Cimetidine: Package Insert and Label Information (Page 2 of 3)
Gastroesophageal Reflux Disease
In 2 multicenter, double-blind, placebo-controlled studies in patients with gastroesophageal reflux disease (GERD) and endoscopically proven erosions and/or ulcers, cimetidine tablets were significantly more effective than placebo in healing lesions. The endoscopically confirmed healing rates were:
| Trial | Cimetidine Tablets (800 mg twice daily) | Cimetidine Tablets (400 mg 4 times daily) | Placebo | p-Value (800 mg twice daily vs. placebo) | |
| 1 | Week 6 | 45% | 52% | 26% | 0.02 |
| Week 12 | 60% | 66% | 42% | 0.02 | |
| 2 | Week 6 | 50% | 20% | <0.01 | |
| Week 12 | 67% | 36% | <0.01 |
In these trials cimetidine tablets were superior to placebo by most measures in improving symptoms of day- and night-time heartburn, with many of the differences statistically significant. The 4 times-daily regimen was generally somewhat better than the twice-daily regimen where these were compared.
Pathological Hypersecretory Conditions (such as Zollinger-Ellison Syndrome):
Cimetidine tablets significantly inhibited gastric acid secretion and reduced occurrence of diarrhea, anorexia, and pain in patients with pathological hypersecretion associated with Zollinger-Ellison Syndrome, systemic mastocytosis, and multiple endocrine adenomas. Use of cimetidine tablets were also followed by healing of intractable ulcers.
INDICATIONS AND USAGE
Cimetidine tablets are indicated in:
1. Short-term treatment of active duodenal ulcer. Most patients heal within 4 weeks and there is rarely reason to use cimetidine tablets at full dosage for longer than 6 to 8 weeks (see DOSAGE AND ADMINISTRATION: Duodenal Ulcer). Concomitant antacids should be given as needed for relief of pain. However, simultaneous administration of cimetidine tablets and antacids is not recommended, since antacids have been reported to interfere with the absorption of cimetidine.
2. Maintenance therapy for duodenal ulcer patients at reduced dosage after healing of active ulcer. Patients have been maintained on continued treatment with cimetidine tablets 400 mg at bedtime for periods of up to 5 years.
3. Short-term treatment of active benign gastric ulcer. There is no information concerning usefulness of treatment periods of longer than 8 weeks.
4. Erosive gastroesophageal reflux (GERD). Erosive esophagitis diagnosed by endoscopy. Treatment is indicated for 12 weeks for healing of lesions and control of symptoms. The use of cimetidine tablets beyond 12 weeks has not been established (see DOSAGE AND ADMINISTRATION: GERD).
5. The treatment of pathological hypersecretory conditions (i.e., Zollinger-Ellison Syndrome, systemic mastocytosis, multiple endocrine adenomas).
CONTRAINDICATIONS
Cimetidine tablets are contraindicated for patients known to have hypersensitivity to the product.
PRECAUTIONS
General
Rare instances of cardiac arrhythmias and hypotension have been reported following the rapid administration of cimetidine hydrochloride injection by intravenous bolus.
Symptomatic response to treatment with cimetidine tablets do not preclude the presence of a gastric malignancy. There have been rare reports of transient healing of gastric ulcers despite subsequently documented malignancy.
Reversible confusional states (see ADVERSE REACTIONS) have been observed on occasion, predominantly, but not exclusively, in severely ill patients. Advancing age (50 or more years) and preexisting liver and/or renal disease appear to be contributing factors. In some patients these confusional states have been mild and have not required discontinuation of cimetidine tablets. In cases where discontinuation was judged necessary, the condition usually cleared within 3 to 4 days of drug withdrawal.
Drug Interactions
Cimetidine tablets, apparently through an effect on certain microsomal enzyme systems, has been reported to reduce the hepatic metabolism of warfarin-type anticoagulants, phenytoin, propranolol, nifedipine, chlordiazepoxide, diazepam, certain tricyclic antidepressants, lidocaine, theophylline, and metronidazole, thereby delaying elimination and increasing blood levels of these drugs.
Clinically significant effects have been reported with the warfarin anticoagulants; therefore, close monitoring of prothrombin time is recommended, and adjustment of the anticoagulant dose may be necessary when cimetidine tablets are administered concomitantly. Interaction with phenytoin, lidocaine, and theophylline has also been reported to produce adverse clinical effects.
However, a crossover study in healthy subjects receiving either 300 mg 4 times daily or 800 mg at bedtime of cimetidine tablets concomitantly with a 300 mg twice-daily dose of theophylline extended-release tablets demonstrated less alteration in steady-state theophylline peak serum levels with the 800 mg at bedtime regimen, particularly in subjects aged 54 years and older. Data beyond 10 days are not available. (Note: All patients receiving theophylline should be monitored appropriately, regardless of concomitant drug therapy.)
Dosage of the drugs mentioned above and other similarly metabolized drugs, particularly those of low therapeutic ratio or in patients with renal and/or hepatic impairment, may require adjustment when starting or stopping the concomitant administration of cimetidine tablets to maintain optimum therapeutic blood levels.
Alteration of pH may affect absorption of certain drugs (e.g., ketoconazole). If these products are needed, they should be given at least 2 hours before cimetidine administration.
Additional clinical experience may reveal other drugs affected by the concomitant administration of cimetidine tablets.
Carcinogenesis, Mutagenesis, Impairment of Fertility
In a 24-month toxicity study conducted in rats, at dose levels of 150, 378 and 950 mg/kg/day (approximately 8 to 48 times the recommended human dose), there was a small increase in the incidence of benign Leydig cell tumors in each dose group; when the combined drug-treated groups and control groups were compared, this increase reached statistical significance. In a subsequent 24-month study, there were no differences between the rats receiving 150 mg/kg/day and the untreated controls. However, a statistically significant increase in benign Leydig cell tumor incidence was seen in the rats that received 378 and 950 mg/kg/day. These tumors were common in control groups as well as treated groups and the difference became apparent only in aged rats.
Cimetidine has demonstrated a weak antiandrogenic effect. In animal studies this was manifested as reduced prostate and seminal vesicle weights. However, there was no impairment of mating performance or fertility, nor any harm to the fetus in these animals at doses 8 to 48 times the full therapeutic dose of cimetidine tablets, as compared with controls. The cases of gynecomastia seen in patients treated for 1 month or longer may be related to this effect.
In human studies, cimetidine tablets have been shown to have no effect on spermatogenesis, sperm count, motility, morphology or in vitro fertilizing capacity.
Pregnancy
Teratogenic Effects. Pregnancy Category B
Reproduction studies have been performed in rats, rabbits and mice at doses up to 40 times the normal human dose and have revealed no evidence of impaired fertility or harm to the fetus due to cimetidine tablets. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproductive studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Nursing Mothers
Cimetidine is secreted in human milk and, as a general rule, nursing should not be undertaken while a patient is on a drug.
Pediatric Use
Clinical experience in children is limited. Therefore, therapy with cimetidine tablets cannot be recommended for children under 16, unless, in the judgement of the physician, anticipated benefits outweigh the potential risks. In very limited experience, doses of 20 to 40 mg/kg/day have been used.
Immunocompromised Patients
In immunocompromised patients, decreased gastric acidity, including that produced by acid-suppressing agents such as cimetidine, may increase the possibility of a hyperinfection of strongyloidiasis.
ADVERSE REACTIONS
Adverse effects reported in patients taking cimetidine tablets are described as follows by body system. Incidence figures of 1 in 100 and greater are generally derived from controlled clinical studies.
Gastrointestinal
Diarrhea (usually mild) has been reported in approximately 1 in 100 patients.
CNS
Headaches, ranging from mild to severe, have been reported in 3.5% of 924 patients taking 1,600 mg/day, 2.1% of 2,225 patients taking 800 mg/day and 2.3% of 1,897 patients taking placebo. Dizziness and somnolence (usually mild) have been reported in approximately 1 in 100 patients on either 1,600 mg/day or 800 mg/day.
Reversible confusional states, e.g., mental confusion, agitation, psychosis, depression, anxiety, hallucinations, disorientation, have been reported predominantly, but not exclusively, in severely ill patients. They have usually developed within 2 to 3 days of initiation of treatment with cimetidine tablets and have cleared within 3 to 4 days of discontinuation of the drug.
Endocrine
Gynecomastia has been reported in patients treated for 1 month or longer. In patients being treated for pathological hypersecretory states, this occurred in about 4% of cases while in all others the incidence was 0.3% to 1% in various studies. No evidence of induced endocrine dysfunction was found, and the condition remained unchanged or returned toward normal with continuing treatment with cimetidine tablets.
Reversible impotence has been reported in patients with pathological hypersecretory disorders, e.g., Zollinger-Ellison Syndrome, receiving cimetidine tablets, particularly in high doses, for at least 12 months (range 12 to 79 months, mean 38 months). However, in large-scale surveillance studies at regular dosage, the incidence has not exceeded that commonly reported in the general population.
Hematologic
Decreased white blood cell counts in patients treated with cimetidine tablets (approximately 1 per 100,000 patients), including agranulocytosis (approximately 3 per million patients), have been reported, including a few reports of recurrence on rechallenge. Most of these reports were in patients who had serious concomitant illnesses and received drugs and/or treatment known to produce neutropenia. Thrombocytopenia (approximately 3 per million patients) and, very rarely, cases of pancytopenia or aplastic anemia have also been reported. As with some other H2 -receptor antagonists, there have been extremely rare reports of immune hemolytic anemia.
Hepatobiliary
Dose-related increases in serum transaminase have been reported. In most cases they did not progress with continued therapy and returned to normal at the end of therapy. There have been rare reports of cholestatic or mixed cholestatic-hepatocellular effects. These were usually reversible. Because of the predominance of cholestatic features, severe parenchymal injury is considered highly unlikely. However, as in the occasional liver injury with other H2 -receptor antagonists, in exceedingly rare circumstances fatal outcomes have been reported.
There has been reported a single case of biopsy-proven periportal hepatic fibrosis in a patient receiving cimetidine tablets.
Rare cases of pancreatitis, which cleared on withdrawal of the drug, have been reported.
Hypersensitivity
Rare cases of fever and allergic reactions including anaphylaxis and hypersensitivity vasculitis, which cleared on withdrawal of the drug, have been reported.
Renal
Small, possibly dose-related increases in plasma creatinine, presumably due to competition for renal tubular secretion, are not uncommon and do not signify deteriorating renal function. Rare cases of interstitial nephritis and urinary retention, which cleared on withdrawal of the drug, have been reported.
Cardiovascular
Rare cases of bradycardia, tachycardia and AV heart block have been reported with H2 -receptor antagonists.
Musculoskeletal
There have been rare reports of reversible arthralgia and myalgia; exacerbation of joint symptoms in patients with preexisting arthritis has also been reported. Such symptoms have usually been alleviated by a reduction in the dosage of cimetidine tablets. Rare cases of polymyositis have been reported, but no causal relationship has been established.
Integumental
Mild rash and, very rarely, cases of severe generalized skin reactions including Stevens-Johnson syndrome, epidermal necrolysis, erythema multiforme, exfoliative dermatitis and generalized exfoliative erythroderma have been reported with H2 -receptor antagonists. Reversible alopecia has been reported very rarely.
Immune Function
There have been extremely rare reports of strongyloidiasis hyperinfection in immunocompromised patients.
Respiratory
A large epidemiological study suggested an increased risk of developing pneumonia in current users of histamine-2-receptor antagonists (H2 RAs) compared to patients who had stopped H2 RA treatment, with an observed adjusted relative risk of 1.63 (95% CI, 1.07 to 2.48). However, a causal relationship between use of H2 RAs and pneumonia has not been established.
OVERDOSAGE
Studies in animals indicate that toxic doses are associated with respiratory failure and tachycardia that may be controlled by assisted respiration and the administration of a beta-blocker.
Reported acute ingestions orally of up to 20 grams have been associated with transient adverse effects similar to those encountered in normal clinical experience. The usual measures to remove unabsorbed material from the gastrointestinal tract, clinical monitoring, and supportive therapy should be employed.
There have been reports of severe CNS symptoms, including unresponsiveness, following ingestion of between 20 and 40 grams of cimetidine, and extremely rare reports following concomitant use of multiple CNS-active medications and ingestion of cimetidine at doses less than 20 grams. An elderly, terminally ill dehydrated patient with organic brain syndrome receiving concomitant antipsychotic agents and 4,800 mg of cimetidine intravenously over a 24-hour period experienced mental deterioration with reversal on discontinuation of cimetidine.
There have been two deaths in adults who were reported to have ingested over 40 grams orally on a single occasion.
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