Background and objective: To survey all bedside-prepared analgesic infusions (two or more drugs within one vehicle) at a 1000-bed general hospital. To evaluate appropriate vehicles and acceptable drug combinations in analgesic infusions with regard to evidence-based therapy.
Design: Literature review; computer simulation of pharmacokinetics with MATLAB 6.5; evaluation of pharmacokinetic or pharmacodynamic interactions and dose regimens.
Main outcome measures: Categorisation of 19 infusion combinations used for the management of pain into acceptable and questionable combinations of components in terms of quality assurance evaluation.
Results: Diclofenac sodium (CAS 15307-79-6), metamizole sodium (CAS 68-89-3) and tramadol hydrochloride (CAS 36282-47-0) were combined with diazepam (CAS 439-14-5), B-vitamins (CAS 67-03-8, 130-40-5, 58-56-0, 68-19-9, 98-92-0, 137-08-6), lidocaine hydrochloride (CAS 73-78-9), metoclopramide dihydrochloride (CAS 54143-57-6) and pantoprazole sodium (CAS 138786 7-1). The vehicles were Ringer, Ringer lactate, normal saline or an infusion product containing diclofenac sodium and orphenadrine citrate (CAS 4682-36-4). In 37% the vehicle used was not one recommended by the manufacturer or an incompatibility was mentioned in the product information. The combinations of diclofenac sodium or tramadol with diazepam induce a long-lasting sedative effect by diazepam and its metabolite, but only a moderate duration of analgesia. The combination of diclofenac sodium and metamizole sodium is acceptable, although, at a lower dosage of metamizole, the duration of analgesia is shortened. No or insufficient data on therapeutic plasma levels and safe dosages has been reported for lidocaine and B-vitamins.
Conclusions: For all of the drug combinations in use, no interactions of clinical relevance are to be expected. In 37% of the nineteen bedside-prepared infusions, the vehicle was not suitable or incompatibilities were cited in the product information. The combinations of metamizole sodium and diclofenac sodium or tramadol in normal saline solution were in accordance with evidence-based medicine. However, changing some infusion regimens might achieve optimisation of pain treatment with respect to duration of analgesia, and the applied number of drugs could be reduced by omitting additives with little clinical effectiveness.