Amitiza dosage, forms, and strengths

Amitiza is a brand-name prescription drug used for the treatment of chronic idiopathic constipation (CIC), opioid-induced constipation (OIC), and irritable bowel syndrome with constipation (IBS-C). The active ingredient in Amitiza, lubiprostone, increases fluid secretion from the intestinal lining. The additional water speeds up the movement of stools through the colon, increasing the number of spontaneous bowel movements. Amitiza is taken as a capsule with food and water twice a day.

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Amitiza forms and strengths

Amitiza is available in only one dosage form, gelatin-coated capsules.

• Capsules: 8 micrograms (mcg), 24 mcg

For reference, a microgram is one-millionth of a gram, so each dose of Amitiza is very tiny. The capsule itself mainly consists of gelatin, water, and fats.

Amitiza capsules can be distinguished by their color. Both have “SPI” written on them, but the 8 mcg capsules are pink and the 24 mcg capsules are orange.

Amitiza dosage for adults

Amitiza is FDA-approved to improve bowel motility and the frequency of spontaneous bowel movements in adults with chronic idiopathic constipation, opioid-induced constipation, and irritable bowel syndrome with constipation (IBS-C).

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Source: Epocrates, PDR

Amitiza dosage for chronic idiopathic constipation

Constipation is a medical condition in which bowel movements are difficult and infrequent. Symptoms include irregular bowel movements, straining, hard stools, bloating, and abdominal discomfort. Chronic idiopathic constipation is diagnosed when people experience constipation symptoms for three months or more without any identifiable cause. Also called functional constipation, CIC is believed to result from improper functioning of the colon. This condition affects about 10% to 15% of adults during their lifetime.

Lubiprostone, the active ingredient in Amitiza, belongs to a family of drugs called prosecretory agents, that is, drugs that stimulate the colon tissues to secrete more fluids into the colon. Its mechanism of action is to activate pumps in the membranes of cells lining the intestinal walls. These pumps are called chloride channels, so lubiprostone is also called a “chloride channel activator.” When chloride channels are activated, the cells pump out water and chlorine ions into the colon. The increased fluid secretion improves intestinal motility and, as a result, increases the movement of stools through the colon. The more rapid movement of stools through the colon increases the daily number of spontaneous bowel movements, helping to relieve the symptoms of CIC. 

• Standard dosage for chronic idiopathic constipation: 24 mcg taken twice daily

• Maximum dosage for chronic idiopathic constipation: 48 mcg per day

Amitiza dosage for opioid-induced constipation

Amitiza is also FDA-approved to treat constipation due to opioid treatment for chronic noncancer pain. Amitiza can be used in people taking opioids for chronic pain due to previous cancer, but only if they don’t need regular increases in their opioid doses.

Opioids frequently cause constipation as part of a larger medical condition called opioid bowel dysfunction. To relieve pain, opioids attach to opioid receptors in the brain. However, the intestinal lining also has opioid receptors. When opioids attach to intestinal opioid receptors, they relax colon muscles and reduce the secretion of water into the colon. Stools become hard and move more slowly through the colon. Although the body quickly develops a tolerance for opioids as pain relievers, the gut does not develop tolerance for constipation side effects, so opioid-induced constipation does not get better until the opioids are discontinued. As with CIC, Amitiza speeds up the movement of stools through the colon by stimulating the intestinal lining to secrete more fluids into the colon.

• Standard dosage for opioid-induced constipation: 24 mcg taken twice daily

• Maximum dosage for opioid-induced constipation: 48 mcg per day

Amitiza dosage for treatment of irritable bowel syndrome with constipation

Amitiza is also FDA approved to treat adult women with irritable bowel syndrome with constipation, also called constipation-predominant irritable bowel syndrome. IBS is a common gut problem that affects 9% to 23% of the population and is characterized by a host of symptoms including abdominal pain, diarrhea, and constipation. As with CIC, there is usually no identifiable cause, so IBS is considered a functional gastrointestinal disorder (FGID). Amitiza increases fluid secretion into the colon, stimulating the colon to push its contents faster through the gut and increasing spontaneous bowel movements.

• Standard dosage for IBS-C: 8 mcg taken twice daily

• Maximum dosage for IBS-C: 16 mcg per day

Amitiza dosage for children

Amitiza is only approved for adults 18 years of age and older. Its safety and effectiveness have not been studied in children or teens.

Amitiza dosage restrictions

Lubiprostone does not enter the bloodstream in detectable amounts. However, it’s broken down into a metabolite that is absorbed into the bloodstream, so Amitiza dosages are restricted for people with liver problems. 

• Renally impaired patients (kidney disease): no dosage adjustment 

• Hepatically impaired patients (liver disease)—maximum dose: 

  • Moderate hepatic impairment (Child-Pugh Class B): 16 mcg per day

  • Severe hepatic impairment (Child-Pugh Class C): 8 mcg per day; may be increased to 16 mcg per day if side effects are not a problem

Because of pre-existing medical conditions, some people are never given Amitiza. These contraindications include gastrointestinal obstruction, severe diarrhea, and hypersensitivity to Amitiza.

How to take Amitiza

Amitiza gel capsules are taken with food and water twice per day to relieve constipation.

• A healthcare provider will indicate how much medicine to take and when to take it. Do not use more than directed.

• Swallow the capsule whole. Do not crush, break, or chew it.

• Take this medicine with food and water to reduce the chance of nausea.

• Store Amitiza in a closed container at room temperature (59° to 86°F) protected from light and extreme temperatures.

Amitiza dosage FAQs

How long does it take Amitiza to work?

Amitiza should begin to affect the colon within one hour of taking a dose. Most people should experience partial constipation relief on the first day. In one clinical study, twice as many people taking lubiprostone had a bowel movement within 24 hours of the first dose (61%) than people who took a placebo (34%). Because Amitiza doses are so tiny, the pharmacokinetics (the effects of the drug in the body) are hard to pin down exactly because drug concentrations in the blood are undetectable. 

Some people may experience side effects such as low blood pressure, fainting (syncope), or trouble breathing (dyspnea) on the very first dose. Although these side effects may resolve within three hours, they can happen repeatedly with subsequent doses.

How long does Amitiza stay in your system?

Based on animal studies, healthcare professionals believe lubiprostone is quickly broken down in the stomach and intestines. It is probably not absorbed into the blood. With a half-life of around an hour to an hour and a half, most adverse effects, such as nausea, diarrhea, and trouble breathing (dyspnea) resolve in about three hours. 

What happens if I miss a dose of Amitiza?

If a dose is missed, take it as soon as it’s remembered. If it is almost time for the next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

How long can you take Amitiza?

Amitiza can be taken as long as it works and side effects are tolerable. The longest that Amitiza was taken in clinical trials was three months.

How do I stop taking Amitiza?

Amitiza can be stopped at any time without causing side effects or withdrawal symptoms. 

Some people may need to stop taking Amitiza if they experience serious adverse effects such as severe diarrhea, low blood pressure, breathing problems, or loss of consciousness (syncope). Some of these adverse reactions can be serious enough to require hospitalization. Even common side effects such as diarrhea, nausea, vomiting, weakness (asthenia), loose stools, abdominal distension, swelling in the hands or feet (peripheral edema), or flatulence can make Amitiza difficult to take because they sometimes occur after nearly every dose.

If Amitiza cannot be taken for any reason, people with CIC, IBS-C, or OIC can turn to other solutions such as fiber supplements, laxatives, other prosecretory agents similar to Amitiza, ileal bile acid inhibitors, and serotonergic agents.

What is the maximum dosage for Amitiza?

The maximum dosage for Amitiza is 48 mcg per day.

Can you overdose on Amitiza?

If too much Amitiza is taken, call a poison helpline or get medical help. People who overdose on Amitiza are likely to experience problems such as nausea, vomiting, dizziness, headache, trouble breathing, fainting, and other common side effects. 

What interacts with Amitiza?

Because Amitiza is broken down very quickly in the digestive system, it does not have very many serious drug interactions. Drugs that may cause problems include:

• Blood pressure drugs

• Drugs that slow down intestinal motility such as opioids, tricyclic antidepressants, antidiarrheal medications, anticholinergic drugs, and some antipsychotic medications

• Laxatives

• Loop diuretics

What happens when you mix Amitiza and alcohol?

The FDA and Takeda Pharmaceuticals, the manufacturer of Amitiza, do not prohibit or caution against drinking alcohol when taking Amitiza. Alcohol may, however, worsen some Amitiza side effects, such as dizziness. Keep in mind that people with CIC, OIC, or IBS are frequently placed on restrictive diets by their doctor or a nutritionist. These diet restrictions or suggestions should rigorously be followed.

Is it safe to take Amitiza during pregnancy?

Women should get medical advice about the pros and cons of taking Amitiza while pregnant. There is no information on whether Amitiza can harm a human fetus. It is believed to be safe because lubiprostone is minimally absorbed. Animal studies did show, however, that there is an increased risk of fetal loss at very high doses.

Women who are breastfeeding are also advised to be cautious about taking Amitiza. Again, there is minimal information about its effects on milk production or a nursing infant, but healthcare providers believe it is safe because the drug is only minimally absorbed into the body.

Related resources for Amitiza dosages:

• Amitiza, Epocrates

• Amitiza prescribing information, U.S. National Library of Medicine

• Irritable bowel syndrome: Pathogenesis, diagnosis, treatment, and evidence-based medicine, World Journal of Gastroenterology

• Lubiprostone compound summary, U.S. National Library of Medicine

• Lubiprostone drug summary, Prescriber’s Digital Reference

• Lubiprostone in the treatment of chronic idiopathic constipation: An update on health-related  quality of life and patient-reported outcomes, Patient Related Outcome Measures

• Opioid, StatPearls

• Physiology, opioid receptor, StatPearls

• Update on the management of chronic idiopathic constipation, AJMC