Page 56 Guide to Pain Management in Low-Resource Settings

44 Michael Schäfer

should not be given to patients being treated with (s.l.) (0.2–0.4 mg capsules) and parenteral (0.3 mg/
monoamine oxidase inhibitors (MAOI), since the mL) formulations. Its metabolites are inactive and are
combination may produce severe respiratory depres- mainly excreted via the biliary duct. Oral bioavailabil-
sion, hyperpyrexia, central nervous system excitation, ity is 20–30% and sublingual bioavailability is 30–60%.
delirium, and seizures. For acute pain, 0.2–0.4 mg s.l. buprenorphine or 0.15
mg i.v. is applied every 4–6 hours. Because of its very
Fentanyl stable and long duration of action, buprenorphine is
used for substitution therapy for drug addicts (4–32
Fentanyl, a strong μ-opioid agonist, belongs to step 3 of mg/daily). Similar to fentanyl, there is a transdermal
the WHO ladder with 80–100 times the analgesic po- application system. Buprenorphine’s respiratory de-
tency of morphine. Fentanyl mainly exists as a paren- pressant eff ects are reversed only by relatively large
teral formulation (0.1 mg/2 mL); however, sublingual and repeated doses of naloxone (2–4 mg).
application is sometimes used. A transdermal applica-
tion system is widely used in industrial countries, but Naloxone/naltrexone
because of its costs and the delayed delivery system
with additional risks (delayed respiratory depression), it Both substances are classical opioid receptor antago-
may only be of use in rare cases. Fentanyl is metabo- nists with a preference for μ-opioid receptors. Naloxone
lized in the liver to inactive metabolites. Th e rapid on- is available only as a parenteral formulation (0.4 mg/1
set, high potency, and short duration of fentanyl is an mL), and it has a fast onset (within 5 min) and a short
advantage in the titration and controllability of periop- duration (30–60–90 min) of action. It is commonly used
erative pain. However, incorrect use may lead to large preoperatively to treat opioid overdosing and needs to
fl uctuations in plasma concentration and increase the be titrated and administered repeatedly under constant
risk of psychological dependence and addiction. Impor- monitoring. Naltrexone exists only as an oral formula-
tantly, repeated administration of fentanyl may lead to tion (50 mg/tablet) with a delayed onset (within 60 min)
drug accumulation due to redistribution from fat and and a long duration (12–24 h) of action. Naltrexone is
muscle tissue into the circulation with increased risk of mainly used for maintenance treatment for alcohol and
respiratory depression. drug dependence. Both substances can precipitate acute
life-threatening withdrawal symptoms when improperly
Sufentanil used, e.g., hyperexcitability, delirium, hallucinations, hy-
peralgesia, hypertension, tachycardia, arrhythmia, and
Sufentanil, a very strong μ-opioid agonist, with 800– increased sweating.
1000 times the analgesic potency of morphine, is ex-
clusively available as a parenteral formulation (0.25 Pearls of wisdom
mg/5 mL) and can be given i.v. (10–100 μg boluses)
as well as epidurally (initially: 5–10 μg, repeated bo- • Although they have been available for almost
lus: 0.5–1 μg). Because of its very high potency, suf- 200 years, opioids still remain the mainstay of
entanil is mainly used intraoperatively. In comparison pain management. While opioids are effective
to fentanyl, it is much less prone to drug accumula- in most postoperative and cancer patients, and
tion, because of its low tissue distribution, low pro- in some patients with neuropathic pain, most
tein binding, and high hepatic metabolization rate to other noncancer pain is hardly responsive to
inactive metabolites. opioid medication.
• While opioids are regarded with a lot of preju-
Buprenorphine dice because of their side eff ects and abuse po-
tential, clinical practice and research have dem-
Buprenorphine belongs to the mixed agonist/antago- onstrated in the last few decades that opioid
nist opioids binding to μ- and k-opioid receptors. It medication for short- and long-term treatment
usually has a slow onset (45–90 min), a delayed maxi- can be accomplished safely. Th ere is no evidence
mal eff ect (3 hours), and a long duration of action about a diff erential indication of the opioids
(8–10 hours). Buprenorphine is available as sublingual available. Consequently, availability, costs, and