Drug Interactions between chlorpheniramine / guaifenesin / phenylephrine and valproic acid

Alcohol can increase the nervous system side effects of valproic acid such as dizziness, drowsiness, and difficulty concentrating. Some people may also experience impairment in thinking and judgment. You should avoid or limit the use of alcohol while being treated with valproic acid. Do not use more than the recommended dose of valproic acid, and avoid activities requiring mental alertness such as driving or operating hazardous machinery until you know how the medication affects you. Talk to your doctor or pharmacist if you have any questions or concerns.

Alcohol can increase the nervous system side effects of chlorpheniramine such as dizziness, drowsiness, and difficulty concentrating. Some people may also experience impairment in thinking and judgment. You should avoid or limit the use of alcohol while being treated with chlorpheniramine. Do not use more than the recommended dose of chlorpheniramine, and avoid activities requiring mental alertness such as driving or operating hazardous machinery until you know how the medication affects you. Talk to your doctor or pharmacist if you have any questions or concerns.

Both phenylephrine and caffeine can increase blood pressure and heart rate, and combining them may enhance these effects. Talk to your doctor before using these medications, especially if you have a history of high blood pressure or heart disease. You may need a dose adjustment or more frequent monitoring by your doctor to safely use both medications. Contact your doctor if your condition changes or you experience increased side effects. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

The use of valproate derivatives is contraindicated in patients with hepatic disease or significant hepatic dysfunction. Serious and potentially fatal hepatotoxicity has been reported in patients treated with these agents. The risk appears to be greatest in children less than 2 years of age--particularly those on multiple anticonvulsants and those with congenital metabolic disorders, severe seizure disorders accompanied by intellectual disability, or organic brain disease--and decreases considerably in progressively older patient groups. Therapy with valproate products should be administered with extreme caution and as a sole agent in patients with risk factors for valproate-related hepatotoxicity. In reported cases, the onset has generally been within the first 6 months of treatment and may be preceded by nonspecific symptoms such as malaise, weakness, lethargy, facial edema, anorexia, nausea, vomiting, and a loss of seizure control. Patients should be monitored closely for appearance of these symptoms, and therapy withdrawn immediately if significant hepatic dysfunction occurs. Liver function tests should be performed prior to initiating therapy and at frequent intervals thereafter, especially during the first 6 months. However, clinicians should bear in mind that transient, dose-related, asymptomatic elevations in serum transaminase, amylase and ammonia levels may commonly occur and often return to normal with or without dosage adjustment.

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.

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.

Antiepileptic drugs can increase depression and suicidal thoughts or behaviors in patients receiving these drugs for any indication. Patients should be monitored for the emergence or worsening of depression, suicidal thoughts and unusual changes in mood or behavior. Caregivers and family should be alert for the emergence or worsening of symptoms. Behaviors of concern should be reported immediately to the healthcare providers.

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 valproate derivatives is contraindicated in patients with hepatic disease or significant hepatic dysfunction. Serious and potentially fatal hepatotoxicity has been reported in patients treated with these agents. The risk appears to be greatest in children less than 2 years of age--particularly those on multiple anticonvulsants and those with congenital metabolic disorders, severe seizure disorders accompanied by intellectual disability, or organic brain disease--and decreases considerably in progressively older patient groups. Therapy with valproate products should be administered with extreme caution and as a sole agent in patients with risk factors for valproate-related hepatotoxicity. In reported cases, the onset has generally been within the first 6 months of treatment and may be preceded by nonspecific symptoms such as malaise, weakness, lethargy, facial edema, anorexia, nausea, vomiting, and a loss of seizure control. Patients should be monitored closely for appearance of these symptoms, and therapy withdrawn immediately if significant hepatic dysfunction occurs. Liver function tests should be performed prior to initiating therapy and at frequent intervals thereafter, especially during the first 6 months. However, clinicians should bear in mind that transient, dose-related, asymptomatic elevations in serum transaminase, amylase and ammonia levels may commonly occur and often return to normal with or without dosage adjustment.

Valproic acid and derivative products are contraindicated in patients with known urea cycle disorders (UCD), as hyperammonemic encephalopathy, sometimes fatal, has been reported on these patients following the initiation of treatment. Prior to the initiation of therapy, the evaluation for UCD should be considered in patients with history of unexplained encephalopathy or comma, encephalopathy associated with a protein load, pregnancy- related or postpartum encephalopathy, unexplained intellectual disability, or history of elevated plasma ammonia or glutamine. Also, those with family history of UCD or family history of unexplained infant deaths. Patients who develop symptoms of hyperammonemic encephalopathy while receiving valproate therapy should receive prompt treatment including treatment discontinuation and be evaluated for underlying urea cycle disorders.

The use of valproate derivatives is contraindicated in patients with hepatic disease or significant hepatic dysfunction. Serious and potentially fatal hepatotoxicity has been reported in patients treated with these agents. The risk appears to be greatest in children less than 2 years of age--particularly those on multiple anticonvulsants and those with congenital metabolic disorders, severe seizure disorders accompanied by intellectual disability, or organic brain disease--and decreases considerably in progressively older patient groups. Therapy with valproate products should be administered with extreme caution and as a sole agent in patients with risk factors for valproate-related hepatotoxicity. In reported cases, the onset has generally been within the first 6 months of treatment and may be preceded by nonspecific symptoms such as malaise, weakness, lethargy, facial edema, anorexia, nausea, vomiting, and a loss of seizure control. Patients should be monitored closely for appearance of these symptoms, and therapy withdrawn immediately if significant hepatic dysfunction occurs. Liver function tests should be performed prior to initiating therapy and at frequent intervals thereafter, especially during the first 6 months. However, clinicians should bear in mind that transient, dose-related, asymptomatic elevations in serum transaminase, amylase and ammonia levels may commonly occur and often return to normal with or without dosage adjustment.

The use of valproate derivatives is contraindicated in patients with hepatic disease or significant hepatic dysfunction. Serious and potentially fatal hepatotoxicity has been reported in patients treated with these agents. The risk appears to be greatest in children less than 2 years of age--particularly those on multiple anticonvulsants and those with congenital metabolic disorders, severe seizure disorders accompanied by intellectual disability, or organic brain disease--and decreases considerably in progressively older patient groups. Therapy with valproate products should be administered with extreme caution and as a sole agent in patients with risk factors for valproate-related hepatotoxicity. In reported cases, the onset has generally been within the first 6 months of treatment and may be preceded by nonspecific symptoms such as malaise, weakness, lethargy, facial edema, anorexia, nausea, vomiting, and a loss of seizure control. Patients should be monitored closely for appearance of these symptoms, and therapy withdrawn immediately if significant hepatic dysfunction occurs. Liver function tests should be performed prior to initiating therapy and at frequent intervals thereafter, especially during the first 6 months. However, clinicians should bear in mind that transient, dose-related, asymptomatic elevations in serum transaminase, amylase and ammonia levels may commonly occur and often return to normal with or without dosage adjustment.

Valproic acid and derivative products are contraindicated in patients with known urea cycle disorders (UCD), as hyperammonemic encephalopathy, sometimes fatal, has been reported on these patients following the initiation of treatment. Prior to the initiation of therapy, the evaluation for UCD should be considered in patients with history of unexplained encephalopathy or comma, encephalopathy associated with a protein load, pregnancy- related or postpartum encephalopathy, unexplained intellectual disability, or history of elevated plasma ammonia or glutamine. Also, those with family history of UCD or family history of unexplained infant deaths. Patients who develop symptoms of hyperammonemic encephalopathy while receiving valproate therapy should receive prompt treatment including treatment discontinuation and be evaluated for underlying urea cycle disorders.

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.

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.

The use of valproate derivatives may be associated with dose-related thrombocytopenia, the incidence of which is generally low but has been reported at up to 27% in one study using high dosages (approximately 50 mg/kg/day of valproic acid). In that study, platelet counts returned to normal in all patients, some despite continued treatment. Valproate may also inhibit the secondary phase of platelet aggregation, although this effect is unlikely to be of clinical significance except during the concomitant use of other drugs that affect coagulation. However, altered bleeding time, ecchymosis, petechiae, bruising, hematoma formation, epistaxis, and frank hemorrhage have been reported rarely. Hypofibrinogenemia has also been observed. Therapy with valproate products, particularly at high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothrombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The manufacturers recommend platelet counts and coagulation tests prior to initiating therapy and at periodic intervals thereafter, as well as before planned surgery. The dosage should be reduced or the drug withdrawn if clinical evidence of hemorrhage, bruising, or a disorder of hemostasis or coagulation occurs.

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.

The use of valproate derivatives may be associated with dose-related thrombocytopenia, the incidence of which is generally low but has been reported at up to 27% in one study using high dosages (approximately 50 mg/kg/day of valproic acid). In that study, platelet counts returned to normal in all patients, some despite continued treatment. Valproate may also inhibit the secondary phase of platelet aggregation, although this effect is unlikely to be of clinical significance except during the concomitant use of other drugs that affect coagulation. However, altered bleeding time, ecchymosis, petechiae, bruising, hematoma formation, epistaxis, and frank hemorrhage have been reported rarely. Hypofibrinogenemia has also been observed. Therapy with valproate products, particularly at high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothrombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The manufacturers recommend platelet counts and coagulation tests prior to initiating therapy and at periodic intervals thereafter, as well as before planned surgery. The dosage should be reduced or the drug withdrawn if clinical evidence of hemorrhage, bruising, or a disorder of hemostasis or coagulation occurs.

Antiepileptic drugs (AEDs) have been associated with an increased risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Pooled analyses of 199 placebo-controlled clinical studies involving the use of 11 different AEDs showed that patients receiving AEDs had approximately twice the risk of suicidal thinking or behavior compared to patients receiving placebo. AEDs should be administered cautiously in patients with depression or other psychiatric disorders; phentermine-topiramate should be avoided in patients with history of suicidal attempts or active suicidal ideation. The risk of suicidal thoughts and behavior should be carefully assessed against the risk of untreated illness, bearing in mind that epilepsy and many other conditions for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior. Patients, caregivers, and families should be alert to the emergence or worsening of signs and symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts or behavior. If patients have symptoms of suicidal ideation or behavior, a dosage reduction or treatment discontinuation should be considered.

Valproate is partially eliminated in the urine as a ketone-containing metabolite, which may lead to a false interpretation of the urine ketone test. Clinicians should be cognizant of this interaction when prescribing or administering valproate products to patients with diabetes.

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.

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 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.

Some in vitro studies suggest that valproate stimulates the replication of the HIV and CMV viruses under certain experimental conditions. The clinical consequences are unknown, and the relevance of these findings is uncertain for patients receiving maximally suppressive antiretroviral therapy. However, this should be borne in mind when interpreting the results from regular monitoring of the viral load in HIV infected patients receiving valproate or when following CMV infected patients clinically.

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.

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.

Antiepileptic drugs (AEDs) have been associated with an increased risk of suicidal thoughts or behavior in patients taking these drugs for any indication. Pooled analyses of 199 placebo-controlled clinical studies involving the use of 11 different AEDs showed that patients receiving AEDs had approximately twice the risk of suicidal thinking or behavior compared to patients receiving placebo. AEDs should be administered cautiously in patients with depression or other psychiatric disorders; phentermine-topiramate should be avoided in patients with history of suicidal attempts or active suicidal ideation. The risk of suicidal thoughts and behavior should be carefully assessed against the risk of untreated illness, bearing in mind that epilepsy and many other conditions for which AEDs are prescribed are themselves associated with morbidity and mortality and an increased risk of suicidal thoughts and behavior. Patients, caregivers, and families should be alert to the emergence or worsening of signs and symptoms of depression, any unusual changes in mood or behavior, or the emergence of suicidal thoughts or behavior. If patients have symptoms of suicidal ideation or behavior, a dosage reduction or treatment discontinuation should be considered.

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.

The use of valproate derivatives may be associated with dose-related thrombocytopenia, the incidence of which is generally low but has been reported at up to 27% in one study using high dosages (approximately 50 mg/kg/day of valproic acid). In that study, platelet counts returned to normal in all patients, some despite continued treatment. Valproate may also inhibit the secondary phase of platelet aggregation, although this effect is unlikely to be of clinical significance except during the concomitant use of other drugs that affect coagulation. However, altered bleeding time, ecchymosis, petechiae, bruising, hematoma formation, epistaxis, and frank hemorrhage have been reported rarely. Hypofibrinogenemia has also been observed. Therapy with valproate products, particularly at high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothrombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The manufacturers recommend platelet counts and coagulation tests prior to initiating therapy and at periodic intervals thereafter, as well as before planned surgery. The dosage should be reduced or the drug withdrawn if clinical evidence of hemorrhage, bruising, or a disorder of hemostasis or coagulation occurs.

The use of valproate derivatives may be associated with dose-related thrombocytopenia, the incidence of which is generally low but has been reported at up to 27% in one study using high dosages (approximately 50 mg/kg/day of valproic acid). In that study, platelet counts returned to normal in all patients, some despite continued treatment. Valproate may also inhibit the secondary phase of platelet aggregation, although this effect is unlikely to be of clinical significance except during the concomitant use of other drugs that affect coagulation. However, altered bleeding time, ecchymosis, petechiae, bruising, hematoma formation, epistaxis, and frank hemorrhage have been reported rarely. Hypofibrinogenemia has also been observed. Therapy with valproate products, particularly at high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothrombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The manufacturers recommend platelet counts and coagulation tests prior to initiating therapy and at periodic intervals thereafter, as well as before planned surgery. The dosage should be reduced or the drug withdrawn if clinical evidence of hemorrhage, bruising, or a disorder of hemostasis or coagulation occurs.

The manufacturers state that there have been reports of altered thyroid function tests associated with the use of valproate. However, no specific information is given. Clinicians should be cognizant of this potential effect when prescribing or administering valproate products to patients with thyroid disease.

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.

The use of valproate derivatives may be associated with dose-related thrombocytopenia, the incidence of which is generally low but has been reported at up to 27% in one study using high dosages (approximately 50 mg/kg/day of valproic acid). In that study, platelet counts returned to normal in all patients, some despite continued treatment. Valproate may also inhibit the secondary phase of platelet aggregation, although this effect is unlikely to be of clinical significance except during the concomitant use of other drugs that affect coagulation. However, altered bleeding time, ecchymosis, petechiae, bruising, hematoma formation, epistaxis, and frank hemorrhage have been reported rarely. Hypofibrinogenemia has also been observed. Therapy with valproate products, particularly at high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothrombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The manufacturers recommend platelet counts and coagulation tests prior to initiating therapy and at periodic intervals thereafter, as well as before planned surgery. The dosage should be reduced or the drug withdrawn if clinical evidence of hemorrhage, bruising, or a disorder of hemostasis or coagulation occurs.