Guanethidine lowers blood pressure by forcing the walls of the blood vessels to relax. This medication may be recommended for a patient with persistent high blood pressure who does not respond to more conservative treatment options like an exercise plan. In some areas, it has limited availability and other drugs may be considered first to ensure the patient can get an adequate supply of the medication and will not run out abruptly. People using guanethidine who are preparing to travel internationally should make sure they have enough for their entire trip.
This drug lowers concentrations of certain compounds in the body that encourage the smooth muscles to contract. By reducing their presence, it lowers blood pressure, as the tissue in the walls of the blood vessels relaxes, widening them. Patients need to take a consistent dose at the same time every day for the medication to be most effective. If they do not, the amount of medication in the body can fluctuate and the blood vessels may start to contract between doses, causing changes in blood pressure.
The most common guanethidine side effect is low blood pressure, which can occur when patients are adjusting to the medication or when they take an excessive dose. This can cause dizziness and may make the patient feel lightheaded. Some patients develop diarrhea and other signs of gastrointestinal upset while on guanethidine. These side effects may dissipate as the patient adapts to the drug, or they may become worse, indicating that the patient is not responding well.
Like other drugs used to control blood pressure, guanethidine doesn’t mix well with similar medications. If it is used with another medication intended to limit hypertension, the result can be a sudden and dangerous drop in pressure. Patients transitioning between medications may need to taper off one slowly before starting the new one, to make sure their bodies have time to adjust. If a doctor specifically recommends mixing medications, patients should be careful with doses and make sure they understand the directions.
While on guanethidine, patients may want to consider carrying a medic alert card with this information so care providers are aware of it in an emergency. It can also be a concern when preparing for surgery. A surgeon or anesthesiologist may ask a patient to stop taking it or adjust the dosage shortly before surgery to prevent complications. Once the patient gains approval, it is acceptable to start taking it again.