Pharmacokinetic/pharmacodynamic relationship of eptazocine, a narcotic-antagonist analgesic, in rats.

The relationship between the pharmacokinetics and the pharmacodynamics of eptazocine, a narcotic-antagonist analgesic, was investigated in rats. The analgesic effect of eptazocine (2.5, 5 and 10 mg/kg) following intravenous (i.v) administration was evaluated by both the Randall-Selitto method and the D'Amour-Smith method. The analgesic effects were determined before and at designed intervals for a period of 120 min after eptazocine administration, and are expressed as area under the effect-time curve (AUC(E)). The plasma concentration of eptazocine was determined by fluorescence HPLC and was analyzed with a two compartment open model using the nonlinear least-squares method. Eptazocine produced a dose-dependent analgesic effect. It was demonstrated that eptazocine has a linear relationship between AUC(E) and the area under the plasma concentration-time curve (AUC) following i.v. administration for three different doses ranging from 2.5 to 10 mg/kg.

Stereospecific opiate binding in living human polymorphonuclear leucocytes.

Living human polymorphonuclear leucocytes were incubated with various opiate agonists and antagonists in radioreceptor assays. Binding of the opiate antagonists 3H-naloxone and 3H-diprenorphine and of the benzomorphan 3H-ethylketocyclazocine was found at 4 degrees C and at 37 degrees C, 3H-naloxone binding was stereospecific. Binding of the opiate agonist 3H-dihydromorphine was present at 37 degrees C but not at 4 degrees C and had a different time course as compared to the antagonists. At both temperatures no specific binding of the proteolytic stable analogue 3H-D-Ala-D-Leu-enkephalin was found. Autoradiography showed an unspecific accumulation of 3H-naloxone inside the cells and a specific localization of grains at the cell membrane.

Enzyme immunoassay of cyclazocine using peroxidase as label.

A sensitive enzyme immunoassay for the determination of serum or urinary cyclazocine was developed. Horseradish peroxidase was used as the labelling enzyme; it was conjugated with cyclazocine derivatives by the mixed anhydride method. After the immune reaction, bound and free fractions were separated by a double-antibody solid-phase method, using Sepharose 4B gel coupled with purified IgG from goat anti-rabbit IgG serum. The enzyme activity was measured fluorophotometrically, with p-hydroxyphenyl propionic acid and hydrogen peroxide as substrates. The correlation coefficients verified that there was excellent agreement between the results obtained by the new enzyme immunoassay and those of radioimmunoassay (r=0.92) and gas chromatography-mas spectrometry (r=0.94).

Radioimmunoassay of cyclazocine and stereospecificity of antibody.

A new radioimmunoassay, using 3H-cyclazocine, rabbit antiserum and charcoal-dextran separation of bound and free cyclazocine, for the direct analysis of serum cyclazocine is described. This method, which is specific for cyclazocine and has a detection limit of ca. 25 pd/assay tube, was successful in determining the cyclazocine level in the sera of beagles intramuscularly injected with 3 or 10 microgram/kg cyclazocine. The drug half-life was 90 min; the apparent distribution volumes were 4.0 and 5.26 liter/kg, respectively. One of the antisera raised in rabbits immunized with dl-cyclazocine derivative-BSA conjugates was highly specific for l-cyclazocine.

Analysis of cyclazocine in plasma.

The analysis of plasma cyclazocine by two methods is described. The radioimmunoassay employed a 125I-labeled radioligand, rabbit antiserum, and sepration of bound from free cyclazocine with a second antibody. The radioimmunoassay was specific for cyclazocine and had a detection limit of approximately 20 pg/ml. The GLC method employed a mass spectrometer as the detector and had a detection limit of approximately 109 pg/ml. Both techniques had acceptable accuracy and precision when used to quantitate cyclazocine in dog and human plasma. The methods were used successfully to quantitate cyclazocine from beagle hounds receiving 0.5 mg of 3H-cylazocine/kg iv. The decline in plasma cyclazocine fitted a two-compartment body model with a mean plasma clearance rate of 39.2 liters/hr.