We’re discussing treatments for feline constipation. We’ve covered fluids, soluble and insoluble fiber, prebiotics & probiotics, and Chinese herbs. Now, let’s consider laxatives.
What are laxatives?
Laxatives are oral medications that promote defecation. We use laxatives only in cats that can be unplugged, but not in cats with mechanical or physiological blockages. To ensure the cat is not blocked, blood tests and X-rays may be required. When some pet families hear how much it costs to treat a “simple” constipation, they’re shocked, but we can we can kill obstructed cats by giving them laxatives, and that’s a really shitty shock.
What is obstipation?
Constipation is having difficulty defecating, but when the difficulty becomes an impossibility, the cat is obstipated rather than constipated. Constipation=stuck. Obstipation=blocked.
Types of laxatives
All laxatives have the same goal—get fecal material out—but they have different methods of working. Five different laxative approaches are:
1. Bulk forming—ground flax seed, psyllium (metamucil), bran
2. Softening emollient--DSS (Colace),dioctyl calcium sulfosuccinate (Surfax)
3. Lubricant--fish oil, flax oil, mineral oil, petroleum jelly,
4. Hyperosmotic—glycerine, lactulose, polyethylene glycol, magnesium salts
5. Stimulant –Dulcolax, senna, aloe, castor oil, bisacodyl, cascara
1. Bulk forming laxatives
Bulk forming laxatives are finely ground plant materials that bulk up the feces. These bulk formers absorb fluids and create a mass that signals the intestines to contract. Intestinal contractions move stool down the intestines and out the rectum.
Because bulk formers are “natural” treatments for constipation, many cats tolerate them better than they tolerate some other treatments, however, bulk formers cannot be used in all cats. Bulk forming laxatives shouldn’t be used in dehydrated cats. For these cats, give 1-4 tablespoons of pumpkin, sweet potatoes or squash. These vegetables proivide bulk but because they’re moist, they don’t pull fluid from the cat.
Cats with megacolon should not be given bulk formers as the goal is to have as small amount of fecal material in their distal colon as possible.
2. Softening emollient laxatives
The chemical emollient laxatives, such as Colace, have an slick method of action. They help the body absorb more lipid molecules so the feces slides better. Emollients also help hold water in the stool so the feces is softer. Emollients lose their effectiveness if they are used long term, so no cat should be on them for an extended period. Nor should dehydrated cats be given emollients.
3. Lubricant laxatives
Lubricant laxatives can be given orally, such as fish oil and flax oil; they can be rubbed on paws, such as the hairball medications that contain petroleum jelly; or they can be used as enemas, such as mineral oil. Lubricants work by holding lipids inside the stool rather than allowing them to be absorbed into the body. This gives the stool volume and slickness.
The negative aspect of lubricant laxatives is that some of them also attract and hold onto fat soluble vitamins A, D, E, and K, causing these vitamins to slide out of the body with the feces. We can prevent vitamin loss, by using lubricant laxatives that are themselves rich in fat soluble vitamins, such as fish and flax oils. Lubricant laxatives such as mineral oil or petroleum jelly in hairball medications don’t provide vitamins and should not be used very often.
Please don’t give your cat mineral oil by mouth. Because mineral oil is odorless and tasteless, some cats accidentally inhale it into their lungs. If using mineral oil, give it as an enema.
4. Hyperosmotic laxatives
The gut wall is not a solid barrier like the old Berlin wall, it’s more like the US-Mexican border that water and molecules cross as easily as citizens. Movement of water and molecules creates an osmotic balance inside and outside the gut. We can disrupt the balance by feeding molecules that are so large they cannot pass the gut wall. This pulls water into the gut.
Lactulose and the other hyperosmotic laxatives are large molecules that stay within the gut. They force water to move toward them and into the feces, which helps soften the feces.
then a balance is achieved by having water move from the body into the feces. Laxatives containing large molecules that pull water into the feces are called hyperosmotic laxatives. Examples of hyperosmotic laxatives are polysaccharides (lactulose and lactose) magnesium salts (magnesium sulfate, magnesium citrate; and polyethylene glycols (GoLYTELY and Colyte). The safest of these hyperosmotic laxatives for cats is lactulose. The magnesium laxatives are ok in some cats, but not cats with kidney disease and many constipated cats have kidney disease. Polyethylene glycol is unsafe for cats whose nerves aren’t working so they have a “functional” obstruction or for cats with a blockage and a “mechanical” obstruction. Hyperosmotic laxatives shouldn’t be given to dehydrated cats.
5. Stimulant laxatives
Stimulant laxatives cause gut movement. Some cause movement because they irritate the nerves to the gut. For example Dulcolax (bisacodyl) stimulates the nerves to fire. If stimulants such as Dulcolax are used long tern, they lose their effectiveness either because the nerves are damaged or they’re habituated to the signals. Cats that have an occasional problem with constipation are best candidates for stimulant laxatives, such as 5 mg of Dulcolax once a day. Geriatric cats, Manx cats, and cats with chronic kidney disease should not routinely use stimulant laxatives.
Coming up
With all the treatments we’ve discussed for constipated cats (five types of laxatives, fluids, soluble and insoluble fiber, prebiotics & probiotics, and Chinese herbs) you’d think we’d have exhausted the topic, but not even close. We’ve still got suppositories, enemas, and drugs to cover. Suppositories are up next.
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