Elimination Timeline Visualizer

Select a drug or enter a custom half-life to visualize the complete elimination timeline. Shows clinical milestones: 50% eliminated (1 half-life), 87.5% (3), 96.9% (5), and 99.2% (7 half-lives). Useful for understanding drug washout periods, drug testing windows, and safe re-dosing timing.

Disclaimer: This tool is for educational purposes only. Always consult a healthcare professional for medication decisions.

Common drugs:

Initial Dose (mg)

Half-Life (hours)

Time Range (hours)

Initial Dose

~97% Eliminated (5 x t½)

Elimination Curve

Time (h)	Half-Lives Elapsed	Amount Remaining (mg)	% Remaining	% Eliminated

Drug Elimination Kinetics

Drug elimination follows first-order kinetics for most therapeutically used compounds. Under first-order elimination, a constant fraction of the drug is removed per unit time, producing an exponential decay in plasma concentration. The amount remaining at any time point can be calculated as: Amount = Dose x (0.5)^(t / t½), where t is the elapsed time and t½ is the elimination half-life. This predictable relationship allows clinicians to estimate when a drug will fall below therapeutic or detectable levels.

The clinical significance of elimination kinetics extends to drug discontinuation planning, washout periods before surgery (anticoagulants require 3-5 half-lives of washout), urine drug testing windows, and understanding the duration of both therapeutic effects and side effects. For drugs with active metabolites, the effective elimination timeline must account for both parent compound and metabolite half-lives.

Importantly, first-order elimination assumes that clearance mechanisms are not saturated. Drugs exhibiting zero-order (saturable) kinetics at therapeutic doses, such as phenytoin and ethanol, follow different elimination patterns where a constant amount rather than a constant fraction is eliminated per unit time. This distinction has critical clinical implications: small dose increases of zero-order drugs can produce disproportionately large concentration increases and toxicity risk.

Tıbbi Sorumluluk Reddi

This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making medication decisions.

Data sources: ChEMBL, PubChem, DailyMed.

How to Use

1
Enter drug and dosing information
Select the drug from the database or enter its elimination half-life and last dose time. Specify the total dose administered and whether the drug follows single-compartment or multi-compartment elimination kinetics, as the latter produces non-linear plasma concentration decline curves.
2
Generate plasma concentration timeline
The tool plots predicted plasma drug concentration versus time from the last dose, using first-order elimination equations and published pharmacokinetic parameters. Concentration at each time point is expressed as a percentage of the initial post-dose concentration and in absolute units where population PK data supports estimation.
3
Identify clearance milestones
The timeline marks key pharmacokinetic milestones: 50% remaining (1 half-life), 25% remaining (2 half-lives), 12.5% remaining (3 half-lives), 3.125% remaining (5 half-lives), and near-complete elimination (10 half-lives). Clinical applications — such as drug washout before surgery, pregnancy planning, or drug switching — are contextualized against these milestones.

About

Understanding the time course of drug elimination is fundamental to safe prescribing decisions involving drug switching, surgical planning, teratogen management, and interpretation of therapeutic drug monitoring results. First-order elimination kinetics — the pharmacokinetic standard for the vast majority of small molecule drugs at therapeutic doses — produce predictable, mathematically defined concentration-time profiles governed by the drug's elimination half-life and volume of distribution. These predictable profiles enable rational planning of washout periods, re-dosing intervals, and monitoring schedules without the need for direct plasma concentration measurement in most clinical scenarios.

The pharmacokinetic community has developed population pharmacokinetic (PopPK) models that characterize elimination half-life as a distribution across patient populations, with covariates such as age, weight, renal function, and hepatic function as predictors of between-patient variability. FDA's Modeling and Simulation guidance encourages use of PopPK models to predict drug behavior in subpopulations underrepresented in clinical trials, generating clinical pharmacology sections of drug labeling that provide half-life estimates across GFR ranges and in pediatric age categories. These labeled parameters are the authoritative source for the drug-specific elimination kinetics used in this tool.

This elimination timeline visualizer provides clinicians, pharmacists, and patients with a clear graphical representation of predicted drug concentration decline after the last dose, grounded in FDA-approved pharmacokinetic parameters. By marking clinically relevant milestones (number of half-lives elapsed) against a real-time calendar projection from the specified last dose, the tool supports informed decisions about washout timing, procedure scheduling, and drug transition planning. All predictions are population-level estimates and should be refined by therapeutic drug monitoring when individual patient pharmacokinetic variability is clinically consequential.

FAQ

When is it clinically necessary to wait for drug elimination?

Drug elimination timing is clinically critical in several scenarios. Before switching from a reversible MAO inhibitor to an SSRI or tricyclic antidepressant, a washout of 2 weeks is required (5 half-lives for most MAOIs) to prevent serotonin syndrome. Fluoxetine, with an active metabolite norfluoxetine half-life of 4–6 days, requires a 5-week washout before initiating an MAOI. Before invasive procedures with bleeding risk, anticoagulants must be held for durations based on their half-lives and procedural bleeding risk; apixaban (t½ 12 hours) requires 24 hours for low-risk procedures and 48 hours for high-risk procedures. For fertility treatment and pregnancy planning, teratogenic drugs such as isotretinoin (t½ 20 hours, fat-stored retinoids) require cessation one month before conception.

Why does plasma concentration graph as a straight line on a semi-log plot?

First-order elimination kinetics produce an exponential decrease in drug concentration over time: C(t) = C₀ × e^(−k_el × t). When plotted on a logarithmic y-axis versus linear time (semi-logarithmic plot), the exponential function transforms into a straight line with slope equal to −k_el. This linearization is the foundation for calculating half-life from concentration-time data using least-squares linear regression of the log-linear terminal phase. Departure from linearity on the semi-log plot indicates multi-compartment kinetics (initial concave curvilinear decline reflecting distribution phase, followed by terminal linear elimination phase), or concentration-dependent (non-linear) kinetics.

How do metabolites affect the elimination timeline?

Pharmacologically active metabolites with longer half-lives than the parent compound can extend drug effects well beyond the elimination of the parent drug. Diazepam (t½ 20–70 hours) is metabolized to nordiazepam (t½ 36–200 hours) and oxazepam (t½ 4–15 hours), with nordiazepam's long half-life responsible for prolonged sedation and accumulation on repeated dosing. Codeine is converted to morphine (active) and to morphine-6-glucuronide (M6G), which accumulates in renal failure. Prodrugs such as clopidogrel and tamoxifen require metabolic activation; their elimination timelines must track the active metabolite, not just the parent compound.

How does renal or hepatic disease alter elimination kinetics?

Renal impairment reduces the clearance of renally eliminated drugs and active metabolites, prolonging their effective half-lives in proportion to the degree of GFR reduction. For drug-specific estimation, published dosing guidelines provide predicted half-life at specific eGFR cutoffs. Hepatic impairment reduces hepatic clearance in proportion to loss of functional hepatocyte mass and CYP enzyme activity. Child-Pugh and MELD scores are used to stage hepatic impairment, and FDA pharmacokinetic guidelines use Child-Pugh classes A, B, and C to stratify PK studies in hepatically impaired patients. For drugs primarily cleared by either organ, elimination timeline predictions must be adjusted using impairment-specific PK parameters when available.

How long after stopping a drug can it be detected in urine or blood?

Drug detection windows in biological matrices depend on the drug's elimination half-life, the detection threshold of the analytical method, the specimen type (blood, urine, hair, oral fluid), and metabolic factors including urine pH. Urine is the primary matrix for workplace and forensic drug testing; detection windows range from 1–2 days for short-half-life drugs to 4–12 weeks for cannabis in heavy chronic users due to lipophilic THC accumulation in adipose tissue. Hair analysis can detect drug exposure up to 90 days retrospectively. Oral fluid testing correlates more closely with recent use (hours to days). The clinical half-life and the analytical detection window are distinct concepts: clinical activity ceases before analytical detectability is lost for most drugs.