Pharmaceutical Calculations pp 301-327 | Cite as

# Fundamental Concepts of Dosage Calculations

## Abstract

This chapter demonstrates how one calculates dosage regimens using certain pharmacokinetic parameters and the simplest of the pharmacokinetic models, the one-compartment model. Prior to describing the one-compartment model, the chapter discusses the difference between drug selectivity and receptor biological event specificity, relates drug selectivity with therapeutic efficacy and toxicity, and explains how to relate the physicochemical properties of drugs to their extent of tissue distribution. It also discusses the difference between excretion, clearance, and elimination and defines the concept of bioavailability which is critical in understanding the difference between dose and effective dose. Ultimately, you will learn how to calculate effective drug doses using the concept of bioavailability and salt factor. The second part of the chapter describes the operational principles of the one-compartment pharmacokinetic model, defines the therapeutic index of drugs, the concepts of drug volume of distribution, and clearance, and demonstrates how to calculate their values from plasma drug concentrations. Finally, it demonstrates how to apply these pharmacokinetic parameters and the concepts of drug accumulation and fluctuation to calculate optimum drug loading and maintenance dosages that achieve plasma drug levels within therapeutic range. After reading Chaps. 11– 13, you are definitely ready to study the main course of pharmacokinetics.

## Keywords

Selectivity Specificity Absorption Distribution Elimination Clearance Metabolism Excretion Dose Dosage interval Volume of distribution Therapeutic range Accumulation Fluctuation Loading dose Maintenance dose## Supplementary material

Fundamental concepts of dosage calculations—Part I: ADME, bioavailability, and effective dose. Description: (a) The difference between drug selectivity and receptor biological event specificity. (b) Drug selectivity with therapeutic efficacy and toxicity. (c) Physicochemical properties of drugs with tissue distribution. (d) Difference between excretion, clearance, and elimination. (e) The concept of bioavailability. (f) Difference between dose and effective dose. (g) Use the concept of bioavailability and salt factor to calculate effective drug dose (MP4 883636 kb)

Fundamental concepts of dosage calculations—Part II: One-compartment pharmacokinetic model. Description: (a) Operational principles of the one-compartment pharmacokinetic model. (b) The concepts of drug volume of distribution and clearance and assessing their values from plasma drug concentrations. (c) Relative distribution of a drug in the plasma and tissues from its volume of distribution (MP4 849797 kb)

Fundamental concepts of dosage calculations—Part III: Therapeutic index, loading, and maintenance doses. Description: (a) Therapeutic index of drugs. (b) The concepts of drug accumulation and fluctuation. (c) Application of pharmacokinetic parameters to calculate optimum drug loading and maintenance dosages that achieve plasma drug levels within therapeutic range (MP4 938227 kb)