1. Measurement of Bioavailability:
Direct and indirect methods may be used to assess drug bioavailability. The in-vivo bioavailability of a drug product is demonstrated by the rate and extent of drug absorption, as determined by comparison of measured parameters, e.g., concentration of the active drug ingredient in the blood, cumulative urinary excretion rates, or pharmacological effects.
For drug products that are not intended to be absorbed into the bloodstream, bioavailability may be assessed by measurements intended to reflect the rate and extent to which the active ingredient or active moiety becomes available at the site of action.
The design of the bioavailability study depends on the objectives of the study, the ability to analyze the drug (and metabolites) in biological fluids, the pharmacodynamics of the drug substance, the route of drug administration, and the nature of the drug product.
Pharmacokinetic and/or pharmacodynamic parameters as well as clinical observations and in-vitro studies may be used to determine drug bioavailability from a drug product.
1.1. Pharmacokinetic methods:
These are very widely used and based upon the assumption that the pharmacokinetic profile reflects the therapeutic effectiveness of a drug. Thus these are indirect methods. The two major pharmacokinetic methods are:
The major pharmacokinetic methods are:
Plasma / blood level time profile.
o Time for peak plasma (blood) concentration (t max)
o Peak plasma drug concentration (Cmax)
o Area under the plasma drug concentration–time curve (AUC)
Urinary excretion studies.
o Cumulative amount of drug excreted in the urine (Du)
o Rate of drug excretion in the urine (dDu/dt)
o Time for maximum urinary excretion (t)
C. Other biological fluids
1.2. Pharmacodynamic methods:
IT involves direct measurement of drug effect on a (patho) physiological process as a function of time. Disadvantages of it may be high variability, difficult to measure, limited choices, less reliable, more subjective, drug response influenced by several physiological & environmental factors.
They involve determination of bioavailability from:
Acute pharmacological response.
Therapeutic response.
1.3. In-vitro dissolution studies
Closed compartment apparatus
Open compartment apparatus
Dialysis systems.
1.4. Clinical observations
Well-controlled clinical trials
United State Pharmacopoeia (USP)The establishment of a rational relationship between a biological property, or a parameter derived from a biological property produced by a dosage form, and a physicochemical property or characteristic of the same dosage form.
Food and Drug Administration (FDA) definitionIVIVC is a predictive mathematical model describing the relationship between an in vitro property of a dosage form and a relevant in vivo response. Generally, the in vitro property is the rate or extent of drug dissolution or release while the in vivo response is the plasma drug concentration or amount of drug absorbed.
It is defined as “the predictive mathematical model that describes the relationship between in vitro property (such as rate & extent of dissolution) of a dosage form and in vivo response (such as plasma drug concentration or amount of drug absorbed)”.
DISSOLUTION
Dissolution is defined as a process in which a solid substance solubilises in a given solvent.
(i.e. mass transfer from the solid surface to the liquid phase.)
Three Theories:
Diffusion layer model / Film theory
Danckwert’s model / Penetration or Surface renewal theory
Interfacial barrier model / Double barrier or Limited solvation theory
PHARMACOKINETIC MODELS
Drug movement within the body is a complex process. The major objective is therefore to develop a generalized and simple approach to describe, analyse and interpret the data obtained during in vivo drug disposition studies.
The two major approaches in the quantitative study of various kinetic processes of drug disposition in the body are
Model approach, and
Model-independent approach (also called as non-compartmental analysis).
1. Measurement of Bioavailability:
Direct and indirect methods may be used to assess drug bioavailability. The in-vivo bioavailability of a drug product is demonstrated by the rate and extent of drug absorption, as determined by comparison of measured parameters, e.g., concentration of the active drug ingredient in the blood, cumulative urinary excretion rates, or pharmacological effects.
For drug products that are not intended to be absorbed into the bloodstream, bioavailability may be assessed by measurements intended to reflect the rate and extent to which the active ingredient or active moiety becomes available at the site of action.
The design of the bioavailability study depends on the objectives of the study, the ability to analyze the drug (and metabolites) in biological fluids, the pharmacodynamics of the drug substance, the route of drug administration, and the nature of the drug product.
Pharmacokinetic and/or pharmacodynamic parameters as well as clinical observations and in-vitro studies may be used to determine drug bioavailability from a drug product.
1.1. Pharmacokinetic methods:
These are very widely used and based upon the assumption that the pharmacokinetic profile reflects the therapeutic effectiveness of a drug. Thus these are indirect methods. The two major pharmacokinetic methods are:
The major pharmacokinetic methods are:
Plasma / blood level time profile.
o Time for peak plasma (blood) concentration (t max)
o Peak plasma drug concentration (Cmax)
o Area under the plasma drug concentration–time curve (AUC)
Urinary excretion studies.
o Cumulative amount of drug excreted in the urine (Du)
o Rate of drug excretion in the urine (dDu/dt)
o Time for maximum urinary excretion (t)
C. Other biological fluids
1.2. Pharmacodynamic methods:
IT involves direct measurement of drug effect on a (patho) physiological process as a function of time. Disadvantages of it may be high variability, difficult to measure, limited choices, less reliable, more subjective, drug response influenced by several physiological & environmental factors.
They involve determination of bioavailability from:
Acute pharmacological response.
Therapeutic response.
1.3. In-vitro dissolution studies
Closed compartment apparatus
Open compartment apparatus
Dialysis systems.
1.4. Clinical observations
Well-controlled clinical trials
United State Pharmacopoeia (USP)The establishment of a rational relationship between a biological property, or a parameter derived from a biological property produced by a dosage form, and a physicochemical property or characteristic of the same dosage form.
Food and Drug Administration (FDA) definitionIVIVC is a predictive mathematical model describing the relationship between an in vitro property of a dosage form and a relevant in vivo response. Generally, the in vitro property is the rate or extent of drug dissolution or release while the in vivo response is the plasma drug concentration or amount of drug absorbed.
It is defined as “the predictive mathematical model that describes the relationship between in vitro property (such as rate & extent of dissolution) of a dosage form and in vivo response (such as plasma drug concentration or amount of drug absorbed)”.
DISSOLUTION
Dissolution is defined as a process in which a solid substance solubilises in a given solvent.
(i.e. mass transfer from the solid surface to the liquid phase.)
Three Theories:
Diffusion layer model / Film theory
Danckwert’s model / Penetration or Surface renewal theory
Interfacial barrier model / Double barrier or Limited solvation theory
PHARMACOKINETIC MODELS
Drug movement within the body is a complex process. The major objective is therefore to develop a generalized and simple approach to describe, analyse and interpret the data obtained during in vivo drug disposition studies.
The two major approaches in the quantitative study of various kinetic processes of drug disposition in the body are
Model approach, and
Model-independent approach (also called as non-compartmental analysis).
Pharmacokinetic concepts and principles in humans in order to design individualized dosage regimens which optimize the therapeutic response of a medication while minimizing the chance of an adverse drug reaction.
The presentation concisely describes the different pharmacokinetic parameters and basics of compartment modelling. It will help undergraduate students to understand the basic concepts of Biopharmaceutics.
Drug distribution typically refers to the process of getting pharmaceutical products from manufacturers or wholesalers to pharmacies, hospitals, clinics,
micro teaching on communication m.sc nursing.pdfAnurag Sharma
Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
263778731218 Abortion Clinic /Pills In Harare ,sisternakatoto
263778731218 Abortion Clinic /Pills In Harare ,ABORTION WOMEN’S CLINIC +27730423979 IN women clinic we believe that every woman should be able to make choices in her pregnancy. Our job is to provide compassionate care, safety,affordable and confidential services. That’s why we have won the trust from all generations of women all over the world. we use non surgical method(Abortion pills) to terminate…Dr.LISA +27730423979women Clinic is committed to providing the highest quality of obstetrical and gynecological care to women of all ages. Our dedicated staff aim to treat each patient and her health concerns with compassion and respect.Our dedicated group ABORTION WOMEN’S CLINIC +27730423979 IN women clinic we believe that every woman should be able to make choices in her pregnancy. Our job is to provide compassionate care, safety,affordable and confidential services. That’s why we have won the trust from all generations of women all over the world. we use non surgical method(Abortion pills) to terminate…Dr.LISA +27730423979women Clinic is committed to providing the highest quality of obstetrical and gynecological care to women of all ages. Our dedicated staff aim to treat each patient and her health concerns with compassion and respect.Our dedicated group of receptionists, nurses, and physicians have worked together as a teamof receptionists, nurses, and physicians have worked together as a team wwww.lisywomensclinic.co.za/
Acute scrotum is a general term referring to an emergency condition affecting the contents or the wall of the scrotum.
There are a number of conditions that present acutely, predominantly with pain and/or swelling
A careful and detailed history and examination, and in some cases, investigations allow differentiation between these diagnoses. A prompt diagnosis is essential as the patient may require urgent surgical intervention
Testicular torsion refers to twisting of the spermatic cord, causing ischaemia of the testicle.
Testicular torsion results from inadequate fixation of the testis to the tunica vaginalis producing ischemia from reduced arterial inflow and venous outflow obstruction.
The prevalence of testicular torsion in adult patients hospitalized with acute scrotal pain is approximately 25 to 50 percent
Knee anatomy and clinical tests 2024.pdfvimalpl1234
This includes all relevant anatomy and clinical tests compiled from standard textbooks, Campbell,netter etc..It is comprehensive and best suited for orthopaedicians and orthopaedic residents.
Couples presenting to the infertility clinic- Do they really have infertility...Sujoy Dasgupta
Dr Sujoy Dasgupta presented the study on "Couples presenting to the infertility clinic- Do they really have infertility? – The unexplored stories of non-consummation" in the 13th Congress of the Asia Pacific Initiative on Reproduction (ASPIRE 2024) at Manila on 24 May, 2024.
NVBDCP.pptx Nation vector borne disease control programSapna Thakur
NVBDCP was launched in 2003-2004 . Vector-Borne Disease: Disease that results from an infection transmitted to humans and other animals by blood-feeding arthropods, such as mosquitoes, ticks, and fleas. Examples of vector-borne diseases include Dengue fever, West Nile Virus, Lyme disease, and malaria.
Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
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Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
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TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
These simplified slides by Dr. Sidra Arshad present an overview of the non-respiratory functions of the respiratory tract.
Learning objectives:
1. Enlist the non-respiratory functions of the respiratory tract
2. Briefly explain how these functions are carried out
3. Discuss the significance of dead space
4. Differentiate between minute ventilation and alveolar ventilation
5. Describe the cough and sneeze reflexes
Study Resources:
1. Chapter 39, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 34, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 17, Human Physiology by Lauralee Sherwood, 9th edition
4. Non-respiratory functions of the lungs https://academic.oup.com/bjaed/article/13/3/98/278874
Recomendações da OMS sobre cuidados maternos e neonatais para uma experiência pós-natal positiva.
Em consonância com os ODS – Objetivos do Desenvolvimento Sustentável e a Estratégia Global para a Saúde das Mulheres, Crianças e Adolescentes, e aplicando uma abordagem baseada nos direitos humanos, os esforços de cuidados pós-natais devem expandir-se para além da cobertura e da simples sobrevivência, de modo a incluir cuidados de qualidade.
Estas diretrizes visam melhorar a qualidade dos cuidados pós-natais essenciais e de rotina prestados às mulheres e aos recém-nascidos, com o objetivo final de melhorar a saúde e o bem-estar materno e neonatal.
Uma “experiência pós-natal positiva” é um resultado importante para todas as mulheres que dão à luz e para os seus recém-nascidos, estabelecendo as bases para a melhoria da saúde e do bem-estar a curto e longo prazo. Uma experiência pós-natal positiva é definida como aquela em que as mulheres, pessoas que gestam, os recém-nascidos, os casais, os pais, os cuidadores e as famílias recebem informação consistente, garantia e apoio de profissionais de saúde motivados; e onde um sistema de saúde flexível e com recursos reconheça as necessidades das mulheres e dos bebês e respeite o seu contexto cultural.
Estas diretrizes consolidadas apresentam algumas recomendações novas e já bem fundamentadas sobre cuidados pós-natais de rotina para mulheres e neonatos que recebem cuidados no pós-parto em unidades de saúde ou na comunidade, independentemente dos recursos disponíveis.
É fornecido um conjunto abrangente de recomendações para cuidados durante o período puerperal, com ênfase nos cuidados essenciais que todas as mulheres e recém-nascidos devem receber, e com a devida atenção à qualidade dos cuidados; isto é, a entrega e a experiência do cuidado recebido. Estas diretrizes atualizam e ampliam as recomendações da OMS de 2014 sobre cuidados pós-natais da mãe e do recém-nascido e complementam as atuais diretrizes da OMS sobre a gestão de complicações pós-natais.
O estabelecimento da amamentação e o manejo das principais intercorrências é contemplada.
Recomendamos muito.
Vamos discutir essas recomendações no nosso curso de pós-graduação em Aleitamento no Instituto Ciclos.
Esta publicação só está disponível em inglês até o momento.
Prof. Marcus Renato de Carvalho
www.agostodourado.com
Novas diretrizes da OMS para os cuidados perinatais de mais qualidade
Non linear pharmacokinetics
1. Non-linear Pharmacokinetics
Submitted to:-
Dr. D.C.Bhatt
Dean Faculty of Medical
Sciences
Submitted by:-
Shashi Yadav
Reg.No.- 190121220012
M.Pharma 2nd Sem
Dept. of Pharmaceutical Sciences
Guru Jambheshwar University of Science and
Technology
2. CONTENTS
• Introduction
• Linear & Nonlinearity Pharmacokinetics
• Detection of non-linearity in
pharmacokinetics
• Causes of nonlinearity
• Michaelis – Menten equation
• Estimation of Km and Vmax
3. Linear Pharmacokinetics
• At therapeutic doses, the change in the amount of drug in the body
or the change in its plasma concentration due to absorption,
distribution, binding, metabolism or excretion, is proportional to its
dose, whether administered as a single dose or as multiple doses.
• In such situation the rate processes are said to follow first order or
linear kinetics and all semilog plots of Conc. vs Time for different
doses when collected for dose administered, are superimposable.
• The important pharmacokinetic parameters viz. F, Ka, KE, Vd, Clr, Clh
which describes the time course of a drug in the body remain
unaffected by the dose.
• Pharmacokinetics is dose independent.
4. Non-linear Pharmacokinetics
• The rate process of drug’s ADME are depend upon carrier or enzymes
that are substrate specific, have definite capacities and are
susceptible to saturation at a high drug concentration.
• In such cases, an essentially first-order kinetics transform into a
mixture of first-order and zero-order rate processes and the
pharmacokinetic parameters are changed with the size of the
administered dose.
• Pharmacokinetics of such drugs are said to be dose-dependent.
Terms synonymous with it are mixed-order, nonlinear and capacity-
limited kinetics.
5. • A number of drugs demonstrate saturation or capacity-limited
metabolism in humans.
• Examples of these saturable metabolic processes include
- glycine conjugation of salicylate
- sulphate conjugation of salicylamide
- acetylation of p-aminobenzoic acid
- elimination of phenytoin
6. Drugs that demonstrate saturation kinetics usually
show the following characteristics:
• Elimination of drug does not follow simple first-order kinetics- that is,
elimination kinetics are nonlinear.
• The elimination half-life changes as dose is increased. Usually, the
elimination half-life increases with increased dose due to saturation of an
enzyme system. However, the elimination half-life might decrease due to
“self”-induction of liver biotransformation enzymes, as is observed for
carbamazepine.
• The area under the curve (AUC) is not proportional to the amount of
bioavailable drug.
• The saturation of capacity-limited processes may be affected by other drugs
that require the same enzyme or carrier-mediated system (i.e., competition
effects).
• The composition and/or ratio of the metabolites of a drug may be affected
by a change in the dose.
7. Detection of Non-Linearity in Pharmacokinetics
•There are several tests to detect non–linearity in
pharmacokinetics but the simplest ones are:
1) First test:- Determination of steady state plasma concentration
at different doses.
2) Second test:- Determination of some important pharmacokinetic
parameters such as fraction bioavailability, elimination half life or
total systemic clearance at different doses of drug. Any change in
these parameters is indicative to non-linearity which are usually
constant.
8. Causes of Non-Linearity
Drug absorption
Three causes:-
• Solubility/dissolution of drug is rate-limited; Griseofulvin - at high
concentration in intestine.
• Carrier - mediated transport system; Ascorbic acid - saturation of transport
system.
• Presystemic gut wall/hepatic metabolism attains saturation; Propranolol.
These parameters affected F, Ka, Cmax and AUC.
A decrease in these parameters is observed in former two causes and an
increase in latter cause.
9. Drug distribution
At high doses non-linearity due to
• Two causes:-
I) Binding sites on plasma proteins get saturated; Phenylbutazone.
II) Tissue binding sites get saturated.
• In both cases there is increase in plasma drug concentration.
• Increase in Vd only in (I)
• Clearance with high ER get increased due to saturation of binding
sites.
10. Drug metabolism
• Non-linearity occurs due to capacity limited metabolism, small
changes in dose administration - large variations in plasma
concentration at steady state - large intersubject variability.
• Two imp causes:-
I) Capacity-limited metabolism – enzyme/cofactor saturation; Phenytoin,
Alcohol.
II) Enzyme induction - decrease in plasma concentration;
Carbamazepine.
• Autoinduction in dose dependent concentration.
• Saturation of enzymes - decrease in Clh - increase in Css.
• In case of enzyme induction reverse condition.
• Other reasons includes saturation of binding sites, inhibitory effects of
the metabolites on the action of enzymes.
11. Drug excretion
• Two active processes which are saturable,
I) Active tubular secretion - Penicillin G
II) Active tubular reabsorption - Water soluble vitamins & Glucose.
• Saturation of carrier systems - decrease in renal clearance in case of I
& increase in II. Half life also increases.
• Other reasons like forced diuresis, change in urine pH, nephrotoxicity
& saturation of binding sites.
• In case of biliary excretion non - linearity due to saturation -
Tetracycline & Indomethacin.
13. Michaelis-Menten Enzyme Kinetics
It is also called as Capacity-limited metabolism or
Mixed order kinetics.
E + D <—> ED —> E + M
Enzymes usually react with the substrate to form
enzyme substrate complexes; then the product is
formed. The enzyme can go back to react with
another substrate to form another molecule of the
product.
14. Michaelis-Menten equation
• The kinetics of capacity limited or saturable processes is best described by Michaelis-
Menten equation.
−
𝑑𝐶
𝑑𝑡
= 𝑉max.C/ Km + C………….I
• Where , -dC/dt = rate of decline of drug conc. with time
Vmax = theoretical maximum rate of the process
Km= Michaelis constant
• Three situation can now be considered depending upon the value of Km and C.
1) when Km = C
under this situation , eq I reduces to,
-dC/dt =Vmax/2 ...................II
•The rate of process is equal to half of its maximum rate.
•This process is represented in the plot of dc/dt vs. C. shown in fig. 1
15. 2) If a drug at low conc. undergoes a saturable biotransformation then
KM>>C
• here, Km+C =Km and eq. I reduces to,
-dC/dt =Vmax C /Km………………III
• above eq. is identical to the one that describe first order elimination of
drug, where Vmax/KM= KE.
3) When Km<<C
• Under this condition ,Km +C= C and eq. I will become,
-dC/dt =Vmax …………….IV
• above eq. is identical to the one that describe a zero order process i.e.
the rate process occurs at constant rate Vmax and is independent of
drug conc.
E.g. metabolism of ethanol
17. Estimation of Km and Vmax from Steady State Conc.
• When a drug is administered as a constant rate i.v. infusion or in a multiple
dose regimen, the steady-state concentration Css is given in terms of
dosing rate DR as:
• where DR = Ro when the drug is administered as zero-order i.v. infusion
and it is equal to FXo/τ when administered as multiple oral dosage
regimen (F is fraction bioavailable, Xo is oral dose and is dosing interval).
• At steady-state, the dosing rate equals rate of decline in plasma drug
concentration and if the decline (elimination) is due to a single capacity-
limited process (for e.g. metabolism), then;
18. • A plot of Css versus DR yields a typical hockey-stick shaped curve as
shown in Fig.-2
Curve for a drug with nonlinear kinetics obtained by plotting the steady-state
concentration versus dosing rates. (Fig.-2)
19. • To define the characteristics of the curve with a reasonable degree of
accuracy, several measurements must be made at steady-state during
dosage with different doses.
• Practically, one can graphically compute Km and Vmax in 3 ways:
1. Lineweaver-Burke Plot/Klotz Plot
2. Direct Linear Plot
3. Graphical method
20. Lineweaver-Burke Plot/Klotz Plot
• Taking reciprocal of DR equation, we
get:
• A plot of 1/DR versus 1/Css yields a
straight line with slope Km/Vmax and y-
intercept 1/Vmax (Fig.-3). Lineweaver-Burke/Klotz plot for estimation of
Km andVmax at steady-state concentration of
drug.
21. Direct Linear Plot
• A pair of Css viz. Css,1 and Css,2
obtained with two different dosing rates
DR1 and DR2 is plotted. The points
Css,1 and DR1 are joined to form a line
and a second line is obtained similarly by
joining Css,2 and DR2. The point where
these two lines intersect each other is
extrapolated on DR axis to obtain Vmax
and on x-axis to get Km. Direct linear plot for estimation of Km andVmax
at steady-state concentrations of a drug given at
different dosing rates. (Fig.-4)
22. Graphical method
• The graphical method of estimating Km and Vmax involves
rearranging DR equation to yield:
• A plot of DR versus DR/Css yields a straight line with slope -Km and Y-
intercept Vmax.
• Km and Vmax can also be calculated numerically by setting up
simultaneous equations as shown below:
23. • Combination of the above two equations
yields:
• After having computed Km, its subsequent
substitution in any one of the two
simultaneous equations will yield Vmax.
24. Nonlinear Pharmacokinetics (Phenytoin)
• Phenytoin is an example of a drug which commonly has a Km value
within or below the therapeutic range.
– The average Km value is about 4 mg/L.
– The normally effective plasma concentrations for phenytoin are
between 10 and 20 mg/L.
• Therefore it is quite possible for patients to be overdosed due to drug
accumulation.
• At low concentration the apparent half-life is about 12 hours, whereas
at higher concentration it may well be much greater than 24 hours.
25. • Dosing every 12 hours, the normal half-
life, can rapidly lead to dangerous
accumulation.
• At concentrations above 20 mg/L
elimination maybe very slow in some
patients. Dropping for example from 25 to
23 mg/L in 24 hours, whereas normally
you would expect it to drop from -25> -
12.5> 6 mg/L in 24 hours.
• Typical Vm values are 300 to 700 mg/day.
These are the maximum amounts of drug
which can be eliminated by these patients
per day. Giving doses approaching these
values or higher would cause very
dangerous accumulation of drug.
Cpss profile following different doses
of Phenytoin.
26. REFERENCE
• Applied biopharmaceutics and pharmacokinetics by Shargel L.,
Andrew B.C.
• Biopharmaceutics and Pharmacokinetics a treatise by Brahmankar
DM, Jaiswal SB.