Concentration of drug in plasma

There are special problems in bioequivalency determinations when conventional pharmacokinetic studies are not possible. For example, when drugs are administered intranasally for direct treatment of receptors in the nasal mucosa, the concentration of drug in plasma may be below the limit of quantification. In such cases we are forced to attempt measurement of clinical response. The subjectivity and/or low precision of this type of study can be a serious problem. 

One such distribution phenomenon can occur as a result of hemolysis of the sample. Preparation of the TDM sample involves centrifugation to separate the cells and platelets from the plasma. If the sample is hemolyzed, then the centrifugation may not adequately separate cell fragments from the plasma. That can result in an increase in the apparent concentration of drug in plasma. 

Therapeutic range The concentration of drug in plasma that usually provides a therapeutically desirable response in the majority of individuals without substantial risk of serious toxicity. The target concentration for an individual patient is usually chosen from within the therapeutic range. 

After systemic administration, a drug is generally delivered to tissues in the body through blood circulation. Therefore, the concentration of drug in plasma defines the rate of tissue uptake. 

The concentration of drug in plasma is due to three factors the rate of drug input (rate of infusion) the rate of elimination and the volume of distribution. Since the rate of input is a constant, only a change in the rate of elimination or volume of distribution emerge as possible reasons for such an unusual finding. It is possible that the volume of distribution changes over time. It is also possible that tasidotin is distributed by a transporter that must be activated. Basically, with this... 

Effect of infusion rate on the steady-state concentration of drug in plasma. (R0 = rate of infusion of drug.)... 

Rate of attainment of steady-state concentration of drug in plasma. 

The elimination of a drug usually follows first order kinetics, and the concentration of drug in plasma drops exponentially with time. This may be used to determine the half-life of the drug (the time during which the concentration of the drug decreases from C to 1/2C). 

The most basic, direct method is to measure the concentration of drug in plasma unfortunately, this method is usually biased because in most instances its reflection of prior dosing history is limited only to a day or two prior to the time that blood is drawn for the analysis. These problems arise because... 

If the clinician chooses the desired concentration of drug in plasma and knows the clearance and bioavailability for that drug in a particular patient, the appropriate dose and dosing interval can... 

A demonstrated relationship exists between the concentration of drug in plasma and the desired therapeutic effect or the toxic effect to be avoided. The range of plasma levels between that required for efficacy and that at which toxicity occurs for a given individual is designated the therapeutic window. 

Toxicity correlates with the total amount of drug administered and is more likely to be encountered with longer courses of therapy. Constantly elevated concentration of drug in plasma above a critical level (i.e., an elevated trough concentration) correlates with toxicity. The most important result of... 

In Equation 1.8, Cq is the concentration of drug in plasma at time zero, and A and B are equation parameters that result from curve fitting a biexponential curve (i.e., a two-compartment model). ... 

For the purpose of this textbook, the dependent variable (Y) is either mass of drug in the body (X), mass of drug in the urine (X ) or the concentration of drug in plasma or serum (Cp or Q, respectively). For a very small time interval, there will be a very small change in the value of Y as follows ... 

This binding follows the law of mass action (Kniger-Thiemer and Biinger, 1965). Hence O (concentration of drug in plasma) and C (concentration of drug in the water of plasma) are related thus ... 

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