Pharmacokinetics and Pharmacodynamics
It is necessary to have some basic understanding on what the body does to medications (pharmacokinetics) and what medications do to the body (pharmacodynamics).
Pharmacokinetics
Once a medication is taken orally, intramuscularly, sublingually, transdermally, or intravenously into the bloodstream, it can be eliminated in many different ways. Plasma proteins bind part of the medication, making this part inactive, or not bioavailable. Some of the medication is carried to the kidney, where it may be excreted unchanged in the urine. Some of the medication is carried to the liver, where it is transformed into a more water-soluble, active or inactive metabolite. Once transformed by the liver, the medication may be excreted in the urine or in the bile (then in the feces) and out of the body. Individual differences in the biotransformation through known or unknown mechanisms contribute to the observed wide range of clinical responses to a standard dose.
Pharmacodynamics
Psychiatric drugs can produce clinical responses even when only a small portion of the medication can reach their sites of action, that is, the receptors in the synapses. The drug molecules can facilitate or inhibit the effect of neurotransmitters by interacting with receptors on neuronal cells in different neurotransmitter systems. These systems are often described by the predominant neurotransmitter present. Examples include the dopamine, serotonin, norepinephrine, acetylcholine, histamine, and gamma-aminobutyric acid (GABA) systems.
The dopamine system in the brain has been thought to play a major role in causing psychotic symptoms. Blockade of certain types of dopamine receptors has been associated with alleviation of psychotic symptoms. It is recognized that blockade of other types of dopamine receptors causes neurological or endocrine side effects, as discussed later.
The serotonin system has been thought to be associated with symptoms of depression, anxiety, and hallucinations. It is also postulated that blocking of certain serotonin receptors may be associated with controlling negative symptoms of schizophrenia, as discussed later. However, blocking of other types of serotonin receptors is associated with such side effects as hypotension, sedation, and ejaculatory dysfunction.
The norepinephrine system may be associated with mood and motivation. Some of the new antidepressants target this system. Blockade of certain norepinephrine receptors is thought to be associated with such adverse effects as postural hypotension, dizziness, tachycardia, and sexual dysfunction.
The acetylcholine system may be associated with memory and smooth muscle functions.
Different types of pharmacological interactions with the muscarinic type of acetylcholine receptors have been associated with alleviating parkinsonian symptoms or causing such side effects as dry mouth, constipation, blurred vision, urinary retention, electrocardiographic (ECG) changes, and memory impairment.
The histamine system is thought to be associated with the sedative effects of medications that interact with the histamine receptors. It is also postulated that postural hypotension and weight gain can be caused by pharmacological manipulation of the histamine system.
The GABA system in the brain is an inhibitory network that lowers the activity levels of all other neurotransmission systems. The efficacy of the benzodiazepine (BZ) family of medications is associated with their effect of blocking the activity of this system.
Major Categories of Common Psychiatric Medications
Major advances in psychopharmacology include discoveries of psychiatric uses of chloral hydrate (1860s), barbiturates (1900s), antipsychotic medications (1950s), nonselective (tricyclic) and monoamine oxidase inhibitor (MAOIs) antidepressants (1950s), BZs (1960s), lithium (1970s), selective serotonin reuptake inhibitors (SSRIs, 1980s), atypical antipsychotics (1990s), serotonin and norepinephrine reuptake inhibitors (SNRIs, 1990s), and selective BZ receptor agonists (1990s). Most of these categories of medications are currently in use except the barbiturates, most of which were replaced by relatively safer agents such as BZs and SSRIs.
Commonly used psychiatric medications for adults can be identified under the following conventional categories: antianxiety agents (anxiolytics, sedatives, and hypnotics), antidepressants (older and newer agents), mood stabilizers, antipsychotic agents, and medications to control side effects. The generic and trade names for the medications are listed in boxes in each section. The possible daily dosage ranges (usually in milligrams per day) are also provided for each drug.
Target Symptoms
When the pharmacological interventions are considered, the treatment team and the patient or family should specifically define the psychiatric symptoms that the drugs of each category are treating.
Refer to the appropriate chapters to review common psychiatric symptoms as targets for pharmacological treatment. After defining specific target symptoms with the patient or family, each symptom may be rated on a 10-point scale before the therapy is started and periodically afterward. This way, both the treatment team and the patient or family can keep better track of changes in reactions to medications over time.
Educational needs of patients and their families should be assessed in the following areas in relation to psychopharmacological treatments: