Experimental determination of pharmacokinetic parameters of sulfonamides

Summary

This experiment is from the official website of the Fourth Military Medical University

Operation method

Experimental determination of pharmacokinetic parameters of sulfonamides

Principle

Pharmacokinetics focuses on the body's disposition of drugs, including absorption, distribution, metabolism, and excretion. In order to describe the in vivo disposition process of drugs, it is usually simulated using atrial and ventricular models. Relevant pharmacokinetic parameters, such as clearance (CL), apparent volume of distribution (Vd), half-life (t1/2), elimination rate constant (k), etc., can be calculated using the atrial chamber model. Total drug clearance (CL) is defined as the volume of plasma containing the total amount of drug cleared from the body per unit of time.Vd is the apparent volume of distribution, which is not the volume of the anatomical compartment for most drugs. The single-compartment model (Fig. 1) is a highly simplistic model that envisions the body as a single homogeneous compartment with a volume of Vd, into which the amount of Q drug may enter rapidly after intravenous injection or from which it may be removed by metabolism or excretion. The single-compartment model delivers the drug at a constant rate of infusion, and the blood concentration reaches a steady-state value in a near-exponential form. The two-compartment model (Fig. 23-2) is a widely used approximation in which the tissues are grouped together in one place as the peripheral compartment, and the central compartment is usually the plasma (or, for a few drugs that distribute very rapidly, the sum of the plasma and the extravascular space). In the two-compartment model, entry and exit of drug molecules into and out of the peripheral compartment can only occur through the central compartment. Sulfonamides react with sodium nitrite under acidic conditions to produce a diazonium salt. This diazonium salt can be coupled with muscimol under alkaline conditions to produce an azo compound, which appears orange in color. Therefore, the plasma concentration of sulfonamides can be obtained by measuring the absorbance value at 525nm.

Materials and Instruments

Rabbit
Ullatan solution Trichloroacetic acid Sodium nitrite solution Muscimol solution Sulfadiazine solution Heparin Distilled water; 721 Spectrophotometer Cuvette Centrifuge Vortex mixer Balance Arterial cannula Test tubes Syringes Graduated pipettes Earwash balls Markers

Move

1. Anesthesia, carotid artery cannulation One rabbit was taken, weighed, sex recorded, and anesthetized by intravenous injection of 20% urethane 5 ml/kg at the ear margin. After heparin anticoagulation, carotid artery was cannulated and arterial blood was taken for spare.

2. Blood samples were taken and a blank arterial blood sample was taken before administration. Rabbits were then injected intravenously at the ear margin with 0.05% sulfadiazine solution, 0.3 g/kg, and arterial blood samples were taken at 0, 3, 5, 15, 30, 45, 60, and 90 min after the injection, recording the time of completion of the administration.

3. Determination of sulfadiazine concentration

(1) Standard curve preparation: dilute 0.05% sulfadiazine standard solution into 0.05%, 0.025%, 0.0125%, 0.005% concentration standard solution.

(2) Determine the absorbance values of the standard solution and blood samples at different time points (Table 23-3).

(3) Calculate the concentration of sulfadiazine: According to the principle that the concentration of the same solution is proportional to its antidensity, the concentration of sulfadiazine in the sample tube can be calculated from the concentration of the blank blood standard tube and its optical density value.

4. Calculate the pharmacokinetic parameters of sulfadiazine Solve the linear regression with logc on t to get the equation logc=a+bt

(1) Elimination rate constant: K = (min-1) = -2.303b

(2) Plasma half-life: t1/2 (min) = 0.693/k

(3) Initial concentration: C0 (mg/ml) = Log-1a

(4) Performance volume of distribution Vd (ml/kg) = D0/C0 (D0 is the administered dose)

(5) Elimination rate: CL (ml/kg-min) = K x Vd

(6) Area under the drug time curve AUC (mg-min/ml) = C0/K

Caveat

1. After adding 7.5% trichloroacetic acid, mix immediately with a vortex mixer to prevent coagulation.

2. the order of addition of the color developer must be: 0.5% sodium nitrite solution first, followed by 0.5% muscimol solution.

3. The pharmacokinetic profile of sulfadiazine is usually described using a two-compartment model. In addition to the pharmacokinetic parameters clearance (CL) and apparent volume of distribution (Vd), the elimination rate constant (k) and half-life (t1/2) can also be derived. In the two-compartment model, if the drug is transferred between the central and peripheral compartments relatively faster than its elimination rate, the fast phase (α-phase, distribution phase) can be regarded as reflecting the redistribution process of the drug (i.e., the drug molecules are transported from the plasma to the tissues, and therefore the blood concentration will fall rapidly); the total volume of distribution of the two compartments can be calculated from the blood concentration reached after the end of the fast phase and before elimination begins; the clearance rate constant (Kt) can be obtained by the slow phase (β-phase, elimination phase) half-life The slow phase (β-phase, elimination phase) half-life gives the predicted value of the clearance rate constant (Ktl).

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