Direct-acting vasodilators: Nursing pharmacology

Direct-acting vasodilators are a class of antihypertensive medications that are used for severe refractory hypertension, malignant hypertension, and hypertensive emergencies.

These medications include hydralazine, which can be administered orally, intravenously, and intramuscularly; minoxidil, which can be administered orally or topically; and sodium nitroprusside, which is given intravenously.Once administered, direct acting vasodilators rapidly work on the vascular smooth muscle cells by preventing the increase of intracellular calcium concentration.

As a result, direct acting vasodilators prevent vasoconstriction and promote vasodilation, leading to a reduction in the total peripheral resistance and blood pressure.

Keep in mind that hydralazine and minoxidil mainly work on arterioles, while sodium nitroprusside works on both arterioles and venules.

Now, since direct acting vasodilators tend to work rapidly, they can result in sudden vasodilation and hypotension. This may lead to side effects, including dizziness, headache, reflex tachycardia, palpitations, and edema.

Other side effects include nausea, vomiting, and gastrointestinal distress. So to counteract side effects like reflex tachycardia and edema, direct acting vasodilators can be used in combination with beta-blockers or diuretics, but under close monitoring for adverse effects.

Now, through an unclear mechanism, hydralazine may trigger a lupus-like syndrome, which can involve multiple organs. Clients may experience severe malaise, myalgia, arthralgia, pericarditis, and hepatosplenomegaly, and upon blood tests, they may present with leukopenia, thrombocytopenia, and positive autoantibodies.

What’s important to keep in mind is that hydralazine-induced lupus-like syndrome mainly affects clients who take higher doses for a prolonged period of time, and can be reversed upon discontinuation of hydralazine.Regarding minoxidil, an important boxed warning is that it can cause pericardial effusion, which may progress to cardiac tamponade, and it can exacerbate angina pectoris.

On that account, minoxidil should be reserved for hypertensive clients who don’t respond adequately to the maximum therapeutic doses of two other antihypertensive medications and a diuretic.

Another interesting side effect of minoxidil is hypertrichosis, which means excessive hair growth! In fact, minoxidil can be applied topically to promote hair growth and treat hair loss or alopecia.Finally, sodium nitroprusside has a boxed warning because it contains cyanide, which is released when nitroprusside is metabolized; normally the liver is able to convert the cyanide into a less toxic byproduct called thiocyanate, but if nitroprusside is given over several days, the cyanide can accumulate and cause problems such as disorientation and delirium.

Moreover, if sodium nitroprusside is administered too quickly, clients may develop cyanide poisoning, which can lead to hypoxia and metabolic acidosis.

Cyanide poisoning typically presents with dizziness, confusion, headache, mydriasis, tachypnea, and tachycardia; while severe cases can develop hypotension, apnea, seizures, and even coma.

Finally, sodium nitroprusside can also suppress iodine uptake by thyroid cells, which can lead to hypothyroidism.Direct-acting vasodilators are contraindicated in clients with cerebrovascular insufficiency and any other condition that could be worsened by a sudden decrease in blood pressure, like peripheral vascular disease, coronary artery disease, heart failure, and mitral valve disease, as well as septic shock.

In addition, these medications should be used with caution during pregnancy and breastfeeding. Regarding interactions, generally all direct-acting vasodilators should not be combined with alcohol, especially not hydralazine, while combination with other antihypertensives or diuretics should only be done under close monitoring, as they may increase the risk of hypotension.Alright, before administering a direct-acting vasodilator, perform a baseline assessment of your client, including vital signs, especially heart rate and blood pressure; ECG, heart and lung sounds and weight.

Next, review the client’s latest lab values, including CBC, electrolytes, as well as hepatic and renal function. Be sure your client understands why the medication is prescribed, to take their medication as directed, avoid abruptly stopping the medication, and to keep their follow-up appointments for blood pressure monitoring.

Finally, if their healthcare provider has also prescribed a prescribed beta-blocker or diuretic along with the hydralazine or minoxidil, explain how these medications help counteract some of the side effects of the medications such as reflex tachycardia and water retention.

Now, if your client is prescribed PO hydralazine, instruct them to take it with meals to help promote absorption. Let them know that if they experience side effects such as dizziness, weakness, headache, fatigue or a fast heartbeat, that they should contact their healthcare provider.

Also stress the importance of reporting symptoms such as muscle aches, joint pain or fever, which can indicate the development of a serious lupus-like syndrome.

If your client is prescribed PO minoxidil, instruct them to take the medication at a consistent time of the day, but without regard to meals.

Let them know that an increase in body hair growth is a possible side effect, that it is reversible, and if it occurs they should contact their healthcare provider.

Also be sure your client understands the importance of reporting side effects such as shortness of breath, swelling, chest pain or a very fast heart beat.Now, if you are administering hydralazine IV, be sure to monitor your client’s vital signs frequently and assess for signs of fluid overload, such as edema, pulmonary crackles or orthopnea.Alright, nitroprusside is a high alert medication administered for problems like acute hypertensive emergencies.

Before beginning the IV infusion, confirm that the client is on continuous cardiorespiratory monitoring and automatic blood pressure monitoring; that they have an established, patent IV access; and have emergency equipment and the antidote sodium thiosulfate readily available.

Then, program the pump settings to infuse the medication as ordered, and double-check all settings with a second nurse. During the infusion, monitor the IV site for extravasation and prompt your client to report any feelings of burning or stinging.

Keep a close eye on their vital signs and assess for signs of toxicity, including altered mental status, agitation, tremor, or a report of tinnitus.

If toxicity is suspected, stop the infusion, notify the physician immediately, and prepare to administer the antidote. Alright, as a quick recap ….

Direct-acting vasodilators are a class of anti-hypertensive medications that are used for refractory hypertension, malignant hypertension, and hypertensive emergencies.

Hydralazine, minoxidil and nitroprusside promote vasodilation, reduce peripheral resistance and lower blood pressure. Nurses are responsible for safe administration and close monitoring of the client’s response to medication administration, including vital signs, heart and lung sounds, weight, fluid status and side effects.

Lastly, nurses provide teaching for clients on self-administration as well as what the client can expect during treatment.