Prolong
Shorten
Antibiotics: aminoglycosides (gentamicin, tobramycin), tetracycline
Carbamazepine
Calcium channel blockers
Methylxanthines
Lithium
Phenytoin (chronic exposure)
Local anesthetics
Ranitidine
Magnesium
Theophylline
Quinidine
Volatile inhalational anesthetics
3.
Effect on coagulation (anticoagulants, antiplatelet drugs, herbal medications)
Anesthetics may have synergic or additive interactions between them allowing desired effects such as improvement in hypnosis and muscle relaxation. Propofol, ketamine, thiopental, etomidate, opioids, benzodiazepines, and alpha-2 agonists have synergistic interaction with the volatile anesthetic agents, leading to a decrease in MAC. An example of additive interaction is the theoretical use of two inhalational agents, which will not decrease MAC for any of the two agents. Common medications that interact with neuromuscular blocking drugs and volatile anesthetic agents are shown in Tables 20.1 and 20.2, respectively. Some specific drug interactions are listed in Table 20.3.
Table 20.2
Drugs affecting minimum alveolar concentration of inhalational anesthetics
Decrease MAC | Increase MAC |
|---|---|
Propofol | Cyclosporine |
Ketamine | MAOIs |
Nitrous oxide | Chronic alcohol exposure |
Opioids | |
Benzodiazepines | |
Local anesthetics | |
Clonidine | |
Dexmedetomidine | |
Acute alcohol exposure |
Table 20.3
Specific drug interactions
Drug | Mechanism of interaction | Notes |
|---|---|---|
Central nervous system | ||
Selective serotonin reuptake inhibitors (SSRIs): fluoxetine, paroxetine,sertraline, citalopram | Inhibition of cytochrome P450 (CP450), increase in serotonin transmission | Serotonin syndrome (cognitive-headache, agitation, confusion, autonomic-hypertension, tachycardia, diaphoresis, hyperthermia, somatic-myoclonus, hyperreflexia) |
Tricyclic antidepressants: amitriptyline, imipramine, doxepin, protriptyline | Metabolized by CP450 system, increase in serotoninergic and noradrenergic transmission, decrease in cholinergic, histaminergic and alpha-adrenergic transmission | Orthostatic hypotension, cardiac arrhythmias, antimuscarinic actions (dry mouth, blurred vision), prolonged action by cimetidine, fluoxetine, calcium channel blockers |
Monoamine oxidase inhibitors: phenelzine, tranylcypromine | Increase in serotoninergic, noradrenergic and other amine transmission | Hypertensive crisis-ephedrine, meperidine, foods (tyramine-aged cheese, alcohol), serotonin syndrome-tryptophan |
Levodopa | Increases dopaminergic transmission, used to treat parkinsonism | Avoid metoclopramide and phenothaizines (block dopamine), arrhythmias |
Bromocriptine, lisuride | Direct acting dopamine agonist | Vomiting, hypotension, worsening psychotic symptoms |
Lithium | Increase in glutaminergic and serotonin transmission, may affect acetylcholine activity at nerve terminal, narrow therapeutic/toxic dose ratio | Prolongs neuromuscular blockade, use with haloperidol-toxic encephalopathy, inhibits ADH-nephrogenic diabetes insipidus |
Carbamazepine | Induces CP450 enzymes, competition for acetylcholine receptors at the neuromuscular junction | Accelerates metabolism or elimination of warfarin, phenytoin, benzodiazepines, decreased duration of neuromuscular blockade |
Phenytoin | Anticonvulsant, up-regulation of acetylcholine receptors | Warfarin and trimethoprim increase phenytoin levels, acute exposure prolongs NMB, chronic exposure shortens NMB |
Cardiovascular system | ||
Vasodilators: nitroprusside, nitroglycerin | Release nitric oxide and increase cGMP, potentiation of vasodilatation caused by volatile inhalational agents | Increased vascular smooth muscle relaxation, hypotension, not to be used with sildenafil |
Beta-blockers: metoprolol, propranolol | Decreased beta-adrenergic transmission, decrease cardiac muscle contractility | Hypotension, bradycardia, hypoglycemia, must not be used as first line treatment in cocaine overdose (unopposed alpha-adrenergic effects) |
Calcium channel blockers: diltiazem, verapamil
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