Tiêu đề 2. NOMOGRAMS AND TABULATIONS IN DESIGNING DOSAGE REGIMEN.pdf ✅

PHARMD GURU Page 1  Nomograms and Tabulations in Dosage Regimen Designs For ease of calculation of dosage regimens, many clinicians rely on nomograms to calculate the proper dosage regimen for their patients.  The use of a nomogram may give a quick dosage regimen adjustment for patients with characteristics requiring adjustments, such as age, body weight, and physiologic state.  In general, the nomogram of a drug is based on population pharmacokinetic data collected and analyzed using a specific pharmaco-kinetic model.  In order to keep the dosage regimen calculation simple, complicated equations are often solved and the results displayed diagrammatically on special scaled axes or as a table to produce a simple dose recommendation based on patient information.  Some nomograms make use of certain physiologic parameters, such as serum creatinine concentration, to help modify the dosage regimen according to renal function.  Pharmaceutical manufacturers provide dosage recommendations in the approved label for many marketed drugs in the form of a table or as a nomogram.  These are general guidelines to aid the clinician in establishing an initial dosage regimen for patients.  The tables may include loading and maintenance doses that are modified for the demographics of the patient (ex: age, weight) and for certain disease states ex: renal insufficiency).  For drugs with a narrow therapeutic range, such as theophylline, a guide for monitoring serum drug concentrations is given.  Another example is the aminoglycoside antibiotic, tobramycin sulfate USP (Nebcin, Eli Lilly), which is eliminated primarily by renal clearance. Thus, the dosage of tobramycin sulfate should be reduced in direct pro-portion to a reduction in creatinine clearance. 2. NOMOGRAMS AND TABULATIONS IN DESIGNING DOSAGE REGIMEN
PHARMD GURU Page 2  The manufacturer provides a nomogram for estimating the percent of the normal dose of tobramycin sulfate assuming the serum creatinine level (mg/100 mL) has been obtained. Empirical Dosage Regimens: In many cases, the physician selects a dosage regimen for the patient without using any pharmacokinetic variables. In such a situation, the physician makes the decision based on empirical clinical data, personal experience, and clinical observations. The physician characterizes the patient as representative of a similar well-studied clinical population that has used the drug successfully. General Approach for Individualization of Dosage Regimens: The individualization of dosage regimen usually involves 3 steps:- a) Design of initial dosage regimen: When a patient is to be treated with a drug for the first time, or whenever the pharmacokinetic parameters of the drug in the individual patient are not known, one may recommend a dosage regimen (dose and dosage interval) based on either of the following 2 methods: (1) To recommend a general dosage regimen for all the patients based on the recommendations of the manufacturer. In most cases, this method may take into account only the bodyweight or surface area of the patient for individualization. (2) To use the so-called adjusted population pharmacokinetic parameters, which are based on the population values adjusted for the patient characteristics, to design a dosage regimen based on pharmacokinetic principles. b) Estimation of patient specific pharmacokinetic parameters: Blood samples should be taken at appropriate times after the administration of the initial dosage regimen to determine the patient specific PK parameters which may differ from those estimated based on the adjusted population value.
PHARMD GURU Page 3 c) Adjustment of dosage regimen: If the measured blood concentrations are in agreement with population values then there is no need of any dosage adjustment but if they are not in appropriate then PK parameters should be used to design a new dosage regimen for the patient. So, further blood samples are to be collected till the desired concentrations are achieved.