Yes

False Neurotransmitter

Treatment of moderate to severe hypertension

C

Hypersensitivity to guanethidine or any component; known or suspected pheochromocytoma; concurrent use or within 1 week of any monoamine oxidase inhibitor; exacerbation of CHF (unrelated to HTN)

Orthostatic hypotension is common. Avoid using other drugs that cause orthostatic hypotension (alpha-blocking agents or reserpine). Discontinue 2 weeks before elective surgery (reduces potential for vascular collapse). If emergency surgery required, notify anesthesiologist of the drug regimen. Fever reduces dosage requirements. 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), renal dysfunction (can worsen renal function), recent MI, cerebrovascular disease with encephalopathy, and PUD (may aggravate condition). Safety and efficacy have not been established in pediatric patients. Dosage adjustment required with severe renal dysfunction.

>10%:

Cardiovascular: Palpitations, bradycardia, chest pain, peripheral edema, orthostatic hypotension

Central nervous system: Fatigue, headache, faintness, drowsiness, confusion

Gastrointestinal: Increased bowel movements, gas pain, constipation, anorexia, weight gain/loss

Genitourinary: Nocturia, polyuria, impotence, ejaculation disturbances

Neuromuscular & skeletal: Paresthesia, aching limbs, leg cramps, backache, arthralgia

Ocular: Visual disturbances

Respiratory: Shortness of breath, coughing

1% to 10%:

Central nervous system: Psychological problems, depression, sleep disorders

Gastrointestinal: Glossitis, nausea, vomiting, dry mouth

Renal: Hematuria

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

Symptoms of overdose include hypotension, blurred vision, dizziness, and syncope. Treatment is supportive and symptomatic.

TCAs decrease hypotensive effect of guanethidine.

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

Amphetamines, related sympathomimetics, and methylphenidate decrease the antihypertensive response to guanethidine; 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 guanethidine; consider an alternative antihypertensive with different mechanism of action. Reassess the need for ephedrine.

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

Oral contraceptives may decrease hypotensive effect; avoid concurrent use.

Minoxidil may cause severe orthostatic hypotension; avoid concurrent use.

Enflurane may cause hypotension; avoid concurrent use.

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

Onset of effect: Within 0.5-2 hours

Peak antihypertensive effect: Within 6-8 hours

Duration: 24-48 hours

Absorption: Irregular (3% to 55%)

Serum half-life: 5-10 days

Oral:

Adults:

Ambulatory patients: Initial: 10 mg/day; increase at 5- to 7-day intervals to an average of 25-50 mg/day.

Hospitalized patients: Initial: 25-50 mg/day; increase by 25-50 mg/day or every other day to desired therapeutic response.

Elderly: Initial: 5 mg once daily

Dosing interval in renal impairment: Cl_cr <10 mL/minute: Administer every 24-36 hours.

Not routinely used in clinical practice because of significant and marked hypotension.

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

Contraindicated with MAOIs; TCAs and antipsychotics may decrease the hypotensive effects of guanethidine

Manufacturer's information states that haloperidol 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

Take as directed. Do not skip dose or discontinue without consulting prescriber. Store medication container away from light. Follow recommended diet and exercise program. Do not use OTC medications which may affect blood pressure (eg, cough or cold remedies, diet pills, stay-awake medications) without consulting prescriber. This medication may cause drowsiness, dizziness, or impaired judgment (use caution when driving or engaging in tasks that require alertness until response to drug is known); decreased libido or sexual function (will resolve when drug is discontinued); postural hypotension (use caution when rising from sitting or lying position or when climbing stairs - this may be worse in early morning, during hot weather, following exercise, or with alcohol use); or dry mouth or nausea (frequent mouth care or sucking lozenges may help). Report difficulty, pain, or burning on urination; increased nervousness or depression; sudden weight gain (weigh yourself in the same clothes at the same time of day once a week); unusual or persistent swelling of ankles, feet, or extremities; wet cough or respiratory difficulty; chest pain or palpitations; muscle weakness, fatigue, or pain; or other persistent side effects. Pregnancy/breast-feeding precautions: Inform prescriber if you are or intend to be pregnant. Consult prescriber if breast-feeding.

Tablet may be crushed

Monitor blood pressure, standing and sitting/supine; observe for orthostasis

Tablet, as monosulfate: 10 mg, 25 mg

Kalmanovitch DV and Hardwick PB, "Hypotension After Guanethidine Block," Anaesthesia, 1988, 43(3):256.