endoscopy.

Non-malignant gastric ulcer and gastroesophageal reflux disease: Adults: 300mg 4 times daily with meals and at bedtime. Although healing of a non-malignant gastric ulcer may occur within the first 2 weeks, continue treatment for at least 6 weeks, unless healing has been demonstrated endoscopically. Administer antacids with caution concomitantly if required.

Management of upper g.i. hemorrhage: Adults: 300mg every 6 hours. In some patients it may be necessary to increase dosage; however, do not exceed a total daily dosage of 2400mg.

Impaired renal function: Patients with moderate or sever renal impairment should receive an initial dose if 200 or 300mg every 12 hours. If any increase in dosage is necessary, increase the frequency of administration.

For patients undergoing hemodialysis, perform dialysis just prior to the next scheduled dose, as some drug will be removed by dialysis.

Pathological hypersecretory conditions: e.g Zollinger-Ellison Syndrome : Adults : 300mg 4 times daily with meals and at bedtime, or 200mg 3 times daily wit meals and 400mg at night. Some patients may require more frequent administration or higher individual doses to control symptoms. Adjust dosage to patient's needs; do not exceed 2400mg/day.

Availability of dosage forms:
Apo-Cimetidine 200mg:
Each pale green, biconvex, round, film-coated tablets, one side engraved "APO" over "200" uniform very slightly off white core contains cimetidine 200mg. Available in PVC blisters of 500 tablets.

Apo-Cimetidine 400mg:
Each pale green, oblong, biconvex, film-coated tablets, one side engraved "APO-400" contains cimetidine 400mg. Available in PVC blisters of 500 tablets.

Storage conditions:
Protect from light. Store between 15-30C.

3 years from date of manufacture.











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