The preventive effect of diphenhydramine on bacterial growth in propofol: a laboratory study.

BACKGROUND AND OBJECTIVE: Diphenhydramine has local anaesthetic and antimicrobial activity and may be used to prevent intravenous propofol injection pain. We studied the effect of adding diphenhydramine to propofol emulsions for preventing bacterial growth. METHODS: Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans cultures were inoculated into the following solutions: 1% propofol, 0.05% diphenhydramine + 1% propofol, 0.1% diphenhydramine + 1% propofol, 0.2% diphenhydramine + 1% propofol, 0.3% diphenhydramine + 1% propofol, 1% diphenhydramine and 0.1% lidocaine + 1% propofol. A 100-microL of inoculum suspension adjusted for each of the micro-organisms was added separately to each tube and left at 20 degrees C. A 10-microL aliquot of each mixture was inoculated onto blood agar medium at 5 and 24 h. These plates were incubated at 35 degrees C for 24 h. Each plated medium was read, and the number of colony-forming units were counted and recorded (n = 2). Analysis of variance (ANOVA) with a post hoc Tukey HSD test and paired t-tests were used for data analysis. P < 0.05 was considered as significant. RESULTS: Diphenhydramine inhibited bacterial growth in propofol solutions in a dose-dependent manner. It was more effective than 0.1% lidocaine at similar concentrations in preventing bacterial growth for all organisms. CONCLUSION: Diphenhydramine had a significant inhibitory effect on bacterial growth in propofol.

Comparison of diphenhydramine and lidocaine for prevention of pain after injection of propofol: a double-blind, placebo-controlled, randomized study.

BACKGROUND AND OBJECTIVE: Pain on injection is still a problem with propofol. The purpose of the study was to compare the effectiveness of diphenhydramine and lidocaine on pain caused by propofol at the site of injection. METHODS: One hundred and eighty ASA I-II adults undergoing elective surgery were randomly assigned into three groups of 60 each. Group I (placebo) received 2 mL normal saline, Group II received 2 mL (40 mg) 2% lidocaine and Group III received 2 mL (20 mg) diphenhydramine intravenously (i.v.) during a 1-min venous occlusion, followed by propofol into a cephalic forearm vein of the antecubital fossa. Pain assessment was made immediately after propofol injection. RESULTS: In the placebo group 25 (41.7%) patients experienced pain during propofol injection as compared to 2 (3.3%) and 3 (5.0%) in the lidocaine and diphenhydramine groups, respectively. The prevalence of pain and pain score were significantly less in both the lidocaine and diphenhydramine groups than in the placebo group (P = 0.00). No difference was found between the diphenhydramine and lidocaine groups (P = 0.60). CONCLUSION: Previous injection of diphenhydramine with venous occlusion can be considered as an alternative to lidocaine for reducing the prevalence of pain caused by injection of propofol into peripheral veins.