Weekly dose: Lyrica, the epilepsy drug that treats chronic nerve pain
Lyrica is the brand name for a prescription medicine called pregabalin. Although it is an anticonvulsant, or an anti-epileptic drug, pregabalin is commonly prescribed to alleviate nerve or neuropathic pain – a type of pain caused by damage to, or a disease affecting, nerves.
Neuropathic pain doesn’t normally respond to common painkillers such as ibuprofen or paracetemol. This is because the mechanisms that cause neuropathic pain are different to the underlying causes of other pain.
History
Pregabalin is closely related to gabapentin, a medication developed to treat partial seizures. This is a type of epilepsy caused by a surge in nerve cell excitability in one area of the brain.
Because nerve pain and epilepsy are related by abnormal levels of nerve excitability, an American neurologist tested gabapentin on patients in the mid-1990s and found it relieved their neuropathic pain.
Both are recommended as first line treatments for nerve pain by the International Association for the Study of Pain. Lyrica was approved in 2004 in the United States for the treatment of partial seizures of epilepsy and some neuropathic pain.Subsequently, pregabalin was developed as an improved version of gabapentin. The amount of pregabalin absorbed into the bloodstream increases in a linear fashion; unlike gabapentin where as the dose goes up, the proportion absorbed into the bloodstream goes down. This makes the effects of pregabalin more predictable than those of gabapentin.
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In 2007, pregabalin was approved in the United States to treat fibromyalgia, a chronic disorder characterised by pain and muscle tenderness throughout the body. In Australia, it was registered by the Therapeutic Goods Administration in 2005.
How it works
In neuropathic pain, damaged nerve fibres are hyper-excitable, which means sensations such as light pressure or touch, which are normally barely felt, are perceived as painful.
Pregabalin (and gabapentin) are thought to interact with specific proteins in nerve endings in the brain and spinal cord. This reduces entry of calcium ions into nerve terminals to dampen release of pain neurotransmitter molecules in the spinal cord and brain.
How Lyrica is used for pain
Nerve pain is more severe than non-neuropathic pain. Patients with persistent nerve pain often describe it as intense burning or shooting sensations in their arms, hands, fingers, legs, feet or toes. Because it’s often poorly relieved by available medications, the pain is unrelenting and intrudes into all activities of daily living.
About 7% to 8% of adults have chronic pain with neuropathic characteristics. These include: feeling pain from light pressure or touch, such as clothing; hypersensitivity to mildly painful events such as bumps or knocks; burning, tingling and pins and needles; and abnormal sensations, such as ants crawling under the skin when touched.
Some groups have a higher prevalence of neuropathic pain than others, particularly those who suffer from conditions that cause damage to the nerves, such as those with diabetes or following a bout of shingles.
Neuropathic pain is also common after certain operations, such as a mastectomy and affects about 35% of people with HIV infection. About 20% of cancer patients with chronic pain will have pain with neuropathic characteristics either because a tumour is pinching one or more nerves or because of damage to nerves that results from the cancer treatment itself.
The recommended pregabalin dose to relieve nerve pain is 150 mg to 600 mg per day. The doctor will initially prescribe a relatively low dose that is typically 75 mg once or twice daily; and 25 mg once or twice daily for the elderly or children. This will gradually be increased over several months.
How Lyrica is used for epilepsy
In people with partial seizures, a doctor may prescribe pregabalin as an add-on treatment to other anti-epileptic medications. But it is not the best add-on treatment for everyone.
The doctor will gradually increase the dose, usually starting at 75 mg twice a day or 50 mg three times a day. The goal is to reach the dose that gives the best control of partial seizures without causing troublesome side-effects.
What it costs
Pregabalin capsules are marketed in strengths ranging from 25 mg to 300 mg. It’s listed on the Pharmaceutical Benefits Scheme in Australia, which means you pay up to A$38.30 for a pack of 56 capsules or A$6.20 if you have a concession card.
How many people use it?
When pregabalin was first listed on the Pharmaceutical Benefits Scheme in 2013 to treat neuropathic pain, the then health minister announced it would help 270,000 Australians. However, between June 2015 and 2016, pregabalin’s item number was claimed around 650,000 times. This may be because the effects of pregabalin are more predictable than those of its predecessor, gabapentin.
Side-effects
The main side-effects of pregabalin are drowsiness, dizziness, impaired balance and an inability to think properly. These are more likely to occur soon after treatment starts and may diminish with time. Less common side-effects include blurred vision, dry mouth, fatigue and weight gain.
Side-effects are the main reason patients stop taking pregabalin for nerve pain. So it is really important that the initial dose is not too high and that the dosage gets increased slowly, especially in older people and those with impaired kidney function.
Special considerations
Pregabalin is excreted from the body in urine through the kidneys. People with impaired kidney function need lower doses of pregabalin as the drug would be excreted more slowly. Pregabalin is not broken down in the liver so it does not interfere with the liver breakdown of other medications.
Prolonged use of pregabalin does not produce tolerance and dependence, nor does it have the same potential for misuse, abuse or addiction. Pregabalin can also be used safely with other pain-killers such as paracetamol and morphine.
Source: theconversation.com
