Classifications: central acting antihypertensive;
Therapeutic: antihypertensive

Prototype: Methyldopa
Pregnancy Category: C


2.5 mg tablets


Potent, long-acting nondepolarizing ganglionic blocking agent. Blocks neurotransmission at both sympathetic and parasympathetic ganglia by competing with acetylcholine (Ach) for cholinergic receptor sites on postsynaptic membranes. Reduces BP generally with greater decrease in standing or sitting BP than in supine BPs.

Therapeutic Effect

Reduces BP in both normotensive and hypertensive individuals.


Moderately severe to severe hypertension and uncomplicated malignant hypertension.


Coronary insufficiency, pyloric stenosis; glaucoma; uremia, chronic pyelonephritis; recent MI; mild labile hypertension; unreliable uncooperative patients; pregnancy (category C), lactation.

Cautious Use

Rising or elevated BUN; renal, cerebral, or coronary vascular pathology; recent CVA; prostatic hypertrophy, bladder neck obstruction, urethral stricture.

Route & Dosage

Moderately Severe to Severe Hypertension
Adult: PO 2.5 mg b.i.d. p.c. for 2 d, increased by increments of 2.5 mg at intervals of ≥2 d until desired BP response is attained (2.5–25 mg/d in 2–4 divided doses)


  • Give after meals for more gradual absorption and smoother control of BP. Schedule consistently relative to meals.
  • Note: Because of diurnal variations in BP, physician may prescribe a relatively small dose in the morning or omission of morning dose (morning BP usually lower) and larger doses for afternoon or evening.
  • Do not suddenly discontinue drug; may result in severe hypertensive rebound with CVA and acute CHF. Usually, other antihypertensive therapy must be substituted gradually, and patient must be supervised daily during period of dosage adjustment.
  • Store at 15°–30° C (59°–86° F) unless otherwise directed.

Adverse Effects (≥1%)

CNS: Weakness, fatigue, sedation, headache, paresthesias, confusion, depression, choreiform movements, tremor. CV: Orthostatic hypotension, changes in heart rate, dizziness, syncope, precipitation of angina. Special Senses: Mydriasis, blurred vision, cycloplegia, nasal congestion, dry mouth with dysphagia, glossitis. GI: Anorexia, nausea, vomiting, constipation, diarrhea, adynamic ileus. Urogenital: Decreased libido, impotence, urinary retention.


Drug: Alcohol, other antihypertensive agents, bethanechol, thiazide diuretics potentiate hypotensive effects; acetazolamide, sodium bicarbonate increase mecamylamine toxicity because they decrease its elimination.


Absorption: Almost completely from GI tract. Onset: 30 min–2 h. Peak: 3–5 h. Duration: 6–12 h. Distribution: Crosses blood–brain barrier and placenta; distributed into breast milk. Metabolism: In liver. Elimination: Primarily in urine.

Nursing Implications

Assessment & Drug Effects

  • Monitor therapeutic effectiveness by taking BP readings in standing position at time of maximal drug effect. Assess for symptoms of orthostatic hypotension (faintness, dizziness, light-headedness). Also note any changes in pulse rate.
  • Monitor BP closely. Partial tolerance may develop in some patients, necessitating dosage adjustment.
  • Report promptly constipation, frequent loose stools with abdominal distension, or decreased bowel sounds; may be the first signs of paralytic ileus (relatively frequent). Paralytic ileus is sometimes preceded by small, frequent stools.

Patient & Family Education

  • Make position changes slowly and in stages, particularly from recumbent to upright posture; sit on edge of bed and move ankles and feet before walking.
  • Lie down immediately if feeling light-headed or dizzy. Report adverse reactions immediately because drug effects may last hours to days after drug is discontinued.
  • Seasonal variations may alter the hypotensive effect (e.g., usually smaller doses are required in summer than in winter).
  • Do not drive or engage in potentially hazardous activities until response to drug is known.
  • Learn measures to relieve dry mouth; rinse mouth frequently with water, suck hard candy.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2022 Last Updated On: 12/03/2022 (0)
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