Clonidine Alpha blockers

Caution [C, ] CrCl <30 Contra Component sensitivity, asthma, severe COPD, sinus bradycardia Disp Soln SE Irritation, bitter taste, superficial keratitis, ocular allergic Rxn EMS Drug is absorbed systemically OD May cause electrolyte disturbances (K), acidosis and bradycardia monitor ECG Doxazosin (Cardura, Cardura XL) [Antihypertensive/Alpha Blocker] Uses HTN symptomatic BPH Action < [-Adrenergic blocker relaxes bladder neck smooth muscle Dose HTN Initial 1 mg/d PO may be T to 16 mg/d PO BPH Initial 1 mg/d PO, may T to 8 mg/d XR 2-8mg qAM Caution [B, ] Use w/ PDE5 inhibitor (eg, sildenafil) can cause 1 BP Contra Component sensitivity Disp Tabs SE Dizziness, HA, drowsiness, sexual dysfxn, doses >4 mg T postural BP risk Interactions T Effects W/ nitrates, antihypertensives, EtOH i effects W/ NSAEDs, butcher s broom -t effects OF clonidine EMS Concurrent EtOH use can T drowsiness syncope may occur w/in 90 min of initial dose OD May cause profound hypotension place pt in supine position, give IV fluids, use pressors if needed... 

CENTRALLY ACTING ANTI HYPERTENSIVES -CLONIDINE ALPHA-BLOCKERS-PRAZOSIN Small case series indicate that prazosin may 1 the antihypertensive effect of donidine Uncertain at present Monitor BP at least weekly until stable... 

Those sympathoplegic drugs that act indirectly via the CNS include methyidopa and clonidine. Sympathoplegic drugs also may act directly as adrenergic neuron blockers, alpha blockers, or beta blockers. Examples of each class are provided. 

Accidental local infiltration of potent alpha agonists such as norepinephrine may lead to tissue ischemia and necrosis if not promptly reversed infiltration of the ischemic area with phentolamine is sometimes used to prevent tissue damage. Overdose with drugs of abuse such as amphetamine, cocaine, or phenylpropanolamine may lead to severe hypertension because of their indirect sympathomimetic actions. This hypertension will usually respond well to alpha-blockers. Sudden cessation of clonidine therapy leads to rebound hypertension (Chapter 11) this phenomenon is often treated with phentolamine. 

Sympatholytic syndrome. Blood pressure and pulse rate are both decreased (peripheral alpha blockers may cause hypotension with reflex tachycardia). The pupils are small, often of pinpoint size. Peristalsis is often decreased. (Examples centrally acting alpha-2 agonists [clonidine and methyidopa], opiates, and phenothiazines.)... 

For mention of the possibility of increased sedation with alcohol and clo-nidine or indoramin, see Clonidine and related drugs + CNS depressants , p.883 and Alcohol + Alpha blockers , p.42. 

ACE inhibitors Alpha blockers Beta blockers Calcium-channel blockers Clonidine Diuretics... 

Beta blockers ACE inhibitors Alpha blockers Angiotensin II receptor antagonists Calcium-channel blockers Dihydrofyridines Calcium-channel blockers Dikiazem Calcium-channel blockers Verapamil Clonidine Ketanserin Vasodilators... 

Geriatric Considerations - Summary Discontinuation of clonidine is likely to require a slow taper. If the patient is receiving a concomitant beta-blocker, the beta-blocker must be tapered and discontinued before discontinuing clonidine. Clonidine discontinuation in the presence of a beta-blocker can lead to severe hypertension and cardiovascular events due to unopposed alpha-receptor stimulation. CNS effects often preclude its use in older adults. A higher clonidine dose (0.4 mg/day) is generally needed to control peri- or postmenopausal vasomotor symptoms however, adverse effects often make it difficult to achieve effective doses. 

CENTRALLY ACTING ANTI HYPERTENSIVES BETA-BLOCKERS Risk of withdrawal t BP (rebound t BP) with clonidine and possibly moxonidine Withdrawal of clonidine, and possibly moxonidine, is associated with t circulating catecholamines beta-blockers, especially non-cardioselective ones, will allow the catecholamines to exert an unopposed alpha action (vasoconstriction) Do not withdraw clonidine or moxonidine while a patient is taking beta-blockers. Withdraw beta-blockers several days before slowly withdrawing clonidine and moxonidine... 

Clonidine (Catapres) is an alpha-2 adrenergic agonist, which thereby functions as a presynaptic irdiibitor of norepinephrine release. It is usually used to treat hypertension (like the beta blockers) but has been used to treat amciety disorders with some success. It is also used to treat opiate withdrawal. A typical starting dose is 0.1 mg two to three times daily (see figure 16-C). It is also available as a transdermal patch. 

B. Guanabenz is structurally similar to guanethidine, a ganglionic blocker. Guanfacine is related closely to guanabenz and has more selective alpha-2-agonist activity than clonidine. 

The presence of a beta blocker can exacerbate the rebound hypertension that follows the withdrawal of clonidine (see Clonidine + Beta blockers , p.882). Moxonidine is reported to have less affinity for central alpha-receptors than clonidine, and no such rebound hypertension has actually been seen when moxonidine is withdrawn. However, to be on the safe side the manufacturers advise that any beta blocker should be stopped first, followed by the moxonidine a few days later. ... 

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