How is drug concentration measured?

When measuring the drug concentration in plasma, a sample of whole blood is drawn from the patient (like cylinder on the left). The sample is then centrifuged to separate the RBC and plasma (like the cylinder on the right). The plasma is withdrawn and analyzed for drug concentration and the RBC is discarded.

What affects drug concentration?

Likewise, plasma levels will depend on dosage, time and route of drug administration, the bioavailability of the drug and time of blood sampling. In addition, absorption, distribution, metabolism, excretion and concurrent drug administration may profoundly affect plasma drug concentrations.

Why does concentration must be considered in taking medications or drugs?

Therefore, measuring the plasma concentration of a drug allows the doctor to track the dosage to the individual patient and to obtain the maximum therapeutic effect with minimal risk of toxicity. Information about plasma concentration is helpful for a number of drugs in clinical practice.

How do you calculate blood concentration of a drug?

C (t) = C0 e – rt, where C (t) represents the concentration at time t (in hours), C0 is the concentration of the drug in the blood immediately after injection, and r > 0 is a constant indicating the removal of the drug by the body through metabolism and/or excretion. The rate constant r has units of 1/time (1/hr).

How do you calculate the plasma concentration of a drug?

Maintenance dose rate (mg/hr) = [Cp (mg/L) x Cl (L/hr)] / F

Cp represents the desired plasma concentration of drug.
Cl represents the clearance rate of drug.
F represents the bioavailability of drug (IV administration = 1)

What is free drug concentration?

Many drugs are bound to serum proteins, and it is important to remember that it is the free (unbound) drug which is responsible for pharmacological activity of the drug. Typically, the total drug concentration (bound drug + free drug) is measured for the purpose of TDM.

What is minimum effective concentration?

Minimum effective concentration (MEC) is the minimum plasma concentration of a drug needed to achieve sufficient drug concentration at the receptors to produce the desired pharmacologic response, if drug molecules in plasma are in equilibrium with drug molecules in the various tissues (Figure 1.3).

Which drugs that are suitable for TDM?

TDM is suggested for: amikacin, carbamazepine, cyclosporin, digoxin, gentamicin, lithium, methotrexate, phenobarbital, phenytoin, valproic acid and vancomycin (see Table 1.3.).

What is peak plasma concentration of a drug?

peak plasma drug concentration. (Science: pharmacology) The highest level of drug that can be obtained in the blood usually following multiple doses.

How are drug concentrations determined in the body?

Drug concentrations are generally determined in plasma so that Vss is the theoretical volume of plasma at a given drug concentration that would be required to account for the entire amount of drug in the body. Free drug concentrations correlate to therapeutic effects better than total drug concentrations, for both small and large molecules.

Which is better free concentration or total concentration?

Free drug concentrations correlate to therapeutic effects better than total drug concentrations, for both small and large molecules. Unfortunately, current technical difficulties in accurately measuring free concentrations prevent full clinical application, and further research in this field is needed.

What does potency mean in pharmacology and clinical efficacy?

RESULTS: Potency is an expression of the activity of a drug in terms of the concentration or amount of the drug required to produce a defined effect, whereas clinical efficacy judges the therapeutic effectiveness of the drug in humans. One may also ask, what is summation in pharmacology?

Which is the best ratio of free to bound drug concentrations?

Free drug concentrations correlate best with clinical effect and toxicity. In most cases, the ratio of free to bound drug is relatively constant for a particular patient; therefore, total drug concentrations usually are adequate.