What are tricyclic antidepressants?
Tricyclic antidepressants, such as amitriptyline and nortriptyline, were once widely used as antidepressants before being replaced by newer antidepressant medications with better side effect profiles. Other uses of tricyclic antidepressants include the treatment of insomnia, enuresis, and chronic pain syndromes such as fibromyalgia.
The tricyclic antidepressants are finding a place in the treatment of chronic pain and itch associated with some dermatological conditions.
What are tricyclic antidepressants used for?
Tricyclic antidepressants are useful in reducing the symptoms of chronic pain in the following skin conditions:
- Vulvodynia (vulval pain)
- Vestibulodynia (pain with sexual intercourse)
- Dyaesthetic vulvodynia (neuropathic pain)
- Shingles and post-herpetic neuralgia
- Trigeminal trophic syndrome
Pain arising from these conditions is defined as sympathetically maintained pain (SMP). The pain is usually described as having a burning sensation and is often in response to stimuli that do not ordinarily cause pain. This pain originates from the nervous system. Amitriptyline appears to be effective in reducing this type of neuropathic pain in doses lower than those used to treat depression.
Tricyclic medications may reduce the pain of chronic ulcers including:
- Pyoderma gangrenosum
- Polyarteritis nodosum
- Venous ulceration
- Epidermolysis bullosa.
Tricyclic antidepressants are sometimes successfully prescribed for pruritus (itch), especially when this is of neuropathic origin:
Tricyclic medication has some antihistamine H1 blocking activity and may be useful in the treatment of urticaria even when conventional antihistamines have failed.
The dosage of tricyclic medications
Patients are usually started on tricyclic medications at a low dose of 5–10 mg daily, taken at night to minimise side effects. This is gradually increased to a maximum daily dose of 50–150 mg, depending on the response and tolerability of side effects by the patient. Patients need to be warned that pain/itch relief is not immediate as it may take several weeks for the drug to become fully effective.
Side effects of tricyclic medications
The side effects of amitriptyline and nortriptyline include:
- Dry mouth (which could contribute to dental decay)
- Blurred vision
- Increased sweating (hyperhidrosis)
- Difficulty urinating
- Dizziness due to a drop in blood pressure on standing up (postural hypotension)
- Nausea, confusion or a headache due to hyponatraemia (sodium imbalance)
- Weight gain
- Heart rhythm disturbances.
Anticholinergic/antimuscarinic side effects may occur in up to 50% of patients and elderly patients are at greater risk. Intolerance of these effects often leads to discontinuation of the drug. Other tricyclic antidepressants such as desipramine and nortriptyline may be better tolerated than amitriptyline.
It may be dangerous to take a tricyclic medicine with a monoamine oxidase inhibitor (MAOI) antidepressant medication or within 14 days of discontinuing an MAOI. Adverse effects are likely to be worse with alcohol.
Tricyclic medications may not be suitable for people with certain medical conditions or taking certain medications such as anticholinergic agents. Tell your doctor if you have had any of the following health problems:
- Heart disease
- Urinary retention
- Overactive thyroid gland
- Drug-related hyperpyrexia.
It may be wise to under an electrocardiograph prior to treatment and have this repeated after a few weeks. Tricyclic medications are dangerous in overdose.
We suggest you refer to your national drug approval agency such as the Australian Therapeutic Goods Administration (TGA), US Food and Drug Administration (FDA), UK Medicines and Healthcare products regulatory agency (MHRA) / emc, and NZ Medsafe, or a national or state-approved formulary eg, the New Zealand Formulary (NZF) and New Zealand Formulary for Children (NZFC) and the British National Formulary (BNF) and British National Formulary for Children (BNFC).