Oral controlled-release morphine preparations, given 12-hourly, are the treatment of choice for patients able to take oral morphine, once the general dose requirements have been established.

There are two different controlled-release (CR) morphine sulphate preparations commercially available. They have the advantage of requiring only twice daily administration and are well tolerated by most patients; Kapanol capsules can be given either 12-hourly or once daily. The efficacy and side effects of the controlled-release preparations are essentially similar to immediate-release morphine given 4-hourly with the exception that the maintenance of analgesia may be smoother. In practice, the major problems with the controlled-release preparations are establishing the starting dose, treating breakthrough pain and making dose adjustments.

Morphine controlled-release preparations should be swallowed whole. MS Contin tablets must not be broken, crushed or chewed. Kapanol capsules contain pellets which may be sprinkled on soft food for patients with dysphagia and it is the pellets which must not be broken or crushed. Disruption of the MS Contin tablet or Kapanol pellets renders the controlled-release mechanism ineffective and the patient is in effect taking immediate-release morphine which will produce analgesia for only 4 hours and, as the dose is calculated to cover 12 hours, there is a risk of toxicity if the whole dose is promptly absorbed.

MS Contin suspension consists of morphine sulphate bound to ion-exchange bead resins which are then coated. Morphine release depends on the amount of coating, which is adjusted to provide controlled release over a 12-hour period. The suspension is useful for patients with dysphagia.

The plasma morphine concentration rises slowly over a few hours after the initial dose and it is customary to give a dose of immediate-release morphine or other short acting analgesic at the same time to cover this period. With repeated 12-hourly dosing, there is less fluctuation in plasma morphine concentrations with Kapanol than with MS Contin. These differences suggest that there might be a lesser incidence of side effects in the first few hours and less breakthrough pain towards the end of each 12-hour period with Kapanol, but these have not been apparent in the comparative studies performed.

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