Phosphorus is a naturally occurring substance that is important in every cell in the body. The majority of phosphorus in the body is found in the bones. The potassium and sodium salt forms of phosphorus are called phosphates.

PHOS-NaK is a combination medicine used to make the urine more acid to help prevent kidney stones.

PHOS-NaK may also be used for purposes not listed in this medication guide.

You should not take PHOS-NaK if you have severe kidney disease, or high levels of phosphorus in your body.

Follow all directions on your prescription label. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Take this medicine with a full glass of water.

PHOS-NaK works best if you take it with meals and at bedtime.

While using this medicine, you may need frequent blood or urine tests.

The powder form must be mixed with water before you take it. Mix 1 packet of the powder with about 1/3 cup (2.5 ounces) of water and stir until completely dissolved. Swallow the mixture right away after mixing. Do not save for later use.

The tablet form may need to be dissolved in water, or swallowed whole. Carefully follow any dosing instructions provided with your medicine.

If you have a history of kidney stones, it is possible that you will pass old stones after starting treatment with PHOS-NaK.

Store at room temperature away from moisture, heat, and light. Keep the bottle tightly closed when not in use.

You should not take PHOS-NaK if you are allergic to it, or if you have:

• severe kidney disease; or

• high levels of phosphorus in your blood (hyperphosphatemia).

To make sure this medicine is safe for you, tell your doctor if you have:

• a history of kidney stones in the distant past;

• kidney disease;

• cirrhosis or other liver disease;

• high blood levels of potassium (hyperkalemia), calcium (hypercalcemia), or sodium (hypernatremia);

• heart disease, high blood pressure;

• toxemia of pregnancy;

• Addison's disease (an adrenal gland disorder);

• breathing problems;

• pancreas disorder;

• thyroid disorder;

• swelling in your hands or feet;

• if you are dehydrated; or

• if you take a diuretic or "water pill."

FDA pregnancy category C. It is not known whether PHOS-NaK will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using this medicine.

It is not known whether this medicine passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

PHOS-NaK should not be given to a child younger than 4 years old without a doctor's advice.

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include numbness or tingly feeling, muscle stiffness or limp feeling, loss of movement, confusion, heavy feeling in your legs, irregular heartbeats, or feeling like you might pass out.

Ask your doctor before using an antacid, and use only the type your doctor recommends. Some antacids can make it harder for your body to absorb PHOS-NaK.

Avoid taking a vitamin or mineral supplement that contains calcium or vitamin D, unless your doctor tells you to.

Do not use potassium supplements or salt substitutes while you are taking PHOS-NaK, unless your doctor has told you to.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

PHOS-NaK may cause serious side effects. Call your doctor at once if you have:

• severe or ongoing diarrhea;

• seizures (convulsion);

• shortness of breath; or

• signs of a kidney problem--little or no urinating; painful or difficult urination; swelling in your feet or ankles; feeling tired or short of breath.

Common side effects of PHOS-NaK may include:

• nausea, vomiting, stomach pain, diarrhea;

• bone or joint pain;

• headache, dizziness, tired feeling;

• muscle pain or weakness;

• increased thirst; or

• numbness or tingly feeling.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Other drugs may interact with potassium phosphate and sodium phosphate, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now and any medicine you start or stop using.