Drug Interactions between chlorpheniramine / guaifenesin / phenylephrine and levomethadyl acetate

GENERALLY AVOID: The concurrent use of levomethadyl acetate and alcohol may result in additive CNS and respiratory depression, hypotension, sedation, or coma. Grapefruit juice may increase the plasma concentrations of orally administered drugs which are substrates of the CYP450 3A4 isoenzyme, such as levomethadyl acetate. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. The extent and clinical significance are unknown. Moreover, pharmacokinetic alterations associated with interactions involving grapefruit juice are often subject to a high degree of interpatient variability.

MANAGEMENT: Patients who are known to abuse alcohol should be warned of the risk of potentially fatal overdose if these substances are taken concurrently. Patients who regularly consume grapefruits and grapefruit juice should be monitored for adverse effects and altered plasma concentrations of levomethadyl acetate. A 12-lead ECG should be performed before initiating therapy, 12 to 14 days after initiating therapy, and periodically thereafter. Patients should be advised to immediately seek medical attention if they experience palpitations, dizziness, lightheadedness, fainting, or seizures. Grapefruits and grapefruit juice should be avoided if an interaction is suspected. Orange juice is not expected to interact.

GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

MONITOR: Coadministration of two or more sympathomimetic agents may increase the risk of adverse effects such as nervousness, irritability, and increased heart rate. Central nervous system (CNS) stimulants, particularly amphetamines, can potentiate the adrenergic response to vasopressors and other sympathomimetic agents. Additive increases in blood pressure and heart rate may occur due to enhanced peripheral sympathetic activity.

MANAGEMENT: Caution is advised if two or more sympathomimetic agents are coadministered. Pulse and blood pressure should be closely monitored.

The use of levomethadyl acetate has been associated with prolongation of the QTc interval in some patients during serial EKGs performed in a pharmacokinetics study. This change was not dose-related, and adverse cardiac events have not been attributed to the drug during clinical trials. Therapy with levomethadyl acetate should be administered cautiously in patients with a history of known cardiac conduction defects. Clinical monitoring of cardiovascular status is recommended during therapy.

The use of opiate agonists is contraindicated in patients with acute alcohol intoxication exhibiting depressed vital signs. The central nervous system depressant effects of opiate agonists may be additive with those of alcohol. Severe respiratory depression and death may occur. Therapy with opiate agonists should be administered cautiously in patients who might be prone to acute alcohol intake.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

The use of levomethadyl acetate has been associated with prolongation of the QTc interval in some patients during serial EKGs performed in a pharmacokinetics study. This change was not dose-related, and adverse cardiac events have not been attributed to the drug during clinical trials. Therapy with levomethadyl acetate should be administered cautiously in patients with a history of known cardiac conduction defects. Clinical monitoring of cardiovascular status is recommended during therapy.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

The hypoventilation associated with administration of opiate agonists, particularly by the intravenous route, can induce cerebral hypoxia and vasodilatation with resultant increase in intracranial pressure. Opiate agonists should not be used in patients with suspected or known head injury or increased intracranial pressure. Also, clinicians treating such patients should be aware that opiate agonists may interfere with the evaluation of CNS function, especially with respect to consciousness levels, respiratory status, and pupillary changes.

Sympathomimetic agents may cause adverse cardiovascular effects, particularly when used in high dosages and/or in susceptible patients. In cardiac tissues, these agents may produce positive chronotropic and inotropic effects via stimulation of beta- 1 adrenergic receptors. Cardiac output, oxygen consumption, and the work of the heart may be increased. In the peripheral vasculature, vasoconstriction may occur via stimulation of alpha-1 adrenergic receptors. Palpitations, tachycardia, arrhythmia, hypertension, reflex bradycardia, coronary occlusion, cerebral vasculitis, myocardial infarction, cardiac arrest, and death have been reported. Some of these agents, particularly ephedra alkaloids (ephedrine, ma huang, phenylpropanolamine), may also predispose patients to hemorrhagic and ischemic stroke. Therapy with sympathomimetic agents should generally be avoided or administered cautiously in patients with sensitivity to sympathomimetic amines, hyperthyroidism, or underlying cardiovascular or cerebrovascular disorders. These agents should not be used in patients with severe coronary artery disease or severe/uncontrolled hypertension.

The hypoventilation associated with administration of opiate agonists, particularly by the intravenous route, can induce cerebral hypoxia and vasodilatation with resultant increase in intracranial pressure. Opiate agonists should not be used in patients with suspected or known head injury or increased intracranial pressure. Also, clinicians treating such patients should be aware that opiate agonists may interfere with the evaluation of CNS function, especially with respect to consciousness levels, respiratory status, and pupillary changes.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Sympathomimetic agents may cause adverse cardiovascular effects, particularly when used in high dosages and/or in susceptible patients. In cardiac tissues, these agents may produce positive chronotropic and inotropic effects via stimulation of beta- 1 adrenergic receptors. Cardiac output, oxygen consumption, and the work of the heart may be increased. In the peripheral vasculature, vasoconstriction may occur via stimulation of alpha-1 adrenergic receptors. Palpitations, tachycardia, arrhythmia, hypertension, reflex bradycardia, coronary occlusion, cerebral vasculitis, myocardial infarction, cardiac arrest, and death have been reported. Some of these agents, particularly ephedra alkaloids (ephedrine, ma huang, phenylpropanolamine), may also predispose patients to hemorrhagic and ischemic stroke. Therapy with sympathomimetic agents should generally be avoided or administered cautiously in patients with sensitivity to sympathomimetic amines, hyperthyroidism, or underlying cardiovascular or cerebrovascular disorders. These agents should not be used in patients with severe coronary artery disease or severe/uncontrolled hypertension.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Opiate agonists can induce vasodilation and significant hypotension, particularly when given in high dosages and/or by rapid intravenous administration. Opiate analgesics cause vasodilatation that may exacerbate hypotension and hypoperfusion and, therefore, are contraindicated in circulatory shock. At therapeutic analgesic dosages, ambulatory patients are more likely to experience dizziness and hypotension than patients who are confined to bed. However, orthostatic hypotension may occur in supine patients upon rising. Therapy with opiate agonists should be administered cautiously and initiated at reduced dosages in patients with hypovolemia, or a predisposition to hypotension. When given by intramuscular or subcutaneous administration, clinicians should also be aware that impaired perfusion in these patients may prevent complete absorption of the drug. With repeated injections, an excessive amount may be absorbed suddenly if normal circulation is reestablished.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Opioid analgesics are contraindicated in patients with known or suspected gastrointestinal obstruction, including paralytic ileus.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

The hypoventilation associated with administration of opiate agonists, particularly by the intravenous route, can induce cerebral hypoxia and vasodilatation with resultant increase in intracranial pressure. Opiate agonists should not be used in patients with suspected or known head injury or increased intracranial pressure. Also, clinicians treating such patients should be aware that opiate agonists may interfere with the evaluation of CNS function, especially with respect to consciousness levels, respiratory status, and pupillary changes.

Sympathomimetic agents may cause adverse cardiovascular effects, particularly when used in high dosages and/or in susceptible patients. In cardiac tissues, these agents may produce positive chronotropic and inotropic effects via stimulation of beta- 1 adrenergic receptors. Cardiac output, oxygen consumption, and the work of the heart may be increased. In the peripheral vasculature, vasoconstriction may occur via stimulation of alpha-1 adrenergic receptors. Palpitations, tachycardia, arrhythmia, hypertension, reflex bradycardia, coronary occlusion, cerebral vasculitis, myocardial infarction, cardiac arrest, and death have been reported. Some of these agents, particularly ephedra alkaloids (ephedrine, ma huang, phenylpropanolamine), may also predispose patients to hemorrhagic and ischemic stroke. Therapy with sympathomimetic agents should generally be avoided or administered cautiously in patients with sensitivity to sympathomimetic amines, hyperthyroidism, or underlying cardiovascular or cerebrovascular disorders. These agents should not be used in patients with severe coronary artery disease or severe/uncontrolled hypertension.

Opiate agonists can induce vasodilation and significant hypotension, particularly when given in high dosages and/or by rapid intravenous administration. Opiate analgesics cause vasodilatation that may exacerbate hypotension and hypoperfusion and, therefore, are contraindicated in circulatory shock. At therapeutic analgesic dosages, ambulatory patients are more likely to experience dizziness and hypotension than patients who are confined to bed. However, orthostatic hypotension may occur in supine patients upon rising. Therapy with opiate agonists should be administered cautiously and initiated at reduced dosages in patients with hypovolemia, or a predisposition to hypotension. When given by intramuscular or subcutaneous administration, clinicians should also be aware that impaired perfusion in these patients may prevent complete absorption of the drug. With repeated injections, an excessive amount may be absorbed suddenly if normal circulation is reestablished.

Narcotic (opioid) analgesic agents may prolong and/or worsen diarrhea associated with organisms that invade the intestinal mucosa, such as toxigenic Escherichia coli, Salmonella, Shigella, and pseudomembranous colitis due to broad-spectrum antibiotics. These agents decrease gastrointestinal motility, which may delay the excretion of infective gastroenteric organisms and/or their toxins. Other symptoms and complications such as fever, shedding of organisms, and extraintestinal illness may also be increased or prolonged. Therapy with opioids should be avoided or administered cautiously in patients with infectious diarrhea, particularly that due to pseudomembranous enterocolitis or enterotoxin-producing bacteria or if accompanied by high fever, pus, or blood in the stool.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Sympathomimetic agents may cause adverse cardiovascular effects, particularly when used in high dosages and/or in susceptible patients. In cardiac tissues, these agents may produce positive chronotropic and inotropic effects via stimulation of beta- 1 adrenergic receptors. Cardiac output, oxygen consumption, and the work of the heart may be increased. In the peripheral vasculature, vasoconstriction may occur via stimulation of alpha-1 adrenergic receptors. Palpitations, tachycardia, arrhythmia, hypertension, reflex bradycardia, coronary occlusion, cerebral vasculitis, myocardial infarction, cardiac arrest, and death have been reported. Some of these agents, particularly ephedra alkaloids (ephedrine, ma huang, phenylpropanolamine), may also predispose patients to hemorrhagic and ischemic stroke. Therapy with sympathomimetic agents should generally be avoided or administered cautiously in patients with sensitivity to sympathomimetic amines, hyperthyroidism, or underlying cardiovascular or cerebrovascular disorders. These agents should not be used in patients with severe coronary artery disease or severe/uncontrolled hypertension.

The use of narcotic (opioid) analgesic agents is contraindicated in premature infants. These agents may cross the immature blood-brain barrier to a greater extent than in adults, resulting in disproportionate respiratory depression.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Opiate agonists can induce vasodilation and significant hypotension, particularly when given in high dosages and/or by rapid intravenous administration. Opiate analgesics cause vasodilatation that may exacerbate hypotension and hypoperfusion and, therefore, are contraindicated in circulatory shock. At therapeutic analgesic dosages, ambulatory patients are more likely to experience dizziness and hypotension than patients who are confined to bed. However, orthostatic hypotension may occur in supine patients upon rising. Therapy with opiate agonists should be administered cautiously and initiated at reduced dosages in patients with hypovolemia, or a predisposition to hypotension. When given by intramuscular or subcutaneous administration, clinicians should also be aware that impaired perfusion in these patients may prevent complete absorption of the drug. With repeated injections, an excessive amount may be absorbed suddenly if normal circulation is reestablished.

Patients with Addison's disease may have increased risk of respiratory depression and prolonged CNS depression associated with the use of narcotic (opioid) analgesic agents. Conversely, these agents may cause or potentiate adrenal insufficiency. Therapy with opioids should be administered cautiously and initiated at reduced dosages in patients with adrenocortical insufficiency. Subsequent doses should be titrated based on individual response rather than a fixed dosing schedule.

It has been suggested that the anticholinergic effect of antihistamines may reduce the volume and cause thickening of bronchial secretions, resulting in obstruction of respiratory tract. Some manufacturers and clinicians recommend that therapy with antihistamines be administered cautiously in patients with asthma or chronic obstructive pulmonary disease.

Sympathomimetic agents may cause or worsen urinary difficulty in patients with prostate enlargement due to smooth muscle contraction in the bladder neck via stimulation of alpha-1 adrenergic receptors. Therapy with sympathomimetic agents should be administered cautiously in patients with hypertrophy or neoplasm of the prostate.

Opioid agonists may cause spasm of the sphincter of Oddi, which may increase biliary tract pressure. Other opioid-induced effects may include a reduction in biliary and pancreatic secretions and transient elevations in serum amylase. Patients with biliary tract disease (including acute pancreatitis) should be regularly evaluated for worsening symptoms. Therapy with opioids should be administered cautiously in patients with biliary tract disease, gallbladder disease, or acute pancreatitis.

Antihistamines may infrequently cause cardiovascular adverse effects related to their anticholinergic and local anesthetic (quinidine-like) activities. Tachycardia, palpitation, ECG changes, arrhythmias, hypotension, and hypertension have been reported. Although these effects are uncommon and usually limited to overdosage situations, the manufacturers and some clinicians recommend that therapy with antihistamines be administered cautiously in patients with cardiovascular disease, hypertension, and/or hyperthyroidism.

It has been suggested that the anticholinergic effect of antihistamines may reduce the volume and cause thickening of bronchial secretions, resulting in obstruction of respiratory tract. Some manufacturers and clinicians recommend that therapy with antihistamines be administered cautiously in patients with asthma or chronic obstructive pulmonary disease.

Sympathomimetic agents may cause increases in blood glucose concentrations. These effects are usually transient and slight but may be significant with dosages higher than those normally recommended. Therapy with sympathomimetic agents should be administered cautiously in patients with diabetes mellitus. Closer monitoring of blood glucose concentrations may be appropriate.

Opioid agonists may cause spasm of the sphincter of Oddi, which may increase biliary tract pressure. Other opioid-induced effects may include a reduction in biliary and pancreatic secretions and transient elevations in serum amylase. Patients with biliary tract disease (including acute pancreatitis) should be regularly evaluated for worsening symptoms. Therapy with opioids should be administered cautiously in patients with biliary tract disease, gallbladder disease, or acute pancreatitis.

Antihistamines often have anticholinergic activity, to which elderly patients are particularly sensitive. Therapy with antihistamines should be administered cautiously, if at all, in patients with preexisting conditions that are likely to be exacerbated by anticholinergic activity, such as urinary retention or obstruction; angle-closure glaucoma, untreated intraocular hypertension, or uncontrolled primary open-angle glaucoma; and gastrointestinal obstructive disorders. Conventional, first-generation antihistamines such as the ethanolamines (bromodiphenhydramine, carbinoxamine, clemastine, dimenhydrinate, diphenhydramine, doxylamine, phenyltoloxamine) tend to exhibit substantial anticholinergic effects. In contrast, the newer, relatively nonsedating antihistamines (e.g., cetirizine, fexofenadine, loratadine) reportedly have low to minimal anticholinergic activity at normally recommended dosages and may be appropriate alternatives.

Sympathomimetic agents can induce transient mydriasis via stimulation of alpha-1 adrenergic receptors. In patients with anatomically narrow angles or narrow-angle glaucoma, pupillary dilation can provoke an acute attack. In patients with other forms of glaucoma, mydriasis may occasionally increase intraocular pressure. Therapy with sympathomimetic agents should be administered cautiously in patients with or predisposed to glaucoma, particularly narrow-angle glaucoma.

Antihistamines often have anticholinergic activity, to which elderly patients are particularly sensitive. Therapy with antihistamines should be administered cautiously, if at all, in patients with preexisting conditions that are likely to be exacerbated by anticholinergic activity, such as urinary retention or obstruction; angle-closure glaucoma, untreated intraocular hypertension, or uncontrolled primary open-angle glaucoma; and gastrointestinal obstructive disorders. Conventional, first-generation antihistamines such as the ethanolamines (bromodiphenhydramine, carbinoxamine, clemastine, dimenhydrinate, diphenhydramine, doxylamine, phenyltoloxamine) tend to exhibit substantial anticholinergic effects. In contrast, the newer, relatively nonsedating antihistamines (e.g., cetirizine, fexofenadine, loratadine) reportedly have low to minimal anticholinergic activity at normally recommended dosages and may be appropriate alternatives.

Antihistamines may infrequently cause cardiovascular adverse effects related to their anticholinergic and local anesthetic (quinidine-like) activities. Tachycardia, palpitation, ECG changes, arrhythmias, hypotension, and hypertension have been reported. Although these effects are uncommon and usually limited to overdosage situations, the manufacturers and some clinicians recommend that therapy with antihistamines be administered cautiously in patients with cardiovascular disease, hypertension, and/or hyperthyroidism.

Antihistamines may infrequently cause cardiovascular adverse effects related to their anticholinergic and local anesthetic (quinidine-like) activities. Tachycardia, palpitation, ECG changes, arrhythmias, hypotension, and hypertension have been reported. Although these effects are uncommon and usually limited to overdosage situations, the manufacturers and some clinicians recommend that therapy with antihistamines be administered cautiously in patients with cardiovascular disease, hypertension, and/or hyperthyroidism.

Limited pharmacokinetic data are available for the older, first-generation antihistamines. Many appear to be primarily metabolized by the liver, and both parent drugs and metabolites are excreted in the urine. Patients with renal and/or liver disease may be at greater risk for adverse effects from antihistamines due to drug and metabolite accumulation. Therapy with antihistamines should be administered cautiously in such patients. Lower initial dosages may be appropriate.

Narcotic (opioid) analgesic agents are extensively metabolized by the liver, and several of them (e.g., codeine, hydrocodone, meperidine, methadone, morphine, propoxyphene) have active metabolites that are further converted to inactive substances. The serum concentrations of these agents and their metabolites may be increased and the half-lives prolonged in patients with impaired hepatic function. Therapy with opioids should be administered cautiously and initiated at reduced dosages in patients with liver disease. Subsequent doses should be titrated based on individual response rather than a fixed dosing schedule.

Opioid agonists may cause spasm of the sphincter of Oddi, which may increase biliary tract pressure. Other opioid-induced effects may include a reduction in biliary and pancreatic secretions and transient elevations in serum amylase. Patients with biliary tract disease (including acute pancreatitis) should be regularly evaluated for worsening symptoms. Therapy with opioids should be administered cautiously in patients with biliary tract disease, gallbladder disease, or acute pancreatitis.

Sympathomimetic agents may cause or worsen urinary difficulty in patients with prostate enlargement due to smooth muscle contraction in the bladder neck via stimulation of alpha-1 adrenergic receptors. Therapy with sympathomimetic agents should be administered cautiously in patients with hypertrophy or neoplasm of the prostate.

Limited pharmacokinetic data are available for the older, first-generation antihistamines. Many appear to be primarily metabolized by the liver, and both parent drugs and metabolites are excreted in the urine. Patients with renal and/or liver disease may be at greater risk for adverse effects from antihistamines due to drug and metabolite accumulation. Therapy with antihistamines should be administered cautiously in such patients. Lower initial dosages may be appropriate.

Although narcotic (opioid) analgesic agents are generally metabolized by the liver, renal impairment can alter the elimination of these agents and their metabolites (some of which are pharmacologically active), resulting in drug accumulation and increased risk of toxicity. Therapy with opioids should be administered cautiously and initiated at reduced dosages in patients with significantly impaired renal function. Subsequent doses should be titrated based on individual response rather than a fixed dosing schedule.

Narcotic (opioid) analgesic agents may increase the frequency of seizures in patients with seizure disorders, may increase the risk of seizures occurring in other clinical settings associated with seizures, and, at higher dosages, have been reported to induce seizures in patients without history of seizures. Patients with history of seizure disorders should be regularly evaluated for worsened seizure control during therapy. Prolonged meperidine use may increase the risk of toxicity (e.g., seizures) from the accumulation of the active metabolite (normeperidine).

Narcotic (opioid) analgesic agents may inhibit the urinary voiding reflex and increase the tone of the vesical sphincter in the bladder. Acute urinary retention requiring catheterization may occur, particularly in patients with prostatic hypertrophy or urethral stricture and in older adult patients. These agents may also decrease urine production via direct effects on the kidney and central stimulation of the release of vasopressin. Therapy with opioids should be administered cautiously in patients with or predisposed to urinary retention and/or oliguria. The effects on smooth muscle tone appear to be the most pronounced with morphine.

Antihistamines often have anticholinergic activity, to which elderly patients are particularly sensitive. Therapy with antihistamines should be administered cautiously, if at all, in patients with preexisting conditions that are likely to be exacerbated by anticholinergic activity, such as urinary retention or obstruction; angle-closure glaucoma, untreated intraocular hypertension, or uncontrolled primary open-angle glaucoma; and gastrointestinal obstructive disorders. Conventional, first-generation antihistamines such as the ethanolamines (bromodiphenhydramine, carbinoxamine, clemastine, dimenhydrinate, diphenhydramine, doxylamine, phenyltoloxamine) tend to exhibit substantial anticholinergic effects. In contrast, the newer, relatively nonsedating antihistamines (e.g., cetirizine, fexofenadine, loratadine) reportedly have low to minimal anticholinergic activity at normally recommended dosages and may be appropriate alternatives.