Nitrates vs. phosphates: What’s the difference?
- Nitrates are vasodilators used to treat or prevent heart pain (angina, chest pain) caused by heart disease, usually of the arteries in the heart.
- Phosphates are laxatives used to clean out the intestines before a colonoscopy.
- Examples of nitrates include nitroglycerin sublingual tablet (Nitrostat), nitroglycerin lingual aerosol (Nitromist), nitroglycerin pumpspray (Nitrolingual Pumpspray), nitroglycerin transdermal ointment (Nitro-Bid), nitroglycerin transdermal infusion system (Nitro-Dur), nitroglycerin transdermal therapeutic system (Transderm-Nitro), nitroglycerin oral capsule (Nitro-Time), nitroglycerin intravenous, and isosorbide mononitrate and dinitrate (Isordil, Isordil Titradose, Dilatrate-SR).
- A brand name of sodium phosphate is OsmoPrep.
- Side effects of nitrates and phosphates that are similar include headache, dizziness, and nausea.
- Side effects of nitrates that are different from phosphates include lightheadedness, flushing, burning and tingling under the tongue, low blood pressure, skin irritation, itching, and topical allergic reactions with the topical patch form.
- Side effects of phosphates that are different from nitrates include vomiting, stomach/abdominal pain, and bloating.
What are nitrates? What are phosphates?
Nitrates are vasodilators used to treat or prevent heart pain (angina, chest pain) caused by heart disease, usually of the arteries in the heart. Angina pectoris ("heart pain") is due to an inadequate flow of blood and oxygen to the muscle of the heart. Nitrates increase the flow of blood and oxygen to the heart and thereby increase the amount of work that the heart can do by dilating (expanding) the arteries and veins in the body so the heart works less and requires less blood and oxygen. Dilation of the veins reduces the amount of blood that returns to the heart that must be pumped, while dilation of the arteries lowers the pressure in the arteries against which the heart must pump.
Phosphates are used to clean out the intestines before a colonoscopy. Sodium phosphate is a laxative that works by drawing large amounts of water into the colon, causing watery bowel movements. This cleans out the intestines so a doctor can clearly view them during a colonoscopy. Phosphates should not be used for weight loss or constipation due to the possibility of severe side effects.
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In the U.S., 1 in every 4 deaths is caused by heart disease.
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What are the side effects of nitrates and phosphates?
Nitrates
Common side effects of nitrates include:
- Headache
- Dizziness
- Lightheadedness
- Nausea
- Flushing
- Burning and tingling under the tongue
- Low blood pressure
Other side effects include:
- Skin irritation
- Itching
- Topical allergic reactions may also occur with the topical patch form
Phosphates
WARNING
There have been rare, but serious reports of acute phosphate nephropathy in patients who received oral sodium phosphate products for colon cleansing prior to colonoscopy. Some cases have resulted in permanent impairment of renal function and some patients required long-term dialysis. While some cases have occurred in patients without identifiable risk factors, patients at increased risk of acute phosphate nephropathy may include those with increased age, hypovolemia, increased bowel transit time (such as bowel obstruction), active colitis, or baseline kidney disease, and those using medicines that affect renal perfusion or function (such as diuretics, angiotensin converting enzyme [ACE] inhibitors, angiotensin receptor blockers [ARBs], and possibly nonsteriodal anti-inflammatory drugs [NSAIDs]).
OsmoPrep can cause serious side effects, including:
- Changes in your blood tests. Your doctor may do blood tests after you take OsmoPrep to check your levels of calcium, phosphate, potassium, sodium in your blood.
- Tell your doctor if you have any symptoms of too much fluid loss, including:
- Vomiting
- Nausea
- Abnormal heart beat (arrhythmias)
- Seizures or fainting (black-outs). People who take a medicine that contains sodium phosphate, such as OsmoPrep, can have seizures or faint (become unconscious) even if they have not had seizures before. Tell your doctor right away if you have a seizure or faint while taking OsmoPrep.
- Inflammatory bowel disease.
The most common side effects of OsmoPrep are:
- bloating
- stomach (abdominal) pain
- nausea
- vomiting
Tell your doctor if you have any side effect that bothers you or that does not go away.
These are not all the possible side effects of OsmoPrep. For more information, ask your doctor or pharmacist.
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
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What is the dosage for nitrates vs. phosphates?
Nitrates
Nitrates are available in various formulations. Nitroglycerin is available in:
- oral capsule
- sublingual tablet
- sublingual spray
- intravenous solution
- topical ointment
- topical patch
- isosorbide mononitrate and isosorbide dinitrate are available as immediate and extended-release tablets
Only sublingual tablets, intravenous, or immediate release tablets are used for immediate treatment of angina because the onset of action of the other formulations is not fast enough.
Phosphates
Take OsmoPrep exactly as prescribed by your doctor.
It is important for you to drink clear liquids before, during, and after taking OsmoPrep. This may help prevent kidney damage. Examples of clear liquids are water, flavored water, lemonade (no pulp), ginger ale or apple juice. Do not drink any liquids colored purple or red. You must read, understand, and follow these instructions to take OsmoPrep the right way: On the evening before your colonoscopy, you will take a total of 20 OsmoPrep tablets, as follows:
- Take 4 OsmoPrep tablets with 8 ounces of clear liquids.
- Wait 15 minutes.
- Take 4 more OsmoPrep tablets with 8 ounces of clear liquids.
- Repeat steps 2 and 3 above, three more times. Make sure you wait 15 minutes after each time.
On the day of your colonoscopy, you will take a total of 12 OsmoPrep tablets, starting about 3 to 5 hours before your colonoscopy, as follows:
- Take 4 OsmoPrep tablets with 8 ounces of clear liquids.
- Wait 15 minutes.
- Take 4 more OsmoPrep tablets with 8 ounces of clear liquids.
- Repeat steps 2 and 3 one more time.
If you take too much OsmoPrep, call your doctor or get medical help right away.
What drugs interact with nitrates and phosphates?
Nitrates
- Nitrates can slow down metabolism of cabergoline and ergonovine, resulting in an increase in systolic blood pressure and an increased likelihood of angina symptoms.
- Sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra) increase the blood pressure lowering effects of nitrates and may cause excessive blood pressure reduction. Men taking nitrates should not take sildenafil (Viagra), tadalafil (Cialis), or vardenafil (Levitra).
Phosphates
- You should not take other laxatives or enemas made with sodium phosphate, while taking OsmoPrep.
- You should not use OsmoPrep if you have already used it in the last 7 days.
Are nitrates and phosphates safe to use while pregnant or breastfeeding?
Nitrates
- The FDA classifies nitrates as pregnancy category C, which means that safe and effective use of nitrates in pregnant women has not been established. Nitrates should be given to pregnant women only if clearly needed.
- It is not known whether nitrates enter breast milk; therefore, nitrates must be used with caution in women who are breastfeeding.
Phosphates
- Animal reproduction studies have not been conducted with OsmoPrep. It is not known whether OsmoPrep can cause fetal harm when administered to a pregnant woman, or can affect reproduction capacity.
- OsmoPrep Tablets should be given to a pregnant woman only if clearly needed.