Download Medication Types

Medication Types
This page provides simple, concise online information about commonly used pain
relieving medications and drugs, many of them available over the counter. These
drugs are comonly used to treat acute and chronic painful conditions like low
back pain, neck pain, sciatica, arthritis and joint pain, nerve pain, headaches, and
even menstrual cramps. For more information about emergency pain medicines,
please look at the Analgesic Flow Chart.
Paracetamol
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Use - as an analgesic (pain killer) and an anti-pyretic (temperature
lowering) - used alone for mild pain, or in combination with NSAID's and
opioid's for moderate and severe musculo-skeletal pain.
Mode of action is not completely understood, but is thought to act in the
brain. It has very weak effects on the COX-1 and COX-2 systems (see
NSAID's below), and therefore it has minimal peripheral anti-inflammatory
actions, and does not cause gastric ulceration. Recent research suggests
that it may work through a newly discovered COX-3 enzyme system.
Dose - the maximum oral dose in adults is 1 gram (2 x 500 mg) 4 times
per day. Intravenous paracetamol is also available in some countries for
those in hospital who are not able to take tablets by mouth - the dose
remains the same at 1000 mg IV 4 times a day.
Side effects - Fatal liver failure is very common after overdose.
NSAID's (Non Steroidal Anti-Inflammatory Drugs)
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Use - as an analgesic, anti-inflammatory and anti-pyretic - may be used
alone or in combination with paracetamol and/or weak/strong opioid's.
Mode of action - NSAID's produce a range of effects in the body by
inhibiting the enzyme cyclo-oxygenase (COX). COX is the main enzyme
which converts arachidonic acid to prostaglandins, thromboxane and
prostacyclins. It is found in many central and peripheral tissues in the
body, and this explains why NSAID's have such a wide range of effects.
The known effects of these drugs are:o analgesia - acting on peripheral tissues, the dorsal horn of the
spinal cord, and the brain
o anti-inflammatory - via the prostaglandin effect
o anti-pyretic - temperature control in the brain
o gastric ulceration - impaired gastric lining protection
o anti-platelet - anti-thromboxane effect prevents platelets sticking
together with increased bleeding tendency
o renal impairment - altered kidney blood flow control worse with
dehydration
o increased wheezing in susceptible asthmatics increasing the
muscle tone in the bronchi of the lungs
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There are two forms of the COX enzyme - COX-1 and COX-2. Older
NSAID's inhibit both enzyme types, whereas modern NSAID's have high
specificity for the COX-2 enzyme. COX-2 specific NSAID's produce
comparable analgesia and anti-inflammatory effects, whilst helping to
reduce gastric ulceration and anti-platelet effects.
Below is a list of commonly used NSAID's and the ratio of their COX-2 :
COX-1 selectiveness:-
NSAID
Trade Name
etoricoxib
rofecoxib
valdecoxib
celecoxib
diclofenac
etodolac
meloxicam
indomethacin
naproxen
ibuprofen
piroxicam
Arcoxia
Vioxx
Bextra
Celebrex
Voltarol
Lodine
Mobic
Indocid
Naprosyn
Nurofen
Feldene
COX-2 : COX-1 ratio
Classification
(IC50)
106 : 1 **
35 : 1 **
30 : 1 **
7.6 : 1 **
Selective for COX-2
3.0 : 1 **
2.4 : 1 **
2.0 : 1 **
0.4 : 1 **
0.3 : 1
Selective for COX-1
0.2 : 1 **
0.08 : 1 **
** Whole Blood Assay - from "Etoricoxib (MK-0663): Preclinical Profile and Comparison with
Other Agents That Selectively Inhibit Cyclooxygenase-2." JPET, 296: 558-566, 2001"
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Dose - Ibuprofen can be bought over the counter, where the usual dose is
200 - 400 mg four times a day. For other NSAID's please consult the
product literature or your doctor for further advice.
Side effects - include gastric ulceration and bleeding, kidney impairment
in the susceptible and elderly, increased bleeding risk due to an antiplatelet effect, poor asthma control in susceptible asthmatics, and
potential drug interactions with other drugs. The risk of developing gastric
ulceration is lowest for the COX-2 specific NSAID's (rofecoxib, etodolac,
meloxicam and celecoxib), whilst the older non-specific NSAID's can be
ranked in the following order (this is not an exhaustive list):NSAID
ibuprofen
diclofenac
ketoprofen
indomethacin
naproxen
piroxicam
Trade Name
Nurofen
Voltarol
Oruvail
Indocid
Naprosyn
Feldene
Gastric Bleed Risk
Low
Moderate
azapropazone No longer used High
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Contra-indications
o If you are asthmatic and aspirin causes your asthma control to
deteriorate - you should not take NSAID's because of the risk of
developing severe life threatening wheeze. Consult your doctor for
further advice.
o Previous history of gastric bleeding / ulceration
o Renal impairment - more common over 65 years of age
o Severe liver disease
o There are many drug interactions between NSAID's and medication
used for anti-coagulation (warfarin), hypertension, heart failure,
diabetes, and epilepsy - see your doctor for advice about coadministration in these circumstances.
Interesting Article
o See Drugs and Therapeutics Bulletin - January 2005 (860K) for an
up to date appraisal of COX-2 NSAID's.
Weak Opioid's
Weak opioid's are often used for musculo-skeletal and visceral pain, usually in
combination with paracetamol and/or NSAID's. See Analgesic Flow Chart.
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Codeine is a weak opioid (morphine like effect) which has no analgesic
effect of its own. It is a pro-drug with 10% of the oral dose is converted to
morphine by the liver. About 7% of the population do not have the
necessary enzyme to convert it, and therefore codeine is ineffective in
these people. Studies suggest that it most effective when taken with
paracetamol. Side effects include drowsiness, sickness, constipation, and
tolerance over time. May cause codeine-induced headaches requiring
slow withdrawal. Available as plain codeine tablets 30 mg and 60 mg, and
the combination preparations cocodamol 8 mg/500 mg, cocodamol 30
mg/500 mg. Total daily dose is limited by the paracetamol (1-2 tablets 4
times a day). Taking codeine alone is not recommended. Possible
addiction potential.
Dextropropoxyphene is a weak opioid which has mixed activity at
morphine receptors. At low doses it is active at the receptors producing
analgesia. At higher doses it inhibits these receptors producing a ceiling
effect on analgesia. Dextropropoxyphene is therefore a mixed agonistantagonist. When used with other morphine-like drugs, mixed agonistantagonist drugs reduce the overall analgesia rather than producing an
additive effect. It has the same side effects as codeine as well as
addiction potential. Available as coproxamol (paracetamol 325 mg plus
32.5 mg dextropropoxyphene). Total daily dose limited by paracetamol
restrictions (1-2 tablets 4 times a day). Please note: This drug is being
phased out in the UK. If you've been on this drug for some time, please
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speak to your doctor about how to stop it and which other drug to choose
instead. Choosing a similar strength drug from this section would be the
most sensible option.
Dihydrocodeine is a weak opioid but slightly stronger than codeine. Still
needs to be converted to morphine in the liver, Same side effects as
codeine. Available as codydramol (paracetamol 500 mg plus
dihydrocodeine 10 mg), remedeine (paracetamol 500 mg plus
dihydrocodeine 20 mg), dihydrocodeine normal release (30 / 60 mg up to
4 times a day), dihydrocodeine slow release (60 / 90 / 120 mg twice a
day). Paracetamol containing preparations limited to 1-2 tablets 4 times a
day.
Tramadol is a weak opioid which is also converted to another active
compound by the liver. It has two modes of action 1) a weak morphine like
effect 2) stimulation of the descending nerves from the brain which inhibit
the dorsal horn of the spinal cord. May cause dizziness and sickness. It
may be used with paracetamol and/or NSAID's. Usual dose is 50 - 100 mg
four times a day for the normal release preparation, and 100 - 200 mg
twice a day for the slow release preparation.
Partial agonists of morphine - these drugs are like dextropropoxyphene
in that they have mixed actions at morphine receptors, and have a ceiling
effect in higher dosage. Examples are pentazocine, butorphanol, and
nalbuphine. They are weak in their analgesic action, but unlike morphine
do not cause respiratory depression. Side effects like dysphoria and
nausea are common. Pentazocine has an addiction potential and is slowly
being withdraw from clinical use. Nalbuphine is used by paramedics prior
to transfer to hospital.
Strong Opioid's
Strong opioid's are used for severe pain and their potency for different types of
pain is ranked in the following order:- visceral pain > musculo-skeletal pain >
nerve pain > sympathetic pain. They can be usefully combined with paracetamol
and/or NSAID's. Nerve and sympathetic pain may be partially sensitive to strong
opioid's, but these drugs should not be used alone for this type of pain.
The following publications (PDF) are available from the Pain Society (UK):
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Recommendations for the Appropriate Use of Opioid's for Persistent Noncancer Pain
Opioid Medicines for Persistent Pain: Information for patients
The Use of Drugs Beyond Licence in Palliative Care and Pain
Management
The Use of Drugs Beyond Licence: Information for Patients
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Morphine is the "gold standard" strong opioid against which all other
drugs are compared. It is a potent stimulator of morphine receptors,
blocking pain impulses at several sites:1. in inflamed peripheral tissues (e.g. knee osteoarthritis),
2. in the dorsal horn of the spinal cord,
3. centrally in the brain.
Morphine by mouth has a wide range of effects in different individuals because of
its variable 20 - 50% bioavailability (the proportion of drug taken up from the
bowel after oral administration). This means that by mouth there can be a 2.5
times difference in the dose required to achieve comfort between individuals.
These differences are less obvious after intravenous, intramuscular, or
subcutaneous administration as the bowel is bypassed producing 100%
bioavailability.
The other problem with morphine is that it is converted in the liver to two
metabolites (breakdown products). One product is called M-6-G and is much
more potent than the parent drug, and accumulates in kidney failure causing
drowsiness. The other is called M-3-G which acts as an antagonist of morphine
and M-6-G, and produces anti-analgesia. Analgesia is often the result of the
balance between how much M-3-G and M-6-G is produced by the liver, where
there are separate enzymes controlling the amount of each metabolite produced.
Some individuals produce too much M-6-G and are therefore very sensitive to
small amounts of morphine. Other individuals produce too much M-3-G causing
morphine resistance.
Morphine commonly produces side effects of drowsiness, nausea, vomiting,
constipation, depressed breathing rate, and detachment from reality. Many of
these effects disappear after acclimatization. Tolerance can occur during chronic
administration.
It is available in tablet (sevredol) and liquid (oramorph) normal release
preparations taken every four hours, and also in slow release preparations - MST
every 12 hours, MXL every 24 hours. In hospital it can also be given
intramuscularly, intravenously, subcutaneously, epidurally, and intrathecally. The
starting oral dose for morphine "virgins" is 10 mg normal release every four
hours, allowing calculation of the 24 hour dose requirement, and conversion to a
slow release preparation if necessary.
All patients on strong opioid's will develop constipation. The current laxative
regime of choice is senna combined with lactulose. Senna reverses the bowel
slowing effect of morphine, whilst lactulose assists lubrication.
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Diamorphine (Heroin) is a strong opioid which is twice as potent as
morphine. Morphine 10 mg is equivalent to diamorphine 5 mg. It is a prodrug needing to be converted to morphine in the liver before it is active. It
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has no advantages over morphine by mouth, having the same side
effects. Commonly used in the epidural space with local anaesthetics to
give potent post-operative pain relief. Not available as a tablet by mouth,
but can be used in hospital intravenously, subcutaneously and
intramuscularly. It comes as a white powder and is very soluble in
solution, making it useful for use in the hospice situation by subcutaneous
driver in terminal illness.
Hydromorphone is a strong opioid which is 7.5 times more potent than
morphine by mouth. Morphine 10 mg is equivalent to hydromorphone 1.3
mg. Unlike morphine it has no active breakdown products, but has similar
side effects. It is only available as oral preparations - normal release (1.3
and 2.6 mg every four hours) and slow release (4, 8, 16, 32 mg every 12
hours).
Oxycodone is a strong opioid which is twice as potent as morphine by
mouth. Morphine 10 mg is equivalent to oxycodone 5 mg. It has a basic
morphine chemical structure except for an additional side chain. When
taken by mouth, 60 - 80% of oxycodone is absorbed into the circulation,
compared to only 20 - 50% of an oral morphine dose. When oxycodone is
given intravenously, these advantages are lost. Better bioavailability gives
faster and more reliable onset. It is said to have fewer side effects when
compared to morphine. It is available in normal release (4 hourly) and
slow release (12 hourly) preparations.
Fentanyl is a strong opioid which is 100 times as potent as morphine.
Morphine 10 mg is equivalent to fentanyl 100 micrograms. It is commonly
used during operations by anaesthetists in the intravenous form. It has no
active breakdown products and is relatively short acting. Fentanyl is
commonly used in post-operative epidurals to complement the action of
local anaesthetics, giving excellent pain relief. It is also available as a
continuous delivery transdermal patch (Durogesic) delivering 25, 50, 75 or
100 ug per hour, with each patch staying in position on the skin for 3 days.
It is commonly used to treat malignant and non-malignant pain. As this
patch uses a reservoir system for drug delivery it should not be cut in half
or damaged in any way. Normal release lollipops (Actiq) are also available
in 200 ug and 400 ug sizes. Only 50% of each lollipop dose is absorbed
into the circulation, and the effects of the drug last for only 2 hours. There
is uptake of the drug partly from the lining of the mouth, and partly from
absorption in the stomach.
Buprenorphine is a strong opioid which is now coming back into favour. It
was once thought that it was a partial agonist of morphine, but recent
studies have suggested that it is a full agonist in the normal clinical range.
It is about 30 times more potent than morphine. Morphine 10 mg is
equivalent to buprenorphine 0.3 mg (or 300 ug). It stimulates morphine
receptors to produce potent pain relief, and has many of the side effects of
morphine. It is available as normal release sublingual tablets (200 ug
every 4 - 6 hours), and as a new continuous delivery transdermal 3 day
patch Transtec delivering 35 ug/hr, 52.5 ug/hr, or 70 ug/hr. The patch can
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be cut in half delivering 17.5 ug/hr to help adjust doses up or down,
however, this practice is not recommended by the manufacturers (Napp
Pharmaceuticals).
Pethidine is a strong opioid which is 1/10th as potent as morphine.
Morphine 10 mg is equivalent to pethidine 100 mg. It has an active
breakdown product called norpethidine which can accumulate in kidney
failure, producing epileptic seizures. In hospital it can be used
intramuscularly, intravenously, and epidurally. It is very short acting which
ever way it is administered, and is a poor choice orally for continuous pain
as it only gives relief for 1.5 hours. It is available as normal release 50 mg
and 100 mg tablets, there being no slow release preparation. Once
thought to be good for renal and biliary colic because of its smooth muscle
relaxing effect. This has been discounted recently with other strong
opioid's being just as efficacious when compared to pethidine.
Methadone is a strong opioid which is equipotent with morphine.
Morphine 10 mg is equivalent to methadone 10 mg orally. Methadone has
a very long and variable length of action (20 - 45 hours), and can be taken
once a day. It is readily absorbed from the bowel into the circulation (high
bioavailability), but can take many days before equilibrium is reached.
Commonly used for maintenance therapy for heroin addicts.
Morphine Equivalents - below is a table showing how potent different
opioid's are when compared to the gold standard of morphine 10mg IV:-
Drug
Dose
Route / Duration
Morphine
10 mg
IV - 2 hr
IM - 3 hr
Morphine
20 mg
NR - 3 hr
SR - 12 hr
Pethidine
100 mg
NR - 1.5 hr
IM - 1.5 hr
IV - 1.5 hr
Fentanyl
100 ug
IV - 15 min
Patch - 72 hr Oxycontin
5 mg
NR - 3 hr
SR - 12 hr
Diamorphine
5 mg
IV - 3 hr
SC - 3 hr
Buprenorphine
300 ug
SL - 4 hr
Patch - 72 hr Hydromorphone
1.3 mg
NR - 3 hr
SR - 12 hr
Methadone
10 mg
NR - 12 to 24 hr Codeine
100 mg
NR - 3 hr
IM - 3 hr
NR = oral normal release, SR = oral slow release, IM = intramuscular injection, IV
= intravenous injection, Patch = transdermal patch, SC = subcutaneous injection,
ug = micrograms, mg = milligrams.
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Please be aware that a 100 ug fentanyl patch delivers 100 ug of fentanyl
every hour (similar for buprenorphine 35 ug / 52.5 ug / 70 ug patches),
and that this needs to be taken into consideration when converting from
one drug or preparation to another.
Warning
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Do not suddenly stop strong opioid medications as this can cause a
serious withdrawal reaction.
 Mild withdrawal can present with restlessness, mydriasis
(dilated pupils), lacrimation (tears in the eyes), rhinorrhea
(runny nose), sneezing, piloerection (hairs standing up on
end), yawning, perspiration, restless sleep and aggressive
behavior.
 Severe withdrawal can present with muscle spasms, back
aches, abdominal cramps, hot and cold flashes, insomnia,
nausea, vomiting, diarrhoea, tachypnoea (rapid breathing),
hypertension (high blood pressure), hypotension (low blood
pressure), tachycardia (high heart rate), bradycardia (low
heart rate) and cardiac dysrhythmias (abnormal heart
rhythms). Seizures may be observed in neonates (only).
 Should you wish to reduce or stop these types of drugs,
please discuss it with your doctor first.
Do not mix strong opioid's with other sedatives such as alcohol and
sleeping tablets - this can cause severe sedation, life threatening
respiratory depression, and increased risk of aspiration of stomach
contents into your lungs.
Strong opioid's should be used with caution in those with a
psychiatric history or in those taking psychotropic medications.
Muscle Relaxants
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Diazepam is from the benzodiazepine group of drugs. It is used as a
muscle relaxant and for the control of anxiety (anxiolysis). It can be used
for a maximum period of one week to aid muscle relaxation in acute
severe back pain. It is not recommended for the control of chronic low
back pain. It works by stimulating GABA receptors in the brain, enhancing
descending inhibition of the spinal cord dorsal horn mechanism. The usual
dose is 2 - 5 mg two to three times a day. All benzodiazepine drugs cause
sedation and can aid sleep. However, they cause an increase in the
number of hours spent in REM sleep (rapid eye movement sleep = dream
sleep), reducing the time spent in restful deep sleep. Patients often awake
unrefreshed, feeling as if they had never been to sleep at all, because of
the disturbed REM sleep / deep sleep ratio. When benzodiazepine drugs
are withdrawn, they cause rebound sleeplessness for up to six weeks
afterwards. Hence they can be highly addictive, because patients have to
resort to re-starting them again just to get some sleep, even though the
quality of sleep is poor. Diazepam may be withdrawn in the next few
months because of its poor track record in relation to addiction. Spinal
manipulation is an alternative to taking muscle relaxants for acute low
back pain.
Methacarbamol is used in the treatment of acute muscle spasm in spinal
pain and other musculo-skeletal disorders. It is not recommended for the
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control of chronic low back pain. Dose requirements vary between 750 mg
three times a day to 1500 mg four times a day. The dose should be halved
in the elderly. Extreme caution is urged in those with liver and kidney
insufficiency due to drug accumulation. There may be an interaction with
all other drugs which cause drowsiness or central nervous system
depression. Driving or the operation of machinery is not advised when
drowsiness occurs. Spinal manipulation is an alternative to taking muscle
relaxants for acute low back pain.
Baclofen is another drug which works through the GABA system. It is
commonly used to help reduce spasticity associated with brain and spinal
cord injuries, and is less commonly used for painful back spasms. The
usual dose is between 30 - 80 mg per day in three divided doses, and
comes in 10 mg tablets. Side effects are often dose related and include
sedation, confusion, dizziness, insomnia, global muscle weakness and
poor coordination. May be administered via an implanted intrathecal pump
system for the long term relief of spasticity.
Anti-depressants
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Amitriptyline is an older tricyclic anti-depressant. It is converted in the
liver to the active metabolite nortriptyline. It has several uses in the pain
clinic (some of which are unlicensed) :o for the control of nerve pain either alone or with an anti-convulsant
o normalising disturbed REM sleep / deep sleep patterns in
fibromyalgia-type syndromes
o elevation of mood in depression
For nerve pain, the main mode of action is to increase descending
inhibition of the spinal cord dorsal horn by affecting levels of noradrenaline
and 5-HT. For depression it affects the balance of inhibitory and excitatory
chemicals in the brain.
The usual starting dose is between 10 - 25 mg at night. Most pain clinics
do not use more than 50 mg per day due to side effects.
Common side effects include dryness of the mouth (inhibits saliva
production) and sedation. When given at night, the sedation can be useful
for sleep. Mouth dryness often declines after the first two weeks with low
dose amitriptyline. High doses can produce cardiac rhythm disturbances in
the people with ischaemic heart disease. Contra-indicated in glaucoma seek medical advice. May worsen bladder function due to anticholinergic
effects (uncommon).
Alternatives to amitriptyline include dothiepin, nortriptyline, lofepramine,
desipramine, clomipramine and imipramine, all of which are said to have
similar effects on descending inhibition of the spinal cord dorsal horn, and
therefore useful in nerve pain.
Anti-convulsants
Anti-convulsants are used to treat nerve and sympathetic pain. Their mode of
action is stabilisation of irritable nerve membranes by blocking certain ion
channels. They are commonly co-prescribed with tricyclic anti-depressants like
amitriptyline.
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Gabapentin (Neurontin) is licensed for use in nerve pain and epilepsy. It
is also used to treat anxiety states. It is a nerve calcium channel blocker
with a fairly short duration of action. It has become popular in recent
years because of its lower side effect potential. Even so, common side
effects encountered are sedation, dizziness, and headaches. Some
people have also described weight gain, fluid retention, upper stomach
pain and nausea. It is administered three times a day and needs to be
gradually titrated upwards over several days and weeks. The upper
licensed dose in the UK is 1800 mg per day, whereas in the USA doses of
between 2400 mg and 3600 mg per day are frequently used. It
accumulates in renal impairment, and therefore lower doses and more
careful monitoring are required in this situation.
Normal Kidney Function
Time Breakfast Lunch Supper
Step 1 300 mg
Step 2 300 mg 300 mg
Step 3 300 mg 300 mg 300 mg
Step 4 300 mg 300 mg 600 mg
Step 5 600 mg 300 mg 600 mg
Step 6 600 mg 600 mg 600 mg
o
o
Each step may be 3 or 7 days depending on side effects.
In young adults with normal renal function and acute nerve pain
(e.g. Trigeminal Neuralgia), I would suggest each step should be 1
- 3 days.
Impaired Kidney Function
Time Breakfast Lunch Supper
Step 1 100 mg
Step 2 100 mg 100 mg
Step 3 100 mg 100 mg 100 mg
Step 4 100 mg 100 mg 200 mg
Step 5 200 mg 100 mg 200 mg
Step 6 200 mg 200 mg 200 mg
o
Renal Impairment Doses are suggestions only - doses may need to
be lower or higher according to patient response and side effects.
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Pregabalin (Lyrica) is a new drug in the UK, licensed for use in nerve pain
and epilepsy. It may have some effect in anxiety states but further work is
ongoing to investigate this. It works at specific types of nerve calcium
channels. It has more potent activity at these calcium channels than
gabapentin. It has a predictable and rapid onset of action and shows less
inter-patient variability in terms of dose requirements because of
predictable absorption. It has been shown to help nerve pain even at the
initial starting dose of 150 mg per day. If required, higher doses may be
used on day 3 - 4, and the maximum dose may be used if necessary after
a further 7 days (see table below). There are very few interactions with
other drugs, the exceptions being potentiation with alcohol and
oxycodone. 98% of pregabalin is excreted in the urine, and therefore dose
adjustments are required where there is poor renal function (elderly, renal
failure). Positive effects on sleep interference have been found, and
further research into the mechanism behind this is ongoing. The positive
effects on sleep seem to out perform low dose amitriptyline. Side effects
are similar to gabapentin and include dizziness, drowsiness, and fluid
retention. It may be given twice or three times a day.
Normal Kidney Function
Time Breakfast Supper
Step 1 75 mg
75 mg
Step 2 150 mg 150 mg
Step 3 300 mg 300 mg
o
o
o
Step 1 is the starting point.
If necessary on day 3 - 4 you can go to Step 2.
If necessary on day 7 you can go to Step 3.
Impaired Kidney Function
Time Breakfast Supper
Step 1 50 mg
50 mg
Step 2 100 mg 100 mg
Step 3 150 mg 150 mg
o
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Renal Impairment Doses are suggestions only - doses may need to
be lower or higher according to patient response and side effects.
Converting from Gabapentin to Pregabalin
o Below are some suggested conversion regimes. Each step could
be 3 - 7 days. Doses may need to be adjusted according to patient
response and side effects. If excessive drowsiness occurs, reduce
the Gabapentin dose faster than instructed
Convert From Gabapentin 2400 mg / day To Pregabalin 600 mg / day
Time
Breakfast
Lunch
Supper
Drug
Gaba
Pregab
Gaba
Pregab
Gaba
Pregab
Step 0
900 mg
600 mg
900 mg
Step 1
600 mg
75 mg
600 mg
600 mg
75 mg
Step 2
300 mg
150 mg
300 mg
300 mg
150 mg
Step 3
300 mg
300 mg
Convert From Gabapentin 1800 mg / day To Pregabalin 600 mg / day
Time
Breakfast
Lunch
Supper
Drug
Gaba
Pregab
Gaba
Pregab
Gaba
Pregab
Step 0
600 mg
600 mg
600 mg
Step 1
300 mg
100 mg
300 mg
600 mg
100 mg
Step 2
300 mg
200 mg
300 mg
200 mg
Step 3
300 mg
300 mg
Convert From Gabapentin 900 mg / day To Pregabalin 300 mg / day
Time
Breakfast
Lunch
Supper
Drug
Gaba
Pregab
Gaba
Pregab
Gaba
Step 0
300 mg
300 mg
300 mg
Step 1
300 mg
50 mg
300 mg
Step 2
100 mg
300 mg
Step 3
150 mg
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Pregab
50 mg
100 mg
150 mg
Carbamazepine is licensed for use in nerve pain. It has useful membrane
stabilising properties, but is more likely to cause side effects than
gabapentin. Dose titration is necessary from 100 mg per day upwards.
The usual adult dose is 200 mg three times a day. Dose reduction is
necessary in the elderly, with the usual dose being 100 mg twice a day.
Doses above 600 mg per day are likely to cause drowsiness and ataxia
(unsteadiness).
Oxcarbamazepine is the 10-ketoanalogue of carbamazepine with similar
mode of action. Its principal advantage over carbamazepine is that the
former causes little if any, induction of hepatic enzyme with consequent
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lack of autoinduction and fewer pharmacokinetics interactions. In view of
its longer half life, this drug can be administered in twice daily dosages.
Phenytoin is licensed for use in trigeminal neuralgia. It is highly bound to
proteins in the blood, and can therefore affect blood levels (and therefore
drug effects) of other drugs which are also highly protein bound. It is a
more difficult drug to use and needs to have levels in the blood stream
checked regularly. More frequent side effects means that phenytoin is
rarely used for nerve pain today.
Sodium Valproate is used for nerve pain, but has no license for it. May
cause abnormal liver enzymes and low blood platelets, and therefore
needs careful monitoring of liver function tests and full blood count.
Lamotragine is used for nerve pain, but has no license for it. Rarely used
today because of side effects.
Anti-arrhythmics
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Lignocaine is a local anaesthetic which acts by blocking sodium channels
in nerves. In the pain clinic it is used by intravenous infusion in hospital
under full vital signs monitoring. Short infusion periods over 30 minutes
can be used to help classify the type of pain in question (usually 300 mg
over 30 minutes). Long infusion periods over days and weeks have been
described to treat nerve pain in the longer term. Some clinics use a short
diagnostic test in order to assess suitability for a trial of mexiletine. (See
also Lignocaine 5% patch).
Mexiletine is a older drug used to treat heart rhythm disturbances. It is
chemically related to lignocaine and can be taken by mouth. It has a
license for nerve pain up to 50 mg three times a day. Clinically doses as
high as 600 mg per day may be needed, but is often associated with a
high rate of side effects such as indigestion, nausea, dizziness and
palpitations. Others in the same group include flecainide and tocainide but
are rarely used due to side effects.
Topical Agents
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Capsaicin is the active ingredient in chilli peppers. It is licensed for use in
post-herpetic neuralgia after shingles, and also in osteoarthritis. The
cream is absorbed through the skin to reduce substance P (a neurotransmitter) levels in peripheral C-fibre nerves, and in the dorsal horn of
the spinal cord. Substance P in the periphery is often associated with
inflammatory processes like osteoarthritis, whilst in the dorsal horn it is
involved in the gate control of pain. Capsaicin produces depletion of
stored substance P in nerve endings, and therefore causes initial heat and
redness in the skin. With regular use (4 times a day), nerve ending levels
of substance P are kept very low, meaning that the heat and redness do
not recur. It is important to use only a small amount of the cream to avoid
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excessive redness and heat. Hands must be washed in soap and water
afterwards to avoid contact with sensitive mucous membranes.
Lignocaine 5% Patch (Lidoderm) is available in the USA for use in postherpetic neuralgia following shingles. Each patch contains 700 mg of
lignocaine. Up to 3 three patches can be worn for up to maximum of 12
hours in any 24 hour period. The patch can be trimmed with a pair of
scissors to exactly match the area affected by the neuralgia. It provides
topical analgesia to the affected skin. The lignocaine absorbed into the
circulation may also have an effect on pain processing by the central
nervous system. May also be appropriate for any neuralgia so long as the
patch can adhere to the affected skin. May be specially imported from the
USA by your local hospital pharmacy. Please contact your local Pain
Clinic to investigate whether it is available in your area. To locate your
nearest Pain Clinic in the UK please go to www.britishpainsociety.org.
NMDA Antagonists
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Ketamine is an intravenous induction agent used in anaesthesia, and is
also an NMDA (N-methyl-D-aspartate) receptor antagonist. It has been
suggested that NMDA receptor activation in the dorsal horn helps
contribute to dorsal horn sensitisation. Ketamine has NMDA blocking
effects and therefore can reduce the degree of dorsal horn sensitisation
and overall pain relief. Ketamine has been used orally and by intravenous
infusion in patients with severe neuropathic pain states. The intravenous
infusion rate is between 5 - 10 mg per hour used 48 hours prior to, and 5-7
days after limb amputation. The suggested oral ketamine dose for
neuralgia is 10 - 20 mg three times per day. Oral Ketamine tastes foul and
therefore needs to be mixed 50 / 50 with Ribena. It's oral bioavailability is
only 17%.
Dextromethorphan is an over the counter cough suppressant which has
the same but weaker effect as ketamine at NMDA receptors.