DRUG-COMBINATIONS IN SYRINGE DRIVERS - THE COMPATIBILITY AND STABILITY OF DIAMORPHINE WITH CYCLIZINE AND HALOPERIDOL

The compatibility and stability of 28 combinations of diamorphine hydr ochloride (5-100 mg/ml) with cyclizine lactate (5-50 mg/ml), eight com binations of diamorphine (10-100 mg/ml) with haloperidol (2-4 mg/ml) a nd eight combinations of all three drugs was assessed after storage in 1 ml polypropylene syringes. Samples were stored for periods up to se ven days in the light and at room temperature (22 degrees C). Five com binations of diamorphine with cyclizine precipitated immediately upon preparation. After analysis and determination of t(90%) values (the ti me taken for 10% degradation), 10 of the remaining 23 combinations wer e judged to be compatible (no signs of crystallization or precipitatio n) and stable (less than 10% loss of potency of either drug) after sto rage for 24 h. After seven days storage only four remained compatible and stable. The results indicate that ratios of diamorphine to cyclizi ne of 1:1 are stable at concentrations up to 20 mg/ml. An increase in diamorphine concentration necessitates a reduction in cyclizine to 10 mg/ml, and an increase in cyclizine concentration necessitates a reduc tion in concentration of diamorphine to 15 mg/ml to maintain stability over 24 h. All the combinations of diamorphine with haloperidol remai ned compatible and stable for seven days. The addition of haloperidol (2 mg/ml) to the diamorphine and cyclizine combinations had no detrime ntal effect on their compatibility and stability. A stability curve is included as an easy way for palliative care personnel to avoid potent ial problems with incompatibilities and reduced stability when using t hese combinations. Furthermore, to reduce the possibility of precipita tion with mixtures containing cyclizine, the use of 0.9% sodium chlori de should be avoided.