Antihypertensives Sodium nitroprusside

Hydrogen cyanide (HCN) is a colorless, rapidly acting, highly poisonous gas or liquid that has an odor of bitter almonds. Most HCN is used as an intermediate at the site of production. Major uses include the manufacture of nylons, plastics, and fumigants. Exposures to HCN may occur in industrial situations as well as from cigarette smoke, combustion products, and naturally occurring cyanide compounds in foods. Sodium nitroprusside (Na2[Fe(CN)5 N0]-2H20), which has been used as an antihypertensive in humans, breaks down into nonionized HCN. 

It is usually recommended that ACE inhibitors be continued peri-operatively in common with other antihypertensives. There is some evidence that postoperative haemodynamic stability is improved and renal function protected. Pretreatment with ACE inhibitors may reduce tachyphylaxis to sodium nitroprusside and help to prevent rebound hypertension. On the other hand, there is evidence that ACE inhibitors may predispose to hypotension during anaesthesia and that they reduce cerebral blood flow during any period of systemic hypotension. Furthermore, the response to and recovery from hypotensive episodes due to blood loss or circulatory depletion may be impaired. At present, the advice concerning these drugs would be to continue therapy up to and including the day of operation. Another rare side-effect of ACE inhibitors is angioneurotic oedema, which has occasionally been seen complicating intubation. 

Q9 Sodium nitroprusside can be used to rapidly reduce BP in hypertensive emergencies, but it is not suitable as a regular antihypertensive medication. Why is this ... 

Q9 Sodium nitroprusside acts via the production of NO. It is a powerful vasodilator and a potent, rapidly acting antihypertensive agent. The drug is administered by intravenous infusion but is then converted to thiocyanate in plasma. Thiocyanate toxicity can occur with continued use consequently, sodium nitroprusside can be used only for short-term treatment. 

VASODILATOR ANTIHYPERTENSIVES BETA-BLOCKERS t hypotensive effect Additive hypotensive effect with diazoxide, hydralazine, minoxidil and sodium nitroprusside. In addition, hydralazine may T the bioavailability of beta-blockers with a high first-pass metabolism (e.g. propanolol and metoprolol), possibly due to alterations in hepatic blood flow or inhibited hepatic metabolism Monitor BP closely... 

At first the drug was used orally as an antihypertensive, but it was phased out with the advent of the ganglionic blockers and reserpines. Sodium nitroprusside was subsequently resurrected as a parenteral emergency drug. It is now a most powerful vasodilator, given by IV infusion to obtain almost immediate reduction in pressure in hypertensive crises. By regulating the rate of administration minute by minute, blood pressure control becomes possible. 

Diazoxide is a parenteral, rapid, and direct-acting vasodilating antihypertensive used in hypertensive emergencies. An IV injection can drop blood pressure by as much as 80 mmHg in 5 minutes. Unlike sodium nitroprusside, however, venous dilation is not part of its mechanism. Chemically it is a benzothiadiazide without the sulfamoyl function at the 7 position (see diuretics). In fact, diazoxide is not a diuretic. Chronic use of diazoxide reflexly increases renin release, which actually counteracts the antihypertensive effect of the drug by expanding the volume of circulating fluid. 

Smaller doses of sodium nitroprusside might be required in patients receiving antihypertensive drugs. There is a risk of severe hypotension if phosphodiesterase inhibitors (e.g. sildenafil, tadaiafil and vardenafil) are used with sodium nitroprusside. 

The use of phosphodiesterase inhibitors (e.g. sildenafil, tadaiafil and var-denafil) with sodium nitroprusside is contraindicated by the manufacturers, due to the risk of severe hypotension. See also Phosphodiesterase type-5 inhihitors +Nitrates , p.l272. A case report describes the therapeutic use of sildenafil to enhance the hypotensive effect of sodium nitroprusside and other antihypertensives in a patient with a hypertensive crisis. ... 

The antihypertensive properties of nitroprusside have been known since the late 1920s but they were not clinically used until the 1950s.10 It can be easily synthesized from sodium ferrocyanide and strong nitric acid by heating. 

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