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Sometimes drugs are formulated in an inactive form that is designed to break down inside the body to form the active drug. These are called prodrugs.The reasons for this type of formulation may be because the drug is more stable during manufacture and storage as the prodrug form, or because the prodrug is better absorbed by the body or has superior pharmacokinetics (e.g., lisdexamphetamine).
l-DOPA is produced from the amino acid l-tyrosine by the enzyme tyrosine hydroxylase. l-DOPA can act as an l-tyrosine mimetic and be incorporated into proteins by mammalian cells in place of l-tyrosine, generating protease-resistant and aggregate-prone proteins in vitro and may contribute to neurotoxicity with chronic l-DOPA administration. [10]
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug ...
Drug delivery to the brain is the process of passing therapeutically active molecules across the blood–brain barrier into the brain. This is a complex process that must take into account the complex anatomy of the brain as well as the restrictions imposed by the special junctions of the blood–brain barrier.
The primary active metabolites of amphetamine are 4-hydroxyamphetamine and norephedrine; [12] at normal urine pH, about 30–40% of amphetamine is excreted unchanged and roughly 50% is excreted as the inactive metabolites (bottom row). [3] The remaining 10–20% is excreted as the active metabolites. [3]
A dopamine molecule consists of a catechol structure (a benzene ring with two hydroxyl side groups) with one amine group attached via an ethyl chain. [14] As such, dopamine is the simplest possible catecholamine, a family that also includes the neurotransmitters norepinephrine and epinephrine. [15]
Testosterone, via its active metabolite 3α-androstanediol, is a potent positive allosteric modulator of the GABA A receptor. [ 150 ] Testosterone has been found to act as an antagonist of the TrkA and p75 NTR , receptors for the neurotrophin nerve growth factor (NGF), with high affinity (around 5 nM).
Besides the preceding metabolites, selegiline-N-oxide and formaldehyde are also known to be formed. [28] More than 40 minor metabolites of selegiline have been either detected or proposed. [28] Due to the amphetamine metabolites of selegiline, people taking selegiline may test positive for "amphetamine" or "methamphetamine" on drug screening tests.