PHARMACOLOGY
Are all Generics
Created Equal ?
Vinny Naidoo BVMCh , MSc ( Vet ) , PhD Faculty of Veterinary Science , University of Pretoria
Bioequivalence is the comparison of the plasma profile between the test and reference product . A generic product is bioequivalent to the innovator product and it thus essentially identical , in a species group . There is no pharmacokinetic evidence to support human medicines being generics for veterinary species .
Introduction
A good way to start this article , would be for you to close your eyes and contemplate the valuable role veterinarians play in the health and welfare of animals . At this point , you would probably agree that veterinarians play an invaluable role of the diagnosis and treatment of animal disease or disease conditions . However have you ever considered what the function of the veterinarian would be , if we as a profession , had no medication available to treat our patients ? Probably very little , and even less so since the profession has moved away from the use of Materia Medica ( books describing how to prepare one ’ s own medicines ). So what has changed ? The answer is simple and reflects our acceptance of modern pharmaceutical science as the means of treating disease .
These prepared formulations offer a number of benefits over practice-based drug preparations . These include :
• Ready availability ( e . g . does not need to be prepared which save times and the need to keep raw ingredients as in an apothecary );
• they have long shelf lives ( which means one does not need to keep restocking with new / fresh ingredients );
• one could rely on the use of synthetic chemicals ( that would otherwise not be readily available )
• purer formulations ( in that they ’ re not contaminated with foreign material or bacteria );
• potential for parenteral administration for rapid or sustained effect ( since they ’ re sterile and pure ) and lastly ,
• they control for variable effects that can result from inconsistencies in absorption . All of which is possible through our better understanding of various aspects in pharmacology , such the drug ’ s pharmacokinetic profile , mechanisms of action , the interaction between pharmacokinetics and effect and the importance of biopharmaceuticals in the effects of medication .
Pharmacokinetics
Pharmacokinetics is the study of the movement of drug through the body , from the site of administration , to the site of effect and finally to the method of elimination . Of these absorption is dependent on the site of administration , the amount administered , the ability to body to remove the drug before it is absorbed and drug ’ s chemical profile . Similar factors determine whether the drug gets to the site of action , while elimination is dependent on the need for the drug to be metabolised or excreted .
The processes involved in the pharmacokinetics of a drug are studied by following the change in concentration of drug in the plasma over time ( Figure 1 ). Using differential calculus , one can follow the change characteristics of the curve and establish mathematically how the drug is absorbed , distributed and / or eliminated . In pharmacokinetics the key controlling aspect is the drug formulation which controls absorption and elimination , and the endogenous / systemic processes which control elimination
Figure 1 is a typical plasma concentration versus time that results following extravascular administration of a drug . A : Is the absorptive phase ; B : a combination of the absorptive and distributive phase and C : The elimination phase . The dotted line represents the relationship of the plasma concentration with the effect concentration ( For the latter , one can see that it ' s ’ not vet360
Issue 03 | JUNE 2017 | 16