Chronic Pain

Chronic pain is defined as pain which persists a month beyond the usual course of an acute disease or a reasonable time for an injury to heal, or is associated with a chronic pathological process which causes continuous pain, or pain which recurs at intervals for months or years.

General Principles

A detailed description of treatment of chronic pain is beyond the scope of this chapter. But some general principles are given here.

• Chronic pain can be treated successfully, in 80% of cases at least, with drugs.
• Nociceptive pain (the ordinary pain which occurs by stimulation of the pain-sensing nerve endings) must be distinguished from neuropathic pain and sympathetically maintained pain.
• Quantitation of pain by the patient is vital for successful treatment.
• The WHO three-step ladder pattern of treatment of pain is recommended for use in the majority of patients with cancer pain. Special procedures like neurolysis are reserved for those who do not respond adequately to drug therapy
• Drugs must be administered orally whenever possible.
• Drugs must be given by the clock, depending on the duration of action of the drug.

Nonopioids

• Paracetamol: Up to 20 mg/kg orally 4-6 hourly Contrary to popular belief, such dose will not cause any toxicity
• NSAIDs as advised for acute pain, given orally. Drugs for neuropathic pain Anticonvulsants
• Sodium valproate, starting with 200-400 mg daily, gradually increased to up to 1200 mg a day, best given as a single dose at night. Carbamazepine and phenytoin are other options.

Tricyclic antidepressants

• Amitriptyline or other tricyclics can be used. Amitriptyline is started a single bed time dose of 12.5 or 25 mg and gradually increased up to 75 mg
• Gabapentin: 900-1800 mg a day in divided doses.
• Mexiletine and local applications of capsaicin have limited role. In some cases, nerve blocks may be indicated.

Weak Opioids

Codeine: Usually 30-60 mg orally 4 hourly

• Dextropropoxyphene: 65-130 mg orally 6-8 hourly (cumulation may cause drowsiness in the elderly). Pentazocine is not recommended in the treatment of chronic pain.

Strong Opioids

• Buprenorphine: 0.2-0.6 mg as sublingual tablets every 6- 8 hour
• Morphine sulphate: Oral morphine is the mainstay of treatment of cancer pain. The following points about oral morphine would be worth remembering: — In doses adequate for relief of pain, oral morphine does not cause addiction — In doses adequate for relief of pain, oral morphine does not cause respiratory depression
• Oral opioids cause constipation in the majority of patients, and routine laxatives are a must.
• Less than one third of patients may have vomiting, tiredness or drowsiness, particularly early in treatment.
• Oral morphine does not cause any significant tolerance.