Last reviewed by Editorial Team on August 28th, 2018.
How long can Gabapentin be detected in your urine, blood, saliva?
Gabapentin, also known as Neurontin, is a drug that acts on the central nervous system. It was widely used for the treatment of epilepsy and relief of neuropathic pain but it has now been replaced by more effective and potent drugs such as carbamazepine.
Gabapentin is however popularly used for recreational purposes. It is used for recreational purposes as a social drug and in the treatment of bipolar disorder due to its action as a central nervous system depressant.
Gabapentin is a unique drug because it goes through the body without being metabolized. It is an analogue of GABA (gamma amino butyric acid), which is used in anticonvulsant therapy to treat partial seizures, ALS (amyotrophic lateral sclerosis), refractory seizures, painful neuropathies such as trigeminal neuralgia, multiple sclerosis, tremors, dementia, restless leg syndrome and bipolar disorders.
Gabapentin is highly lipid soluble (lipophilic) and is not metabolized by the liver. It does not bind to proteins and has a clearance rate of 190ml/min. It is excreted by the kidneys via the urine as an unchanged drug.
It has a half- life of 5 to 7 hours and is unaltered by the dose. 50% of gabapentin is cleared from the system within 5 to 7 hours and it can stay in the body for up to 1.15 to 1.60 days after the final dose, meaning that the drug is completely excreted from the system after approximately 2 days after ingestion. However, in certain situations such as renal impairment, Gabapentin takes several days to a week to get cleared from the system following ingestion.
Several variables affect the rate of clearance of Neurontin from the system. These variables include age of the patient, dosage of the drug, health stats of the kidneys, body mass of the user and urinary pH. These factors can either potentiate the excretion of the drug or delay its excretion.
Routes of Gabapentin excretion
The main excretion route of Neurontin is through the kidneys. This is because of the fact that Neurontin is not metabolized in the liver. This means that there are no active metabolites of the drug that bind to other sites in the body, therefore, the most reliable method of detection is by urine drug test.
However, trace amounts can be present but remain undetectable by conventional test methods. It must be noted that despite this, the drug can be detected from the bloodstream, but this undertaking is expensive and less cost effective than the urine drug test.
The detection of gabapentin in the bloodstream is more evident in cases of renal impairment. This can be explained by the fact that in renal impairment, the drug is not effectively eliminated and thus lingers within the body for an extended period. During this period, the drug becomes more detectable via the bloodstream.
The plasma concentrations of the drug will be enhanced in such situations and the therapeutic effects of the drug will be more pronounced. In chronic users of gabapentin, the drug has been reported to be detectable in hair follicles. The detection of the drug in hair follicles is a great indicator for determining when the user took their last dose.
Clearance of Gabapentin
Gabapentin is effectively eliminated from the system via the kidneys, through the urine. The rate of clearance is directly proportional to creatinine clearance. The Neurontin present in gabapentin is detectable in the urine within 5 to 7 hours from ingestion. The time taken for half of the drug to be excreted is known as half- life. This implies that it takes 5 to 7 hours for 50% of the drug to be excreted from the system.
Therefore, the drug will take approximately 18 to 22 hours to be completely eliminated from the system. It must be noted that this excretion time applies to healthy individuals, with kidneys that are in good health.
In diseased states of the kidneys, the elimination half- life is increased, meaning that it takes longer for half of the drug to be excreted from the system. The clearance of gabapentin is 3.5 hours in patients undergoing renal dialysis. On non-dialysis days, the excretion timeframe goes up to 136 hours.
Gabapentin is not metabolized by the liver, therefore, a large quantity of the drug can be detected within a short period of time from ingestion. However, depending on the influence of the factors that affect the excretion rate of the drug, the elimination time can take longer than 22 hours.
It can take up to 2 days to get completely cleared from the circulation, or a week for users that have been taking larger doses of the drug. The increased excretion timeframe is also seen in chronic users of Gabapentin.
Gabapentin appears as an unchanged drug because the liver does not metabolize it. This means that active metabolites of the drug do not linger in the circulation after ingestion of the drug. It also implies that the enzymatic action is not applicable to gabapentin hence, gabapentin excretion is not significantly induced or inhibited by liver enzymes.
In hepatic impairment, the metabolism and subsequent excretion of the drug is not significantly affected. In normal state of the kidneys, its complete elimination takes place within 2 days but can vary and go on in the circulation for up to 4 days to a week.
There are several variables that have an effect on the elimination timeframe of gabapentin from the system. These variables can either cause the drug to be cleared from the system at a faster rate or they can slow down its clearance. These variables influence the difference in clearance rates in different individuals and they can also show different excretion patterns in the same individual, at different times.
Variables influencing the clearance of Gabapentin
Gabapentin takes longer to be cleared in renal impairment. This is because in renal insufficiency, the clearance rate is greatly diminished due to impaired filtration rate and impaired permeability of the renal tubules which facilitate the excretion the drug.
In such cases, the drug can be excreted via hemodialysis. Gabapentin is not significantly affected by hepatic impairment. This is because it is not metabolized by the liver, meaning it makes its way to the kidneys, without being altered by the liver and its enzymes. Gabapentin clearance from the system is influenced by a number of factors.
In normal renal function, gabapentin is completely cleared from the system within 2 days from ingestion of the last dose. However, in renal impairment, there is higher plasma concentration of Neurontin, with an evident increase in elimination half- life. It can take up to 20 to 32 days for the drug to be cleared from the system, in such circumstances.
The individual factors or variables that determine or influence the excretion rate of gabapentin include age, body mass, frequency of hydration, urinary pH and dosage. In the elderly, the elimination half- life is increased due to age related renal impairment. However, a younger individual will clear the drug much faster because of the efficient function of the kidneys.
Clearance in taller and fatter individuals is faster. The frequency of hydration influences the excretion rate of the drug because the more hydrated one is, the faster the glomerular filtration rate. This means that the drug will be cleared from the system at a much faster rate than would be in an individual who is less hydrated.
The urinary pH also influences the clearance rate of gabapentin. With high alkalinity of urine, there is slower clearance of gabapentin. Alkaline urine promotes reabsorption and recirculation prior to systemic excretion, thereby, leading to increased elimination half- life of substances. Acidic urine inhibits reabsorption and maximizes clearance speed. Diet of high acidity promotes clearance of gabapentin. Foods rich in acid content include oranges and lemons.
The dosage of gabapentin varies from 300 mg to 3600 mg.The higher the dosage, the longer it will take to get cleared from the system because of compromise in excretion efficiency of the kidneys. This means that an individual taking a dose of 3600 mg gabapentin will take longer to have it eliminated from the system than will an individual taking the 300mg dose.
Term of administration of gabapentin, whether acute or chronic cases also determine how long it will take to be cleared from the system. The longer one has been taking gabapentin, the more the drug will circulate within the system and the longer it will take for it to be cleared from the system.
Other variables such as race and gender do not significantly influence the excretion rate of gabapentine.
Gabapentin is a drug that acts primarily on the brain. The active ingredient of gabapentin is Neurontin. Gabapentin is used recreationally to depress the central nervous system. It is used in the treatment of partial seizures and neuropathies. Once ingested, it is eliminated via the kidneys, without being metabolized by the liver.
This means that gabapentin is not affected by the action of the hepatic enzymes, which would either increase or reduce the amount of the drug in the system by inhibition or induction. Therefore, its active metabolites are undetectable in the circulatory system, within a short space of time. The elimination half- life of gabapentin is 5 to 7 hours, with total elimination taking place within a space of 2 days.
Complete excretion of the drug from the body can take up to 19 hours to 22 hours in normal renal function. However, in chronic users and larger doses, it takes longer to get eliminated from the system.
There are a number of variables that influence the excretion rate of gabapentin. These include kidney function, urinary pH, acid content of the diet, body mass, dosage and age of the user.
- Semple D, Smith R et al. Oxford Handbook Of Psychiatry (2005) 1st Edition, Oxford University Press, Oxford, UK.
- Hahn RK, Abers L et al. Psychiatry (2003-2004 Edition). Current Clinical Strategies Publishing. California, USA.
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