To evaluate at which pH level various local anesthetics precipitate, and to confirm which combination of corticosteroid and local anesthetic crystallizes.
Each of ropivacaine-HCl, bupivacaine-HCl, and lidocaine-HCl was mixed with 4 different concentrations of NaOH solutions. Also, each of the three local anesthetics was mixed with the same volume of 3 corticosteroid solutions (triamcinolone acetonide, dexamethasone sodium phosphate, and betamethasone sodium phosphate). Precipitation of the local anesthetics (or not) was observed, by the naked eye and by microscope. The pH of each solution and the size of the precipitated crystal were measured.
Alkalinized with NaOH to a certain value of pH, local anesthetics precipitated (ropivacaine pH 6.9, bupivacaine pH 7.7, and lidocaine pH 12.9). Precipitation was observed as a cloudy appearance by the naked eye and as the aggregation of small particles (<10 µm) by microscope. The amount of particles and aggregation increased with increased pH. Mixed with betamethasone sodium phosphate, ropivacaine was precipitated in the form of numerous large crystals (>300 µm, pH 7.5). Ropivacaine with dexamethasone sodium phosphate also precipitated, but it was only observable by microscope (a few crystals of 10–100 µm, pH 7.0). Bupivacaine with betamethasone sodium phosphate formed precipitates of non-aggregated smaller particles (<10 µm, pH 7.7). Lidocaine mixed with corticosteroids did not precipitate.
Ropivacaine and bupivacaine can precipitate by alkalinization at a physiological pH, and therefore also produce crystals at a physiological pH when they are mixed with betamethasone sodium phosphate. Thus, the potential risk should be noted for their use in interventions, such as epidural steroid injections.
Citations
The purpose of this study is to evaluate the efficacy of epidural injections with steroids and local anesthetics for the low back pain patients.
Two hundred fifty patients with low back pain and sciatica were selected for the study. The patients were treated with the epidural injection of steroid(Depo-medrolⰒ) weekly for 2 weeks and local anesthetics(lidocaine and bupivacaine) daily via epidural catheter. The efficacy of epidural injections was assessed with the Visual Analog Scale(VAS) on pre- and 2weeks post-epidural injections. The VAS scores of pre- and post-epidural injections were 6.14⁑2.14 and 3.65⁑1.93(p＜0.05) respectively. The VAS scores were not different by the disease subgroups(p＞0.05). By the main symptoms, VAS scores were reduced prominently in patients with the pseudoclaudication symptom after post-epidural injections.
In conclusion, epidural injections of steroid and local anesthetics are effective for patients with a low back pain and sciatica in the short term. Further prospective long-term follow up studies will be necessary in the future.
To investigate the skeletal muscle changes, intramuscular injections of local anesthetics were performed using animal, Sprague-Dawley rat.
The experiments were composed of two procedures, experiment I and II. In experi ment I, single injection was performed using 0.4 cc of 1 and 2% of procaine and lidocaine.
In experiment II, repeated injection of 0.4 cc of 2% lidocaine on weekly bases 3 times were performed.
The experimental rats were divided into five groups in experiment I: Four experimental groups 40(10 rats for each local anesthetics) and Control 10 and were divided into two groups in experiment II: Experimental group 8 and Control 4. The muscle biopsies were performed in 15 minutes, 2, 4, 8 and 16 days after injection in two experiments.
No muscle fiber changes were shown in control group, and 1~2 % procaine, and 2% lidocaine injected groups of experiment I and control group of experiment II. In the groups of single and repeated injections of 2% lidocaine, muscular inflammatory changes were shown on 2 and 4 days after injection. The changes were more extensive in the group of repeated injections. The inflammatory reaction was usually abated on 8 days after injection and the muscles appeared to be normal in quality and quantity on 16 days after injection. These histopathologic results indicated reversible muscular changes.
Although the muscular changes are reversible after local anesthetics injection, the concentration of local anesthetics and injection interval should be considered to minimize the muscle fiber changes in the repeated injections.
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