WARNINGS
Chlorthalidone should be used with caution in severe renal disease. In patients with renal disease, chlorthalidone or related drugs may precipitate azotemia. Cumulative effects of the drug may develop in patients with impaired renal function. Chlorthalidone should be used with caution in patients with impaired hepatic function or progressive liver disease, because minor alterations of fluid and electrolyte balance may precipitate hepatic coma.
Sensitivity reactions may occur in patients with a history of allergy or bronchial asthma.
The possibility of exacerbation or activation of systemic lupus erythematosus has been reported with thiazide diuretics which are structurally related to chlorthalidone. However, systemic lupus erythematosus has not been reported following chlorthalidone administration.
PRECAUTIONS
Clonidine Hydrochloride
General
In patients who have developed localized contact sensitization to transdermal clonidine, substitution of oral clonidine hydrochloride therapy may be associated with the development of a generalized skin rash.
In patients who develop an allergic reaction from transdermal clonidine that extends beyond the local patch site (such as generalized skin rash, urticaria, or angioedema), oral clonidine hydrochloride substitution may elicit a similar reaction.
As with all antihypertensive therapy, clonidine hydrochloride should be used with caution in patients with severe coronary insufficiency, recent myocardial infarction, cerebrovascular disease or chronic renal failure.
Withdrawal
Patients should be instructed not to discontinue therapy without consulting their physician. Sudden cessation of clonidine treatment has resulted in subjective symptoms such as nervousness, agitation and headache, accompanied or followed by a rapid rise in blood pressure and elevated catecholamine concentrations in the plasma, but such occurrences have usually been associated with previous administration of high oral doses (exceeding 1.2 mg/day) and/or with continuation of concomitant beta-blocker therapy. Rare instances of hypertensive encephalopathy and death have been reported. When discontinuing therapy with clonidine hydrochloride, the physician should reduce the dose gradually over 2 to 4 days to avoid withdrawal symptomatology.
An excessive rise in blood pressure following clonidine hydrochloride discontinuance can be reversed by administration of oral clonidine or by intravenous phentolamine. If therapy is to be discontinued in patients receiving beta-blockers and clonidine concurrently, beta-blockers should be discontinued several days before the gradual withdrawal of clonidine hydrochloride.
Perioperative Use
Administration of clonidine hydrochloride should be continued to within four hours of surgery and resumed as soon as possible thereafter. The blood pressure should be carefully monitored and appropriate measures instituted to control it as necessary.
Information for Patients
Patients who engage in potentially hazardous activities, such as operating machinery or driving, should be advised of a potential sedative effect of clonidine. Patients should be cautioned against interruption of clonidine hydrochloride therapy without a physician's advice.
Drug Interactions
If a patient receiving clonidine hydrochloride is also taking tricyclic antidepressants, the effect of clonidine may be reduced, thus necessitating an increase in dosage. Clonidine hydrochloride may enhance the CNS-depressive effects of alcohol, barbiturates or other sedatives. Amitriptyline in combination with clonidine enhances the manifestation of corneal lesions in rats (see Ocular Toxicity).
Ocular Toxicity
In several studies, oral clonidine hydrochloride produced a dose-dependent increase in the incidence and severity of spontaneously occurring retinal degeneration in albino rats treated for six months or longer. Tissue distribution studies in dogs and monkeys revealed that clonidine hydrochloride was concentrated in the choroid of the eye. In view of the retinal degeneration observed in rats, eye examinations were performed in 908 patients prior to the start of clonidine hydrochloride therapy, who were then examined periodically thereafter. In 353 of these 908 patients, examinations were performed for periods of 24 months or longer. Except for some dryness of the eyes, no drug-related abnormal ophthalmologic findings were recorded and clonidine hydrochloride did not alter retinal function as shown by specialized tests such as the electroretinogram and macular dazzle.
In rats, clonidine hydrochloride in combination with amitriptyline produced corneal lesions within 5 days.
Carcinogenesis, Mutagenesis, Impairment of Fertility
In a 132-week (fixed concentration) dietary administration study in rats, clonidine hydrochloride administered at 32 to 46 times the maximum recommended daily human oral dose was unassociated with evidence of carcinogenic potential.
Fertility of male or female rats was unaffected by clonidine hydrochloride doses as high as 150 mcg/kg or about 3 times the maximum recommended daily human oral dose (MRDHD). Fertility of female rats did, however, appear to be affected (in another experiment) at dose levels of 500 to 2000 mcg/kg or 10 to 40 times the MRDHD.
Usage in Pregnancy
Teratogenic Effect
Pregnancy Category C
Reproduction studies performed in rabbits at doses up to approximately 3 times the maximum recommended daily human dose (MRDHD) of clonidine hydrochloride have revealed no evidence of teratogenic or embryotoxic potential. In rats however, doses as low as 1/3 the MRDHD were associated with increased resorptions in a study in which dams were treated continuously from 2 months prior to mating. Increased resorptions were not associated with treatment at the same or at higher dose levels (up to 3 times the MRDHD) when dams were treated days 6 to 15 of gestation. Increased resorptions were observed at much higher levels (40 times the MRDHD) in rats and mice treated days 1 to 14 of gestation (lowest dose employed in that study was 500 mcg/kg). There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Nursing Mothers
As clonidine hydrochloride is excreted in human milk, caution should be exercised when it is administered to a nursing woman.
Pediatric Use
Safety and effectiveness in the pediatric population have not been established.
Chlorthalidone
General
Hypokalemia and other electrolyte abnormalities, including hyponatremia and hypochloremic alkalosis, are common in patients receiving chlorthalidone. These abnormalities are dose-related but may occur even at the lowest marketed doses of chlorthalidone. Serum electrolytes should be determined before initiating therapy and at periodic intervals during therapy. Serum and urine electrolyte determinations are particularly important when the patient is vomiting excessively or receiving parenteral fluids. All patients taking chlorthalidone should be observed for clinical signs of electrolyte imbalance, including dryness of mouth, thirst, weakness, lethargy, drowsiness, restlessness, muscle pains or cramps, muscular fatigue, hypotension, oliguria, tachycardia, palpitations and gastrointestinal disturbances, such as nausea and vomiting. Digitalis therapy may exaggerate metabolic effects of hypokalemia especially with reference to myocardial activity.
Any chloride deficit is generally mild and usually does not require specific treatment except under extraordinary circumstances (as in liver disease or renal disease). Dilutional hyponatremia may occur in edematous patients in hot weather: appropriate therapy is water restriction, rather than administration of salt, except in rare instances when the hyponatremia is life-threatening. In cases of actual salt depletion, appropriate replacement is the therapy of choice.
Uric Acid
Hyperuricemia may occur or frank gout may be precipitated in certain patients receiving chlorthalidone.
Other
Increases in serum glucose may occur and latent diabetes mellitus may become manifest during chlorthalidone therapy (see PRECAUTIONS: Chlorthalidone: Drug Interactions). Chlorthalidone and related drugs may decrease serum PBI levels without signs of thyroid disturbance.
Information for Patients
Patients should inform their doctor if they have: 1) had an allergic reaction to chlorthalidone or other diuretics or have asthma 2) kidney disease 3) liver disease 4) gout 5) systemic lupus erythematosus, or 6) been taking other drugs such as cortisone, digitalis, lithium carbonate, or drugs for diabetes.
Patients should be cautioned to contact their physician if they experience any of the following symptoms of potassium loss: excess thirst, tiredness, drowsiness, restlessness, muscle pains or cramps, nausea, vomiting or increased heart rate or pulse.
Patients should also be cautioned that taking alcohol can increase the chance of dizziness occurring.
Laboratory Tests
Periodic determination of serum electrolytes to detect possible electrolyte imbalance should be performed at appropriate intervals.
All patients receiving chlorthalidone should be observed for clinical signs of fluid or electrolyte imbalance: namely, hyponatremia, hypochloremic alkalosis and hypokalemia. Serum and urine electrolyte determinations are particularly important when the patient is vomiting excessively or receiving parenteral fluids.
Drug Interactions
Chlorthalidone may add to or potentiate the action of other antihypertensive drugs. Insulin requirements in diabetic patients may be increased, decreased or unchanged. Higher dosage of oral hypoglycemic agents may be required. Chlorthalidone and related drugs may increase the responsiveness to tubocurarine. Chlorthalidone and related drugs may decrease arterial responsiveness to norepinephrine. This diminution is not sufficient to preclude effectiveness of the pressor agent for therapeutic use. Lithium renal clearance is reduced by chlorthalidone, increasing the risk of lithium toxicity.
Drug/Laboratory Test Interactions
Chlorthalidone and related drugs may decrease serum PBI levels without signs of thyroid disturbance.
Carcinogenesis, Mutagenesis, Impairment of Fertility
No information is available.
Usage in Pregnancy
Teratogenic Effects
Pregnancy Category B
Reproduction studies have been performed in the rat and the rabbit at doses up to 420 times the human dose and have revealed no evidence of harm to the fetus due to chlorthalidone. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Non-Teratogenic Effects
Thiazides cross the placental barrier and appear in cord blood. The use of chlorthalidone and related drugs in pregnant women requires that the anticipated benefits of the drug be weighed against possible hazards to the fetus. These hazards include fetal or neonatal jaundice, thrombocytopenia, and possibly other adverse reactions that have occurred in the adult.
Nursing Mothers
Thiazides are excreted in human milk. Because of the potential for serious adverse reactions in nursing infants from chlorthalidone, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.
Pediatric Use
Safety and effectiveness in the pediatric population have not been established.
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