Question

explain in detail about

Application of pharmacokinetics and pharmacodynamics to dose individualization

Answer 1

SOLUTION:

• Dose individualization in simpler term means that the dose required to produce a particular response that differ from one patient to another. Dose individualization is necessary to fit a particular patient's needs and to solve his or her health problems.For this the application of pharmacokinetic and pharmacodynamic principles is essential for safe and effective management of illness in a patient.

PHARMACOKINETICS

Pharmacokinetics in simpler term refers to the movement of drugs into,within and out of the body.It includes four main proccess.They are,

Absorption

Distribution

Metabolism

Excretion of drugs

Drugs may be transported across the membranes of the cells by passive or active transport

Passive transport: The drug moves across a membrane without any need for energy.

Active transport: It is the transfer of drugs against a concentration gradient and needs energy for transportation.In this type of transport the drugs are carried by a specific carrier protein.

PHARMACODYNAMICS

Pharmacodynamics in simpler term refers to the action of a drug on the body.It is the mechanism of action of a particular drug.Pharmacodynamics helps us to know what drugs do and how they do it.

Drugs produce their effects by interacting with the physiological sysyems of the body thereby modifying the rate of functions of those systems to bring about that particular effect.

Thus drugs act by,

Stimulation

Depression

Irritation

Replacement

Modification of immune status

Anti infective action

APPLICATION OF PHARMACOKINETICS AND PHARMACODYNAMICS TO DOSE INDIVIDUALIZATION

For some drugs especially the ones with low safety margin,the dose has to be tailored or modified to the needs of each patient.For example anticonvulsants and antiarrhythmics.Individualization of dosage regimen is the most accurate method or approach and is based on pharmacokinetics and pharmacodynamics variability.

Pharmacokinetics variability:

This is attributed to the differences in the concentration of the the drug at the site of action because the absorption,distribution,metabolism and excretion of the drug varies from one individual to another individual.

Pharmacodynamic variability:

This is attributed to the differences in effect produced by a given drug concentration.

STEPS INVOLVED IN DOSE INDIVIDUALIZATION

Estimation of Pharmacokinetic parameters in individual patient to evaluate degree of variability and attributing the variability to some measurable characteristics such as age, weight, renal diseases,hepatic diseases etc,.

Designing the new dosage regimen from the collected data.It involves adgustment of dosage and or dosing interval.

Dosing of drugs in obese patients

The Ideal Body Weight (IBW), for men and women can be calculated using the below mentioned formulae.

IBW For men: 50kg+/-1kg/2.5cm above or below 150cm in height

IBW for women:45kg+/-1kg/2.5cm above or below 150cm in height

Person whose body weight is more than 25% above the IBW is considerd as obese.

The drugs that do not significantly distribute in excess body space the dose should be calculated on basis of IBW since degree of variability do not change in such situation.for example,drudg Digoxin.

But some antibiotics distribute in excess fat of obese patients .in such condition the dose should be lower than per kg total body weight basis but more than that on IBW basis.

Dosing of drugs in elderly

Drug dose should be reduced in elderly patients because elderly people has declined body functions generally due to their advanced age.

Degree of variability of water soluble drugs may decrease with increasing age and that of fat or lipid soluble drugs(example diazepam) may increase with age.The maintenance dose for such patients can be calculated using the formula,

Patient dose=(Weight in kg)(140-age in years)/1660 *adult dose

Dose adjustment in renaland hepatic failure conditions:

Disease contributes to much variations in the drug response.

Therefore the drug dosage should be reduced in patients with hepatic dysfunction since clearance is reduced and availability is increased in such hepatic dusfunction cases.

In case of renal failurethe regimen may be adjusted by reducing the dosage and or increasing dose interval since the renal clearance and elimination rate are reduced and distribution is alterd in such situation.

Conclusion:

The nurse should ensure that the correct drug is administerd in the right dose

The nurse must monitor the adverse effects of the drug on the patients.