Editing Pharmacology (section)

=== Neurologic and Psychiatric ===

* '''Opioids''' (morphine, hydromorphone, fentanyl, oxycodone): the most dangerous adverse effect is respiratory depression, and sedation precedes it, so monitor the level of arousal. Constipation is the effect that does not develop tolerance, so start a bowel regimen. Antidote is '''naloxone''', which has a shorter duration than most opioids, so continued monitoring and repeat dosing may be needed. Hydromorphone is substantially more potent than morphine milligram for milligram, a frequent source of serious errors.
* '''Non-opioid analgesics''': acetaminophen has a maximum of 4 grams per day for most healthy adults, with lower limits in liver disease, chronic alcohol use, and older adults; the antidote for overdose is '''acetylcysteine'''. NSAIDs cause gastrointestinal bleeding, kidney injury, and fluid retention, and should be taken with food and avoided with anticoagulants.
* '''Benzodiazepines''' (lorazepam, diazepam, midazolam): sedation, respiratory depression especially when combined with opioids, and dependence. Antidote is '''flumazenil''', used cautiously because it can precipitate seizures in chronic users.
* '''Antiepileptics''': phenytoin has a narrow therapeutic range of roughly 10 to 20 mcg/mL and causes gingival hyperplasia (teach meticulous oral care), nystagmus and ataxia with toxicity, and severe skin reactions. Intravenous phenytoin is compatible with normal saline only, not dextrose, and must be given slowly. Valproate and carbamazepine require monitoring of liver function and blood counts; carbamazepine is a strong enzyme inducer. Levetiracetam is associated with behavioral changes.
* '''Antidepressants''': SSRIs take 2 to 4 weeks for mood response, and energy may improve before mood, transiently increasing suicide risk in young patients. Watch for '''serotonin syndrome''': agitation, hyperthermia, hyperreflexia, clonus, diaphoresis, and tremor, especially when an SSRI is combined with another serotonergic drug such as tramadol, triptans, linezolid, or St. John's wort. Tricyclics cause anticholinergic effects, orthostatic hypotension, and cardiac conduction problems, and are dangerous in overdose. MAO inhibitors require a '''tyramine-restricted diet''' (avoid aged cheese, cured and smoked meats, fermented soy, tap beer, and overripe or fermented foods) to prevent hypertensive crisis, and require a washout period of about 2 weeks when switching to or from an SSRI.
* '''Lithium''': therapeutic serum range about 0.6 to 1.2 mEq/L; levels above 1.5 mEq/L are toxic. Early toxicity presents as nausea, vomiting, diarrhea, fine tremor, and thirst; advancing toxicity brings coarse tremor, confusion, ataxia, and seizures. Teach adequate and consistent sodium and fluid intake, since dehydration, sodium loss, thiazide diuretics, NSAIDs, and ACE inhibitors all raise lithium levels. Monitor thyroid and renal function.
* '''Antipsychotics''': first generation agents (haloperidol, fluphenazine) most often cause extrapyramidal symptoms including acute dystonia, akathisia, pseudoparkinsonism, and tardive dyskinesia, which may be irreversible. Second generation agents (risperidone, olanzapine, quetiapine, aripiprazole) carry a greater metabolic burden with weight gain, hyperglycemia, and dyslipidemia. '''Neuroleptic malignant syndrome''' is a medical emergency: high fever, lead-pipe rigidity, altered mental status, autonomic instability, and elevated creatine kinase. Clozapine requires ongoing absolute neutrophil count monitoring because of agranulocytosis risk.