Opioids
Adverse effects
There are a number of side effects associated with opioid use that should be discussed with patients prior to initiating therapy. These should be clearly understood by both patients and their physicians to aid compliance with opioid treatment.
Commonly reported side effects
Nausea and emesis
Common side effects of opioid therapy, both nausea and emesis should be treated with antiemetics, such as phenothiazines or metoclopramide. Depending on the antiemetic chosen, patients should be monitored for increased sedation.
There are a variety of management approaches for opioid induced nausea:1
- Antiemetics: start with low-cost dopamine antagonists (e.g. prochlorperazine) or anti-cholinergics (e.g. scopolamine); use 5HT3 antagonists for more refractory cases. Antihistamines may be helpful for patients who report a 'spinning sensation'.
- Dose adjustment: if good pain relief is achieved, but is associated with nausea, it may be possible to lower the dose, still retain good analgesia, but eliminate the nausea.
- Opioid switching: patients may be more sensitive to one opioid compared with another, thus a change is warranted when the above options are not effective.
Constipation
The most common side effect of opioid therapy is constipation. Constipation can add to the mix of pain and discomfort the patient is already suffering from.
The intestinal tract has receptors for opioids, and the drug activates or stimulates these receptors, just as the pain receptors are affected. But instead of pain relief, opioids slow down the intestines and make them sluggish. This sluggishness can lead to constipation or even a total lack of bowel movement (obstipation).
While tolerance to other side effects is likely to develop with continued treatment. Most patients receiving strong opioids will require continuous prophylaxis against constipation.
Patients should stop taking all non-essential drugs with the potential to cause constipation, and, in most patients, levels of fluid and fibre intake should be increased (notable exceptions include patients with a likely bowel obstruction).
There are many laxatives available for the treatment of constipation, including bulk-forming agents, lubricants, osmotic agents, surfactants, contact cathartics, prokinetic drugs, agents for colonic lavage, and oral opioid antagonists.
Oral opioid antagonist therapy can partially reverse opioid-induced constipation without causing systemic opioid withdrawal through local action on opioid receptors in the gut. At the present time, this treatment can be implemented using methylnaltrexone. The oral bioavailability of this compound is very low and the goal of oral therapy is to block the effects of opioids in the gut, without the development of systemic withdrawal or reversal of analgesia. Some patients, however, develop adverse abdominal symptoms such as cramping, and others absorb sufficient methylnaltrexone to develop uncomfortable signs of systemic opioid withdrawal.
Drowsiness, sedation and mental clouding
When possible, opioid-related drowsiness should be treated by reducing the dose and increasing the frequency of opioid administration. CNS stimulants such as methylphenidate may be useful to help decrease opioid sedative effects.
Less common opioid side effects include:
- itching;
- headaches;
- decrease in sexual interest;
- urinary retention;
- dizziness;
- hypotension;
- sweating;
- hormonal disorders;
- immune system suppression and modulation;
- infertility;
- neurotoxicity;
- psychotoxicity;
- respiratory depression.
Reference:
1) Adapted from the St Anthony's Hospice guide to symptom management: Opioids and Nausea - Available from: URL: http://www.stanthonyshospice.com/elb/palliative_care/symptom/opnausea.htm.