Tacrine is a centrally acting acetylcholinesterase inhibitor and indirect cholinergic agonist. It was the first centrally acting cholinesterase inhibitor approved for the treatment of Alzheimer's disease, and was marketed under the trade name Cognex. Tacrine (9-amino-1,2,3,4-tetrahydroacridine) is a low-molecular-weight, lipophilic heterocycle that crosses the blood brain barrier to increase synaptic acetylcholine through reversible inhibition of acetylcholinesterase. It is absorbed orally, undergoes extensive hepatic metabolism primarily via cytochrome P450 1A2 to hydroxylated metabolites that are subsequently conjugated, and is eliminated mainly as metabolites in urine. Clinically important properties include a relatively short plasma half-life requiring multiple daily dosing historically, a narrow therapeutic index with dose-related hepatotoxicity observed in a subset of patients, and potential for drug interactions with other CYP1A2 substrates or inhibitors.
The impurity profile for tacrine API and formulated material typically reflects oxidative metabolites and related synthetic byproducts, most commonly 1-hydroxytacrine and other mono-hydroxylated species, potential N-oxide and deaminated derivatives, trace polymeric or dimeric species from manufacturing, and low levels of residual solvents and inorganic impurities. Typical quality control targets used in small-molecule APIs are assay purity greater than or equal to 98.0 percent, individual related substances commonly limited to 0.1 to 0.5 percent depending on impurity identification and toxicological qualification, and total related substances commonly limited to 1.0 percent or at most 2.0 percent for legacy compounds where full qualification is established. Genotoxic or mutagenic impurities, if present, should meet ICH M7 and related thresholds and be controlled to parts-per-million levels; residual solvents and heavy metals should comply with ICH Q3C and Q3D limits.
Tacrine inhibits acetylcholinesterase in the central nervous system, reducing hydrolysis of acetylcholine and thereby increasing acetylcholine levels at cholinergic synapses; its indirect cholinergic agonist effect enhances cholinergic neurotransmission associated with cognition.
Tacrine was used to symptomaticly treat cognitive decline in Alzheimer’s disease by enhancing central cholinergic transmission; it was not a disease modifying therapy but provided modest short-term cognitive benefit in some patients.
Tacrine use declined and it was withdrawn or discontinued in many markets primarily because of dose-related hepatotoxicity requiring routine liver monitoring, limited clinical benefit relative to safety risks, and the development of newer cholinesterase inhibitors with improved safety and dosing profiles.
Another name for tacrine is 9-amino-1,2,3,4-tetrahydroacridine, and it was marketed under the trade name Cognex.
