Drugs Prescribed in the Pain Clinic
Patients frequently come to the pain clinic on medications which are either simply not working on their pain or are giving them inadequate pain relief.
There may be many reasons for this and the simplest one and probably most common one is non-compliance; that is they are not taking the drugs regularly as prescribed. If the body has a constant, adequate level of a drug then it fights pain much more effectively.
Another reason for a painkiller not working is because it is not the right painkiller for the job. Pain may be felt coming from the tissues and organs e.g. muscles, bones and liver and this is nociceptive pain which responds well to classic painkillers such as aspirin, paracetamol, codeine and morphine. Pain may be felt from nerves and this is called neuropathic pain and is frequently poorly responsive to aspirin, paracetamol, codeine and morphine.
The pain clinic often therefore will prescribe painkillers because it is felt that the pain described is neuropathic in nature. These painkillers are usually used for other purposes such as treating epilepsy or depression. In common with their normal modes of treatment, they stop nerve cells firing spontaneously and this is basically what is happening in neuropathic pain.
The symptoms of neuropathic pain are quite distinct and include such descriptive words as burning, shooting, sensitive, cramping, itchy, lancinating.
Drugs for neuropathic pain include the antiepileptics such Gabapentin and Tegretol (Carbamezepine) and the Antidepressants such as Amitriptyline and Dothiepin. The greatest problem with using these medications is that they give patients unpleasant side-effects much more frequently than aspirin, paracetamol etc. To this end Gabapentin is the only one which is licensed for all neuropathic pains and is the one which is most agreeable with patients as its side-effects are the ones most tolerated by the majority. Exact doses and information on side-effects can be given in the clinic but the most effective dose appears to be at least 600mgs. three time a day and common side-effects include tummy upset, headaches, sleepiness and rashes.
Drugs for nociceptive pain are those most commonly thought of as painkillers, that is paracetamol, aspirin etc. There are the weaker painkillers as already mentioned and the stronger pain killers such as morphine, oxycodone and palladone. Massive controversy exists over their use in patients without cancer as they are widely thought of as having a great potential for addiction and abuse. Slowly but surely the medical world is coming round to seeing that where a patient has pain which is not due to cancer and where the weaker drugs are ineffective, then there is very little addiction and abuse potential if the drugs are being used as painkillers alone. The greatest risk with long term use is of the body getting used to a particular dose with a worstening of pain and a need therefore to increase the dose. This whole area is extremely complex and needs a great deal of trusts between clinician and patient.
Another, less controversial area where there has been recent advances in painkiller therapy is the advent of safer aspirin-like drugs. Aspirin, Ibuprofen, Voltarol, Mefanamic Acid, Ketoprofen etc. are known as the non-steroidal anti-inflammatory drugs (NSAIDS). They are very useful in nociceptive pain but can cause severe side-effects such as gastric ulcers and kidney damage. Unfortunately the newer drugs in this area (the cox2 antagonists) Celecoxib, Rofecoxib and Parecoxib/Valdecoxib have now been found to have a statistically significant incidence of causing cardiovascular problems in at risk groups. Parecoxib and Valdecoxib can cause unpleasant rashes. Rofecoxib has been taken off the market and caution is urged in the use of all of these drugs. Glucosamine is a medication that can be bought over the counter. It appears that research has shown it to be effective in reduces the pain of knee arthritis alone in a dose of 1500mgs per day.
Drugs may also be effective when applied as creams or in patches. Capsaicin cream comes in 2 strengths (0.025% and 0.075%). The lower strength can help the pain of arthritis and the stronger solution can help some neuropathic pains such as scar pain and that of postherpetic neuralgia. The problem with this cream is that it can burn and irritate before it works and more often than not it will stop working if its use is stopped.
Lidoderm patches can also be useful in scar pain and postherpetic neuralgia. These patches are impregnated with local anaesthetic. They do not make the skin greasy and stop working after they are removed so constant use may be needed.
NSAIDS are also available in creams and apart from being effective, cause almost negligible damage to the stomach and kidneys. They help approximately 1 in 3 people who use them regularly.
Patches containing the strong painkillers fentanyl and buprenorphine are also available and may help in both cancer and non-cancer pain unresponsive to weaker painkillers. Both are licensed for use in patients with chronic non-cancer pain.
Delivery of drugs to the body
Most people take drugs by mouth. Increasing numbers of people absorb drugs using patches. There are of course other ways of delivering drugs to people. These ways are used because not everyone can swallow drugs and even if they do, the dose required is higher than that achieved. Other routes include into muscles, directly into veins and under the skin, under the tongue, inhaled through the nose and lungs and also via the back passage.
The most effective way of delivering drugs, however, is by putting them directly into the nervous system as this where the drugs actually do most of their work. This is done by ‘tapping’ into the space around the spinal cord as already talked about in the section on low back pain and epidurals.
Tapping a little further leads to the subarachnoid (item 5 in the picture) or spinal space where the spinal cord and cerebrospinal fluid are. In both areas a catheter or hollow tube can be left and drugs infused into it. It has to be stressed that this is a highly specialised area of drug delivery and only the very basics can be explained without tremendous background detail being required. It is also used in very few patients with chronic non-cancer pain is has a greater place in the treatment of cancer pain.