What Is Opioid Malabsorption?

Opioid malabsorption is a condition in which pain is not adequately relieved by appropriate dosages of oral opioid medications, such as oxycodone, hydromorphone, or morphine. A diagnosis of opioid malabsorption should be considered when multiple types of oral opioids have been ineffective at relieving pain.

Possible causes of opioid malabsorption

Several factors may cause opioid malabsorption, including, but not limited to, the following:

• Genetic variations
  Genetic variations in enzymes that metabolize opioids may cause malabsorption. Cytochrome P450 (CYP450) enzymes are essential for the metabolization of opioids and can be found in the small intestine where the metabolism of opioids begins. If enzyme abnormalities are present, opioid malabsorption may be an issue.
• Autoimmune disorders
  Autoimmune disorders, such as ulcerative colitis, Crohn’s disease, and celiac disease, can cause opioid malabsorption due to potential damage to the digestive system.
• Diabetes
  Type 2 diabetes may cause changes to the gastrointestinal tract, which can lead to opioid malabsorption. Related complications, such as gastroparesis, may also lead to opioid malabsorption.
• Surgery
  Certain surgeries can lead to malabsorption of oral opioids. Surgery involving the gastrointestinal tract, such as weight loss surgery, is the most common type of surgery that can lead to malabsorption of oral opioids. It can also occur with surgery for endometriosis or other pelvic or abdominal conditions.

Diagnosing opioid malabsorption

Opioid malabsorption is typically diagnosed through a medical history, physical examination, opioid blood level testing, and CYP450 enzyme testing. Opioid blood level testing involves measuring the level of opioids in the blood both before an oral opioid dose and one to two hours after an oral opioid dose. With opioid malabsorption, opioid blood levels will be lower than expected after the opioid dose.

Alternative administration options

If opioid malabsorption is an issue, non-oral opioids can be prescribed. Non-oral administration options include the following:

• Sublingual — Medication is placed under the tongue where it dissolves and is absorbed into the bloodstream.
• Buccal — Medication is placed between the gum and cheek where it dissolves and is absorbed into the bloodstream.
• Rectal — A suppository containing the medication is inserted into the rectum.
• Transdermal — A patch placed on the skin allows the medication to slowly enter the bloodstream over time.
• Intrathecal — Medication is injected into the fluid around the spinal canal (the cerebral spinal fluid).
• Subcutaneous — Medication is injected under the skin but not into the muscle.

The appropriate alternative administration of opioids is determined according to the underlying pain condition and the individual’s ability to administer the medication.