Page 171 Guide to Pain Management in Low-Resource Settings

Lung Cancer with Plexopathy 159

around 2400 mg/day. Due to the drug’s common side Among opioids, morphine is the best studied
eff ects such as drowsiness and sedation, a slow titra- drug. It is a mu-receptor agonist. Morphine is available
tion is necessary. in immediate-release formulations and (in some coun-
tries) in sustained-release formulations. As the duration
Antidepressants of action of the immediate-release formulation is ap-

Among the antidepressants, the tricyclic antidepres- proximately 4 hours, frequent administration is neces-
sants (TCAs) such as amitriptyline are most fre- sary. Titration should start with 5–10 mg every 4 hours.
quently applied in neuropathic pain. TCAs have been On occurrence of breakthrough pain, an additional 1/6
studied extensively in noncancer pain patients. Th ey to 1/10 of the total daily morphine dose should be ap-
enhance the endogenous inhibitory pathways by in- plied as an initial step. Later, the adequate dose to treat
hibiting the presynaptic reuptake of serotonin and episodes of breakthrough pain must be adjusted ac-
norepinephrine in spinal pain pathways. TCAs also cording to the individual patient’s needs and responses.
have agonistic eff ects on histamine and muscarinic In the case of painful procedures, immediate-release
receptors, which contributes to side eff ects such as morphine might be administered approximately half
sedation and dry mouth. Additionally, there may be an hour before the procedure (such as wound manage-
binding to sodium channels as well as inhibition of ment) will be performed. Th e most common side eff ects
voltage-dependent calcium channels. Due to its seda- include sedation, constipation, nausea, and vomiting. It
tive eff ects, amitriptyline should be administered dur- is essential to take care of side eff ects (for constipation,
ing the evening and should be slowly titrated. Par- prescribe laxatives and advise the patient about fl uid in-
ticularly in older patients, the initial dose should not take; for nausea, prescribe antiemetics and inform the
exceed 25 mg. Th e maximum dose for cancer pain patient that nausea is often self-limiting). In cases of he-
is approximately 75–100 mg/day. Contraindications patic dysfunction (e.g., liver cirrhosis), the duration of
might arise from preexisting cardiac diseases such as action might be prolonged, so dosing intervals should
arrhythmias or conduction defects. Secondary anti- be extended. In renal impairment, dose reduction is rec-
depressants such as nortriptyline or desipramine are ommended while maintaining the application intervals.
as eff ective as TCAs but are often better tolerated Other opioids to be used include tramadol,
due to less side eff ects. Selective serotonin reuptake which is a synthetic opioid not only stimulating mu-re-
inhibitors (SSRIs) such as fl uoxetine are better toler- ceptors but also inhibiting the presynaptic reuptake of
ated as well, but they are also less eff ective in relieving serotonin and norepinephrine. Dosage is every 4 hours
neuropathic pain. New antidepressants with a mixed for immediate-release formulations and three times a
mechanism of action such as venlafaxine, paroxetine, day for sustained-release formulations. When switch-
or duloxetine seem to be eff ective as well, but for can- ing from tramadol, which is sometimes classifi ed as a
cer pain management the evidence is sparse, and they “weak opioid,” to morphine, the conversion ratio has to
are not available in many countries. be considered (e.g., 100 mg oral tramadol is equivalent
to approximately 10 mg of oral morphine). Th e maxi-
Opioids mum dose of tramadol should not exceed 400–600 mg/
Common fallacies about opioids include a lack of effi ca- day. Among the side eff ects, there is a high prevalence
cy in neuropathic pain conditions. Th is belief has been of nausea and vomiting. In renal failure, intervals be-
proven not to be true. Th ere is abundant evidence dem- tween doses should be increased. Th e recommended
onstrating the effi cacy of these drugs. However, neuro- dose in the case of liver cirrhosis amounts to 50 mg ev-
pathic pain may be less responsive to opioids compared ery 12 hours.
to nociceptive pain. Opioids should be titrated indi- Oxycodone is a semisynthetic opioid that ac-
vidually and carefully to fi nd out the optimal balance tivates the mu-receptor as well as the kappa receptor.
between benefi t and side eff ects. By combining opioids Duration of action is 4 hours. Due to the better oral
with adjuvants such as gabapentin, the dose of each bioavailability the conversion ratio to morphine is 1:2
drug can be reduced and the eff ect on pain relief is usu- (e.g., 5 mg oral oxycodone equals 10 mg oral morphine).
ally greater than using only one of those drugs. Th ere- Oxycodone should be used very carefully in situations
fore, a combined therapy should be considered in neu- of renal or hepatic dysfunction, due to the increased
ropathic pain. elimination half-life.