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Caesium in the body has a biological half-life of about one to four months. Mercury (as methylmercury) in the body has a half-life of about 65 days. Lead in the blood has a half life of 28–36 days. [29] [30] Lead in bone has a biological half-life of about ten years. Cadmium in bone has a biological half-life of about 30 years.
The tables below contain a sample list of benzodiazepines and benzodiazepine analogs that are commonly prescribed, with their basic pharmacological characteristics, such as half-life and equivalent doses to other benzodiazepines, also listed, along with their trade names and primary uses.
Context-sensitive half-life or context sensitive half-time is defined as the time taken for blood plasma concentration of a drug to decline by one half after an infusion designed to maintain a steady state (i.e. a constant plasma concentration) has been stopped. The "context" is the duration of infusion.
Triazolam is usually used for short-term treatment of acute insomnia and circadian rhythm sleep disorders, including jet lag. It is an ideal benzodiazepine for this use because of its fast onset of action and short half-life. It puts a person to sleep for about 1.5 hours, allowing its user to avoid morning drowsiness.
Midazolam is a short-acting benzodiazepine in adults with an elimination half-life of 1.5–2.5 hours. [13] In the elderly, as well as young children and adolescents, the elimination half-life is longer. [44] [66] Midazolam is metabolised into an active metabolite alpha-hydroxymidazolam.
When radionuclides are used pharmacologically, for example in radiation therapy, they are eliminated through a combination of radioactive decay and biological excretion.An effective half-life of the drug will involve a decay constant that represents the sum of the biological and physical decay constants, as in the formula:
The unchanged drug was 96% bound to plasma proteins. The blood-level decline of the parent drug was biphasic, with the short half-life ranging from 0.4 to 0.6 hours and the terminal half-life from 3.5 to 18.4 hours (mean 8.8 hours), depending on the study population and method of determination. [62]
Remifentanil's short context-sensitive half-life makes it ideal for intense pain of short duration. As such, it has been used for analgesia in labor successfully; however, it is not as effective as epidural analgesia. [10] In combination with propofol, remifentanil is used for anesthesia of patients undergoing electroconvulsive therapy. [11]