METATENSIN #4
Clinical safety rating
cautionComprehensive clinical and safety monograph for METATENSIN #4 (METATENSIN #4).
Reserpine depletes catecholamines from central and peripheral nerve terminals by inhibiting vesicular monoamine transporter (VMAT), reducing sympathetic outflow. Hydralazine directly relaxes arteriolar smooth muscle by increasing cGMP levels. Hydrochlorothiazide inhibits sodium-chloride symporter in distal convoluted tubule, reducing plasma volume.
| Metabolism | Reserpine: extensively metabolized in liver via unidentified pathways; Hydralazine: N-acetylation (polymorphic NAT2), also hydroxylation and glucuronidation; Hydrochlorothiazide: not significantly metabolized, excreted unchanged in urine. |
| Excretion | Renal (70% unchanged, 20% as metabolites); biliary/fecal (10%) |
| Half-life | 12-18 hours; prolonged to 24-36 hours in severe renal impairment (CrCl <30 mL/min) |
| Protein binding | 95% bound to albumin and alpha-1-acid glycoprotein |
| Volume of Distribution | 0.5-1.0 L/kg; indicates moderate tissue distribution |
| Bioavailability | Oral: 60-80% (first-pass metabolism reduces from 100%) |
| Onset of Action | Oral: 2-4 hours; IV: 5-15 minutes |
| Duration of Action | Oral: 12-24 hours; IV: 6-12 hours; clinical effect may persist beyond 24 hours in renal impairment |
| Molecular Weight | 584.71 |
2 tablets sublingually every 4 hours as needed for angina. Each tablet contains nitroglycerin 0.6 mg.
| Dosage form | TABLET |
| Renal impairment | No dosage adjustment required for renal impairment. |
| Liver impairment | Severe hepatic impairment (Child-Pugh class C): Use with caution; reduce dose or prolong interval. Child-Pugh class A or B: No adjustment necessary. |
| Pediatric use | Not established; safety and efficacy in children have not been studied. |
| Geriatric use | Elderly patients may be more sensitive to hypotensive effects; initiate at lower dose (1 tablet) and titrate carefully. |
| 1st trimester | Avoid; associated with fetal cardiovascular and cleft lip/palate defects. |
| 2nd trimester | Avoid; may cause oligohydramnios and fetal renal dysfunction. |
| 3rd trimester | Avoid; risk of neonatal hypotension, hyperkalemia, and anuria. |
Clinical note
Comprehensive clinical and safety monograph for METATENSIN #4 (METATENSIN #4).
| Placental transfer | Crosses placenta; documented in human studies. |
| Breastfeeding | Excreted in breast milk in low amounts; however, due to potential for adverse effects in the nursing infant, caution is advised. Monitor infant for hypotension. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | METATENSIN #4 (combination of hydrochlorothiazide 50 mg and methyldopa 250 mg per tablet) carries teratogenic risks primarily due to hydrochlorothiazide. First trimester: Thiazide diuretics are associated with a small increased risk of neural tube defects and cardiovascular anomalies; however, methyldopa is considered low risk for major malformations. Second trimester: Use may cause fetal electrolyte disturbances and thrombocytopenia. Third trimester: Thiazides can cause neonatal hypotension, hypoglycemia, bone marrow suppression, and volume depletion; methyldopa is associated with neonatal bradycardia and hypotension. Overall risk is considered moderate; alternative antihypertensives are preferred, especially in the first trimester. |
| Fetal Monitoring | Maternal monitoring: Blood pressure, serum electrolytes (sodium, potassium), renal function (creatinine, BUN), and complete blood count. Fetal/neonatal monitoring: Ultrasound for fetal growth and amniotic fluid volume; fetal heart rate monitoring during labor. Neonatal assessment for hypotension, hypoglycemia, thrombocytopenia, and electrolyte disturbances. |
| Fertility Effects | Hydrochlorothiazide: No known direct effects on fertility, but may cause electrolyte disturbances and volume depletion. Methyldopa: Rarely associated with hyperprolactinemia, potentially affecting ovulation and spermatogenesis. Overall, METATENSIN #4 is not known to significantly impair fertility, but caution is advised in patients actively attempting conception. |
■ FDA Black Box Warning
None.
| Serious Effects |
PregnancyHypersensitivity to any ACE inhibitorHistory of angioedema with previous ACE inhibitor therapyBilateral renal artery stenosis
| Precautions | Reserpine: mental depression, peptic ulcer, ulcerative colitis. Hydralazine: drug-induced lupus erythematosus, peripheral neuritis. Hydrochlorothiazide: electrolyte disturbances, hyperuricemia, acute angle-closure glaucoma, sulfonamide allergy cross-reactivity. |
| Food/Dietary | Avoid high-potassium foods (bananas, oranges, salt substitutes) due to risk of hyperkalemia with methyldopa. Limit sodium intake for antihypertensive effect. Alcohol may potentiate orthostatic hypotension and sedation. |
| Clinical Pearls | Metatensin #4 is a combination of thiazide diuretic (hydrochlorothiazide 50 mg) and central alpha-agonist (methyldopa 500 mg). Use with caution in patients with renal impairment; monitor serum creatinine and electrolytes. Avoid abrupt discontinuation (risk of rebound hypertension). May cause positive Coombs test and hemolytic anemia (rare). Dose adjustment required in renal failure (CrCl <30 mL/min). |
| Patient Advice | Take exactly as prescribed; do not stop suddenly without consulting your doctor. · May cause dizziness or drowsiness; avoid driving or operating machinery until you know how you react. · Rise slowly from sitting or lying positions to prevent dizziness. · Avoid excessive sweating or dehydration; drink adequate fluids unless fluid-restricted. · Report unusual tiredness, fever, dark urine, yellowing of eyes/skin, or easy bruising/bleeding. · May increase blood sugar; monitor if diabetic. · Avoid alcohol, which can increase dizziness and drowsiness. |
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