Phenylephrine should only be given to pregnant women who have a clear need.Extended use may cause rhinitis medicamentosa, a condition of rebound nasal congestion. Interactions
The increase in blood pressure effect of phenylephrine may be increased by drugs such as monoamine oxidase inhibitors, tricyclic antidepressants, and hydrocortisone. Patients taking these medications may need a lower dose of phenylephrine to achieve a similar increase in blood pressure. Drugs that may decrease the effects of phenylephrine may include calcium channel blockers, ACE inhibitors and benzodiazepines. Patients taking these medications may need a higher dose of phenylephrine to achieve a comparable increase in blood pressure. Pharmacology
Pharmacodynamics
Phenylephrine is a sympathomimetic drug, which means that it mimics the actions of epinephrine (commonly known as adrenaline) or norepinephrine. Phenylephrine selectively binds to alpha-1 receptors which cause blood vessels to constrict.Whereas pseudoephedrine causes both vasoconstriction and increase of mucociliary clearance through its nonspecific adrenergic activity, phenylephrines selective α-adrenergic agonism causes vasoconstriction alone, creating a difference in their methods of action. Pharmacokinetics
Oral phenylephrine is extensively metabolized by monoamine oxidase, an enzyme that is present on the mitochondrial membrane of cells throughout the body. Compared to intravenous pseudoephedrine, phenylephrine has a reduced and variable bioavailability; only up to 38%. References
External links
"Phenylephrine". U.S. National Library of Medicine: Drug Information Portal.
Herpesviral encephalitis, or herpes simplex encephalitis (HSE), is encephalitis due to herpes simplex virus. It is estimated to affect at least 1 in 500,000 individuals per year, and some studies suggest an incidence rate of 5.9 cases per 100,000 live births.About 90% of cases of herpes encephalitis are caused by herpes simplex virus-1 (HSV-1), the same virus that causes cold sores. According to a 2006 estimate, 57% of American adults were infected with HSV-1, which is spread through droplets, casual contact and sometimes sexual contact, though most infected people never have cold sores. The rest of cases are due to HSV-2, which is typically spread through sexual contact and is the cause of genital herpes. Two-thirds of HSE cases occur in individuals already seropositive for HSV-1, few of whom (only 10%) have history of recurrent orofacial herpes, while about one third of cases results from an initial infection by HSV-1, predominantly occurring in individuals under the age of 18. Approximately half of individuals who develop HSE are over 50 years of age. Signs and symptoms
Most individuals with HSE show a decrease in their level of consciousness and an altered mental state presenting as confusion, and changes in personality. Increased numbers of white blood cells can be found in patients cerebrospinal fluid, without the presence of pathogenic bacteria and fungi. Patients typically have a fever and may have seizures.