dr.yayooo_s pooled summary note-2

7/22/2019 Dr.yayooo_s Pooled Summary Note-2

http://slidepdf.com/reader/full/dryayooos-pooled-summary-note-2 1/41

Dr.Yayooo's Pooled Summary Note



DR.YAYOOODr.Yasser Alaa ElDeen

First FPGEE Online Lecturer

Unique Egyptian Syndicate Lecturer for

foreign pharmacy board exams

www.dryayooo.myfreeforum.org

[email protected]

[email protected]

011-20-1002445747








[email protected]

[email protected]

011-20-1002445747



15. Accumulation:Multiple dosesSome drugs may be used clinically on a single-dose basis, although most drugs are administeredcontinually over a period of time. When a drug is administered at a regular dosing interval (orally orIV), the drug accumulates in the body and the serum concentration will rise until steady-stateconditions have been reached, assuming the drug is administered again before all of the previousdose has been eliminated.

Steady state

Steady state occurs when the amount of drug administered (in a given time period) is equal to theamount of drug eliminated in that same period. At steady state the plasma concentrations of the drug(Cpss) at any time during any dosing interval, as well as the peak and trough, are similar. The time toreach steady-state concentrations is dependent on the half-life of the drug under consideration.

Time profiles of multiple IV doses – reaching steady state using different doses.

Effect of doseThe higher the dose, the higher the steady-state levels, but the time to achieve steady-state levels isindependent of dose. Note that the fluctuations in Cp max and Cp min are greatest with higher doses.

Effect of dosing intervalConsider a drug having a half-life of 3 h. When the dosing interval, T , is less than the half-life, t1/2,

greater accumulation occurs, i.e. higher steady-state levels are higher and there is less fluctuation inCp max and Cp min.

When T > t1/2, then a lower accumulation occurs with greater fluctuation in Cp max and Cp min.

If the dosing interval is much greater than the half-life of the drug, then Cp min approaches zero. Underthese conditions no accumulation will occur and the plasma concentration –time profile will be theresult of administration of a series of single doses.

Time profiles of multiple IV doses – reaching steady state using different dosing intervals.



16. Drug tolerance:Drug tolerance is basically the body's ability to adapt to the presence of a drug.The magnitude of the body's response to a particular drug depends on two factors:

Concentration of the drug at its site of action

Sensitivity of the target site to the drug

The sensitivity of the target cells is governed by genetic factors and adaptive changes by the body.Adaptive changes occur in response to the repeated exposure to a particular drug. The result isusually a loss of sensitivity to the drug. This decreased response is called toleranceTolerance may be defined as a state of progressively decreased responsiveness to a drug as a resultof which a larger dose of the drug is needed to achieve the effect originally obtained by a smallerdose.

Drug dependence Physical dependence

Physical dependence is a condition in which the body has adjusted to the presence of a drug,resulting in clear symptoms of withdrawal when its use stops. In extreme cases, the effect of rapidwithdrawal can be life threatening because the body has become so dependent on the drug as tointerfere with normal body processes.An individual physically dependent on a drug requires that drug in order to function normally.Physical dependence is associated with tolerance in most cases. The state of physical dependence isrevealed by withdrawing the drug and noting the occurrence of withdrawal symptoms some time afterthe drug is withheld. The symptoms of withdrawal can be terminated by re-administration of the drug.Symptoms of drug withdrawal tend to be the opposite of the effects of the drug. If the effect of the

drug is sedation, the withdrawal effect will likely be hyperexcitability. If the effect was stimulation thewithdrawal effect will likely be be emotional depression.Longer acting drugs tend to produce less intense withdrawal symptoms because the body has moretime to adapt to the decreasing presence of the drug.

Psychological dependenceThis kind of dependence is characterized by emotional and mental preoccupation with the drug'seffects and by a persistent craving for it.The symptoms displayed are not physical symptoms. Craving seems to be the most commonwithdrawal symptom.Psychological dependence is usually manifested by compulsive drug-taking, but the frequency andpattern of use can differ considerably from one individual to another.

Cross Dependence

This is the ability of one drug to suppress the manifestations of physical dependence produced by

another and to maintain the physically dependent state. Cross dependence may be partial orcomplete. One amphetamine will show cross dependence with other amphetamines. Most sedativesshow cross dependence with each other and with alcohol. Cross dependence usually occurs amongcompounds of a given family of drugs but may also occur among drugs of different families that havesimilar pharmacological effects.

AddictionAddiction is a difficult word to define since it can be used in various ways. The World HealthOrganization (WHO) has provided the following definition: "A behavioral pattern of drug use,characterized by overwhelming involvement with the use of a drug (compulsive use), the securing ofthe supply, and a high tendency to relapse after withdrawal. Addiction is viewed as an extreme on acontinuum of drug use patterns. It refers, in a quantitative rather an a qualitative sense, to the degreeto which drug use pervades the total life activity of the user, and to the range of circumstances inwhich drug use controls his/her behaviour."Addiction refers to dependent patterns of drug self-administration without making a distinctionbetween physical or psychological dependence. Moral weakness is often implied by the termaddiction.The WHO has suggested that the term "addiction" be replaced with the term "drug dependence." It isnot possible to identify with precision the point where compulsive use should be consideredaddiction.The term addiction cannot be used interchangeably with physical dependence since one can bephysically dependent on drugs without being addicted and, in some cases, addicted without beingphysically dependent.Self-administration of drugs depends upon a number of factors. These include:

the properties of the drug itself

the route of administration

the size of the individual dose

the amount of work required to obtain a dose

the presence of other drugs

previous experience with other drugs








[email protected]

[email protected]

011-20-1002445747

dr.yayooo_s pooled summary note-2

Documents