MiraLAX (PEG3350)


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Home > Key Issues > Constipation



  • Many CKD cats suffer from constipation, and treating or preventing it can make a big difference to your cat's quality of life.

  • It is important to keep a close eye on your cat's litter tray and to deal promptly with any signs of constipation or straining.

  • There are two considerations with constipation: prevention and treating it if it is present.

  • Obviously the ideal is to prevent constipation from ever happening, but that is not always possible. If a cat has an acute case  of constipation, you will have to use a more powerful treatment.

  • The Cautions section discusses treatments that are usually best avoided.

Causes                                                                                                                                                 Back to Page Index


In addition to concentrating urine, a cat's body also tries to conserve water by reabsorbing it from the stool through the intestinal wall. This mechanism is very efficient, and remains so even in CKD cats, and since CKD cats are largely on the edge of dehydration most of the time, the intestine will wring every drop of water out of the stool that it can, leaving it quite dry. The lack of moisture as a lubricant makes it more difficult for the cat to have bowel movements and can lead to constipation. 


Some cases of constipation are caused by low potassium levels or by high calcium levels. Treating these problems may resolve or improve the constipation.


Feline Constipation is a detailed and helpful website about constipation.

Pets Canada has information on the different colours of cat poop.

The International Cat Care has a helpful overview of constipation.

Merck Veterinary Manual has a helpful overview of the mechanisms by which many of the treatments described below work.


Symptoms                                                                                                                                          Back to Page Index


Some of the symptoms of constipation are:

  • loss of appetite

  • pooping next to the litter tray

  • vomiting before, during or immediately after using the tray

  • dry stools

  • an ungainly walk

  • lying in the litter box

Some of the symptoms of constipation are not what you might expect. Occasionally a cat may urinate outside the litter tray when s/he is constipated - our Karma peed on the sofa so we took her to the vet for a suspected urinary tract infection, but in fact she did not have one, her problem was constipation. Once the constipation was under control, her inappropriate elimination ceased.


Sometimes a cat will appear to have diarrhoea but in fact has constipation, and the runny stool is simply what can squeeze around the solid dry stool.


Harpsie once had an episode of fast breathing and fast heart rate. He had severe constipation, and his problems resolved once he had been given an enema. If a cat is very severely constipated, toxins can back up in the cat's system causing such problems; pain or discomfort can also cause fast breathing, and severe constipation can be extremely uncomfortable. Alternatively you might see lethargy and fainting, known as vasovagal syncope - syncope means to faint. Medicine Net discusses this. Obviously you do not want your cat to have such severe constipation that these problems arise!


The vet can usually feel the backed-up stool when s/he palpates the cat's abdomen, but sometimes an x-ray is necessary to confirm the problem.


Newman Veterinary mentions that constipation may cause vomiting (scroll down a bit).


Treatments for Chronic Constipation                                                                              Back to Page Index


There are two considerations with constipation: prevention and treating it if it is present. The two most popular treatments for chronic constipation in CKD cats are medications called MiraLAX and lactulose.



How MiraLAX Works

MiraLAX is a human constipation treatment containing polyethylene glycol 3350, also known as PEG. (This is not the same as ethylene glycol, or antifreeze, which is toxic to cats). MiraLAX was recently made OTC in the USA, and perhaps as a result of this, it is an increasingly popular treatment for CKD cats in the USA.


MiraLAX is an osmotic laxative like lactulose, but unlike lactulose, it retains water in the colon rather than pulling it into the colon from the rest of the body. The US National Library of Medicine explains more about how it works.


Comparing drugs for constipation (2007) Dean L reports that MiraLAX is more effective than lactulose for treating chronic constipation in humans, and another study, Single and multiple dose pharmokinetics of polyethylene glycol (PEG3350) in healthy young and elderly subjects (2008) Pelham RW, Nix LC, Chavira RE, Cleveland M VB & Stetson P Alimentary Pharmacology & Therapeutics 28(2) pp256-65 found that it started working in some people within a day. Most people using it for their CKD cats seem to like it, finding it easy to give and effective, with no side effects.


Another advantage is that it does not have the potential to cause hypercalcaemia (high calcium levels) which lactulose has, plus it is safe to give to diabetic cats. In addition, since MiraLAX is OTC, you do not need a prescription for it, though please do not use it without your vet's knowledge and approval.


MiraLAX is usually of limited use if a cat is so constipated as to have impacted stool; this may need to be removed by the vet before starting MiraLAX.


MiraLAX Dosage

Unlike lactulose, which is a sticky syrup, MiraLAX comes as an odourless and tasteless powder which can be mixed with water or food. A common starting dose is 1/8 of a teaspoon per day, though if you don't see an improvement in your cat's constipation after three days, you can increase to 1/4 of a teaspoon if necessary. If this still doesn't work, ask your vet about increasing the dose. MiraLAX is supposed to be mixed with water, and can be given via a dropper, though some people mix it with baby food. You can also divide it between your cat's meals over the course of a day if you prefer, it is not essential to give the day's dose all in one go.


MiraLAX and Kidney Disease Warning

I have been asked why there is a warning on MiraLAX stating that it should not be used in patients with renal failure, particularly since this warning is not on generic products.


MiraLAX is often used to empty the bowel before an endoscopy. If you use it for this purpose, it may cause an imbalance in the body's electrolytes, particularly potassium and sodium. Since CKD patients have a tendency towards electrolyte imbalances anyway, this could be risky for a CKD patient. However, when giving MiraLAX to a CKD cat in order to prevent constipation becoming a problem, you are using MiraLAX in a different way which should not affect electrolytes in any way. But of course do check with your vet anyway before using MiraLAX.


One study, Single and multiple dose pharmokinetics of polyethylene glycol (PEG3350) in healthy young and elderly subjects (2008) Pelham RW, Nix LC, Chavira RE, Cleveland M VB & Stetson P Alimentary Pharmacology & Therapeutics 28(2) pp256-65, found that 66% of the elderly people in the study had mild renal impairment but their bodies did not appear to have any problems processing the treatment compared to the other people in the study.


Obtaining MiraLAX



MiraLAX is widely available in the USA from drugstores and supermarkets.



In the UK, MiraLAX is not available but it can often be bought from Amazon, though supplier links change often, so if the link I give doesn't work, search for MiraLAX. The price varies depending upon the supplier. It is usually shipped from the USA, so shipping costs can be relatively high.


Biovea sells MiraLAX for £23.95.


Another product containing MiraLAX's active ingredient (polyethylene glycol 3350, or PEG3350) is widely available under the name of Movicol. Unfortunately Movicol contains added electrolytes. This is presumably to offset the electrolyte imbalances which may result from using these products pre-endoscopy, but since CKD cats are not receiving Movicol for this purpose, the added electrolytes are not necessary. Safety and palatability of polyethylene glycol 3350 as an oral laxative in cats (2011) Tam FM, Carr AP and Myers SL Journal of Feline Medicine & Surgery 13 pp694-7 used a version containing added electrolytes, and found that although it seems to be an effective laxative in cats, it did cause increased potassium levels in some cats. These were not clinically significant, but if you do decide to use PEG3350, I would ask your vet to monitor your cat's potassium levels.



MiraLAX is sold in Canada under the name of RestoraLAX, and is widely available in pharmacies.



Biovea sells MiraLAX in Australia.



Lactulose - How It Works

Lactulose is a popular treatment to prevent constipation on Tanya's CKD Support Group. It is a syrup of long chain indigestible sugars (derived from lactose, a milk sugar) that pulls water into the colon and softens the stool. The US National Library of Medicine explains more about how it works. Lactulose is available OTC in Europe and Canada, but requires a prescription in the USA. 


Lactulose and renal failure (1997) Vogt B & Frey FJ, Scandinavian Journal of  Gastroenterology Supplement 222 pp100-1 indicated that lactulose may help promote the excretion of BUN and creatinine through the faeces in humans, and some people have found that this effect is sometimes seen in CKD cats; but lactulose is not usually given specifically or solely for this purpose because of the obvious side effects of causing diarrhoea in non-constipated patients. The British Medical Journal reports on a 2001 study of human patients that indicates that lactulose may also help to prevent urinary tract infections.


Drs Foster and Smith have some information about lactulose.


Lactulose Dosage

Lactulose is a "dose to effect" treatment, so you should start with a low dose, and work your way up only if necessary (so as not to cause the opposite problem of diarrhoea). A possible starting dose is 0.5ml once a day, but this may need to be adjusted with your vet's approval; Plumb's Veterinary Drug Handbook says that cats may be given up to 1ml per kg (0.5ml per lb) of bodyweight per day. It does take a couple of days for lactulose to work, so do not give too much too soon. I found out the hard way that, if you syringe it in to your cat's mouth, it's a good idea to wipe your cat's chin with a damp cloth after using it, because, being sugar-based, it is incredibly sticky. You may find it easier to mix the lactulose with food; some people use a little baby food each day for this purpose.


Since lactulose is a prescription item in the USA, it can be rather expensive, but Wal-Mart and Target both sell it for US$4 a bottle.


Since lactulose is so sticky, you might wish to ask your vet about a new form of it called Kristalose. This is a powder which can be dissolved in water, and which therefore eliminates the stickiness problem. I do not know anybody who has used it for a cat yet, but it is available from Vet RX Direct in the USA.


Lactulose Side Effects and Interactions

Some people have found that their cats developed hypercalcaemia (high calcium levels) after using lactulose regularly, which then improved when they stopped using lactulose. You may therefore wish to avoid lactulose if your cat is already hypercalcaemic. In such cases you could consider using MiraLAX instead.


Lactulose is usually of limited use if a cat is so constipated as to have impacted stool; this may need to be removed by the vet before starting lactulose.


Although lactulose is indigestible, it is composed of sugar molecules, so Mar Vista Vet advises against using it in diabetic cats because it may raise blood sugar levels.


Antibiotics may reduce the effectiveness of lactulose. 


Lactulose may exacerbate the effects of diuretics. Drugs has more information about this.


I have heard from a couple of people who found that their IBD cats did not seem to do too well  on lactulose. This may be because, as mentioned in Update on the non-invasive monitoring of intestinal disease in dogs and cats (2000) Batt R Revue Médicine Véterinaire 151(7) pp559-563, more lactulose is absorbed by a damaged gut than by a healthy one. If your IBD cat seems to worsen on lactulose, speak to your vet about switching to another treatment.




Sometimes it is also necessary to add fibre to your cat's diet in order to bulk up the stool so that it moves easily through the cat's system. These fibre-based treatments are intended to help prevent constipation, but they cannot cure it  once it is present.


Be careful if using additional fibre in diabetic cats, because fibre may reduce blood sugar levels.


Some vets in the USA recommend a product called Benefiber. This used to contain a type of fibre called guar gum, but it now contains wheat dextrin. I think there are better choices available for cats.


Pumpkin and Other Vegetables

Some  form of vegetables such as baby or tinned peas or pumpkin (not the pie filling) may suffice. Many cats seem to quite like the taste of pumpkin, but different brands can contain different types of pumpkin, so your cat may prefer one brand over another.


You should start gradually, say with half a teaspoon of pumpkin once or twice a day (it can be mixed with food), and increase as needed.


You can freeze un-used pumpkin in ice cube trays and just take out what you need for each day, though freezing it can change the texture somewhat.


I sometimes hear from people that pumpkin is high in phosphorus but that is not the case. According to the USDA National Nutrient Database, pumpkin cooked, boiled and drained without salt contains 0.48% phosphorus on a dry matter analysis basis. Pumpkin canned without salt contains 0.35% phosphorus on a dry matter analysis basis.



In the USA canned pumpkin is usually widely available in supermarkets, but there was a shortage in the summer of 2010; if this happens again, you could consider trying baby food containing squash.


Amazon sells Farmer's Market Organic Pumpkin online, as well as other brands, including Libby's.

Vitacost also sells Farmer's Market Organic Pumpkin.



Tinned pumpkin is hard to find in the UK, but some branches of Waitrose and Sainsbury's sell American canned pumpkin with no additives in the canned vegetables aisle.


Amazon sells the Libby's brand online in the UK.


If you cannot find canned pumpkin, you could consider using Applaws Chicken & Pumpkin cat food and see if that helps. I am awaiting details of the phosphorus content of this food.



A popular fibre-based treatment which is available OTC in the USA is psyllium. You only need to give a tiny amount - the maximum dose is 1/8th of a teaspoon, but you should start with an even smaller dose. With fibre-based treatments, it is very important to ensure that the cat drinks plenty of water, otherwise the fibre can bulk up in the body and make the constipation worse. 


In the USA psyllium is commonly sold under the name of Metamucil, however, be sure not to buy Metamucil Clear and Natural (blue container) because this does not contain psyllium.


If you are in the UK, your vet may offer you a standardised pharmaceutical-grade fibre called Nutrifyba.


Too much fibre may prevent your cat from absorbing sufficient nutrients or calories from his/her food. In humans, fibre may also bind calcium in the small intestine and lead to an increase in calcium levels in the body (hypercalcaemia). If you are only giving a small amount to prevent constipation, your cat will probably be fine, but be careful if your cat already has hypercalcaemia.


Pet Education has some information about psyllium use in cats.

The University of Maryland Medical Center explains more about psyllium.

Uncontrolled study assessing the impact of a psyllium-enriched extruded dry diet on faecal consistency in cats with constipation (2011) Freiche V, Houston D, Weese H, Evason M, Deswarte G, Ettinger G, Soulard Y, Biourge V, German AJ Journal of Feline Medicine & Surgery 13(12) pp903-11 found that a psyllium-enriched diet was effective at controlling chronic constipation in cats.

Psyllium: keeping this boon for patients from becoming a bane for providers (2006) Hoffman D The Journal of Family Practice 55(9) reports on the case of an asthmatic nurse who died after inhaling psyllium powder, and recommends spooning it rather than pouring it.


Other Treatments for Chronic Constipation                                                               Back to Page Index

Fluid Therapy

Fluid therapy can help reduce constipation, but should not be used solely for this purpose. There is more about fluid therapy and when it is appropriate to use it here


Slippery Elm Bark

Slippery Elm Bark is a natural treatment which can be sufficient to keep some CKD cats regular; there is more information on this treatment in Holistic Treatments


Vitamin B12 (Methylcobalamin)

Some people whose cats have megacolon (a bowel disorder which causes severe constipation) have found that giving vitamin B12 in the form of methylcobalamin is a helpful preventative treatment.


Ranitidine (Zantac 75)

Ranitidine (Zantac 75) is commonly used to help treat excess stomach acid in cats. However, it may help also with constipation caused by low motility in the colon, so is certainly worth considering if your cat needs treatment for both constipation and stomach acid.


Feline constipation, obstipation, and megacolon: prevention, diagnosis, and treatment (2001) Washabau R Presentation to the World Small Animal Veterinary Association World Congress has information about this aspect of ranitidine.


Acute Treatments: Enemas and Suppositories                                                      Back to Page Index

If at all possible, you want to avoid the need for an enema or manual evacuation of the bowel by your vet. However, sometimes this becomes a necessity.


Your vet should be able to tell by palpating (feeling) your cat's abdomen whether your cat is blocked up but this is not always reliable, so an x-ray can also be helpful. 


Enemas and Suppositories

Paediatric suppositories containing only glycerin are usually safe to give to cats, though of course check with your vet first, and ideally ask your vet to teach you how to give them. I used a paediatric suppository on Harpsie. It didn't work (he needed veterinary help) but it was easier than I expected, and not stressful for either of us.


Enemas containing sodium phosphate (one common US brand is Fleet) should be avoided because they are extremely dangerous for cats. See below for more information. However, there are some enemas which are safe to use in cats, but check with your vet first.


Feline Pet-Ema is an enema in the USA designed especially for cats.

Vet Depot sells Pet-Emas for US$2.27 each.

Medi Vet sells Pet-Emas for about US$3.50 each.

Feline constipation, obstipation, and megacolon: prevention, diagnosis, and treatment (2001) Washabau R Presentation to the World Small Animal Veterinary Association World Congress has information about rectal suppositories and enemas.


Manual Evacuation

If an enema does not work, the stool may be impacted and have to be removed manually by your vet. Water or saline is introduced into the colon while the vet palpates the cat's abdomen in order to break up the mass. Feline constipation, obstipation, and megacolon: prevention, diagnosis, and treatment (2001) Washabau R Presentation to the World Small Animal Veterinary Association World Congress explains more about this and mentions that it can be safer to do this over a period of several days.


Constipation Cautions                                                                                                              Back to Page Index

Cisapride (Propulsid)

You may be offered a drug called cisapride (trade names are Prepulsid or Propulsid) to treat your cat's constipation, but I would suggest only using this as a last resort since it has been withdrawn from the human market because of serious heart-related side effects which have caused some human deaths.


Rx List has more information about this issue in humans

Pet Education has some information about the implications for animals.


Hairball Remedies

Many vets seem to routinely prescribe Laxatone or Petromalt, but these are really intended for the treatment of hairballs and are not ideal - or particularly effective - for the ongoing constipation problems suffered by many CKD cats.


In addition, they may prevent the absorption of nutrients if used longer-term. The Merck Veterinary Manual has some information about this.


However, such a product may be of use if given for a short period to try and soften the hard stool often seen at initial diagnosis.


Mineral Oil

Mineral oil (liquid paraffin) should not be used, because since it has no smell or taste, it can easily be aspirated and cause pneumonia. If given regularly, it may also interfere with the absorption of nutrients.


Merck Veterinary Manual explains more about the absorption problem with these products.

Pet Place has more information on aspiration pneumonia (no need to register to read the article, just click on Close at the bottom of the registration pop-up).



Enemas containing sodium phosphate (one common US brand is Fleet) should be avoided because they are extremely dangerous for cats.


Electrolyte abnormalities induced by hypertonic phosphate enemas in two cats (1985) Jorgensen LS, Center SA, Randolph JF, Brum D, Journal of the American Veterinary Medical Association 187 pp1367-8 reports on two cats who suffered severe problems after such enemas, and advises against their use for cats with renal problems in particular.

Troublesome toxicoses in cats (2011) Dowers K Veterinary Medicine explains more about this problem, including symptoms and treatment options should a cat accidentally be given such an enema.

The Merck Veterinary Manual also advises against the use of such enemas.



Back to Page Index

This page last updated: 05 December 2013

Links on this page last checked: 27 April 2012






I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.


If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.



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