Average plasma concentration, drug

What would be the dosing interval of a drug that has a volume of distribution of 5 L When a dose of 250 mg is given, 200 mg of the drug is absorbed and the average plasma concentration is 4 mcg/mL. The plasma half-life is 3 hours. 

To obtain an average plasma concentration of 25 ng/mL with a dosing interval of 8 hours, what should be the dose of the drug when the fraction of drug absorbed is 0.8 It is known that the drug has a volume of distribution of 75 L and has an elimination rate constant of 0.173 hour1. 

What is the average plasma concentration when a 500 mg drug is administered with an interval of 6 hours and has a volume of distribution of 50 L It is known that the fraction of dose absorbed is 0.8 and the plasma half-life is 2 hours. 

If the fraction of drug absorbed is 0.9, dose is 25 mg, dosing interval is 6 hours, volume of distribution is 20 L and the average plasma concentration is 25 mcg/mL, what is the plasma half-life of the drug ... 

What would be the average plasma concentration of drug at steady-state if it is known that the plasma concentration at zero time point is 48 meg/ mL when 50 mg of the dose is given every 12 hours, and the elimination rate constant of the drug is 0.173 hour 1 ... 

Metabolism of isoniazid, especially acetylation by liver /V-acetyltransferase, is genetically determined (see Chapter 4). The average plasma concentration of isoniazid in rapid acetylators is about one third to one half of that in slow acetylators, and average half-lives are less than 1 hour and 3 hours, respectively. More rapid clearance of isoniazid by rapid acetylators is usually of no therapeutic consequence when appropriate doses are administered daily, but subtherapeutic concentrations may occur if drug is administered as a once-weekly dose or if there is malabsorption. 

FIGURE 3-4 Relationship between dosing interval and plasma concentrations of the antiasthmatic drug theophylline. A constant intravenous infusion [shown by the smoothly rising line] yields a desired plasma level of 10 mg/L. The same average plasma concentration is achieved when a dose of 224 mg is taken every 8 hours, or a dose of 672 mg every 24 hours. However, note the fluctuations in plasma concentration seen when doses are taken at specific hourly intervals. 

The concept of clearance has found particular application in clinical work as it offers a simple relationship between dose rate (dose divided by the time interval between doses, D t and the average plasma concentration (c) of the drug... 

Systemic clearance, which measures the ability of the body to eliminate a drug, determines the relationship between the dosage rate and the average steady-state plasma concentration. When multiple (fixed) doses of a drug are administered at a constant dosage interval (r) the average plasma concentration that will be attained at steady-state can be predicted ... 

Because the area under the plasma drug concentration-time curve during a dosage interval at steady-state is equal to the total area under the curve after administering a single intravenous dose, the average plasma concentration at steady-state can be estimated from... 

Cj concentration of the drug in the plasma going into a Hlter Cjd plasma concentration after dialysis Cave average plasma concentration CAVH continuous arteriovenous hemoHltration CAVHD continuous arteriovenous hemodialysis CAVHDF continuous arteriovenous hemodiafiltration Cbo plasma concentration prior to the next dialysis session Cdf concentration of drug in the dialysis fluid equated total phenytoin concentration Cm total drug concentration measured in a patient with altered protein binding... 

Items 16-18 A new drug was studied in 20 healthy volunteers to determine basic pharmacokinetic parameters. A dose of 100 mg was administered as an intravenous bolus to each volunteer and blood samples were analyzed at intervals as shown in the graph below. The average plasma concentrations at each time are shown by the solid circles at 10 and 30 minutes and at 1,2, 3, 4, 6, and 8 hours after administration. 

When drugs are administered as repetitive doses (multiple doses), it often is of practical use to determine the average plasma concentration at the plateau or... 

This allows us to calculate the "average -plasma concentration of a drug at steady state from a single dose study by employing the following equation ... 

Regardless of the route of drug administration, the "average" plasma concentration at steady state is influenced by the dose administered, the fraction of the administered dose that reaches the general circulation (for extravascular routes), the systemic clearance of the drug and the chosen dosing interval. 

Calculation of drug accumulation from the "average" plasma concentration... 

During any dosing interval, the "average" plasma concentration of a drug may be defined as ... 

Fluctuation, therefore, is simply a measure of the ratio of the steady-state peak or maximum plasma concentration to the steady-state minimum or trough plasma concentration of a drug or the ratio of the peak or maximum steady-state concentration to the "average" plasma concentration at steady state for the chosen dosage regimen. 

The 20 mg per day dosing of lisinopril will provide an average plasma concentration within the therapeutic range of the drug. 

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