Histamine H 2-receptor Antagonists (Systemic)

Before Using This Medicine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For H ₂ -blockers, the following should be considered:

Allergies - Tell your doctor if you have ever had any unusual or allergic reaction to cimetidine, famotidine, nizatidine, or ranitidine.

Pregnancy - H ₂ -blockers have not been studied in pregnant women. In animal studies, famotidine and ranitidine have not been shown to cause birth defects or other problems. However, one study in rats suggested that cimetidine may affect male sexual development. More studies are needed to confirm this. Also, studies in rabbits with very high doses have shown that nizatidine causes miscarriages and low birth weights. Make sure your doctor knows if you are pregnant or if you may become pregnant before taking H ₂ -blockers.

Breast-feeding - Cimetidine, famotidine, nizatidine, and ranitidine pass into the breast milk and may cause unwanted effects, such as decreased amount of stomach acid and increased excitement, in the nursing baby. It may be necessary for you to take another medicine or to stop breast-feeding during treatment. Be sure you have discussed the risks and benefits of the medicine with your doctor.

Children - This medicine has been tested in children and, in effective doses, has not been shown to cause different side effects or problems than it does in adults when used for short periods of time.

Older adults - Confusion and dizziness may be especially likely to occur in elderly patients, who are usually more sensitive than younger adults to the effects of H ₂ -blockers.

Other medicines - Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking or receiving H ₂ -blockers it is especially important that your health care professional know if you are taking any of the following:

• Aminophylline (e.g., Somophyllin) or
• Anticoagulants (blood thinners) or
• Caffeine (e.g., NoDoz) or
• Metoprolol (e.g., Lopressor) or
• Oxtriphylline (e.g., Choledyl) or
• Phenytoin (e.g., Dilantin) or
• Propranolol (e.g., Inderal) or
• Theophylline (e.g., Somophyllin-T) or
• Tricyclic antidepressants (amitriptyline [e.g., Elavil], amoxapine [e.g., Asendin], clomipramine [e.g., Anafranil], desipramine [e.g., Pertofrane], doxepin [e.g., Sinequan], imipramine [e.g., Tofranil], nortriptyline [e.g., Aventyl], protriptyline [e.g., Vivactil], trimipramine [e.g., Surmontil]) - Use of these medicines with cimetidine has been shown to increase the effects of cimetidine. This is less of a problem with ranitidine and has not been reported for famotidine or nizatidine. However, all of the H ₂ -blockers are similar, so drug interactions may occur with any of them

• Itraconazole (e.g., Sporanox) or
• Ketoconazole (e.g., Nizoral) - H ₂ -blockers may decrease the effects of itraconazole or ketoconazole; H ₂ -blockers should be taken at least 2 hours after these medicines

Other medical problems - The presence of other medical problems may affect the use of H ₂ -blockers. Make sure you tell your doctor if you have any other medical problems, especially:

• Kidney disease or
• Liver disease - The H ₂ -blocker may build up in the bloodstream, which may increase the risk of side effects

• Phenylketonuria (PKU) - Some H ₂ -blockers contain aspartame. Aspartame is converted to phenylalanine in the body and must be used with caution in patients with PKU. The Pepcid AC brand of famotidine chewable tablets contains 1.4 mg of phenylalanine per 10-mg dose. The Pepcid RPD brand of famotidine oral dispersible tablets contains 1.05 mg of phenylalanine per 20-mg dose. The Zantac brand of ranitidine EFFERdose tablets and EFFERdose granules contain 16.84 mg of phenylalanine per 150-mg dose

• Weakened immune system (difficulty fighting infection) - Decrease in stomach acid caused by H ₂ -blockers may increase the possibility of a certain type of infection