Pharmacodynamics antidepressants

Medications that have been used as treatment for anxiety and depression in the postwithdrawal state include antidepressants, benzodia2epines and other anxiolytics, antipsychotics, and lithium. In general, the indications for use of these medications in alcoholic patients are similar to those for use in nonalcoholic patients with psychiatric illness. However, following careful differential diagnosis, the choice of medications should take into account the increased potential for adverse effects when the medications are prescribed to alcoholic patients. For example, adverse effects can result from pharmacodynamic interactions with medical disorders commonly present in alcoholic patients, as well as from pharmacokinetic interactions with medications prescribed to treat these disorders (Sullivan and O Connor 2004). 

Pharmacodynamic interaction clonidine acts as an agonist at a2-receptors, and these TCAs block this receptor to varying degrees the result is an increase in blood pressure either avoid this interaction by choosing another antidepressant or increase the dose of clonidine. 

The major drug interactions of antidepressants are shown in Table 35—6.9,19,30 Antidepressants cause both pharmacodynamic (e.g., additive pharmacologic effects) and pharmacokinetic (e.g., changes in drug levels) interactions with other medications. 

MAOIs Pharmacodynamic—serotonin syndrome Serotonergic antidepressants... 

Proponents of the clinical mirror theory of bioequivalence would like to see increased emphasis placed on quantification of pharmacodynamic values. In some instance we can readily identify how reliable and relevant pharmacodynamic values can be measured. For example, for an antihypertensive drug, measurement of blood pressure changes can be conveniently, inexpensively and objectively determined. However, for other types of drug (e.g., antidepressants) it is not easy to conceive any simple pharmacodynamic attributes that could be readily determined. 

Pharmacodynamic Interactions. Sometimes medications interact pharmacody-namically. If two medications produce similar side effects, then those effects can be additive. This can be advantageous. For examples, coadministering two antidepressants that relieve depression in different ways can be more effective than either medication alone. However, added effects can be problematic. If two medications that each produce drowsiness are coadministered, then the combination may produce intolerable daytime sedation. 

In the treatment of children and adolescents with anxiety disorders clinicians have a wide variety of pharmacologic options beyond the antidepressants (Shader and Greenblatt, 1995 Lydiard et ah, 1996 Riddle et ah, 1999). The benzodiazepines (BZs), with their favorable safety profile and quick onset of action, are attractive alternatives for the treatment of acute anxiety. While the clinical effectiveness of buspirone has not been proven in children, buspirone is used alone or in combination with other drugs in the treatment of anxiety disorders. The antihistamines are often used to treat insomnia and may reduce acute mild agitation. Zolpidem (Ambien) is occasionally used for its sedative properties. This chapter reviews the structure, proposed mechanisms of action, pharmacodynamic principles, and pharmacokinetic principles of these drugs. 

Even in people with the same diagnosis and the same inclusion and exclusion criteria, there are different treatment responses based on individual variability. The most important individual variables are probably sex and age. It is unfortunate that even though affective disorders and some anxiety disorders are more prevalent in women than in men, until recently results of clinical trials did not take into consideration sex differences and variables unique to women [e.g., reproductive status and menstrual cycle]. As is demonstrated by Yonkers et al. [see Chapter 5, in this volume], there are substantial sex differences in the pharmacokinetics and pharmacodynamics of most antidepressants and anxiolytics, which influence treatment response. Attention to these variables will indeed improve the efficacy of treatment. 

Evaluations of gender differences in the pharmacokinetics, pharmacodynamics, and response to treatment for anxiolytics and antidepressants are... 

Przegahnski E, Jurkowska T Repeated treatment with antidepressants does not modify the locomotor effect of dopaminergic stimulants injected into the rat hippocampus. Archives Internationales de Pharmacodynamic et de Therapie 305 152-162, 1990... 

Charles HC, Lazeyras, AQ Krishnan KRR, et al. Brain choline in depression in vivo detection of potential pharmacodynamic effects of antidepressant therapy using hydrogen localized spectroscopy. Prog Neuropsychopharmacol Biol Psychiatry 1994 18 1121 -1127. 

Treatment of these disorders has received less systematic study, in part because these patients are more diverse in terms of their health status, leading to potentially complicating alterations in the pharmacokinetics and pharmacodynamics of antidepressants. 

The recovering patient who remains depressed after appropriate treatment of the abstinence syndrome should be given an antidepressant trial. Treatment planning should take into account the patient s physical status, especially because it may affect the pharmacokinetics and pharmacodynamics of the agent selected (see Chapter 3). 

Members of this class of antidepressants are likely to be involved in pharmacodynamic and CYP-mediated pharmacokinetic drug-drug interactions. The latter are of concern because of the narrow therapeutic index of TCAs. 

This antidepressant can interact with other drugs via its two mechanisms of action serotonin and NE uptake inhibition. The former action means that the same pharmacodynamic interactions will occur with venlafaxine as with SSRIs, including the serotonin syndrome. At higher doses, venlafaxine is also prone to the same pharmacodynamic interactions as NSRIs such as secondary amine TCAs like desipramine and with newer NSRIs such reboxetine. Thus, the combination of high-dose venlafaxine plus an MAOl could produce a hypertensive crisis as well as the serotonin syndrome. 

Although venlafaxine can have more interactions than SSRIs pharmacodynamically, it is comparable with citalopram and sertraline in terms of not causing CYP enzyme mediated pharmacokinetic drug-drug interactions (Table 7-29). Thus, these three antidepressants have a distinct advantage over drugs such as fluoxetine, particularly in patients who are likely to be on other medications in aaaition to their antidepressant. 

MAOIs have the most serious pharmacodynamic interactions of any antidepressant class. As discussed earlier, they can cause a hypertensive crisis and the serotonin syndrome. They potentiate the hypertensive effects of most sympathomimetic amines, as well as tyramine, which is the reason for the avoidance of over-the-counter preparations containing such agents, in addition to the tyramine-free diet ( 508, 509). The serotonin syndrome occurs most often when MAOIs are used in combination with SSRIs and venlafaxine but it can also occur when MAOIs are used with tryptophan, 5-hydroxytryptophan, and some narcotic analgesics. In addition, MAOIs can also significantly potentiate the sedative and respiratory depressant effects of narcotic analgesics. 

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