[Ultrafiltration as a fast and simple method for determination of free and protein bound prilocaine concentration. Clinical study following high-dose plexus anesthesia].

Ultrafiltration as a Fast and Simple Method to Separate Free and Protein Bound Concentrations of Local Anesthetics/Pharmacokinetic studies following high-dose anesthesia of the axillary plexus. As many other drugs amide-type local anesthetics are protein bound in plasma. The extent of binding varies between local anesthetics. The free, non protein-bound fraction of these drugs is mainly responsible for cardiovascular and central-nervous side effects. If high doses are necessary for regional anesthetic procedures it seems reasonable to determine the pharmacological active, non protein-bound fraction in addition to the total concentration of the local anesthetic drug. Analyses of protein binding was performed using an ultrafiltration method which is discussed in this paper. Total (HPLC) and unbound plasma levels (combination of ultrafiltration and HPLC) of the local anesthetic drug in central venous blood were studied in 20 healthy orthopedic patients, undergoing plastic surgery of the upper limb (elbow, forearm, hand), over a time period of 90 min, when performing axillary plexus block with 30 ml prilocaine (CAS 721-50-6) 2% (= 600 mg). Separation of the local anesthetic fractions was achieved using the ultrafiltration system MPS-1, equipped with a YMT-membrane. These membranes have a narrow pore size retaining molecules larger than 30000 Dalton. Ultrafiltration was accomplished by subjecting 1.2 ml of plasma to centrifugation at 2000 x g for 60 min at 30 degrees C using a clinical centrifuge equipped with a 35 degree angle head rotor. The plasma samples were adjusted to physiological pH (7.40) with a sodium-potassium-phosphate buffer. The tightness of the used membrane was controlled by a micromethod for protein estimation (sensitivity 10 micrograms/ml).(ABSTRACT TRUNCATED AT 250 WORDS)