Phosphoral (Sodium Phosphate Oral Solution)
Osmotic bowel cleansing agent for colonoscopy and surgical preparation
Phosphoral is a prescription osmotic bowel cleansing solution containing sodium dihydrogen phosphate dihydrate and disodium phosphate dodecahydrate. It is used exclusively for bowel preparation before colonoscopy, endoscopy, or colon surgery. Phosphoral works by drawing water into the bowel, producing watery bowel movements that result in complete bowel evacuation. It is not indicated for the treatment of constipation and is approved for use in adults only.
Quick Facts
Key Takeaways
- Phosphoral is used only for bowel preparation before medical procedures — it is not a constipation treatment.
- Adults only: do not give Phosphoral to anyone under 18 years of age.
- Drink large amounts of clear fluids throughout the preparation to prevent dehydration.
- Each 45 mL dose contains approximately 5,000 mg sodium — caution in patients on sodium-restricted diets.
- Contraindicated in kidney disease, heart failure, bowel obstruction, and inflammatory bowel disease.
What Is Phosphoral and What Is It Used For?
Phosphoral contains two active phosphate salts — sodium dihydrogen phosphate dihydrate (24.4 g) and disodium phosphate dodecahydrate (10.8 g) — in each 45 mL dose. These phosphate salts work through an osmotic mechanism: they draw significant volumes of water from the body into the intestinal lumen, dramatically increasing the fluid content of the bowel. This increased fluid stimulates peristalsis (the muscular contractions that move contents through the intestines) and produces copious watery stools, ultimately achieving a thorough bowel evacuation.
The medication is supplied in cartons containing two 45 mL bottles. Each bottle represents one dose, and both doses must be taken at specific intervals on the day before and/or the day of the medical procedure. The solution should be diluted with water before drinking. Phosphoral is approved for use in adults throughout the European Economic Area under various brand names, including Phospho-soda in some countries.
It is critically important to understand that Phosphoral is not a treatment for constipation. Its sole indication is bowel preparation prior to medical or surgical procedures. The powerful osmotic effect of the high phosphate dose makes it unsuitable and potentially dangerous if used for routine bowel management. A thoroughly clean bowel is essential for the success of diagnostic procedures such as colonoscopy, where even small amounts of residual matter can obscure polyps or early cancerous lesions.
According to the European Society of Gastrointestinal Endoscopy (ESGE), adequate bowel preparation is one of the most important quality indicators for colonoscopy, directly affecting polyp and adenoma detection rates. Sodium phosphate-based solutions like Phosphoral have been widely studied and used for this purpose, though clinicians must carefully consider each patient's individual risk factors before prescribing them.
What Should You Know Before Taking Phosphoral?
Contraindications
There are several absolute contraindications to the use of Phosphoral. Your doctor must be informed of all medical conditions before this medication is prescribed. Understanding these restrictions is vital for patient safety, as using Phosphoral when contraindicated can lead to serious and potentially life-threatening complications.
- Known allergy to sodium phosphate or any other ingredient in the product
- Age under 18 years
- Nausea, vomiting, or abdominal pain at the time of administration
- Kidney disease or impaired renal function
- Symptomatic heart disease or congestive heart failure
- Abnormal accumulation of fluid in the abdominal cavity (ascites)
- Known or suspected bowel obstruction, perforation, or paralysis (ileus)
- Congenital or acquired enlargement of the colon (megacolon)
- Active inflammatory bowel disease (Crohn's disease or ulcerative colitis)
- Overactive parathyroid glands (hyperparathyroidism)
Do not take Phosphoral together with any other laxative products containing sodium phosphate.
Warnings and Precautions
Even in patients without absolute contraindications, Phosphoral requires careful risk assessment and sometimes enhanced monitoring. The medication's osmotic action can cause significant fluid and electrolyte shifts that may be dangerous in certain populations. Talk to your doctor, pharmacist, or nurse before taking Phosphoral if any of the following apply to you:
- Age 65 or older: Elderly patients are at increased risk of electrolyte disturbances and dehydration. Closer medical supervision may be necessary.
- Impaired heart or kidney function: Even mild reductions in cardiac or renal function increase the risk of dangerous phosphate retention and electrolyte imbalances.
- Electrolyte disturbances: Existing imbalances in sodium, potassium, calcium, or phosphate levels, or risk factors for such disturbances (including dehydration), must be corrected before use.
- Low blood pressure or reduced bowel motility: These conditions may increase the risk of complications during bowel preparation.
- Previous bowel surgery: Including colostomy or ileostomy, which may affect how the medication moves through the digestive system.
- Sodium-restricted diet: Each dose contains approximately 5,000 mg of sodium (250% of the maximum recommended daily intake for adults), which is clinically significant for patients with hypertension, heart failure, or renal impairment.
Phosphoral can subtly alter heart rhythm as a consequence of electrolyte disturbances, and consequently affected patients may require closer cardiac monitoring during bowel preparation. After taking Phosphoral, expect frequent and watery bowel movements. It is essential to drink as much clear fluid as possible to replace lost fluids and prevent dehydration.
This medicine typically begins working within 30 minutes to 6 hours. If no bowel movements occur within 6 hours of taking either the first or second dose, contact your doctor immediately, as you may be becoming dehydrated.
Pregnancy and Breastfeeding
Phosphoral should not be used during pregnancy unless your doctor determines that it is absolutely necessary. The significant fluid and electrolyte shifts caused by the medication could theoretically affect both the mother and the developing foetus, and there is insufficient clinical data from use in pregnant women to establish safety.
If you are breastfeeding, you should express and discard all breast milk from the time of the first dose until 24 hours after the second dose. Do not breastfeed your baby during this 24-hour period following the final dose. The phosphate salts and their effects on maternal electrolyte levels make it prudent to protect the nursing infant from any potential exposure through breast milk.
If you are pregnant, breastfeeding, think you may be pregnant, or are planning to have a baby, always seek advice from your doctor before using this medicine.
Driving and Using Machines
Do not drive or operate machinery if you feel tired, dizzy, or think you may be dehydrated after taking Phosphoral. The frequent bowel movements and fluid loss associated with bowel preparation can cause fatigue, lightheadedness, and impaired concentration. Stay near a toilet at all times after taking this medicine. You are personally responsible for assessing your fitness to drive or perform tasks requiring alertness.
Important Information About Sodium Content
Each 45 mL dose of Phosphoral contains approximately 5,000 mg of sodium (the main component of table salt). This corresponds to 250% of the maximum recommended daily sodium intake for adults. This must be taken into account for patients who require a low-sodium diet, particularly those with hypertension, heart failure, or renal impairment. Patients taking two doses will receive approximately 10,000 mg of sodium in total from the medication alone.
Additionally, each dose contains 29 mg of alcohol (ethanol) and 15 mg of sodium benzoate (E 211). The alcohol content is negligible and equivalent to less than 0.73 mL of beer.
How Does Phosphoral Interact with Other Drugs?
Drug interactions with Phosphoral are clinically significant and can range from altered medication efficacy to dangerous electrolyte disturbances. The osmotic action of the phosphate salts, combined with the large fluid shifts and diarrhoea produced during bowel preparation, creates multiple opportunities for interactions. Always inform your doctor or pharmacist about all medications you are currently taking, have recently taken, or might take.
Major Interactions
The following drug classes have important interactions with Phosphoral that require careful management or possible dose adjustment:
| Drug Class | Examples | Interaction Risk |
|---|---|---|
| ACE Inhibitors | Enalapril, Lisinopril, Ramipril | Increased risk of electrolyte disturbances and renal impairment |
| ARBs | Losartan, Valsartan, Candesartan | Increased risk of electrolyte disturbances and renal impairment |
| Calcium Channel Blockers | Amlodipine, Nifedipine, Diltiazem | May worsen electrolyte imbalance; risk of cardiac effects |
| Diuretics | Furosemide, Hydrochlorothiazide, Spironolactone | Compounded risk of dehydration and electrolyte loss |
| NSAIDs | Aspirin, Ibuprofen, Naproxen | Increased risk of renal impairment and electrolyte disturbance |
| Lithium | Lithium carbonate, Lithium citrate | Altered lithium levels due to fluid/electrolyte shifts; toxicity risk |
| Cardiac Rhythm Drugs | Amiodarone, Sotalol, Digoxin | Electrolyte changes may alter cardiac conduction; arrhythmia risk |
| Parathyroid Hormone | Teriparatide | May compound effects on calcium and phosphate metabolism |
Effect on Oral Medications
Perhaps the most commonly overlooked interaction is Phosphoral's potential to delay or completely prevent the absorption of regular oral medications. The rapid transit time and copious watery diarrhoea produced during bowel preparation can flush oral medications through the gastrointestinal tract before they are absorbed, effectively reducing or eliminating their therapeutic effect. This is particularly important for:
- Oral contraceptives: Efficacy may be lost — use additional contraceptive methods during and after bowel preparation.
- Antiepileptic drugs: Missed absorption could precipitate seizures in epilepsy patients.
- Oral diabetes medications: Blood sugar control may be disrupted.
- Antibiotics: Ongoing courses of antibiotics may need timing adjustments.
- Any critical daily medication: Discuss timing with your prescribing doctor well in advance of the procedure.
Your doctor may advise you to take essential medications at specific times relative to the Phosphoral doses, or may switch you to an alternative route of administration (such as injection or patch) during the preparation period.
What Is the Correct Dosage of Phosphoral?
Always take Phosphoral exactly as described in the product information or as directed by your doctor or pharmacist. The preparation involves taking two doses at specific times, following a strict clear-fluid-only diet from the start of preparation until after the procedure is completed.
How to Prepare Each Dose
For each dose, dilute the contents of one 45 mL bottle of Phosphoral in half a glass (approximately 120 mL) of cold water and drink the solution. Immediately afterwards, drink at least one full glass (240 mL) of cold water. Continue drinking as much clear fluid as possible throughout the preparation period to replace fluid lost through bowel movements.
Clear fluids include: water, strained broth or soup (no solid pieces), strained fruit juice without pulp (avoid red or purple coloured juice), black tea or coffee (without milk or cream), and clear carbonated or non-carbonated soft drinks. No solid food is permitted from the start of preparation until after the procedure.
Adults — Morning Appointment (8:00 – 12:00)
Day Before the Procedure
- 7:00 AM: Instead of breakfast, drink at least one large glass (240 mL) of clear fluid. Then take the first dose.
- 1:00 PM: Instead of lunch, drink at least three large glasses (720 mL) of clear fluid. Continue drinking throughout the afternoon.
- 7:00 PM: Instead of dinner, drink at least one large glass (240 mL) of clear fluid. Then take the second dose.
- You may continue drinking clear fluids until midnight. Drinking after midnight may cause additional toilet visits and disrupted sleep.
Adults — Afternoon Appointment (12:00 – 17:00)
Day Before the Procedure
- 1:00 PM: A light lunch is permitted (e.g., soup and a sandwich). No solid food after this meal.
- 7:00 PM: Instead of dinner, drink at least one large glass (240 mL) of clear fluid. Then take the first dose.
- During the evening, drink at least three full glasses (720 mL) of water or clear fluid before going to bed.
Day of the Procedure
- 7:00 AM: Instead of breakfast, drink at least one large glass of clear fluid. Then take the second dose.
- You may continue drinking clear fluids until 8:00 AM. Drinking after 8:00 AM may cause additional toilet visits during travel to the hospital.
Children and Adolescents
Phosphoral is not approved for use in patients under 18 years of age. The risk of electrolyte disturbances, particularly hyperphosphataemia and hypocalcaemia, is significantly higher in children due to their lower body weight and different renal handling of phosphate. Alternative bowel preparation products specifically approved for paediatric use should be discussed with your child's doctor.
Elderly Patients (65 years and older)
Elderly patients are at increased risk of adverse effects from Phosphoral, particularly dehydration, electrolyte disturbances, and renal impairment. If your doctor determines that Phosphoral is appropriate for you, you may require closer medical supervision during the preparation period. This may include blood tests to monitor electrolyte levels and kidney function before and after the procedure. Ensure you drink adequate clear fluids and report any symptoms of dehydration (extreme thirst, dry mouth, reduced urine output, dizziness) promptly.
Missed Dose
If you forget to take a dose, consult your doctor for advice. Do not take a double dose to compensate for a missed dose. A missed or incorrectly timed dose may result in inadequate bowel preparation, which could lead to your procedure being postponed or rescheduled.
Overdose
If you or someone else has taken too much Phosphoral, or if a child has accidentally ingested any amount, seek immediate medical attention or contact your local poison control centre. An overdose can cause severe dehydration, cardiovascular problems, breathing difficulties, anxiety, and colicky abdominal pain. Electrolyte imbalances from overdose can be life-threatening and require emergency hospital treatment.
After your hospital visit, make sure to drink plenty of fluids to replace the water and electrolytes lost during bowel preparation. Your doctor may advise you on appropriate rehydration strategies, especially if you are elderly or have underlying health conditions.
What Are the Side Effects of Phosphoral?
Like all medicines, Phosphoral can cause side effects, although not everybody gets them. The majority of side effects are directly related to the bowel cleansing action and the associated fluid and electrolyte shifts. Most resolve once the preparation period is over and normal eating and drinking are resumed.
In very rare cases, Phosphoral can cause severe allergic reactions with or without skin rash. Contact your doctor or go to the nearest emergency department immediately if your hands, face, lips, throat, or tongue begin to swell, or if you have difficulty breathing or swallowing.
Very Common
May affect more than 1 in 10 people
- Nausea
- Abdominal pain
- Abdominal bloating and fullness
- Diarrhoea
- Chills
- Weakness and fatigue
- Dizziness
Common
May affect up to 1 in 10 people
- Vomiting
- Chest pain
- Headache
Uncommon
May affect up to 1 in 100 people
- Dehydration
Rare
May affect up to 1 in 1,000 people
- Calcium deposits in the kidneys (nephrocalcinosis)
Very Rare
May affect up to 1 in 10,000 people
- Heart attack (myocardial infarction)
- Palpitations
- Low blood pressure (hypotension)
- Electrolyte disturbances (leading to muscle twitching and spasms)
- Muscle cramps
- Tingling sensations (paraesthesia)
- Loss of consciousness
- Kidney failure
Frequency Not Known
Cannot be estimated from available data
- Hyponatraemia (low blood sodium) — may cause neurological disturbances including confusion, coma, or seizures
The risk of serious side effects is higher in elderly patients, those with pre-existing kidney or heart disease, and patients who do not maintain adequate fluid intake during the preparation period. Following the recommended clear fluid intake protocol significantly reduces the likelihood of dehydration-related complications.
If any side effects become severe, or if you notice any effects not listed above, tell your doctor or pharmacist. Reporting suspected adverse reactions after the medicine has been authorised is important, as it allows continuous monitoring of the medicine's benefit-risk balance.
How Should You Store Phosphoral?
Correct storage of Phosphoral is important to ensure the medication remains effective and safe to use. Follow these storage guidelines:
- Temperature: Store at or below 25°C (77°F). Do not refrigerate or freeze.
- Access: Keep out of the sight and reach of children at all times.
- Expiry: Do not use Phosphoral after the expiry date printed on the carton (marked as "EXP"). The expiry date refers to the last day of that month.
- After opening: Use immediately once the bottle is opened. Discard any unused solution — do not save it for later use.
- Disposal: Do not dispose of medicines through wastewater or household waste. Return unused or expired medicines to your pharmacist for safe disposal to protect the environment.
What Does Phosphoral Contain?
Active Substances
- Sodium dihydrogen phosphate dihydrate: 24.4 g per 45 mL dose
- Disodium phosphate dodecahydrate: 10.8 g per 45 mL dose
Other Ingredients (Excipients)
- Sodium benzoate (preservative, E 211)
- Saccharin sodium (sweetener)
- Glycerol
- Purified water
- Flavouring (ginger and lemon aroma) — consisting of ginger balsam, alcohol, lemon oil, terpene-reduced lemon oil, citric acid, and purified water
Appearance and Pack Sizes
Phosphoral is a clear, colourless oral solution with a ginger and lemon scent. It is available in cartons containing 2 or 100 bottles of 45 mL with screw caps. Each bottle contains one dose. Not all pack sizes may be marketed in all countries.
The marketing authorisation holder and manufacturer is Casen Recordati, S.L., based in Utebo, Zaragoza, Spain. This medicine is approved in the European Economic Area and the United Kingdom (Northern Ireland) under various names, including Phosphoral (Denmark, Finland, Netherlands, Sweden), Phospho-soda (Greece, Ireland, UK, Portugal), and Recholan (France).
Frequently Asked Questions About Phosphoral
References
- European Medicines Agency (EMA). Phosphoral — Summary of Product Characteristics. Available at: www.ema.europa.eu.
- Hassan C, et al. Bowel preparation for colonoscopy: European Society of Gastrointestinal Endoscopy (ESGE) Guideline — Update 2019. Endoscopy. 2019;51(8):775-794. doi:10.1055/a-0959-0505.
- British National Formulary (BNF). Bowel cleansing preparations. National Institute for Health and Care Excellence (NICE). Available at: bnf.nice.org.uk.
- World Health Organization (WHO). Model List of Essential Medicines — 23rd List (2023). Geneva: WHO; 2023.
- Belsey J, et al. Systematic review and meta analysis: oral bowel preparation for colonoscopy. Alimentary Pharmacology & Therapeutics. 2007;25(4):373-384.
- U.S. Food and Drug Administration (FDA). FDA Drug Safety Communication: FDA warns of possible harm from exceeding recommended dose of over-the-counter sodium phosphate products. 2014.
- Markowitz GS, et al. Acute phosphate nephropathy following oral sodium phosphate bowel purgative. Journal of the American Society of Nephrology. 2005;16(11):3389-3396.
- European Society of Gastrointestinal Endoscopy (ESGE). Quality indicators for colonoscopy — Update 2023. Endoscopy. 2023.
Editorial Team
This article was written by the iMedic Medical Editorial Team, a group of licensed physicians specialising in gastroenterology, internal medicine, and clinical pharmacology. All content is reviewed according to international guidelines from the WHO, EMA, and BNF.
All drug information is independently verified against approved product labelling (SmPC), international formularies, and peer-reviewed clinical literature. Content follows the GRADE evidence framework.
iMedic has no commercial funding, pharmaceutical sponsorship, or advertising revenue. All content is produced independently to ensure unbiased medical information.