Dosage regimen can be defined as the manner in which the drug is taken.

1. BY
NAUSHEEN FATHIMA
M.PHARM (PHARMACEUTICS)
TEEGALA KRISHNA REDDY COLLEGE OF PHARMACY1

2. CONTENTS
INTRODUCTION TO DOSAGE REGIMEN
APPROACHES
PARAMETERS
DRUG ACCUMULATION
STEADY STATE DURING MULTIPLE DOSING
MAXIMUM AND MINIMUM CONCENTRATION DURING MULTIPLE
DOSING
AVERAGE CONCENTRATION AND BODY CONTENT
LOADING DOSE
MAINTENANCE OF DRUG WITHIN THE THERAPEUTIC RANGE
MONITORING DRUG THERAPY
CONCLUSION
REFERENCES
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3. INTRODUCTION
Dosage regimen can be defined as the manner in which the
drug is taken. A single dose may provide an effective treatment. But
the duration of illness is longer than the therapeutic effect produced
by a single dose. In such cases drugs are required to be taken on a
repetitive basis over a period of time.
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4. The multiple dosing achieves and maintains drug concentration
in plasma or at the site of action that are both safe and
effectively within the therapeutic window for the entire
duration of therapy.
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5. APPROACHES
1. Empirical dosage regimen: Designed by the physician
based on empirical clinical data, personal experience and
clinical observations. (not accurate)
2. Individualized dosage regimen: Based on
pharmacokinetics of the drug in individual patient. (most
accurate)
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6. 3. Dosage regimen on population averages : most often used.
a. Fixed model: Calculated based on population
average pharmacokinetic parameters.
b. Adaptive model : based on both population average
pharmacokinetic parameters of drug and patient variables like
weight, age ,body surface area.
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7. The dose size: It is the quantity of the drug administered
each time.
PARAMETERS
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8. Dose frequency: It is the time interval between doses.
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9. DRUG ACCUMULATION
Following the 1st dose, if the 2nd dose is given early enough so
that not the entire 1st dose is eliminated then the drug will
start accumulating and we will get higher concentration
with the 2nd and 3rd dose.
Rac = 1/1- e-K 𝜏
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10. The suitable amount of dose and identical dosing interval leads to
steady state at which the mass of drug administered or absorbed is
equal to the mass of drug eliminated
STEADY STATE DURING MULTIPLE
DOSING
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11. MAXIMUM AND MINIMUM
CONCENTRATION DURING MULTIPLE
DOSING
If n is the number of doses administered, the Cmax and Cmin obtained on multiple dosing
after the nth dose is given as:
Cn,max = C0 [ 1- 𝒆−𝒏𝑲𝝉/ 1- 𝒆−𝑲𝝉]
Cn,min = C0 [1-𝒆−𝒏𝑲𝝉/ 1-𝒆−𝑲𝝉] 𝒆−𝑲𝝉 = cn,max 𝒆−𝑲𝝉
The maximum and minimum concentrations of drug in plasma at steady-state are found by
following equations:
Css,max = C0 / 1- 𝒆−𝑲𝝉
Css,min = C0 𝒆−
𝑲𝝉/ 1- 𝒆−
𝑲𝝉 = css,max 𝒆−
𝑲𝝉
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12. 1. Fraction of dose absorbed F,
2. Maintenance dose X0,
3. Clearance Clt of the drug.
4. Dosing interval 𝜏
Css,av = Fx0 / Clt 𝝉
= 1.44FX0 / vd 𝝉
= AUC (single dose) / 𝝉
AVERAGE CONCENTRATION AND
BODY CONTENT
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13. Since X = Vd C, the body content at steady-state is given as:
Xss,av = 1.44FX0 t1/2 / 𝝉
These averages values are not arithmetic mean of Css,max and
Css,min since the plasma drug concentration declines exponentially.
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14. LOADING DOSE
• A drug dose does not show therapeutic activity unless it reaches the desired
steady state.
• It takes about 5 half lives to attain it and therefore time taken will be too
long if the drug has a long half-life.
• Therapeutic effect can be reached immediately by administering a dose that
gives the desired steady state instantaneously before the commencement of
maintenance dose X0.
• Such an initial or first dose intended to be therapeutic is called as priming
dose or loading dose.
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15. Initial dose intended to be therapeutic is known as loading dose.
X0,l = Css,av Vd / F
When Vd is not known, loading dose may be calculated by the following
equation:
X0,L / X0 = 1 / (1 - 𝒆−𝑲𝒂𝝉) (1 - 𝒆−𝑲𝑬𝝉)
The above equation applies when ka>>ke and during is distributed rapidly.
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16. • The ratio of loading dose to maintenance dose X0,L/X0 is called as dose ratio. As a
rule, when
𝜏 = t1/2, dose ratio equals 2.0
𝜏 > t1/2, dose ratio is smaller than 2.0
𝜏< t1/2, dose ratio is greater than 2.0.
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17. MAINTENANCE OF DRUG WITHIN
THE THERAPEUTIC RANGE
Depends upon-
• The therapeutic index of the drug.
• The half-life of the drug.
• Convenience of dosing.
Certain generalization with regards to maintenance of drug within the
therapeutic range can be stated –
• For a drug with a short half-life and narrow therapeutic index e.g. Heparin, dosing
frequency has to essentially less than t1/2.
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18. • For a drug with short half-life and high therapeutic index, dosing frequency can
be several times that of t1/2 but the maintenance dose has to be larger so that the
plasma concentration persists above the minimum inhibitory level.
• A drug with intermediate t1/2 may be given at intervals 𝜏 ≤ t1/2 if therapeutic
index is low and those with high indices can be given at intervals between 1 to 3
half-lives.
• For drugs with very long half-lives e.g. Amlodipine, once daily dose is very
convenient.
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19. MONITORING DRUG THERAPY
• Management of drug therapy in individual patient often requires evaluation of response of
the patient to recommended dosage regimen. Depending upon the drug and the disease to
be treated, management of drug therapy in individual patient can be accomplished by:
1. Monitoring therapeutic effects- Therapeutic Monitoring
2. Monitoring pharmacological action – Pharmacodynamics Monitoring
3. Monitoring plasma drug concentration – Pharmacokinetic Monitoring.
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20. CONCLUSION
Dosage regimen explains the interrelationship between the rate at which drug enters
the body and the rate at which it leaves. It also explains how, in turn, this balance
influences the concentration of drug in the plasma at any time. It is important for
pharmaceutical sciences to come to terms with this problem and then overcome it by
finding ways of maintaining therapeutic drug levels appropriate to a particular disease
state. This can be achieved by the careful design of the appropriate drug delivery
system.
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21. REFERENCES
• D.M. Brahmankar, Sunil.B.Jaiswal- Bio Pharmaceutics And
Pharmacokinetics- A treatise, pg.no: 368 – 376, 382 – 384.
• V.Venkateshwarlu- Bio Pharmaceutics and Pharmacokinetics, second
edition, pg.no:311323.
• http://pharmatechbd.blogspot.in/?search=dosage+regimen#uds-search-
results
• http://www.slideshare.net/vrushankshah/dosage-regimen?from_search=2
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