Extremely slow metabolism of amitriptyline but normal metabolism of imipramine and desipramine in an extensive metabolizer of sparteine, debrisoquine, and mephenytoin.
A 34-year-old man with bipolar manic depressive illness suffered from severe adverse effects during treatment with amitriptyline, 50 mg/day. It was subsequently shown that the patient was a slow metabolizer of amitriptyline. However, he tolerated a dose of 200 mg of imipramine/day, which was necessary in order to reach a therapeutic level of about 900 nM for imipramine plus desipramine. Since both antidepressants are subject to the genetic sparteine/debrisoquine oxidation polymorphism, the patient was phenotyped with sparteine. The test performed during paroxetine treatment indicated that the patient was a poor metabolizer. Subsequent tests performed during a drug-free period, however, showed the patient to be an extensive metabolizer, with a sparteine metabolic ratio (MR) of 1.7 and 2.8 and debrisoquine MR of 2.3. It was subsequently shown that paroxetine is a potent, competitive inhibitor of 1'-hydroxybufuralol formation in a human liver microsome preparation (K1 approximately 800 nM). This patient thus illustrates two problems: (a) the erroneous phenotyping due to concurrent medication, and (b) the existence of a very slow amitriptyline elimination apparently not related to the sparteine/debrisoquine oxidation polymorphism.
Brøsen
K
K
Department of Clinical Pharmacology, Odense University, Denmark.
Gram
L F
LF
Kragh-Sørensen
P
P
D000284:Administration, Oral; D000328:Adult; D000639:Amitriptyline / Q000097:blood / Q000378:metabolism* / Q000627:therapeutic use; D000929:Antidepressive Agents, Tricyclic / Q000097:blood; D002855:Chromatography, Thin Layer; D003647:Debrisoquin / Q000097:blood / Q000378:metabolism*; D003891:Desipramine / Q000031:analogs & derivatives / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D004347:Drug Interactions; D006801:Humans; D007099:Imipramine / Q000097:blood / Q000378:metabolism*; D008297:Male; D008617:Mephenytoin / Q000097:blood / Q000378:metabolism*; D010641:Phenotype; D011802:Quinidine / Q000494:pharmacology; D013034:Sparteine / Q000097:blood / Q000378:metabolism*
D000929:Antidepressive Agents, Tricyclic; D000639:Amitriptyline; D013034:Sparteine; D011802:Quinidine; D007099:Imipramine; D008617:Mephenytoin; D003891:Desipramine; C028653:2-hydroxydesipramine; D003647:Debrisoquin