Application of Pharmacokinetics

Application of Pharmacokinetics in Clinical
Situation

Presented by :
Md. Abdullah Al-Fahim
B.PHRM, East West University, Dhaka, Bangladesh.

Pharmacokinetics:
Pharmacokinetics is currently defined as the study of the time course of drug
absorption, distribution, metabolism, and excretion.
Clinical pharmacokinetics is the application of pharmacokinetic principles to
the safe and effective therapeutic management of drugs in an individual
patient.
Primary goals:
Enhancing efficacy
Decreasing toxicity (Shargel & Yu’s,2016).

Application of Pharmacokinetic to Clinical Situations:
Select drug.
Design dosage regimen.
Evaluate patient response.
Determine need for measuring serum drug concentrations.
Assay for drug concentration in biological fluids.
Perform pharmacokinetic evaluation of drug concentrations.
 Readjust dosage regimen, if necessary.
Monitor serum drug concentrations.
Recommend special requirements. (Shargel & Yu’s,2016).

Evaluation of Patient’s
Response:
the practitioner should evaluate the
patient’s clinical response.
dosage regimen should be reviewed for
adequacy, accuracy, and patient
compliance with the drug therapy.
sound clinical judgment may preclude the
need for measuring serum drug
concentrations.

Measurement of Drug Concentrations
Drug concentrations are measured for -
• Clinical drug monitoring to improve drug therapy
• Drug abuse screening
• Toxicology evaluation such as poisoning and drug overdose.
• Measurement of the presence of abused drugs (Shargel & Yu’s,2016).

Assay for Drug
Drug analyses are usually performed either by a clinical chemistry
laboratory or by a clinical pharmacokinetics laboratory by-
• High-pressure liquid chromatography coupled with mass
spectrometry (LCMS)
• Immunoassay (Shargel & Yu’s,2016).

Assay for Drug
The methods used by the analytic laboratory may depend on such
factors as the -
• Physicochemical characteristics of the drug
• Target drug concentration
• Amount (volume)
• Nature of the biologic specimen (serum, urine, saliva)
• Available instrumentation
• Cost for each assay
• Analytical skills of the laboratory personnel (Shargel & Yu’s,2016).

Assay for Drug
Methods used for the assay of drugs in serum or plasma should be
validated by-
• Specificity
• Linearity
• Sensitivity
• Precision
• Accuracy
• Stability and
• Ruggedness (Shargel & Yu’s,2016).

Pharmacokinetic Evaluation
• The assay results may show that the patient’s serum drug levels are
higher, lower, or similar to the expected serum levels. The pharmacist
should evaluate these results while considering the patient and the
patient’s pathophysiologic condition Therefore, the clinician or
pharmacist should evaluate the data using sound clinical judgment
and observation. The therapeutic decision should not be based solely
on serum drug concentrations (Shargel & Yu’s,2016).

READJUSTMENT DOSAGE REGIMEN
Factors of selecting drug
 The body weight of the patient
 The patient’s renal function
 The patient’s age
 Concomitant disease states (Shargel & Yu’s,2016).

DESIGN OF DOSAGE REGIMENS
 Dosage Regimens Based on Population Averages
 Individualized Dosage Regimens
 Dosage Regimens Based on Partial Pharmacokinetic Parameters
 Nomograms and Tabulations in Dosage Regimen Designs
 Monitoring Serum Drug Concentrations (Shargel & Yu’s,2016).

DOSAGE REGIMENS BASED ON POPULATION AVERAGES
pharmacokinetic parameters such as
 Absorption rate constant (ka)
 Bioavailability factor F
 Apparent volume of distribution VD
 Elimination rate constant k are assumed to remain constant.
 This is One-compartment model. (Shargel & Yu’s,2016).

MONITORING SERUM DRUG CONCENTRATIONS
In many cases, the patient’s pathophysiology may be unstable, either
improving or deteriorating further. For example, proper therapy for
congestive heart failure will improve cardiac output and renal
perfusion, response can be monitored in lieu of actual serum drug
concentration, thereby increasing renal drug clearance.
 prothrombin time might be useful for monitoring anticoagulant
therapy
 blood pressure monitoring for antihypertensive agents. (Shargel &
Yu’s,2016).

Serum Concentrations Lower
Than Anticipated
• Patient compliance
• Wrong drug product
(controlled release instead of
immediate release)
• Poor bioavailability
• Rapid elimination (efficient
metabolizer)
• Reduced plasma–protein
binding
Serum Concentrations Higher Than
Anticipated
• Patient compliance
• Wrong drug product (immediate release
instead of controlled release)
• Rapid bioavailability
• Smaller-than-anticipated apparent
volume of distribution
• Slow elimination (poor metabolizer)
• Increased plasma–protein binding

SPECIAL RECOMMENDATIONS
The patient may be taking the drug after a meal instead of before or
may not be adhering to a special diet ( eg , low-salt diet). Therefore,
the patient may need special instructions that are simple and easy
to follow.
 to discontinue the drug
 prescribe another drug from the same therapeutic class. (Shargel
& Yu’s,2016).

Reference
Shargel and Yu’s(2016) Applied Biopharmaceutics &
Pharmacokinetics. Seventh Edition. New York : McGraw-Hill
Education.

Application of Pharmacokinetics

Application of Pharmacokinetics

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Application of Pharmacokinetics