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Action/Kinetics:
Similar to that of guanethidine. Inhibits vasoconstriction by blocking efferent, peripheral sympathetic pathways by depleting norepinephrine reserves and inhibiting norepinephrine release. Causes increased sensitivity to norepinephrine.
Onset: 2 hr.
Peak plasma levels: 1.5-2 hr.
Peak effect: 4-6 hr.
t
1/2: Approximately 10 hr.
Duration: 4-14 hr. Excreted through the urine as unchanged drug (40%) and metabolites.
Uses:
Hypertension in those not responding to a thiazide diuretic.
Contraindications:
Pheochromocytoma, CHF, within 1 week of MAO drug use, within 2-3 days of elective surgery, lactation.
Special Concerns:
Use with caution in bronchial asthma and peptic ulcer. Safety and efficacy not established in children. Geriatric clients may be more sensitive to the hypotensive effects.
Side Effects:
CNS: Fainting, fatigue, headache, drowsiness, paresthesias, confusion, psychological problems, depression, syncope, sleep disorders, visual disturbances.
CV: Chest pain, orthostatic hypotension, palpitations, peripheral edema.
Respiratory: Exertional or resting SOB, coughing.
GI: Increase in number of bowel movements, constipation, anorexia, indigestion, flatus, glossitis, N&V, dry mouth and throat, abdominal distress or pain.
GU: Difficulty in ejaculation, impotence, nocturia, hematuria, urinary urgency or frequency.
Miscellaneous: Leg cramps during both the day and night, excessive weight gain or loss, backache, neckache, joint pain or inflammation, aching limbs.
Overdose Management:
Symptoms: Postural hypotension, syncope, dizziness, blurred vision.
Treatment: Administration of a vasoconstrictor (e.g., phenylephrine) if hypotension persists. If used, monitor carefully as client may be hypersensitive.
Drug Interactions:
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Beta-adrenergic blocking agents / Excessive hypotension, bradycardia
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Phenothiazines / Reverses effect of guanadrel
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Phenylpropanolamine /
Effect of guanadrel
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Reserpine / Excessive hypotension, bradycardia
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Sympathomimetics / Hypotensive effect of guanadrel may be reversed; also, guanadrel may
the effects of directly acting sympathomimetics
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Tricyclic antidepressants / Reverses effect of guanadrel
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Vasodilators /
Risk of orthostatic hypotension
How Supplied:
Tablet: 10 mg
Dosage
?Tablets
Hypertension.
Individualized. Initial: 5 mg b.i.d.;
then, increase dosage to maintenance level of 20-75 mg/day in two to four divided doses. With a C
CR of 30-60 mL/min, use an initial dose of 5 mg q 24 hr. If the C
CR is less than 30 mL/min, increase the dosing interval to q 48 hr. Make dose changes carefully q 7 or more days for moderate renal insufficiency and q 14 or more days for severe insufficiency.