This medicine half life calculator estimates the action of any medicine and the way concentration decreases in percentage in plasma according to half life and dosage. You can discover more on this subject, check an example calculation and the half times of most known active substances below the form.
How does this medicine half life calculator work?
This is a health tool designed to show you the concentration dosage of the medicine in your body according to half life. There are only two things you need to input, the dosage and half life. For your convenience, the medicine half life calculator provides a series of measurement units and the result will respect the unit selection.
Example calculation:
For a dosage of 46mg with a half life of 2 hours.
| After… | Dosage (mg) | Concentration |
| 2 hrs | 23.0 mg | 50% |
| 4 hrs | 11.5 mg | 25% |
| 6 hrs | 5.8 mg | 12.50% |
| 8 hrs | 2.9 mg | 6.25% |
| 10 hrs | 1.4 mg | 3.13% |
| 12 hrs | 0.7 mg | 1.56% |
| 14 hrs | 0.4 mg | 0% |
Substance half life
The half time or life of a dose represents the period of time, in either hours, minutes or seconds that it takes a dosage to reach half of its concentration in the plasma after administration.
It is basically the peak minus trough concentration divided by the interval. Most medicine recipes provide the half life and this is used by professionals in establishing the dosage and the specific times when the next dose needs to be taken. This is also known as biological or elimination half time and it varies according to factors such as metabolic activity or receptor interactions.
When establishing the dosage it is important to remember that the active substance needs to stay at constant levels in the body long enough to produce the desired results and also that in case of subsequent or parallel intake, some medicines might interact. The table below consists of the most common active substances and their half lives:
|
Substance |
Time (hrs) |
Substance |
Time (hrs) |
|
Acetaminophen |
1 - 4 |
Indinavir |
1 - 3 |
|
Acyclovir |
2 - 3 |
Isoniazid |
1 - 2 |
|
Amikacin |
2 - 3 |
Ketoconazole |
2 - 8 |
|
Amiodarone |
26 - 107 days |
Lidocaine |
1 - 2 |
|
Amphetamine |
7 - 34 |
Lithium |
14 - 30 |
|
Bismuth |
21 - 72 days |
Methotrexate |
3 - 10 |
|
Caffeine |
3 - 12 |
Metronidazole |
8 |
|
Carbamazepine |
14 - 47 |
Morphine |
1 - 7 |
|
Cefuroxime |
1 - 2 |
Oxcarbazepine |
1 - 2 |
|
Cephalexin |
50 - 60 min |
Oxycodone |
3 - 5 |
|
Chlordiazepoxide |
6 - 25 |
Phenobarbital |
81 - 117 |
|
Chlorpromazine |
7 - 119 |
Phenytoin |
18 - 22 |
|
Ciprofloxacin |
4 |
Primidone |
3 - 7 |
|
Clarithromycin |
3 - 4 |
Procainamide |
2 - 5 |
|
Clonazepam |
19 - 60 |
Propafenone |
2 - 10 |
|
Cyclosporine |
6 - 27 |
Propranolol |
2 - 6 |
|
Diazepam |
21 - 37 |
Pyrazinamide |
10 |
|
Digitoxin |
4 - 10 days |
Quinidine |
5 - 9 |
|
Digoxin |
36 - 48 |
Rifabutin |
16 - 69 |
|
Doxepin |
8 - 25 |
Rifampin |
2 - 3 |
|
Doxycycline |
18 - 22 |
Ritonavir |
3 - 5 |
|
Fentanyl |
3 - 12 |
Salicylate |
2 - 3 |
|
Fluconazole |
20 - 50 |
Streptomycin |
5 - 6 |
|
Gabapentin |
5 - 7 |
Tetracycline |
7 - 11 |
|
Ganciclovir |
3 - 6 |
Theophylline |
7 - 11 |
|
Gentamicin |
1 - 3 |
Trimethoprim |
8 - 10 |
|
Haloperidol |
14 - 41 |
Valproic Acid |
9 - 16 |
|
Heparin Anti-Xa |
3 - 6 |
Vancomycin |
3 - 8 |
|
Imipramine |
6 - 20 |
Warfarin |
20 - 60 |
References
1) Garg U, Jacobs DS, Grady HJ, et al. Therapeutic drug monitoring. In: Jacobs DS, Oxley DK, Demott WR, eds. (2001) Jacobs & Demott Laboratory Test Handbook. 5th ed. Cleveland, Ohio: Lexi-Comp, Inc; 731-771.
2) Hammett-Stabler CA, Dasgupta A, eds. (2007) Therapeutic Drug Monitoring Data: A Concise Guide. 3rd ed. Washington, DC: AACC Press.
25 Mar, 2015