Medication and causes of constipation
When medication causes constipation
Occasionally, certain medications for treating a disorder can become causes of constipation. Such constipation is called secondary, meaning that it is a side effect of another agent acting on the body. Treatment of constipation can follow one of the three following courses of action. In the first, the physician may decrease the dosage of the medication if it is indicated that high dosages lead to constipation.
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In the second, the physician may switch a patient to another medication which acts in a chemically distinct way from the first medication, in an effort to remove the constipating side effect. In the third and most drastic, the physician and patient may elect to end treatment by medication altogether, which removes the constipation-inducing agent completely.
Types of constipation-causing medications
A sampling of medications that give rise to chronic constipation are given
as follows. Keep in mind this list is by no means complete, and you
should bring up the matter of chronic constipation with your physician as he or she
is likely to be aware of side effects.
Patients with high blood pressure may take antihypertensive agents such
as a calcium antognist or clonidine. Calcium antagonists have a disruptive
effect on calcium channels in the heart, which lead to decreased heart
output. Calcium antagonists also seem to have an effect on the electrical output
of the heart, which causes it to slow down. Clonidine is a drug that has a
similar effect but is achieved through a different mode of action. Clonidine
is an alpha-2 agonist (or stimulator) that revs up the alpha-2 receptor
in the brain, leading to reduced cardiac output and vascular resistance. The net
effect is that the heart pumps with less force and the blood vessels experience
less resistance. Hence, the blood pressure drops. Patients who
experience chronic constipation may switch to another antihypertensive agent such as an ACE
inhibitor or beta-blockers.
Anti-depressants and constipation
Patients with depression are often treated with what are called tricyclic antidepressants. These depressants are also known to be causes of constipation. Treatment usually involves a switch to selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs), which are much better tolerated in the gastrointestinal tracts.
Anemia treatments and constipation
Patients who are undergoing treatment for anemia (low blood count) or have a blood disorder that requires transfusions, may be taking iron preparations orally. When the iron preparations reach the stomach, they also be causes of constipation. There are no good substitutes for iron, so the standard treatment may be to switch the iron uptake to an IV line so that it bypasses the gastrointestinal tract completely. The physician may also prescribe a laxative to counteract the constipating effects of iron treatment.
Pain-killers and constipation
Patients who are suffering from chronic pain may be taking opiate-derived painkillers, such as morphine or codeine. These drugs have also been found to cause chronic constipation. The physician may pursue one of two courses of action. The opiate-based painkiller may be substituted with another analgesic such as oxycodone. Although oxycodone is known as a 'semi-opiate', meaning that it has chemical properties of the opiate drugs, it nevertheless has a slightly different mode of action and less impact on the intestines. The physician may also opt to prescribe laxatives in any effort to combat opiate-induced chronic constipation.
Sources on causes of constipation:
Long and Vernava, Prokinetic Agents for Lower Gastrointestinal Motility Disorders, Diseases of the Colon & Rectum, 2005