Studies on the disposition of radioactive protriptyline in human test subjects showed significant plasma levels within 2 hours, peaking at 8 to 12 hours, then declining gradually.Urinary excretion studies in the same subjects showed significant amounts of radioactivity in 2 hours. The rate of excretion was slow. Cumulative urinary excretion during 16 days accounted for approximately 50% of the drug. The fecal route of excretion did not seem to be important.Protriptyline has uniquely low dosing among TCAs, likely due to its exceptionally long terminal half-life. It is used in dosages of 15 to 40 mg/day, whereas most other TCAs are used at dosages of 75 to 300 mg/day. The maximum dose is 60 mg/day. Therapeutic levels of protriptyline are typically in the range of 70 to 250 ng/mL (266-950 nmol/L), which is similar to that of other TCAs

Chemistry
Protriptyline is a tricyclic compound, specifically a dibenzocycloheptadiene, and possesses three rings fused together with a side chain attached in its chemical structure. Other dibenzocycloheptadiene TCAs include amitriptyline, nortriptyline, and butriptyline. Protriptyline is a secondary amine TCA, with its N-methylated relative amitriptyline being a tertiary amine. Other secondary amine TCAs include desipramine and nortriptyline. The chemical name of protriptyline is 3-(5H-dibenzo[a,d][7]annulen-5-yl)-N-methylpropan-1-amine and its free base form has a chemical formula of C19H21N1 with a molecular weight of 263.377 g/mol. The drug is used commercially mostly as the hydrochloride salt; the free base form is not used. The CAS Registry Number of the free base is 438-60-8 and of the hydrochloride is 1225-55-4. History
Protriptyline was developed by Merck.
Lusutrombopag, sold under the brand name Mulpleta among others, is a medication that has been developed for certain conditions that lead to thrombocytopenia (abnormally low platelet counts) such as thrombocytopenia associated with chronic liver disease in patients prior to elective invasive procedures. It is being manufactured and marketed in Japan by Shionogi. It was approved by the U.S. Food and Drug Administration (FDA) in July 2018, and NICE in January 2020.It was approved for medical use in the European Union in February 2019. References
External links
"Lusutrombopag". Drug Information Portal. U.S. National Library of Medicine.