Hydralazine dosage

Stohs and Scratchley (53) used thin layer chromatography to identify hydralazine in dosage forms and biological fluids (see Section 6.8). 

Zl. Zacest, R., and Koch-Weser, J., Relation of hydralazine plasma concentration to dosage and hypotensive action. Clin. Pharmacol. Ther. 13, 420-425 (1972). 

Bioavailability of hydralazine tablets is enhanced by the concurrent ingestion of food. Initiate therapy Initiate therapy in gradually increasing dosages individualize dosage. Start with 10 mg 4 times daily for the first 2 to 4 days, increase to 25 mg 4 times daily for the balance of the first week. 

Second and subsequent weeks Increase dosage to 50 mg 4 times daily. Maintenance Adjust dosage to lowest effective level. Twice daily dosage may be adequate. In a few resistant patients, up to 300 mg/day may be required for a significant antihypertensive effect. In such cases, consider a lower dosage of hydralazine combined with a thiazide or reserpine or a beta-blocker. However, when combining therapy, individual titration is essential to ensure the lowest possible therapeutic dose of each drug. 

Sodium nitroprusside (SNP) is both a venous and an arterial vasodilator. An important part of its vasodilator action is caused by the release of nitric oxide (NO), similarly as for the organic nitrates. SNP can only be administered via the intravenous route. It is a rapidly and short acting vasodilator. It has been used in the treatment of hypertensive emergencies and in the management of myocardial ischaemia. In spite of its vasodilator action it hardly influences heart rate, in contrast to hydralazine and minoxidil. The dosage of SNP should not be higher than 3 pg/kg/min within 48 h, in order to avoid the rise of cyanide ions and thiocyanate in the blood. 

V. Das Gupta, Quantitation of hydralazine HC1 in pharmaceutical dosage forms using HPLC, J. Liquid Chromatogr., 5 2497 (1985). 

Hydralazine (Apresoline) is a phthalazine derivative that has been in use for more than three decades, primarily in combination with other types of antihypertensives. One innovation was to combine it with (3-blocking propranolol, which effectively prevents reflex cardiac stimulation and allows lower dosages. Adding a diuretic to the regimen prevents the usual sodium and water retention. Its molecular mechanism of action is not fully understood. Its toxic effects at higher doses can resemble a syndrome of symptoms simulating... 

Das Gupta, V. Quantitation of hydralazine hydrochloride in pharmaceutical dosage forms using high-performance liquid chromatography. J.Liq.Chromatogr, 1985, 8, 2497-2509... 

Discuss dosage adjustments of hydralazine in patients with compromised renal function. 

A. Hydralazine and Minoxidil These older vasodilators have more effect on arterioles than on veins. They are orally active and suitable for chronic therapy. Hydralazine apparently acts through the release of nitric oxide. However, it is rarely used at high dosage because of its toxicity therefore, its efficacy is limited, fts toxicities include compensatory responses (tachycardia, salt and water retention Table 11-2) and drug-induced lupus erythematosus, which is reversible upon stopping the drug. However, this effect is uncommon at dosages below 200 mg/d. 

If hydralazine in moderate dosage is administered for several weeks, compensatory cardiac and renal responses will be observed. Specify the exact mechanisms and structures involved in these responses. The Skill Keeper Answer appears at the end of the chapter. 

A 63-year-old African-American woman with hypertension and dialysis-dependent renal insufficiency developed epigastric pain and jaundice, with h3rperbilmibinemia and a raised alkaline phosphatase activity, in keeping with cholestatic jaundice. It was attributed to hydralazine, which she had taken a dosage of 75 mg tds for 5 months. Imaging and other laboratory tests showed no other causes. There was complete clinical and biochemical recovery within 4 weeks of dmg withdrawaL... 

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