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Co-tenidone (atenolol and chlortalidone)


Tablets containing 50mg atenolol and 12.5mg chlortalidone
Tablets containing 100mg atenolol and 25mg chlortalidone

Drugs List

  • co-tenidone (atenolol 100mg and chlortalidone 25mg) tablets
  • co-tenidone (atenolol 50mg and chlortalidone 12.5mg) tablets
  • TENORET 50mg+12.5mg tablets
  • TENORETIC 100mg+25mg tablets
  • Therapeutic Indications





    One 50mg atenolol with 12.5mg chlortalidone tablet once daily OR one 100mg atenolol with 25mg chlortalidone tablet once daily.


    See adult dose, however dosage requirements are often lower in this age group.


    Not recommended for children.

    Patients with Renal Impairment

    Severe renal impairment

    A reduction in daily dose or dose frequency may be required.

    Patients with Hepatic Impairment

    Avoid in severe liver disease, hypokalaemia may precipitate coma. Increased risk of hypomagnesaemia in alcoholic cirrhosis.


    For oral administration


    Cardiogenic shock
    Metabolic acidosis
    Severe peripheral arterial circulatory disorders
    Second or third degree heart block
    Sinus sick syndrome
    Untreated phaeochromocytoma
    Uncontrolled cardiac failure
    Severe asthma
    Refractory hypokalaemia
    Symptomatic hyperuricaemia
    Addison's disease
    Children under 18years
    Severe liver disease
    Pregnancy (see Pregnancy section)
    Breastfeeding (see Lactation section)

    Precautions and Warnings

    Use with caution in patients with:
    Controlled cardiac failure and patients with poor cardiac reserve.
    Prinzmetal's angina - may increase number and duration of attacks.
    Peripheral arterial circulatory disturbances - condition may be aggravated.
    First degree heart block.
    Raynaud's syndrome.
    Portal hypertension - risk of deterioration in liver function.
    Myasthenia gravis.
    Psoriasis. Nephrotic syndrome.
    Alcoholic cirrhosis.

    May modify the tachycardia in patients with hypoglycaemia and may mask signs of thyrotoxicosis.

    Reduce dose if patient develops symptoms attributable to lowered heart rate.

    Do not discontinue abruptly in patients with ischaemic heart disease.

    Caution in patients with a history of anaphylactic response to allergens. Co-tenidone may increase the severity of an allergic response and the usual doses of adrenaline may not be adequate. Discontinue if allergic reaction occurs.

    Atenolol may also cause a hypersensitivity reaction including angioedema and urticaria.

    Avoid in patients with reversible obstructive airways disease. Use only if there are compelling reasons to do so and monitor lung function. An increase in airway resistance may be seen.

    Hypokalaemia may occur. Monitor potassium levels, especially in elderly patients, those receiving concurrent digitalis preparations for cardiac failure, those taking an abnormal low potassium diet or those suffering from gastrointestinal complaints.

    Severe renal failure - see Dosage Patients with Renal Impairment.

    Impaired glucose tolerance may occur in patients with a pre-disposition to diabetes mellitus.

    Chlortalidone may exacerbate gout. Hyperuricaemia may occur. In cases of prolonged hyperuricaemia a uricosuric agent may be required.

    Chlortalidone may exacerbate systemic lupus erythematosus.

    Advise patient not to drive or operate machinery if feeling dizzy or tired.

    Inform anaesthetist that patient is on a beta blocker prior to anaesthesia.

    NSAIDs may decrease the hypotensive effects of atenolol. Advise patient not to use NSAIDs unless under the advice of a clinician.

    Discontinue if symptoms of acute angle-closure glaucoma occur.

    Monitor patients at risk of glaucoma for increases in intraocular pressure.

    Consider prompt medical or surgical treatments if intraocular pressure remain uncontrolled. History of sulfonamide or penicillin allergies are risk factors for developing acute-closure glaucoma.

    Pregnancy and Lactation


    Atenolol and chlortalidone tablets are contraindicated during pregnancy. The following is information regarding the two separate components.

    Atenolol is not normally recommended, however, if use is absolutely necessary, extreme caution is recommended during use. Atenolol crosses the placental barrier and appears in the cord blood. No studies have been performed on use in the first trimester and the possibility of foetal injury cannot be excluded. Although, Schaefer (2007) suggests that there is no clear evidence that beta-blockers are teratogens. Beta-adrenoceptor blocking agents in general have been associated with a decrease in placental perfusion which may result in intra-uterine deaths, immature and premature deliveries. Administration to pregnant women in the management of mild to moderate hypertension has been associated with intra-uterine growth retardation (IUGR). Schaefer (2007) states that use during pregnancy is not an indication for invasive diagnostic procedures or termination of pregnancy. Atenolol has been used under close supervision for the treatment of hypertension in the third trimester. If used during pregnancy, hypoglycaemia and bradycardia may occur in the foetus and neonate in the postnatal period. Briggs (2008) recommends that newborns exposed to atenolol near delivery should be closely observed during the first 24-48 hours for signs and symptoms of beta-blockade.

    Chlortalidone is able to cross the placenta and has been associated with hyponatraemia, hypokalaemia, thrombocytopenia and reactive hypoglycaemia in the foetus. Due to the action of chlortalidone, perfusion of the placenta maybe reduced causing restriction of intrauterine growth.

    In general diuretics should not be used during pregnancy unless absolutely necessary. If considered essential alternative first line diuretics are more appropriate.

    The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14-17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Licensed in pregnancy? - No

    Recommended for use in pregnancy? - No

    Known human teratogen? - Unknown

    Crosses placenta? - Yes

    Effects on foetus - Schaefer (2007) suggests that there is no clear evidence that beta-blockers are teratogens, although the manufacturer states that there have studies during the first trimester so foetal injury cannot be excluded. Atenolol has been linked to intra-uterine growth retardation.

    Other information - When atenolol is used near delivery there is a risk of beta-blockade in the newborn, for this reason Briggs (2008) recommends that newborns exposed to atenolol near delivery should be closely observed during the first 24-48 hours for signs and symptoms of beta-blockade.


    Atenolol and chlortalidone tablets are contraindicated during breastfeeding. The following is information regarding the two separate components.

    As safer alternatives exist, atenolol is not recommended for use in nursing mothers, caution should be exercised when atenolol is administered to a nursing woman. There is significant accumulation of atenolol in breast milk, greater than some other beta blockers. Breastfeeding may be undertaken but close monitoring of the infants heart and respiratory rate, blood pressure and blood glucose are required. Neonates born to breastfeeding mothers who are receiving atenolol may be at risk of hypoglycaemia, bradycardia, respiratory depression and hypotension and should be monitored for these effects. Schaefer (2007) recommends that if atenolol has been used in a nursing mother, there is no need to limit the breastfeeding, but the medication should be changed.

    Chlortalidone is excreted in breast milk and because of its long half can accumulate in the infant's blood. Chlortalidone should therefore not be used by breastfeeding mothers.

    In general diuretics should not be used by breastfeeding mothers as there is the possibility of decreased milk production. If a diuretic is needed then other first line diuretics should be considered.

    Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
    Specialist advice is available from the UK Drugs in Lactation Advisory Service at

    Drug excreted in breast milk? - Yes.

    Considered suitable or recommended by manufacturer? - No.

    UK Drugs in Lactation Advisory Service Classification - The use of atenolol should be avoided in nursing mothers.

    Drug substance licensed in infants? - No.

    Other information - Newborns (especially premature infants) being breastfeed by mothers taking atenolol should be monitored for the signs of beta- blockade. As with other diuretics, milk production maybe decreased.

    Effects on Ability to Drive and Operate Machinery

    Advise patient not to drive or operate machinery if feeling dizzy or tired.


    Advise patient not to drive or operate machinery if feeling dizzy or tired.

    Advise patient not to use NSAIDs unless under the advice of a clinician.

    Side Effects

    Decreased glucose tolerance
    Cardiac failure
    Postural hypotension
    Cold extremities
    Mood changes
    Sleep disturbances
    Dry mouth
    Gastro-intestinal disturbances
    Increase in serum transaminases
    Intrahepatic cholestasis
    Dry eyes
    Psoriasiform rash
    Visual disturbances
    Hypersensitivity reactions
    Increase in antinuclear antibodies (ANA)
    Heart block
    Exacerbation of intermittent claudication
    Conduction disturbances
    Peripheral vasoconstriction
    Exacerbation of Raynaud's disease
    Sexual dysfunction
    Altered serum lipid profile
    Metabolic changes
    Hypochloraemic alkalosis
    Cardiac arrhythmias
    Pulmonary oedema
    Interstitial nephritis
    Chloroidal effusion
    Visula field defects
    Myopia (transient)
    Glaucoma (closed angle)
    Ocular pain


    It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.

    The following number will direct the caller to the relevant local centre (0844) 892 0111

    Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Shelf Life and Storage

    Store below 25 degrees C.
    Store in original packaging.

    Further Information

    Last Full Review Date: May 2011

    Reference Sources

    British National Formulary, 61st Edition (2011) Pharmaceutical Press, London.

    Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 2nd edition (2007) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.

    Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 8th edition (2008) ed. Briggs, G., Freeman, R. and Yaffe, S. Lippincott Williams & Wilkins, Philadelphia.

    Martindale: The Complete Drug Reference, 37th edition (2011) ed. Sweetman, S. Pharmaceutical Press, London.

    Medications and Mothers' Milk, 14th Edition (2010) Hale, T. Hale Publishing, Amarillo, Texas.

    Summary of Product Characteristics: Tenoret 50mg/12.5mg film coated tablets. AstraZeneca UK Ltd. Revised August 2020.

    Summary of Product Characteristics: Tenoretic 100mg/25mg film coated tablets. AstraZeneca UK Ltd. Revised August 2020.

    UK Drugs in Lactation Advisory Service.
    Available at:
    Last accessed: May 23, 2011.

    US National Library of Medicine. Toxicology Data Network. Drugs and Lactation Database (LactMed).
    Available at:
    Atenolol. Last revised: November 1, 2010.
    Chlortalidone . Last revised: December 7, 2010.
    Last accessed: May 23, 2011

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