Blood pressure falls
- D. Taverner, J. Marley, J.W.G. Tiller
- Aust Prescr 1995;18:21-2
- 1 January 1995
- DOI: 10.18773/austprescr.1995.029
5 min read
Prepared by D. Taverner, Senior Lecturer, Department of Clinical and Experimental Pharmacology, and J. Marley, Senior Lecturer, Department of Community Medicine, University of Adelaide, Adelaide
A 76 year old lady with hypertension attended for a regular review of her blood pressure which had been well controlled. We noticed that she had severe bruising on the right side of her face and right forearm. She told us that for some time she had been suffering from intermittent light-headedness while standing, which she had not reported. Her last episode had been severe enough to cause her to fall, striking her head and arm.
She had been taking prazosin, 2 mg 3 times daily, for the previous 7 months and no other medication. On examination, sitting blood pressure was 140/78, falling to 115/65 on standing. The heart rate was 76/minute both lying and standing. Standing reproduced her light-headedness, which was relieved by sitting down.
The prazosin was stopped and one week later her symptoms had improved and the bruising had resolved. Blood pressure was 150/90 lying and standing on no therapy.
Postural hypotension is usually defined as a blood pressure fall on standing (which may need to be prolonged) of >20 mm Hg systolic, >10 mm Hg diastolic. Symptomatic postural hypotension may occur at levels of blood pressure considered normal in young adults, if hypertensive vascular damage is present.
Remember that postural hypotension may not be present when you examine the patient. Be prepared to consider the diagnosis on the basis of history alone.
With prazosin and other alpha1 (postsynaptic) adrenergic blockers, first dose hypotension due to arterial and venous dilatation is well recognised and is minimised by using a low starting dose. With chronic use, postural hypotension may persist. The normal reflex tachycardia and small rise in diastolic blood pressure on standing is suppressed with these drugs, possibly because alpha2 (presynaptic) inhibition of catecholamine release is not blocked. Postural hypotension is particularly likely to occur when the dose is increased, or when additional drugs (especially beta blockers) are added to the regimen. Postural hypotension can be incapacitating, but is usually self limiting: patients with cerebrovascular disease may be at increased risk.
Normal elderly people have impaired baroreceptor reflexes and have an increased tendency to orthostatic hypotension which is exacerbated by alpha blocking drugs, even with repeated use. Prazosin should be used with care in this patient group, although it may be preferred for men with symptoms of benign prostatic hypertrophy (improving hesitancy).
There is no evidence that rebound hypertension occurs after sudden withdrawal of prazosin (unlike methyldopa and clonidine). It is therefore safe to stop prazosin abruptly in mild hypertension. As with most antihypertensive drugs, there are marked variations in blood pressure response between patients. Tolerance (loss of antihypertensive effect with prolonged use) does not occur with prazosin, although many patients need a dose of 20 mg/day in divided doses for maximal effect. The once daily dose regimen of the newer alpha 1 blockers (e.g. terazosin) may be an advantage.
All patients taking prazosin should have lying and standing blood pressures checked regularly. If postural hypotension (a blood pressure fall of >20 mm Hg systolic, >10 mm Hg diastolic) is detected, alternative drug treatment may be indicated, especially in the elderly and in patients with cerebrovascular disease.
Khoury AF, Kaplan NM. Alpha blocker therapy of hypertension. An unfulfilled promise. JAMA 1991;266:394-8.
A 78 year old man who has had a longstanding sleep disorder presents for a review. He says that each morning he finds he has urinated on the floor during the night, although he has no recollection of this. His elderly wife reports that he often seems very confused at night and on a couple of occasions he has had episodes of nocturnal wandering and getting lost in the house. During the day he is alert, rational and oriented, and not confused. His memory 'is not what it was'. On a number of occasions he has forgotten why he went to the shops, so now he always uses a written shopping list.
After retirement he had had a problem with insomnia. His doctor had prescribed 25 mg of amitriptyline which had helped for some time. When the insomnia recurred, the dose was increased to 50 mg, which he took for the following 12 years. He usually had a brandy nightcap.
On examination, there were no significant clinical findings. There was no evidence of depression or dementia, although the patient was apprehensive about what was happening to him during the night. He had a prostatectomy 11 years ago because of a marked increase in urinary problems, particularly hesitancy. There was a postural drop in blood pressure of 10 mm Hg on standing, which rapidly recovered.
A progressive reduction of amitriptyline, firstly to 25 mg at night for a week, then stopping it, was associated with a manifest worsening of insomnia, which partly settled over 4-6 weeks with counselling and the use of nonpharmacological techniques to encourage sleep. The nighttime confusion and urination ceased.
Insomnia is common in the elderly. More than 25% may complain of symptoms of severe insomnia. It is important to evaluate the patient to see that insomnia is not due to depression, anxiety, pain (e.g. arthritis), physical illness or adverse drug effects. In elderly men, prostatic obstruction and the need to pass urine can disturb sleep. Therefore, it is useful to ask what settles or disturbs the patient through the night.
In the majority of cases, there is no significant cause of insomnia. In these cases, it is useful to discuss the reduced requirement for sleep in older people and introduce nonpharmacological techniques.1 Perseverance with a nonpharmacological approach will often produce satisfactory results within 4-6 weeks.
The hypnotics of choice, when indicated for short term use, are benzodiazepines. However, recent publicity and antibenzodiazepine campaigns have made many doctors reluctant to prescribe these drugs and some patients are unwilling to take them. Zopiclone may be an alternative.
The sedative tricyclic antidepressants are now in vogue as alternatives to benzodiazepines when a hypnotic is needed. However, the sedative tricyclics are appreciably more toxic than benzodiazepines.
In this case, the use of a tricyclic may have precipitated a worsening of urinary hesitancy leading to the prostatectomy. The anticholinergic effects can also add to confusion in the elderly, especially at night, while the alpha adrenergic blocking actions of the tricyclics can result in postural hypotension with the risks of falls and injuries. There is a rapid development of tolerance to the sedative effect of the tricyclics. Within two weeks, patients will tolerate doses of tricyclic antidepressants which would have caused excessive sedation when the treatment was started. There are no studies showing long term hypnotic efficacy, and the efficacy in the short term is mainly confined to data on depressive illness.
Antidepressants have a role in the treatment of insomnia only when associated with depression. On stopping sedative tricyclics, a withdrawal syndrome may occur with rebound insomnia, an increase in dreaming, and some daytime agitation and anxiety. These symptoms usually settle within about 4 weeks.
The patient should be advised about the effects of alcohol. Alcohol, if taken in sufficient quantities, may assist a patient getting off to sleep, but is associated with waking a few hours later. Its diuretic effect can also cause wakefulness and its effects on cognitive function can also lead to nocturnal confusion.
Senior Lecturer, Department of Clinical and Experimental Pharmacology, University of Adelaide, Adelaide
Senior Lecturer, Department of Community Medicine, University of Adelaide, Adelaide
Department of Psychiatry, University of Melbourne, Royal Melbourne Hospital, Melbourne