Saturday , October 24 2020
tmax-and-t12

Difference between tmax and t1/2

tmax and t1/2 or peak plasma time and elimination half-life of a drug often make confusion. Frequently these terms tmax and t1/2 are used to understand many equations or topics in biopharmaceutics. Differences between tmax and t1/2 are:

1. Definition of Peak plasma time or time for peak plasma concentration or time of peak plasma concentration or tmax and t1/2

The t max (time of peak plasma concentration) is the time required to reach maximum drug concentration in the plasma after drug administration.  t max is peak plasma time.  Simply, t max is the time to reach C max. C max is the maximum (peak) plasma drug concentration attained after the oral administration of the drug. Also, at t max, the drug absorption rate exactly equals the drug elimination rate.

On the other hand, t 1/2 (elimination half-life) is the time required to decrease the drug concentration within the body by one-half during elimination. In other words, t ½ (elimination half-life) is the time required for the amount or concentration of a drug to decrease by one-half [1]. In pharmacokinetic, elimination half-life, t 1/2 refers to the time required for half the dose of drug administered to be removed from the body.

2. The t max is dependent on the elimination rate (k) and absorption rate constant (ka). while t 1/2 is dependent on the elimination rate (k) and volume of distribution (Vd).

3. At tmax, the concentration of a drug is in peak. While at t 1/2, the concentration of a drug may or may not in peak.

4. Equations for tmax and t1/2

The equation for calculating t max (peak plasma time):

𝑡 ğ‘šğ‘Žğ‘¥ = ln (ğ‘˜ğ‘Ž / 𝑘) / (ğ‘˜ğ‘Žâˆ’ğ‘˜)

= 2.303 log (ğ‘˜ğ‘Ž / 𝑘)/ (ğ‘˜ğ‘Žâˆ’ğ‘˜)

On the other hand, the equation for calculating t½:

t½ = 0.693 × (Vd /CL)

Where, Vd = Volume of distribution and CL = Clearance.

5. t max  is peak plasma time. On the other hand, t 1/2 is the elimination half-life.

6. t max (peak plasma time) is a rough marker of the average rate of drug absorption. On the other hand, t 1/2 is an indicator of how fast a drug is eliminated from the body.

Summary of the difference between tmax and t1/2

tmax t1/2
1. The time of peak plasma concentration is the time required to reach maximum drug concentration in the plasma after drug administration. t 1/2 (elimination half-life) is the time required to decrease the concentration of a drug within the body by one-half during elimination.
2. The t max is dependent on the absorption rate constant (ka) and elimination rate (k). t 1/2 is dependent on the volume of distribution (Vd) and elimination rate (k).
3. At t max, the drug concentration is in peak. At t 1/2, drug concentration may or may not in peak.
4. Equation for calculating t max:

𝑡 ğ‘šğ‘Žğ‘¥ = ln (ğ‘˜ğ‘Ž / 𝑘) / (ğ‘˜ğ‘Žâˆ’ğ‘˜) = 2.303 log (ğ‘˜ğ‘Ž / 𝑘)/ (ğ‘˜ğ‘Žâˆ’ğ‘˜)

Equation for calculating t ½:

t½ = 0.693 × (Vd /CL)

5. It is Peak plasma time. It is elimination half-life.
6. It is a rough marker of the average rate of drug absorption. The half-life is a useful indicator of how fast a drug is removed from the body.
7. t max t1/2

This article may provide the answer to the following questions:

  • First of all, the difference between tmax and t1/2.
  • Second, the difference between the time of peak plasma concentration (tmax) and elimination half-life (t1/2).
  • Third, what is the difference between peak plasma time and elimination half-life?
  • Finally, what is peak plasma time or time for peak plasma concentration?

Also may read:

References

  1. Shargel, L., & McGraw-Hill Education. (2016). Applied biopharmaceutics & pharmacokinetics. New York: McGraw-Hill Education.

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