For patients taking the nonprescription strengths of these medicines for heartburn, acid indigestion, and sour stomach:

• Do not take the maximum daily dosage continuously for more than 2 weeks, unless directed to do so by your doctor.
• If you have trouble in swallowing, or persistent abdominal pain, see your doctor promptly. These may be signs of a serious condition that may need different treatment.

For patients taking the prescription strengths of these medicines for more serious problems:

• One dose a day Take it at bedtime, unless otherwise directed.
• Two doses a day Take one in the morning and one at bedtime.
• Several doses a day Take them with meals and at bedtime for best results.

It may take several days before this medicine begins to relieve stomach pain. To help relieve this pain, antacids may be taken with the H ₂-blocker, unless your doctor has told you not to use them. However, you should wait one-half to one hour between taking the antacid and the H ₂-blocker.

Take this medicine for the full time of treatment, even if you begin to feel better. Also, it is important that you keep your appointments with your doctor for check-ups so that your doctor will be better able to tell you when to stop taking this medicine.

For patients taking famotidine chewable tablets:

• Chew the tablets well before swallowing.

For patients taking famotidine oral disintegrating tablets:

• Make sure your hands are dry.
• Leave tablets in unopened package until the time of use, then open the pack and remove the tablet.
• Immediately place the tablet on the tongue.
• The tablet will dissolve in seconds, and you may swallow it with your saliva. You do not need to drink water or other liquid to swallow the tablet.

For patients taking ranitidine effervescent granules or tablets:

• Remove the foil wrapping and dissolve the dose in 6 to 8 ounces of water before drinking.

Dosing

The dose of histamine H ₂-receptor antagonists (also called H ₂-blockers) will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The number of capsules or tablets or teaspoonfuls of solution, suspension, or syrup that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking the H .

For cimetidine
• For oral dosage forms (solution and tablets):
  • To treat duodenal or gastric ulcers:
    • Older adults, adults, and teenagers 300 milligrams (mg) four times a day, with meals and at bedtime. Some people may take 400 or 600 mg two times a day, on waking up and at bedtime. Others may take 800 mg at bedtime.
    • Children 20 to 40 mg per kilogram (kg) (9.1 to 18.2 mg per pound) of body weight a day, divided into four doses, taken with meals and at bedtime.
  • To prevent duodenal ulcers:
    • Older adults, adults, and teenagers 300 mg two times a day, on waking up and at bedtime. Instead some people may take 400 mg at bedtime.
    • Children Dose must be determined by your doctor.
  • To treat heartburn, acid indigestion, and sour stomach:
    • Adults and teenagers 100 to 200 mg with water when symptoms start. The dose may be repeated once in twenty-four hours. Do not take more than 400 mg in twenty-four hours.
    • Children Dose must be determined by your doctor.
  • To prevent heartburn, acid indigestion, and sour stomach:
    • Adults and teenagers 100 to 200 mg with water up to one hour before eating food or drinking beverages you expect to cause symptoms. Do not take more than 400 mg in twenty-four hours.
    • Children Dose must be determined by your doctor.
  • To treat conditions in which the stomach produces too much acid:
    • Adults 300 mg four times a day, with meals and at bedtime. Your doctor may change the dose if needed.
    • Children Dose must be determined by your doctor.
  • To treat gastroesophageal reflux disease:
    • Adults 800 to 1600 mg a day, divided into smaller doses. Treatment usually lasts for 12 weeks.
    • Children Dose must be determined by your doctor.
• For injectable dosage form:
  • To treat duodenal ulcers, gastric ulcers or conditions in which the stomach produces too much acid:
    • Older adults, adults, and teenagers 300 mg injected into muscle, every six to eight hours. Or, 300 mg injected slowly into a vein every six to eight hours. Instead, 900 mg may be injected slowly into a vein around the clock at the rate of 37.5 mg per hour. Some people may need 150 mg at first, before beginning the around-the-clock treatment.
    • Children 5 to 10 mg per kg (2.3 to 4.5 mg per pound) of body weight injected into a vein or muscle, every six to eight hours.
  • To prevent stress-related bleeding:
    • Older adults, adults, and teenagers 50 mg per hour injected slowly into a vein around the clock for up to 7 days.
    • Children Dose must be determined by your doctor.

For famotidine
• For oral dosage forms (suspension, tablets, chewable tablets, and oral disintegrating tablets):
  • To treat duodenal ulcers:
    • Older adults, adults, and teenagers 40 milligrams (mg) once a day at bedtime. Some people may take 20 mg two times day.
    • Children Dose must be determined by your doctor.
  • To prevent duodenal ulcers:
    • Older adults, adults, and teenagers 20 mg once a day at bedtime.
    • Children Dose must be determined by your doctor.
  • To treat gastric ulcers:
    • Older adults, adults, and teenagers 40 mg once a day at bedtime.
    • Children Dose must be determined by your doctor.
  • To treat heartburn, acid indigestion, and sour stomach:
    • Adults and teenagers 10 mg with water when symptoms start. The dose may be repeated once in twenty-four hours. Do not take more than 20 mg in twenty-four hours.
    • Children Dose must be determined by your doctor.
  • To prevent heartburn, acid indigestion, and sour stomach:
    • Adults and teenagers 10 mg taken one hour before eating a meal you expect to cause symptoms. The dose may be repeated once in twenty-four hours. Do not take more than 20 mg in twenty-four hours.
    • Children Dose must be determined by your doctor.
  • To treat conditions in which the stomach produces too much acid:
    • Older adults, adults, and children 20 mg every six hours. Your doctor may change the dose if needed.
    • Children Dose must be determined by your doctor.
  • To treat gastroesophageal reflux disease:
    • Older adults, adults, and teenagers 20 mg two times a day, usually for up to 6 weeks.
    • Children weighing more than 10 kg (22 pounds) 1 to 2 mg per kilogram (kg) (0.5 to 0.9 mg per pound) of body weight a day divided into two doses.
    • Children weighing less than 10 kg (22 pounds) 1 to 2 mg per kg (0.5 to 0.9 mg per pound) of body weight a day, divided into three doses.
• For injectable dosage form:
  • To treat duodenal ulcers, gastric ulcers, or conditions in which the stomach produces too much acid:
    • Older adults, adults, and teenagers 20 mg injected into a vein, every twelve hours.
    • Children Dose must be determined by your doctor.

For nizatidine
• For oral dosage forms (capsules and tablets):
  • To treat duodenal or gastric ulcers:
    • Older adults, adults, and teenagers 300 milligrams (mg) once a day at bedtime. Some people may take 150 mg two times a day.
    • Children Dose must be determined by your doctor.
  • To prevent duodenal ulcers:
    • Adults and teenagers 150 mg once a day at bedtime.
    • Children Dose must be determined by your doctor.
  • To prevent heartburn, acid indigestion, and sour stomach:
    • Adults and teenagers 75 mg taken thirty to sixty minutes before eating a meal you expect to cause symptoms. The dose may be repeated once in twenty-four hours.
    • Children Dose must be determined by your doctor.
  • To treat gastroesophageal reflux disease:
    • Adults and teenagers 150 mg two times a day.
    • Children Dose must be determined by your doctor.

For ranitidine
• For oral dosage forms ( effervescent granules, syrup, tablets, effervescent tablets):
  • To treat duodenal ulcers:
    • Older adults, adults, and teenagers 150 milligrams (mg) two times a day. Some people may take 300 mg once a day at bedtime.
    • Children 2 to 4 mg per kilogram (kg) (1 to 2 mg per pound) of body weight per day, usually given as two divided doses. .However, your total dose will not be more than 300 mg a day.
  • To prevent duodenal ulcers:
    • Older adults, adults, and teenagers 150 mg at bedtime.
    • Children Dose must be determined by your doctor.
  • To treat gastric ulcers:
    • Older adults, adults, and teenagers 150 mg two times a day.
    • Children 2 to 4 mg per kilogram (1 to 2 mg per pound) of body weight per day, usually given as two divided doses. However, your total dose will not be more than 300 mg a day.
  • To treat heartburn, acid indigestion, and sour stomach:
    • Adults and teenagers 75 mg with water when symptoms start. The dose may be repeated once in twenty-four hours. Do not take more than 150 mg in twenty-four hours.
    • Children Dose must be determined by your doctor.
  • To prevent heartburn, acid indigestion, and sour stomach:
    • Adults and teenagers 75 mg with water taken thirty to sixty minutes before eating a meal or drinking beverages you expect to cause symptoms. Do not take more than 150 mg in twenty-four hours.
    • Children Dose must be determined by your doctor.
  • To treat some conditions in which the stomach produces too much acid:
    • Older adults, adults, and teenagers 150 mg two times a day. Your doctor may change the dose if needed.
    • Children Dose must be determined by your doctor.
  • To treat gastroesophageal reflux disease:
    • Older adults, adults, and teenagers 150 mg two times a day. Your dose may be increased if needed.
    • Children 5 to 10 mg per kg (2.3 to 4.6 mg per pound) of body weight a day, usually divided and given in two doses during the day. However, most children usually will not take more than 300 mg a day.
• For injectable dosage form:
  • To treat duodenal ulcers, gastric ulcers, or conditions in which the stomach produces too much acid:
    • Older adults, adults, and teenagers 50 mg injected into a muscle every six to eight hours. Or, 50 mg injected slowly into a vein every six to eight hours. Instead, you may receive 6.25 mg per hour injected slowly into a vein around the clock. However, most people will usually not need more than 400 mg a day.
  • To treat duodenal or gastric ulcers:
    • Children 2 to 4 mg per kg (1 to 2 mg per pound) of body weight a day, injected slowly into a vein.

Missed dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store the capsule or tablet form of this medicine in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Keep the liquid form of this medicine from freezing.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

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

• 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