This is a combination product that contains 2 medications: atenolol and chlorthalidone. It is used to treat high blood pressure. Atenolol belongs to the class of medications called beta-blockers. It works by decreasing the workload of the heart. Chlorthalidone belongs to the class of medications called diuretics (water pills). It works by getting rid of excess salt and water.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The eventual dose of atenolol – chlorthalidone is determined by treating with each of the ingredients separately (i.e., atenolol and chlorthalidone) and finding the best daily dose for each. The combination medication may then be used at the appropriate dose.

The recommended dose of atenolol – chlorthalidone ranges from 1 tablet of the 50 mg/25 mg combination daily to 1 tablet of the 100 mg/25 mg combination daily. If blood pressure is not adequately controlled after using the higher strength medication, your doctor may prescribe an additional blood pressure-lowering medication that works in a different way.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue on with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue on with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Do not stop taking this medication suddenly without checking with your doctor first. Stopping this medication suddenly after you have been taking it for a while may cause unpleasant and potentially harmful side effects.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not use atenolol – chlorthalidone if you:

• are allergic to atenolol, chlorthalidone, or any ingredients of the medication
• are allergic to sulfa medications (e.g., sulfamethoxazole)
• are not able to expel urine
• are pregnant or breast-feeding
• are receiving certain anesthetics before surgery
• have a condition called cardiogenic shock
• have a condition known as pheochromocytoma (in the absence of alpha-blockade)
• have a condition known as right ventricular failure caused by pulmonary hypertension
• have a severely slow heart rate
• have a serious heart block, also called atrioventricular (AV) block
• have metabolic acidosis
• have severe peripheral arterial disorders (blockage of blood flow to limbs of body)
• have sick sinus syndrome
• have uncontrolled congestive heart failure
• have very low blood pressure

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• cough
• decreased sexual ability
• diarrhea
• dizziness
• drowsiness (mild)
• dry mouth
• fatigue
• headache
• increased sensitivity of skin to sunlight (skin rash, itching, redness or other discolouration of skin, or severe sunburn)
• joint pain
• nausea
• trouble sleeping

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• breathing difficulty or wheezing
• cold hands and feet
• dizziness when rising from a lying or sitting position
• fainting
• lower back or side pain
• memory problems
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• signs of too much potassium or sodium loss (muscle cramps or pain, weakness, vomiting)
• skin rash or hives
• slow heartbeat (especially less than 50 beats per minute)
• spinning sensation
• swelling of the ankles, feet, or lower legs
• symptoms of irregular heartbeat (e.g., chest pain; dizziness; rapid, pounding heartbeat; shortness of breath)
• vision problems

Stop taking the medication and seek immediate medical attention if any of the following occur:

• chest pain
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Breathing conditions: In general, people who have asthma and certain other breathing problems should avoid taking beta-blockers such as atenolol, as these medications can cause breathing difficulty. Low doses of atenolol may be taken by people with asthma who do not respond to, or cannot tolerate, alternative treatment but they should be monitored by their doctor. If you have breathing problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Cholesterol levels: Increases in cholesterol and triglyceride levels may occur when taking chlorthalidone. Talk to your doctor about whether you need to have your cholesterol levels tested.

Diabetes: Chlorthalidone may make it more difficult for people with diabetes to control their blood sugar. The signs of low blood sugar may not be as noticeable when taking atenolol. Dose adjustment of diabetes medications, including insulin, may be required. If you have diabetes and take insulin or other medications that work by affecting the sugar in the blood, you should monitor your blood sugar carefully while taking this medication.

Drowsiness/reduced alertness: Dizziness or fatigue may occur when starting treatment with this medication. This may impair your ability to drive or operate machinery. Avoid these activities until you determine how this medication affects you.

Fluid and electrolyte balance: The levels of electrolytes in the blood, such as potassium, sodium, magnesium, and chloride can be reduced by the use of chlorthalidone. If you experience symptoms of fluid and electrolyte imbalance such as muscle pains or cramps; dry mouth; numb hands, feet, or lips; or racing heartbeat, contact your doctor as soon as possible. Your doctor will do blood tests regularly to monitor the levels of these electrolytes in your blood while you are taking this medication. A potassium supplement may be necessary when taking this medication.

Gout: High levels of uric acid may occur in the blood or gout may be brought on for certain people receiving chlorthalidone. If you develop painful, warm, and swollen joints or difficulty with urination, contact your doctor as soon as possible.

History of heart failure: Beta-blockers, such as atenolol, can worsen existing heart failure. It is important to take atenolol - chlorthalidone exactly as prescribed by your doctor to decrease the chance of this happening. If you have a history of heart failure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Hyperthyroidism (high level of thyroid hormones): People with hyperthyroidism should be monitored by their doctor while taking this medication, as it may reduce the symptoms of this condition, giving a false impression of improvement.

Kidney disease: Chlorthalidone may contribute to decreased kidney function, particularly if you already have reduced kidney function. If you have kidney problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: This medication may cause a decrease in liver function. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Prinzmetal's angina: Atenolol may increase the number and duration of angina attacks for people with Prinzmetal's angina. If you have this condition, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Severe allergies: If you have allergies severe enough to cause anaphylaxis (a severe allergic reaction where swelling of the face, lips, and throat make it difficult to breathe), talk to your doctor about what to do if you have an allergic reaction. Atenolol, like other beta-blockers, may make it more difficult to treat your allergic reaction with epinephrine.

Stopping the medication: This medication should not be stopped suddenly. People with heart disease who stop taking this medication abruptly may experience severe effects, such as severe worsening of angina, heart attack, or abnormal heart rhythms. When this medication needs to be stopped, it should be done gradually, under the supervision of your doctor.

Surgery: If you are scheduled for surgery, inform all doctors involved in your care that you are taking a medication that contains atenolol.

Systemic lupus erythematosus (SLE or lupus): People with systemic lupus erythematosus should be monitored by their doctor while taking chlorthalidone, as it may worsen this condition.

Pregnancy: This medication can cause harm to the developing baby if it is taken by the mother while she is pregnant. It should not be used during pregnancy. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: Atenolol and chlorthalidone both pass into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children. It is not recommended for use by children.

There may be an interaction between atenolol - chlorthalidone and any of the following:

• aclidinium
• alcohol
• aliskiren
• alpha-agonists (e.g., clonidine, methyldopa)
• alpha-blockers (e.g., alfuzosin, doxazosin, tamsulosin)
• amiodarone
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• ampicillin
• angiotensin converting enzyme inhibitors (ACEIs; captopril, ramipril)
• angiotensin receptor blockers (ARBs; e.g., candesartan, irbesartan, losartan)
• antihistamines (e.g., azelastine, cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine, olopatadine)
• anti-Parkinson's medications (e.g., apomorphine, bromocriptine, pramipexole, rasagiline)
• antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• atropine
• barbiturates (e.g., butalbital, phenobarbital)
• belladonna
• benztropine
• other beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol)
• beta-2 agonists (e.g., salbutamol, formoterol, terbutaline)
• bile acid sequestrants (e.g., cholestyramine, colesevelam, colestipol)
• bortezomib
• brimonidine
• calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
• calcium supplements (e.g., calcium carbonate, calcium citrate)
• carbamazepine
• celecoxib
• ceritinib
• conivaptan
• corticosteroids (e.g., dexamethasone, hydrocortisone, prednisone)
• cyclophosphamide
• darifenacin
• desmopressin
• diabetes medications (e.g., acarbose, canagliflozin, glyburide, insulin, linagliptin, lixisenatide, metformin, rosiglitazone)
• digoxin
• dipyridamole
• disopyramide
• donepezil
• dronedarone
• duloxetine
• epinephrine
• ergot-containing medications (e.g., cabergoline, dihydroergotamine, ergonovine)
• flecainide
• flunarizine
• galantamine
• glycopyrrolate
• grass pollen extract
• guanethidine
• ipratropium
• ivabradine
• ketotifen
• lacosamide
• lanreotide
• levodopa
• lidocaine
• lithium
• methylphenidate
• minoxidil
• multiple vitamin/mineral supplements
• muscle relaxants (e.g., cyclobenzaprine, methocarbamol, orphenadrine, tizanidine)
• nabilone
• narcotic analgesics (e.g., morphine, codeine)
• nitrates (e.g., nitroglycerin, isosorbide dinitrate, isosorbide mononitrate)
• nonsteroidal anti-inflammatory drugs (e.g., diclofenac, ibuprofen, naproxen)
• obinutuzmab
• octreotide
• other diuretics (water pills; e.g., furosemide, hydrochlorothiazide, triamterene)
• oxcarbazepine
• oxybutynin
• pasireotide
• pentoxifylline
• phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• pilocarpine
• propafenone
• quinidine
• riociguat
• rivastigmine
• ropinirole
• rotigotine
• sacubitril
• scopolamine
• selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
• sodium phosphates
• sphingosine 1-phosphate receptor (S1P) receptor inhibitors (e.g., fingolimod, ponesimod, siponimod)
• tamsulosin
• thalidomide
• theophyllines (e.g., aminophylline, oxtriphylline, theophylline)
• tiotropium
• tofacitinib
• tolterodine
• topiramate
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, imipramine, trimipramine)
• umeclidinium
• vitamin D

If you are taking any medications containing this drug, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription) and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or illegal drugs can affect the action of many medications, you should let your prescriber know if you use them.