No

False Neurotransmitter

Considered a second line agent in the treatment of hypertension, usually with a diuretic

B

Hypersensitivity to guanadrel or any component; known or suspected pheochromocytoma; concurrent use or within 1 week of any monoamine oxidase inhibitor; exacerbation of CHF

Orthostatic hypotension is common. Avoid using other drugs that cause orthostatic hypotension (alpha-blocking agents or reserpine). Discontinue 48-72 hours before elective surgery (reduces potential for vascular collapse). If emergency surgery required, notify anesthesiologist of the drug regimen. Avoid using tricyclic antidepressants and indirect-acting sympathomimetics (can reverse the blood pressure lowering effects). Use cautiously in asthma (may aggravate condition), CHF (sodium and water retention), and PUD (may aggravate condition). Safety and efficacy have not been established in pediatric patients. Dosage adjustment required with renal dysfunction.

>10%:

Cardiovascular: Palpitations (30%), chest pain (28%), peripheral edema (29%)

Central nervous system: Fatigue (64%), headache (58%), faintness (47% to 49%), drowsiness (45%), confusion (15%)

Gastrointestinal: Increased bowel movements (31%), gas pain (24% to 32%), constipation (21%), anorexia (19%), weight gain/loss (42% to 44%)

Genitourinary: Nocturia (48%), polyuria (34%), ejaculation disturbances (18%)

Neuromuscular & skeletal: Paresthesia (25%), aching limbs (43%), leg cramps (20% to 26%)

Ocular: Visual disturbances (29%)

Respiratory: Shortness of breath at rest (18%), coughing (27%)

1% to 10%:

Cardiovascular: Orthostatic hypotension

Central nervous system: Psychological problems (4%), depression (2%), sleep disorders (2%)

Gastrointestinal: Glossitis (8%), nausea/vomiting (4%), xerostomia (2%)

Genitourinary: Impotence (5%)

Renal: Hematuria (2%)

<1% (Limited to important or life-threatening symptoms): Cardiovascular: Syncope, angina

TCAs decrease hypotensive effect of guanadrel.

Increased toxicity of direct-acting amines (epinephrine, norepinephrine) by guanadrel; the hypotensive effect of guanadrel may be potentiated.

Increased effect of beta-blockers, vasodilators.

Phenothiazines may inhibit the antihypertensive response to guanadrel; consider an alternative antihypertensive with different mechanism of action.

Amphetamines, related sympathomimetics, and methylphenidate decrease the antihypertensive response to guanadrel; consider an alternative antihypertensive with different mechanism of action. Reassess the need for amphetamine, related sympathomimetic, or methylphenidate; consider alternatives.

Ephedrine may inhibit the antihypertensive response to quanadrel; consider an alternative antihypertensive with different mechanism of action. Reassess the need for ephedrine.

Norepinephrine/phenylephrine have exaggerated pressor response; monitor blood pressure closely.

MAO inhibitors may cause severe hypertension; give at least 1 week apart.

Acts as a false neurotransmitter that blocks the adrenergic actions of norepinephrine; it displaces norepinephrine from its presynaptic storage granules and thus exposes it to degradation; it thereby produces a reduction in total peripheral resistance and, therefore, blood pressure

Peak effect: Within 4-6 hours

Duration: 4-14 hours

Absorption: Oral: Rapid

Serum half-life, biphasic:

Initial: 1-4 hours

Terminal: 5-45 hours

Time to peak serum concentration: Within 1.5-2 hour

Oral:

Elderly: Initial: 5 mg once daily

Dosing interval in renal impairment:

Cl_cr 10-50 mL/minute: Administer every 12-24 hours.

Cl_cr <10 mL/minute: Administer every 24-48 hours.

Use is limited to second-line therapy in the treatment of hypertension.

Sedation is common; may cause confusion; may rarely cause depression

Contraindicated with MAOIs; TCAs and phenothiazines may decrease the hypotensive effects of guanadrel

Manufacturer's information states that guanadrel may block vasopressor activity of epinephrine. This has not been observed during use of epinephrine as a vasoconstrictor in local anesthesia.

No effects or complications reported

May cause orthostatic hypotension, sit or lie down at the first sign of dizziness or weakness; rise slowly from sitting or lying, especially for prolonged periods; take no new prescription or OTC medication without contacting your physician or pharmacist

Monitor blood pressure, standing and sitting/supine

Tablet, as sulfate: 10 mg, 25 mg

Finnerty FA Jr and Brogden RN, "Guanadrel: A Review of Its Pharmacodynamic and Pharmacokinetic Properties and Therapeutic Use in Hypertension," Drugs, 1985, 30(1):22-31.