SUBCUTANEOUS MORPHINE: SOLUBILITY AND THE USE OF MORPHINE TARTRATE AND ADDING OTHER DRUGS TO THE INFUSION

The dose of morphine which can be delivered by subcutaneous infusion is limited by the solubility of the drug. The volume of fluid delivered determines the risk of leakage at the infusion site; it is uncommon with infusion rates of 1-2 ml/h. Most syringe drivers are designed to hold a 10 ml syringe, although there are systems made for larger volumes. As the maximum concentrations of commercially available morphine sulphate and hydrochloride are about 30 mg/ml, problems will occur with a 10 ml system if the patient requires more than 300 mg/day. In this situation the syringe may need to be changed each 12 hours, or the more soluble morphine tartrate substituted. Morphine tartrate has a solubility of 80 mg/ml and potency effectively the same as morphine sulphate (80 mg tartrate is equivalent to 78 mg sulphate).

Adding other drugs to the infusion-The use of continuous SC infusions of morphine in the terminal care setting has led to other appropriate drugs being given in the infusion. The addition of a small amount of hyaluronidase will improve diffusion of the fluids in the subcutaneous tissue and reduce local irritation.

*46\55\2*

Pain Relief/Muscle Relaxers