Estimation of the drug pharmacokinetic parameters in a particular patient is necessary for the selection of the appropriate dosing regimen for this particular patient.

The average values for the drug pharmacokinetic parameters in the general population can be used as an estimate for the patient pharmacokinetic parameters when absolutely no information is known about the patient medical history.

A patient was brought to the emergency room after experiencing an acute attack of cardiac ischemia while walking in the street. After stabilizing the acute symptoms, the antiarryhythmic drug procainamide was prescribed for the patient.

Since no information is known about the patient medical history (e.g. kidney function, liver function, other diseases, or other medications) the average procainamide half-life (3 hr) and Vd (2 L/kg) can be used to calculate the dosing regimen for this patient.

The drug pharmacokinetic parameters can be estimated based on the patient’s medical history by identifying any condition that might alter the drug pharmacokinetics.

A patient with history of renal dysfunction was admitted to the hospital after experiencing an acute attack of cardiac ischemia. After stabilizing the acute symptoms, the antiarrythmic medication procainamide was prescribed.

The average procainamide half-life in patients with renal dysfunction is 5.5 hr and in anuric patients is 12 hr, while Vd (2 L/kg) does not change significantly in patients with renal dysfunction.

When the patient has history of using of the drug under consideration, this information should be used to estimate the drug pharmacokinetic parameters. New changes in the patient’s condition that may alter the drug pharmacokinetics should be considered.

When the drug under consideration has narrow therapeutic index, attempts should be made to determine the patient’s specific pharmacokinetic parameters after starting drug therapy. This specific parameter estimates can be very useful for individualization of drug therapy.