Verapamil, approved by the U.S. Food and Drug Administration in 1981, is a phenylalkylamine calcium channel blocking medication used to treat a wide variety of conditions. In addition to its use as a treatment for angina, heart arrhythmia, and high blood pressure, verapramil is sometimes used to prevent or treat migraines and cluster headaches. Despite this, headache is the drug's most common side effect. Other side effects include dizziness, fatigue, facial flushing, constipation, nausea, increased urination, swelling, and lightheadedness — the incidence of which increase along with the dosage. When determining the appropriate verapamil dose for a patient, the form of medication to be administered must be considered as well as the patient's age, condition, drug regimen, liver health and level of kidney function.
While studies on verapamil's efficacy have included pediatric patients and adult patients under the age of 65, the sample size of these groups have not been large enough to conclusively determine whether dosage adjustments are needed in these populations. If recommending this medication for either young or elderly patients, the lowest recommended dosage level should be used and only cautiously increased, as they may be more sensitive to the drug's effects. Although it has occasionally been used to treat pediatric patients, as of 2011 there is no conclusive evidence that any verapamil dose is effective in the treatment of this population.
Only one week of treatment is necessary for the initial verapamil dose to demonstrate its effect on high blood pressure, making dosage adjustments relatively easy in the treatment of this condition. A low starting dose of the immediate release form is considered to be 40 mg of the drug taken orally three times daily, although an initial dose of 80 mg with the same frequency is acceptable in low-risk patients. After the first week, the verapamil dose may be increased by incorporating a maintenance dose into the daily regimen. While doses as high as 480 mg have been given, there is little evidence to support total daily doses greater than 360 mg.
The lowest initial recommended dose for the prevention of angina is the same as that for the treatment of high blood pressure, although doses as high as 120 mg given three times daily have occasionally been used. When establishing an appropriate maintenance dosage after the first seven days of treatment, it is important to evaluate the patient's response to a dose eight hours after its administration. No clinical benefit has been observed when doses greater than 360 mg per day have been given.
Patients with kidney or liver failure should not generally be given verapamil due to their increased sensitivity to the drug. If necessary, an extremely small verapamil dose should be used. Repeat doses should not be given to patients with either of these conditions.
