The drugs elimination time is dependent on many factors. They can bring a considerable change in the duration of clearance of Fentanyl from the body. Such variables play a major role when more accurate durations are required as in detoxification centers for the drugs.
Individual Factors: The following individual attributes contribute to the changes in the time intervals in different individuals.
- Age:The half-life in elderly people is about 15 hours in comparison to almost 5 hours in younger individuals. This shows the elderly may require up to 4 days for complete excretion of the intravenous drug. It is as a result of age related factors like low tissue perfusion, low plasma proteins, hepatic, and renal dysfunction.
- Body fat: Fentanyl has a propensity for fatty tissues so it will get accumulated in adipose tissues of the body.
- Genetics: Fentanyl is metabolized by the CYP3A4 enzymes. Some people have a poor metabolism due to the inefficiency of enzymes. Many people have powerful functioning of enzymes which leads to a faster metabolism.
- Hydration:A proper intake of water is necessary to regulate the flow of drug through the kidneys into the urine. Therefore, individuals who stay optimally hydrated tend to eliminate the drug at faster rates.
- Hepatic Functions:Any disease condition like cirrhosis can affect the rate of metabolism. The hepatic enzymes play a key role in the processing of drug. Any factor disturbing hepatic enzymes can alter the rate of metabolism.
- Metabolic Rate:It is also known as BMR. People with a high BMR have a more rapid metabolism and more burning of fat sources. These both act to speed up the elimination process.
Route of Administration: This acts as an important factor in determining the time of elimination. As already discussed, the half-life of an intravenous route is the shortest, followed by transmucosal and transdermal. So the full elimination time is different for all these routes.
Dosages: The higher doses are related to storage and slow metabolism. A person continuously abusing Fentanyl would have developed tolerance and increased-up the doses for euphoric effects.
Frequency: More frequent use is associated with high plasma concentration of Fentanyl and slow excretion from the body.
Co-administered agents: Any medicines or supplements that act as CYP3A4 enhancers and inhibitors will increase or decrease the metabolism respectively. Carbamazepine, Phenytoin, phenobarbital, and rifampicin act as inducers. Ketoconazole, Ritonavir, and Clarithromycin act as CYP3A4 inhibitors.