In this file you will find several links that will take you to individual clinical studies that were conducted relative to the
the CYP 2D6 factor.   Why are these studies relevant to you?  Let us explain:

Response to drugs can vary between individuals and between different ethnic populations.  The biological variables
(age, gender, disease and genetics), along with cultural and environmental factors which contribute to these variations are taken into account in these clinical studies.

Individuals vary in their ability to metabolize (detoxification & elimination), drugs due to polymorphism (genetic variance), of certain enzymes.  Genetic polymorphism of drug metabolizing enzymes (DME), can lead to severe toxicity or therapeutic failure.  The most widely studied of the genetic polymorphisms are those involving cytochrome P450 2D6 (CYP2D6), and (CYP2C19).  Of these two, the CYP2D6 is responsible for metabolizing antidepressants and antipsychotic drugs, amongst others. 

The population can be classified into three phenotypes (signifying how an individual metabolizes a certain drug).  Extensive Metabolism (EM) of a drug is characteristic of the normal population.  Poor Metabolism (PM), is asssociated with the accumulation of specific drug substrates, and is typically an autosomol rcessive trait requiring mutation and/or deletion of the gene, while the third class comprises individuals with Ultraextensive Metabolism (UEM), resulting in increased drug metabolism, and is an autosomol dominant trait arising from gene amplification.

For some classes of therapeutic agents (drugs), including the antidepressants/SSRIs, there is good evidence that genetic polymorphisms of drug metabolizing enzymes (in these cases, the CYP 2D6 enzyme), plays a significant role in adverse effects of the therapeutic agent, and even in an increased risk of exposure-linked cancer.

Thus, determination of these genetic polymorphisms are of clinical vale in predicting adverse or inadequate response to the antidepressants/SSRIs, and in predicting increased risk of  other disease.

There is a relatively simple test to determine which class or phenotype an individual falls into.  What is interesting to note is that most individuals are never tested to determine if they are EMs, PMs or UEMs.... We'd like to know why.  If a PM is given a high dose of an SSRI such as Prozac, it is likely that the proper metabolism of this therapeutic agent will not take place.  Thus, the drug can build to toxic levels.... Do you understand the significance of this?

Here now are the individual studies drawn exclusively from PubMed:  In order to more easily access the study, cut the reference beginning with "http, and ending with Abstract" and paste it into your browser's "location" window.  Press enter, and the study will come up.

Inhibition by fluoxetine of cytochrome P450 2D6 activity.
Otton SV, Wu D, Joffe RT, Cheung SW, Sellers EM.

Drug interactions with newer antidepressants: role of human cytochromes P450.
Greenblatt DJ, von Moltke LL, Harmatz JS, Shader RI.

Choreiform syndrome associated with fluoxetine treatment in a patient with deficient CYP2D6 activity.
Marchioni E, Perucca E, Soragna D, Bo P, Malaspina A, Ferrandi D, Albergati A, Savoldi, F.

Cytochrome P450 enzymes: interpretation of their interactions with selective serotonin reuptake inhibitors. Part II.
Harvey AT, Preskorn SH.

"It's the genes, stupid". Molecular bases and clinical consequences of genetic cytochrome P450 2D6 polymorphism.
Kroemer HK, Eichelbaum M.

The effect of selective serotonin re-uptake inhibitors on cytochrome P4502D6 (CYP2D6) activity in human liver microsomes.
Crewe HK, Lennard MS, Tucker GT, Woods FR, Haddock RE.

Newer antidepressants and the cytochrome P450 system.
Nemeroff CB, DeVane CL, Pollock BG.

Identification of the human cytochromes p450 responsible for in vitro formation of R- and S-norfluoxetine.
Ring BJ, Eckstein JA, Gillespie JS, Binkley SN, VandenBranden M, Wrighton SA.
(Department of Drug Disposition, Lilly Research Laboratories, Eli Lilly and Co., Indianapolis, Indiana, USA.)

Cytochrome P450 enzymes: interpretation of their interactions with selective serotonin reuptake inhibitors. Part I.
Harvey AT, Preskorn SH.

Recent advances: the cytochrome P450 enzymes.
Slaughter RL, Edwards DJ.

Cytochrome P450: genetic polymorphism and drug interactions.
Belpaire FM, Bogaert MG.

Genetically determined adverse drug reactions involving metabolism.
Lennard MS.  (Drug Saf 1993 Jul;9(1):60-77)

Genetic polymorphism of CYP2A6 in the German population.
Bourian M, Gullsten H, Legrum W.

Interpatient variability: genetic predisposition and other genetic factors.
West WL, Knight EM, Pradhan S, Hinds TS.

Molecular basis for differences in susceptibility to toxicants: introduction.
Boobis AR.

Genetic differences in drug disposition.
May DG.

Populations and genetic polymorphisms.
Weber WW.

[Individualization of drug therapy and pharmacogenetics].
[Article in Japanese]  Yamamoto I, Azuma J.

Pharmacogenetics: role in modifying drug dosage regimens.
Mah JT, Wong JY, Lee EJ.

Chapter 18. Cytochrome P450 CYP2D6.
Wolf CR, Smith G.

Pharmacogenetic phenotyping and genotyping. Present status and future potential.
Gonzalez FJ, Idle JR.

Polymorphism of cytochrome P-450 in humans.
Guengerich FP.

Pharmacogenetics: a laboratory tool for optimizing therapeutic efficiency.
Linder MW, Prough RA, Valdes R Jr.

Cytochrome P450 enzyme system: genetic polymorphisms and impact on clinical pharmacology.
van der Weide J, Steijns LS.
**By the use of genotyping or phenotyping methods every individual can be classified as either a poor,
    an intermediate, an extensive or an ultrarapid metabolizer. If this could be performed prior to drug
    therapy, the knowledge could be applied to drug selection and dose adjustment in order to reach
    therapeutic serum drug levels.

[The importance of examining genetic polymorphism of drug oxidation in psychiatry].
[Article in Polish]  Beszlej JA, Kiejna A.

Polymorphic drug oxidation in humans.
Eichelbaum M.
**As a consequence of
    impaired metabolism of these drugs, toxicity and therapeutic failure are observed in the PMs. With
    regard to molecular mechanisms, studies with microsomes from human liver provide evidence that
    in the PM phenotype a cytochrome P-450 isozyme is either missing or functionally inadequate.

Clinical importance of genetic polymorphism of drug oxidation.
Edeki T.
**Department of Medicine, Meharry Medical College, Nashville, Tennessee 37208, USA.

    Certain individuals have a metabolic deficiency in the metabolism of debrisoquin, sparteine,
    dextromethorphan, and more than 80 other clinically important drugs. Examples of such drugs
    include tricyclic antidepressants, neuroleptics, selective serotonin reuptake inhibitors,
    beta-adrenoceptor blockers, and antiarrhythmics. CYP2D6, the enzyme responsible for the
    metabolism of these drugs, is polymorphically distributed in different populations. Studies in different
    ethnic groups in particular demonstrate significant variation. CYP2D6 deficiency has important
    therapeutic consequences, such as increased side effects when medications that are substrates of
    this enzyme are prescribed for such individuals. To optimize drug therapy, physicians should
    therefore determine the metabolic capacity of their patients.

Update: genetic polymorphism of drug metabolizing enzymes in humans.
Tanaka E.
**Patients who are poor metabolizers (PMs), extensive metabolizers (EMs) and ultrarapid metabolizers (URMs)
    can be identified. Having such information will help in determining the appropriate dosage of certain
    drugs when treating patients with an inherited abnormality of a drug-metabolizing enzyme.

[Role of pharmacogenetics in psychopharmacotherapy].
[Article in French] Gram LF.
**Genetic polymorphism related to certain P450 isozymes, in particular the sparteine/debrisoquine
    oxygenase, is the dominant cause of interindividual variation in elimination of several drugs.
    The sparteine/debrisoquine oxidation
    polymorphism affects two major classes of drugs in psychopharmacology, the antidepressants and
    the neuroleptics, and this is the best example of clinical relevance of pharmacogenetic
    polymorphism. Routine use of phenotyping thus should be considered for psychiatry departments

[Pharmacogenetics of antidepressant metabolism. Value of the debrisoquin test].
[Article in French] Baumann P.  (Encephale 1986 Jul-Aug;12(4):143-8)
**The drug monitoring of antidepressants in blood plasma has revealed considerable interindividual
    differences in steady-state levels. For some compounds recent results strongly suggest that this
    phenomenon finds an explanation in genetic differences in the metabolism of the drugs by
    monooxygenases (cytochrome P-450) in the liver.....It is predicted that pharmacogenetic tests will
    find their place in psychopharmacotherapy, especially for subjects candidates for a long-term treatment
    or susceptible to suffer from side effects.

Debrisoquine hydroxylation in a Polish population.
Kunicki PK, Sitkiewicz D, Pawlik A, Bielicka-Sulzyc V, Borowiecka E, Gawronska-Szklarz
B. Sterna R, Matsumoto H, Radziwon-Zaleska M.
**Nine persons (5.8%) with MR > 12.6 were classified as poor metabolisers (gene frequency 0.242)
    which is in substantial agreement with the data reported for other Caucasian populations.

Antidepressants and drug-metabolizing enzymes--expert group report.
Meyer UA, Amrein R, Balant LP, Bertilsson L, Eichelbaum M, Guentert TW, Henauer S,
Jackson P, Laux G, Mikkelsen H, Peck C, Pollock BG, Priest R, Sjoqvist F, Delini-Stula A.

Recent developments in hepatic drug oxidation. Implications for clinical pharmacokinetics.
Brosen K.  (Clin Pharmacokinet 1990 Mar;18(3):220-39)

Pharmacogenetics and psychopharmacotherapy.
Poolsup N, Li Wan Po A, Knight TL.

[Individualization of drug therapy and pharmacogenetics].
[Article in Japanese]  Yamamoto I, Azuma J.

The influence of ethnicity and antidepressant pharmacogenetics in the treatment of depression.
Jann MW, Cohen LJ.

Pharmacogenetics of antidepressants: clinical aspects.
Bertilsson L, Dahl ML, Tybring G.

Pharmacogenetics and drug metabolism of newer antidepressant agents.
DeVane CL.

Drug interactions with newer antidepressants: role of human cytochromes P450.
Greenblatt DJ, von Moltke LL, Harmatz JS, Shader RI.

[The importance of examining genetic polymorphism of drug oxidation in psychiatry].
[Article in Polish] Beszlej JA, Kiejna A.

Genetically determined adverse drug reactions involving metabolism.
Lennard MS.

Drug interactions--friend or foe?
Jefferson JW.  (J Clin Psychiatry 1998;59 Suppl 4:37-47)
**An explosion of knowledge about interactions of drugs with other drugs and with foods threatens to
    inundate clinicians. This review provides a better understanding of the cytochrome P450 system
    with a focus on those enzymes most involved in drug metabolism. Emphasis is placed on
    antidepressant medications, how they are metabolized by the P450 system, and how they alter the
    metabolism of other drugs. The role of antidepressants in precipitating the serotonin syndrome is
    also discussed.

We hope to add to this list of studies as they become available.
The Avenging Angel

First Addendum: February 19, 2002 Sallee F, DeVane C, Ferrell R: Fluoxetine-related death in a child with cytochrome P450 2D6 genetic deficiency. Journal of Child and Adolescent Psychopharmacology 2000;10 (Spring):27-34. From the University of Cincinnati, Ohio; and other institutions. See Related Story in Psychiatry Drug Alerts 1996;10 (June):48. CYP2D6 Deficiency-Related Death In 1995, the FDA reported on the death of a 9-year old boy who at various times had received clonidine, fluoxetine, and methylphenidate, and who was found to have extremely high fluoxetine blood levels. The medical examiner concluded that an intentional fluoxetine overdose had been administered by his adoptive parents. Some follow-up information on this case concerning a psychopharmacologic evaluation and genetic testing has been made available. It appears that the boy had an autosomal recessive defect in cytochrome P450 2D6 (CYP2D6), which can result in poor metabolism and elevated levels of fluoxetine. The accusation of intentional overdose was subsequently abandoned. The 9-year old (55-lb) boy died following the onset of nausea, flu-like symptoms, and a seizure that led to cardiopulmonary arrest. The patient's medical history shows that at age 5 he was diagnosed with fetal alcohol syndrome, ADHD, and Tourette's disorder, and that he was treated with 0.6 mg/day clonidine for his tics. He was noted to be extremely hyperactive, with violent outbursts. At age 6, fluoxetine, 5 mg/day was added to 0.9 mg/day clonidine, and fluoxetine was gradually increased to 30 mg/day. The patient experienced vomiting and diarrhea at this dosage and was hospitalized for dehydration. The combination was discontinued during hospitalization and then resumed with a fluoxetine increase to 40 mg/day. The patient experienced 2 more episodes of vomiting and diarrhea. At age 8, the patient was receiving fluoxetine and clonidine for Tourette's disorder and OCD, and 60 mg/day methylphenidate was added to treat ADHD. The patient was also receiving 25 mg/day promethazine for nausea. Fluoxetine was increased to 80 mg/day, and he experienced a seizure. One month later, fluoxetine was increased to 100 mg/day. Subsequently, 3 episodes of dizziness, nausea, and low-grade fever occurred. He experienced 2 seizures, followed by status epilepticus and cardiopulmonary arrest wherein he could not be resuscitated. This appears to be the first report of toxicity and death in a child with confirmed polymorphism of CYP2D6. About 7-10% of Caucasians are estimated to be genetically deficient in CYP2D6. This deficiency, combined with the 100 mg/day dose of fluoxetine, probably contributed to fluoxetine toxicity and death in this patient. The possible effect of the other medications is unknown, and many questions remain about this unfortunate case.