The problem these drugs solve
When you stand up, gravity pulls a meaningful volume of blood down into your legs. A healthy autonomic nervous system reacts within seconds — heart rate ticks up, blood vessels tighten, and the brain stays well-perfused. When that system doesn’t work right, the result is orthostatic intolerance: light-headedness, brain fog, racing heart, sometimes fainting (syncope) when you stand.
Several conditions live under this umbrella:
- Vasovagal syncope — the classic faint, often triggered by standing for a while, heat, pain, or strong emotion.
- POTS (postural orthostatic tachycardia syndrome) — the heart races on standing but blood pressure may not actually drop.
- Orthostatic hypotension — blood pressure drops when you stand, often in older adults or in autonomic dysfunction from diabetes, Parkinson’s disease, or other conditions.
Before we reach for medication, we put effort into the basics: 2 to 3 liters of fluid a day, generous salt intake, compression stockings (waist-high if tolerated), regular exercise (especially lower-body and core), counter-pressure maneuvers, and avoidance of long stationary standing in heat. Most patients improve substantially on these alone. When that’s not enough, we add medication — usually midodrine, fludrocortisone, or both.
Midodrine
What it does
Midodrine is converted in the body to an active form that stimulates alpha-1 receptors on blood vessels, telling them to constrict. The result is higher peripheral resistance — blood vessels stay tighter when you stand, so less blood pools in the legs and more blood pressure is maintained going to the brain. It does not stimulate the heart directly, so it doesn’t cause palpitations the way some other alpha-agonists do.
How to take it
Typical dosing is 2.5 to 10 mg three times a day. We start at 2.5 mg and titrate up based on symptoms and blood pressure response. The drug starts working in about 30 minutes and lasts roughly 3 to 4 hours.
The most important rule: take the last dose by mid-afternoon — usually no later than 4 to 6 hours before bedtime. If midodrine is on board when you lie down, it can drive your blood pressure up significantly while supine. That supine hypertension is the main side effect we worry about.
A common schedule looks like 8 a.m., noon, and 4 p.m.
Side effects to watch for
- Supine high blood pressure — the dose-timing rule prevents most of this. We may ask you to check blood pressure occasionally at home, particularly when lying down.
- Scalp tingling or goosebumps — common, often early in therapy, usually settles.
- Urinary urgency or retention — alpha receptors in the urinary tract get stimulated too.
- Itching.
We avoid midodrine in patients with severe coronary artery disease, severe kidney impairment, or significant urinary retention.
Fludrocortisone (Florinef)
What it does
Fludrocortisone is a synthetic mineralocorticoid — a relative of aldosterone, the hormone the adrenal gland makes to control salt and water balance. It tells the kidneys to reabsorb sodium and excrete potassium, which expands the body’s plasma volume. More volume in the system means more blood pressure when you stand.
It pairs well with midodrine because the two work on different parts of the problem: midodrine tightens the pipes, fludrocortisone fills them.
How to take it
Typical dosing is 0.1 to 0.2 mg once daily, in the morning. It takes a few days to a couple of weeks to see the full effect because the volume expansion builds slowly. Salt intake matters — fludrocortisone works much better when paired with deliberately liberal salt and fluid.
Side effects to watch for
- Low potassium (hypokalemia) — by far the most common issue. We check potassium at baseline and again a few weeks after starting, and periodically thereafter. Some patients need a potassium supplement.
- Swelling (edema) — particularly in the legs and around the eyes. A small amount is expected (it’s working). Significant swelling is a reason to call.
- Headache.
- High blood pressure when lying down — same concern as with midodrine; we check supine readings.
- Weight gain from the fluid retention.
- Worsening heart failure if cardiac function is borderline.
We avoid fludrocortisone in significant heart failure, uncontrolled high blood pressure, or severe kidney disease.
Using them together
For many patients with stubborn orthostatic intolerance, the combination is more useful than either alone. We typically start one first to see its effect, then add the second if needed. Both drugs should always be layered on top of the lifestyle basics — they don’t replace them.
When to call us
Tell us about persistent headaches, unusual swelling, palpitations, supine blood pressure readings above about 160/100, muscle weakness or cramps (which may signal low potassium), or worsening symptoms despite the medication. We will check kidney function, potassium, and blood pressure at routine intervals as long as you are on these drugs.