Pain Medications

Some Commonly used Pain Medications

Whilst the commonly used analgesics used to treat acute pain often have limited or no longterm benefit in treating chronic pain, some of the medications that in other patients are used to treat depression or epilepsy can have very useful analgesic effects in chronic pain patients. Why?

Antidepressants work by increasing the levels of serotonin and/ or noradrenaline in the brain, whilst low levels of these neurotransmitters will predispose to this condition. These neurotransmitters also activate pain blocking areas within the brain. It is likely that antidepressant medications have their analgesic effects though this mechanism.

Anticonvulsants, i.e. epilepsy medications, stabilise nerves in the brain to prevent them from spontaneously discharging and causing a seizure. In some patients with chronic pain a damaged nerve can behave in a similar fashion – spontaneously discharging but causing pain rather than a seizure. Anticonvulsants are likely reducing pain in this setting by either reducing these damaged nerves from discharging, or reducing the transmission of the pain signal.

Amitriptyline

Amitriptyline is a medication from the antidepressant class of drugs. At doses significantly lower than those used to treat depression Amitriptyline has useful effects in managing chronic pain conditions. These are:

• Amitriptyline is a mild non-addictive sedative, which will commonly help patients with chronic pain to improve their overnight sleeping pattern. The onset of sedation occurs around 2 hours after taking the dose, thus taking the medication around 7 PM works well for most patients.
  
  
• Amitriptyline also increases levels of neurotransmitters serotonin and noradrenaline which help to block pain coming from damaged nerves. This is termed "anti-neuropathic" analgesia. The usual commencing dose is 5 or 10 mg at night. Most patients are able to be managed on a dose up to or less than 50 mg at night.

Amitriptyline has some side effects, in addition to the sedation mentioned above. It can cause a dry mouth, and many patients who take this medication find it helpful to keep a bottle of water by the bed at night, from which they can take sips of water if required.

Amitriptyline can also cause some dizziness. For this reason it is important that the dose was commenced at a low level, and increases in the dose are made in slow incremental steps. Even with these precautions it is important that patients taking amitriptyline take care when they sit up or stand up in case they are affected by this dizziness.

Rare complications of amitriptyline can affect some patient ability to pass urine or affect the heart, so discussion regarding this is made on a patient by patient basis when this medication is being considered. That said, amitriptyline is a very old drug which has a long history of use at high doses in psychiatry patients who suffer from depression, and we are therefore confident that there are no long-term tissue damaging effects from this medication.

Gabapentin and Pregabalin

Gabapentin and pregabalin (Lyrica) are medications from the anticonvulsant or epilepsy treating class of medications. They have a useful role in treating patients with nerve injury or neuropathic type pain.

These medications usually need to be taken 2 or 3 times per day, with the starting dose, and the rate with which this dose is increased needing to be individualised for each patient. In particular patients who are elderly or who have renal impairment will generally require much lower doses of this medication.

The common side-effects of gabapentin and pregabalin include drowsiness, dizziness, some impairment of concentration and some impairment of memory. Therefore, this medication requires a low starting dose and a slow dose increase under close medical supervision. 

Sodium Valproate

Sodium valproate (Epilem) is a medication from the anticonvulsant or epilepsy treating class of medications. It can be useful in managing patients with chronic nerve pain or "neuropathic" pain.

The usual commencing dose is 200 mg at night. Most patients are managed on a dose of 500 mg twice daily or less.

The common side-effects of sodium valproate are sedation and dizziness, and so this medication is usually begun at a low-dose, which is then slowly increased under close medical supervision.

Sodium valproate is generally a well-tolerated medication, although some rare side-effects can occur which are discussed with each patient on a case-by-case basis.