The sildenafil concentration-time profile shows how plasma concentration changes after administration as the drug enters systemic circulation, reaches a maximum and then declines through distribution, metabolism and elimination. Unlike a single PK number, the complete curve shows how these processes interact across time.
Current sildenafil labeling provides a useful reference profile after a single 100 mg oral dose in healthy male volunteers. In that profile, plasma concentration rises rapidly toward a peak at about the first hour and then falls progressively across the following hours, reaching only a small fraction of the peak concentration by 24 hours.
This page focuses on reading that complete sildenafil profile rather than redefining its individual parameters. Cmax, Tmax and AUC can all be located on the same curve, while the underlying processes remain covered separately on the absorption, distribution, metabolism and clearance pages.
A sildenafil concentration-time curve plots measured plasma sildenafil concentration on the vertical axis against elapsed time after administration on the horizontal axis. Each plotted point represents a concentration measured from a plasma sample collected at a defined study time.
The resulting shape reflects the net effect of several simultaneous processes. Absorption adds sildenafil to systemic circulation, distribution moves drug between plasma and tissues, and metabolism plus clearance reduce circulating parent-drug concentration.
For a concrete reference, sildenafil labeling includes a mean curve after a single 100 mg oral dose in healthy male volunteers. The profile rises sharply during the first hour, reaches a peak of roughly 440 to 450 ng/mL in the published figure and then declines across the remainder of the 24-hour sampling period. The broader framework is covered in the sildenafil pharmacokinetics framework.
| Curve Element | What It Represents |
|---|---|
| X-axis | Elapsed time after administration. |
| Y-axis | Measured plasma sildenafil concentration. |
| Rising phase | Net systemic input exceeds concentration-lowering processes. |
| Peak region | Highest observed concentration and its timing. |
| Declining phase | Distribution and elimination exceed continuing drug input. |
The sildenafil concentration-time profile can be divided conceptually into a rising phase, peak region and declining phase, with a later terminal region used to characterize elimination-related behavior. These regions are useful for interpretation even though the underlying processes overlap continuously.
In the labeled single-dose profile, the early rise is rapid: concentration increases steeply during approximately the first hour. After the maximum, the curve does not fall vertically; it declines progressively as systemic input diminishes and distribution and elimination increasingly dominate.
The late portion of the curve is much flatter than the early post-peak decline. That shape is consistent with sildenafil's terminal half-life of about 4 hours, although the terminal half-life is a derived PK parameter rather than simply the time required for the whole plotted curve to disappear.
| Phase | Dominant Interpretation |
|---|---|
| Early rising phase | Absorption supplies sildenafil to systemic circulation faster than it is being removed. |
| Peak region | Net concentration reaches its observed maximum, usually around the first hour in the fasted reference profile. |
| Post-peak decline | Continuing input falls while distribution and elimination increasingly lower plasma concentration. |
| Terminal region | Late decline is used to characterize terminal elimination behavior. |
The rising portion of the curve occurs while sildenafil is appearing in systemic circulation faster than distribution and elimination can lower the measured plasma concentration. The slope of this region therefore reflects net systemic input rather than absorption operating in isolation.
Sildenafil is rapidly absorbed after oral administration. Under fasted conditions, labeling reports maximum observed concentrations within 30 to 120 minutes, with a median Tmax of approximately 60 minutes. This rapid early appearance explains the steep ascending portion of the reference concentration-time curve.
The height and timing of that rise can change when gastrointestinal conditions alter absorption. The mechanisms behind oral input, dissolution and uptake are explored in detail on the sildenafil absorption page.
| Factor | Potential Curve Effect |
|---|---|
| Absorption rate | Changes the steepness and timing of the early concentration rise. |
| Bioavailability | Influences the amount of unchanged sildenafil reaching systemic circulation. |
| Food | Can make the early curve rise more slowly and shift the peak later. |
The peak region is where the observed sildenafil concentration reaches its highest measured value. Cmax identifies the vertical height of that maximum, whereas Tmax identifies its location on the time axis.
In the labeled mean concentration-time profile after a single 100 mg dose in healthy male volunteers, the curve peaks near the first hour at roughly 440 to 450 ng/mL. The more general fasted labeling data place Tmax within 30 to 120 minutes, with a median of approximately 60 minutes.
Those values provide useful orientation but are not universal expected concentrations for every exposure. Dose, food, metabolic inhibition, organ function and study design can all shift the curve. The dedicated sildenafil Cmax page and sildenafil Tmax page examine those peak parameters separately.
| Parameter | Curve Question |
|---|---|
| Cmax | How high is the observed concentration peak? |
| Tmax | When does that peak occur? |
| Reference 100 mg profile | Peak near approximately 1 hour and roughly 440–450 ng/mL in healthy male volunteers. |
| AUC | How much integrated exposure lies beneath the entire profile? |
After Cmax, measured sildenafil concentration begins to decline because systemic input no longer exceeds the processes lowering plasma concentration. The descending curve reflects distribution out of plasma, metabolic transformation of parent sildenafil and systemic clearance operating together.
The labeled 100 mg reference profile shows a relatively steep early decline after the peak followed by a progressively flatter late phase. Approximate visual values from the published curve are around 175 ng/mL at 4 hours, around 75 to 80 ng/mL at 6 hours, around 20 ng/mL at 12 hours and only a few ng/mL by 24 hours.
Those plotted values are descriptive of the particular mean healthy-volunteer profile rather than concentration targets. The relationship between decline and removal efficiency is examined on the sildenafil clearance page, while the time scale of terminal decline is covered on the sildenafil half-life page.
| Process | Role in Curve Decline |
|---|---|
| Distribution | Changes plasma concentration as sildenafil partitions between plasma and tissues. |
| Metabolism | Transforms parent sildenafil, predominantly through CYP3A-mediated pathways. |
| Clearance | Quantifies the efficiency of parent-drug removal. |
| Terminal half-life | Approximately 4 hours in current labeling. |
AUC is the mathematical area beneath the sildenafil concentration-time curve over a defined interval. Instead of selecting one concentration point, it integrates the entire sequence of measured and estimated concentrations across time.
This explains why the tallest curve is not necessarily the curve with the greatest total exposure. A profile can have a relatively high Cmax but decline rapidly, while another can have a lower peak yet sustain concentrations long enough to produce a comparable or greater AUC.
Sildenafil labeling describes pharmacokinetics as dose-proportional over the recommended dose range, meaning exposure measures generally increase with dose under comparable study conditions. The detailed calculation and interpretation of the area itself belongs on the sildenafil AUC page.
| Curve Feature | Related PK Metric |
|---|---|
| Peak height | Cmax |
| Peak location | Tmax |
| Area beneath the complete profile | AUC |
| Late decline | Terminal elimination and half-life context |
The full curve contains several different dimensions of sildenafil exposure at once. Its early slope shows how quickly concentrations appear, its maximum shows peak exposure, its area summarizes integrated exposure and its declining region shows how circulating concentrations fall after systemic input decreases.
No single summary parameter can reconstruct every feature of the profile. Two curves can share a similar AUC while differing in peak height or peak timing, and two curves with similar Cmax can differ substantially in how long concentrations remain elevated.
The concentration-time curve is therefore the common data source from which Cmax, Tmax and AUC are interpreted rather than a fourth independent exposure metric. The integrated exposure concept is explained on the sildenafil exposure page.
| Exposure Question | Curve Feature |
|---|---|
| How rapidly does sildenafil appear? | Early rising profile |
| How high is the peak? | Cmax |
| When does the peak occur? | Tmax |
| How much exposure accumulates? | AUC |
| How does concentration decline? | Post-peak and terminal portions of the curve |
The sildenafil concentration-time curve describes pharmacokinetics: the concentration of drug measured in plasma at different times. It does not directly plot erection response, vascular response or any other pharmacodynamic endpoint.
The distinction matters because a plasma-concentration maximum does not automatically represent the maximum clinical effect, and the disappearance of most sildenafil from plasma does not provide an exact timestamp for disappearance of every pharmacological effect. Concentration and biological response are related through pharmacodynamics rather than being identical curves.
For example, labeling describes certain physiological observations near the period of peak plasma levels, but that temporal association does not convert the complete PK profile into an effect-time curve. The relationship between concentration and biological response belongs on the sildenafil pharmacodynamics page.
| Curve Type | What It Describes |
|---|---|
| PK concentration-time curve | Measured plasma sildenafil concentration across time. |
| Pharmacodynamic relationship | How biological response relates to drug exposure. |
| Clinical duration | Persistence of an observed effect, which cannot be read directly from plasma concentration alone. |
A high-fat meal provides a concrete example of how the shape of the sildenafil curve can change. Current labeling reports a mean delay in Tmax of approximately 60 minutes and a mean reduction in Cmax of approximately 29% compared with fasted administration.
Graphically, that means the early curve is shifted toward a slower rise and a later, lower peak. This is different from simply scaling the entire fasted curve downward by 29%, because Cmax and Tmax describe particular aspects of the profile rather than every concentration across time.
Food effects should consequently be interpreted by comparing the shape and multiple PK parameters together. Detailed quantitative meal findings remain on the sildenafil food-effects page.
| Food-Related Change | Effect on Curve |
|---|---|
| Tmax delay | Mean peak shifts approximately 60 minutes later. |
| Cmax reduction | Mean peak height decreases by approximately 29%. |
| Curve interpretation | The early profile becomes later and lower rather than undergoing a simple uniform shift. |
A pharmacokinetic concentration-time curve is reconstructed from discrete plasma samples rather than measured continuously. Investigators therefore need enough early samples to capture the rapid sildenafil rise and enough later samples to characterize the post-peak and terminal regions.
This matters for sildenafil because Tmax can occur as early as 30 minutes in fasted studies. Sparse early sampling could underestimate Cmax or identify Tmax imprecisely, while an observation period that ends too early can provide insufficient information about the later declining profile.
The plotted curve is therefore partly a property of biological pharmacokinetics and partly a representation created from the study's sampling design. Cmax, Tmax, AUC and terminal half-life should always be read together with information about dose, sampling schedule and population.
| Sampling Feature | Interpretation Impact |
|---|---|
| Dense early sampling | Improves characterization of the rapid rise, Cmax and Tmax. |
| Adequate late sampling | Improves characterization of terminal concentration decline. |
| Sparse sampling | Can reduce precision of peak and terminal-phase interpretation. |
| Long enough observation period | Supports more complete AUC and elimination characterization. |
The labeled healthy-volunteer 100 mg curve is a useful reference profile, but individual sildenafil curves do not all have the same height or shape. Absorption conditions, systemic availability, distribution and clearance vary between people and between study conditions.
Changes in clearance can reshape much more than the terminal end of the curve. Severe renal impairment and mild-to-moderate hepatic impairment increase sildenafil exposure in labeling data, while CYP3A inhibition can produce even larger changes in peak and integrated concentrations.
An especially clear example is ritonavir coadministration: labeling reports markedly increased sildenafil exposure and plasma levels around 200 ng/mL even at 24 hours, compared with only about 5 ng/mL when sildenafil was administered alone in that interaction study. This shows how dramatically the entire curve can change rather than merely shifting Cmax. Broader sources of variation are covered on the sildenafil PK variability page.
| Source of Variation | Possible Curve Effect |
|---|---|
| Absorption conditions | Change the early rise and peak timing. |
| Food | Produces a later and lower peak in the labeled high-fat meal comparison. |
| Reduced clearance | Can raise concentrations and increase later exposure. |
| CYP3A inhibition | Can increase both peak and sustained sildenafil concentrations. |
| Study population | Can shift the average concentration profile relative to healthy-volunteer reference data. |
A useful reading of the sildenafil curve starts at the left and follows the balance of competing processes. Concentration first rises rapidly as oral absorption supplies drug to the circulation, reaches Cmax at Tmax, then declines as systemic input falls below distribution and elimination.
The labeled 100 mg healthy-volunteer profile gives that framework concrete scale: a rapid peak near the first hour at roughly 440 to 450 ng/mL, a substantial decline over the next several hours and concentrations near only a few ng/mL at 24 hours. Those values describe one standardized mean study profile rather than a target or prediction for an individual.
No single point explains the full profile. Cmax describes peak height, Tmax describes peak timing, AUC captures integrated exposure and terminal half-life characterizes late decline. For the complete ADME overview, the sildenafil pharmacokinetics hub connects those curve features with absorption, distribution, metabolism and clearance.
| Curve Question | Relevant PK Concept |
|---|---|
| How does concentration increase? | Absorption and systemic input |
| Where is the maximum concentration? | Cmax |
| When does the peak occur? | Tmax |
| How much exposure accumulates? | AUC |
| Why does concentration decline? | Distribution, metabolism and clearance |
| What characterizes late decline? | Terminal half-life |
A sildenafil concentration-time curve plots measured plasma sildenafil concentration against time after administration, showing the rapid rise, observed peak and subsequent decline.
In a labeled mean profile after a single 100 mg oral dose in healthy male volunteers, sildenafil concentration rises rapidly to a peak near the first hour and then declines progressively over the following 24 hours. The exact curve depends on dose, population and study conditions.
Under fasted conditions, labeling reports maximum observed plasma concentrations within 30 to 120 minutes, with a median Tmax of approximately 60 minutes.
Cmax is the highest observed point on the concentration-time profile, while AUC is the integrated area underneath the full curve over a defined interval.
After the peak, systemic input decreases while distribution, metabolism and clearance increasingly dominate, causing measured parent sildenafil concentration to decline.
Yes. A high-fat meal produces a later and lower peak in labeling data, while metabolic interactions that reduce sildenafil clearance can increase peak concentrations and prolong elevated plasma exposure.