Tagamet

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Tell your doctor about all prescription, non-prescription, illegal, recreational, herbal, nutritional, or dietary drugs you're taking, especially:

• Antacids such as Maalox, Mylanta, and Tums
• Anticoagulants (blood thinners) such as warfarin (Coumadin)
• Antidepressants such as amitriptyline (Elavil), amoxapine (Asendin), clomipramine (Anafranil), desipramine (Norpramin), doxepin (Adapin, Sinequan), imipramine (Tofranil), nortriptyline (Aventyl, Pamelor), protriptyline (Vivactil), and trimipramine (Surmontil)
• Chlordiazepoxide (Librium)
• Clopidogrel (Plavix)
• Diazepam (Valium)
• Digoxin (Lanoxin)
• Herbal or dietary supplements
• Iron salts
• Ketoconazole (Nizoral)
• Lidocaine (Xylocaine)
• Metronidazole (Flagyl)
• Nifedipine (Adalat, Procardia)
• Phenytoin (Dilantin)
• Propranolol (Inderal)
• Theophylline (Theobid, Theo-Dur)

Cimetidine and Other Interactions

Cimetidine may cause dizziness or drowsiness. Don't drive or operate machinery until you know how this drug affects you.

Cimetidine and Alcohol

Alcohol may make drowsiness and dizziness worse.

Talk to your doctor before consuming alcohol while taking cimetidine.

Tagamet is part of the drug class:

• H2 receptor antagonists

Medications can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of Tagamet, there are no specific foods that you must exclude from your diet when receiving this medication.

Tell your doctor if you are breastfeeding or plan to breastfeed.

Tagamet has been detected in human breast milk. Because of the possibility for adverse reactions in nursing infants from Tagamet, a choice should be made whether to stop nursing or to stop use of this medication. The importance of the drug to the mother should be considered.

Use this medication exactly as directed on the label, or as your doctor has prescribed it for you. Do not use more of the medication than recommended. Do not use the medication for longer than recommended.

Avoid taking antacids unless your doctor recommends them for heartburn pain. Follow your doctor's advice about the type of antacid to use and when to use it. You may not be able to take the antacid at the same time you take your dose of cimetidine.

Taking cimetidine may make you more susceptible to virus that can cause pneumonia. This has occurred most often in elderly people and in those with diabetes, a weak immune system, or chronic lung disease. Before using cimetidine, tell your doctor if you have any of these conditions.

There are many other drugs that can interact with cimetidine. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

Heartburn can be confused with early symptoms of heart attack. Seek emergency medical attention if you have chest pain or heavy feeling, dizziness, pain spreading to the arm or shoulder, sweating, nausea or vomiting, and a general ill feeling.

Heartburn can be confused with early symptoms of heart attack. Seek emergency medical attention if you have chest pain or heavy feeling, dizziness, pain spreading to the arm or shoulder, sweating, nausea or vomiting, and a general ill feeling.

Taking cimetidine may make you more susceptible to virus that causes pneumonia. You may be more likely to develop pneumonia if you have certain health problems.

Ask a doctor or pharmacist if it is safe for you to take cimetidine if you have:

• diabetes;

• asthma or a chronic lung disorder;

• a weak immune system;

• bone marrow suppression;

• kidney disease; or

• liver disease.

Cimetidine is in the FDA pregnancy category B. This means that it is not expected to be harmful to an unborn baby. Do not use this medication without telling your doctor if you are pregnant or plan to become pregnant during treatment.

Cimetidine passes into breast milk, and may be harmful to a nursing baby. Do not take cimetidine without telling your doctor if you are breast-feeding a baby.

Do not give this medicine to a child younger than 16 years old unless your doctor has told you to.

Inhibits hepatic microsomal enzyme systems, decreases hepatic metabolism of some drugs.118 If necessary, adjust dosage of hepatically metabolized drugs when cimetidine therapy is initiated or discontinued.b

Specific Drugs

Absorption

Bioavailability

Oral: 60–70%.b

Onset

≥70% decrease in basal acid secretion within 45 minutes after single 300- or 400-mg IV dose in healthy males.100

Duration

Food

Delays, slightly decreases absorption.b However, administration with meals achieves maximum blood concentrations and antisecretory effect when stomach is no longer protected by food buffering effect.b

Distribution

Extent

Widely distributed throughout the body.b

Distributed into human milk.b

Crosses the placenta in animals.b

Plasma Protein Binding

15–20%.b

Elimination

Metabolism

Metabolized to sulfoxide (major metabolite) and 5-hydroxymethyl derivatives in liver.a b More extensively metabolized after oral than parenteral administration.a

Elimination Route

Excreted principally in urine.a b Single oral dose: 48% (unchanged) excreted in urine over 24 hours.a IV or IM: about 75% (unchanged) excreted in urine within 24 hours.a Single IV dose of radiolabeled cimetidine: 80–90% (50–73% unchanged, remainder as metabolites) excreted in urine over 24 hours.b About 10% excreted in feces.b

Half-life

2 hours.a

After IV administration in children 4.1–15 years of age: Apparent biphasic decline of plasma cimetidine and cimetidine sulfoxide concentrations with half-lives of 1.4 and 2.6 hours, respectively.102

Special Populations

2.9 hours in patients with Clcr 20–50 mL/minute.b 3.7 hours in patients with Clcr <20 mL/minute.b 5 hours in anephric patients.b

Applies to cimetidine: compounding powder, intravenous solution, oral liquid, oral tablet

Nervous system

Nervous system side effects have included headache (up to 3.5%), dizziness (1%), and somnolence (1%). Severe mental status changes, including depression, agitation, disorientation, confusion, delirium, unsteadiness, slurred speech, lethargy, hallucinations, and coma, while uncommon, have been reported frequently in the literature. Other nervous system effects reported are extrapyramidal symptoms, cerebellar syndrome with encephalopathy, and paresthesias. Critical illness, advanced age, renal, and/or liver disease appear to be associated with an increased risk for central nervous system toxicity.[Ref]

The mechanism by which cimetidine induces mental status changes is not well established but appears to involve increased serum concentrations of cimetidine and, possibly, cimetidine sulfoxide. Advanced age has been implicated in many case reports of mental status changes, however, the pharmacokinetics of cimetidine correlate more closely with renal function, making renal dysfunction associated with advanced age a more likely risk factor than age itself. In addition, enhanced cimetidine penetration of the blood brain barrier has been demonstrated in patients with liver disease. Onset of symptoms have usually developed within 2 to 3 days of start of therapy, but may be delayed. Following discontinuation of cimetidine, mental status usually normalizes over several days.[Ref]

Psychiatric

Psychiatric side effects may accompany other signs and symptoms of neurologic toxicity such as unsteadiness, slurred speech, and lethargy. Age, renal dysfunction, and/or liver disease may be predisposing factors in these cases.

Psychiatric side effects in the form of severe depression, suicidal ideation, paranoia, and frank psychosis have also been reported in otherwise healthy patients.[Ref]

Psychiatric side effects have included depression, paranoia, agitation, mania, hallucinations, psychosis, and loss of libido. These side effects may be accompanied by other signs and symptoms of neurologic toxicity. Critical illness, advanced age, renal, and/or liver disease appear to be associated with an increased risk for central nervous system toxicity, including psychiatric disturbances.[Ref]

Endocrine

Endocrine side effects have included gynecomastia, occurring in 0.3% to 1% of patients treated for nonhypersecretory conditions for 1 month or longer. In patients treated for pathologic hypersecretory conditions, this occurred in about 4% of cases. In the majority of cases, however, hormone levels remain in the normal range. In addition, galactorrhea, impotence, and transient alopecia as well as a case of possible cimetidine-induced hypoparathyroidism have been reported.[Ref]

A large population-based cohort study involving 81,535 men evaluated the risk of gynecomastia associated with cimetidine, ranitidine, misoprostol, and omeprazole. Overall, 37,202 men received cimetidine. Gynecomastia developed in 86 men treated with cimetidine. The relative risk of gynecomastia during cimetidine treatment compared to a control population not treated with cimetidine was 7.2. Use of daily doses of 1000 mg or more was associated with a relative risk of 43.5.

Luteinizing hormone (LH), follicle-stimulating hormone (FSH), serum prolactin, testosterone, and estradiol levels are usually within the normal range in patients who develop gynecomastia or breast tenderness while on cimetidine. However, decreases in serum testosterone and increases in LH and estradiol as well as increases in serum prolactin have been reported on occasion.

Severe hypocalcemia was reported in an elderly woman treated with cimetidine postoperatively. There was some evidence in this case to support a possible cimetidine-induced reduction in parathyroid hormone with subsequent hypocalcemia. More study is needed to confirm this.[Ref]

Cardiovascular

In a study involving medical ICU patients requiring invasive blood pressure monitoring for circulatory instability or with a need for repeated arterial blood gas draws, an average decrease of 14 mmHg in systolic and 9 mmHg in diastolic pressure was noted in 74% (50/68) of patients following administration of cimetidine (the active ingredient contained in Tagamet) 200 mg IV over 3 minutes. In 13% of patients, systolic pressure decreased by more than 30 mmHg.

Most cardiovascular side effects are noted following rapid intravenous administration. While administration by slow infusion appears to reduce the incidence of such effects, serious cardiovascular events, including sinus arrest, have been reported with continuous intravenous infusions as well as oral administration.[Ref]

Cardiovascular side effects have been rarely reported. These are usually associated with rapid intravenous administration. Tachycardia, bradycardia, hypotension, QT interval prolongation, premature ventricular contractions, junctional rhythm, AV block, and sinus arrest have been reported with H2 receptor antagonist.[Ref]

Hematologic

Hematologic side effects have rarely included leukopenia, eosinophilia, neutropenia, thrombocytopenia, agranulocytosis, and aplastic anemia. The manufacturer also reports extremely rare cases of autoimmune hemolytic anemia.[Ref]

Rare cases of irreversible or fatal blood dyscrasias have been reported in the literature. While rare, hematologic abnormalities should be considered in patients treated with cimetidine who develop fever, chills, sore throat, easy bruising, and other signs or symptoms suggestive of a blood dyscrasia.[Ref]

Hepatic

Hepatic side effects have included elevations in liver function tests and hepatitis of both cholestatic and mixed cholestatic-hepatocellular types. Some presentations of cimetidine-induced hepatitis have features suggestive of a hypersensitivity response.[Ref]

Overall, serious hepatotoxicity due to cimetidine is rare. Bridging hepatic necrosis, centrilobular hepatic necrosis, and intrahepatic cholestasis have been noted on biopsy in cases of cimetidine-induced hepatitis. In some cases, liver toxicity has been associated with fever, rash, and eosinophilia, suggesting a hypersensitivity etiology.

Cimetidine-induced hepatitis in a patient with a history of famotidine-induced hepatitis has been reported in at least one case. Extreme caution is recommended when initiating cimetidine therapy in a patient with a history of other H2-antagonist-induced hepatotoxicity.

Liver injury, with fatal outcome, has been reported with the use of other H2 receptor antagonists.[Ref]

Renal

Renal side effects have included elevations in serum creatinine. However, such elevations are generally due to competitive inhibition of tubular secretion of creatinine rather than a result of impaired glomerular filtration or renal toxicity. Rare cases of acute renal failure and interstitial nephritis have been reported.[Ref]

Elevations in serum creatinine by as much as 20% are reported during cimetidine therapy. Cimetidine is thought to competitively inhibit the secretion of creatinine by the renal proximal tubules resulting in a reduction in creatinine clearance. Creatinine does not appear to affect cimetidine transport, except at very high concentrations.

Overt renal toxicity, such as renal failure and interstitial nephritis, is rare. In some cases, cimetidine-induced renal toxicity has been attributed to a delayed-type hypersensitivity.[Ref]

Gastrointestinal

Gastrointestinal side effects have been reported rarely. These have included diarrhea (1%) which is generally mild although severe cases have been reported, nausea/vomiting (0.6%), constipation (0.2%), dry mouth, and taste changes. In addition, cases of parotitis, phytobezoars, and pancreatitis have been reported.[Ref]

Dermatologic

Dermatologic side effects have included mild rash as well as severe dry skin (xerosis), seborrheic dermatitis, erythema annular centrifugum, erythema multiforme, Stevens-Johnson syndrome, exfoliative dermatitis, and toxic epidermal necrolysis. Reversible alopecia has also been reported rarely.[Ref]

Antiandrogen and sebum-inhibitory effects are proposed mechanisms by which cimetidine causes severe xerosis and asteatotic dermatitis.[Ref]

Musculoskeletal

Musculoskeletal side effects have rarely included arthralgias, inflammatory arthritis, gout-like arthritis, and myalgias. The manufacturer reports rare cases of polymyositis although causality is unknown.[Ref]

Immunologic

Immunologic side effects have included a case of exacerbation of cutaneous systemic lupus erythematosus and cimetidine-induced cutaneous vasculitis. Strongyloidiasis hyperinfection has been reported rarely in immunocompromised patients.[Ref]

Hypersensitivity

Hypersensitivity side effects have included urticaria, pruritus, fever, angioedema, and anaphylaxis. In addition, a case of drug fever in association with leukocytosis and abdominal pain has also been reported. Vasculitis has been reported. It resolved on discontinuation of the drug.[Ref]

Some side effects of Tagamet may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.