Choosing a hypnotic

The main requirements for a hypnotic drug are rapid onset of action, a duration of action of 6-8 hours, freedom from residual effects and safety in overdose. All hypnotics carry a risk of withdrawal effects e.g. rebound insomnia, if used for more than a few weeks. Also a degree of tolerance develops with prolonged use. Thus courses should be limited, if possible, to two weeks. Also if the drug has been used for longer than two weeks, the dosage should be tapered off slowly.

Hypnotics presented as the drugs of choice (1) were the newer benzodiazepines (especially loprazolam and lormetazepam) with non-benzodiazepine hypnotics e.g. zopiclone as alternatives. Summary guidance from NICE (2) states:

• when, after due consideration of the use of non- pharmacological measures, hypnotic drug therapy is considered appropriate for the management of severe insomnia interfering with normal daily life, it is recommended that hypnotics should be prescribed for short periods of time only, in strict accordance with their licensed indications
• it is recommended that, because of the lack of compelling evidence to distinguish between zaleplon, zolpidem, zopiclone or the shorter-acting benzodiazepine hypnotics, the drug with the lowest purchase cost (taking into account daily required dose and product price per dose) should be prescribed.
• it is recommended that switching from one of these hypnotics to another should only occur if a patient experiences adverse effects considered to be directly related to a specific agent. These are the only circumstances in which the drugs with the higher acquisition costs are recommended
• patients who have not responded to one of these hypnotic drugs should not be prescribed any of the others

For full details then consult the NICE guidance (1).

Zopiclone, zolpidem and zaleplon are non-benzodiazepine hypnotics that act on benzodiazepine receptors. These drugs may result in rebound effects later in the night e.g. early morning wakening and early morning anxiety. These rebound effects may especially occur with zolpidem because of the very short elimination half-life (2 hours).

The elimination half-lives for some hypnotic drugs are:

• t 1/2 (hours)

benzodiazepines

• loprazolam 6 - 12 hours
• lormetazepam 10 - 12 hours

non-benzodiazepine hypnotics

• zolpidem 2 hours
• zopiclone 5 - 6 hours

Reference:

1. Prescribers' journal (1997), 37 (1), 1 - 10.
2. NICE (April 2004). Guidance on the use of zaleplon, zolpidem and zopiclone in the short-term management of insomnia.