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Heart and Thyroid Meds

Our Heart Conditions group of Pet Care products contains medication for treating congestive heart failure in dogs due to dilated cardiomyopathy and degeneration of heart valves or mitral valve disease. Our Thyroid Medications contain various thyroid hormone products (thyroxine) for treating underactive thyroid (hypothyroidism), including synthetic thyroxine and thyroid gland extracts. 

To see medications currently available from our alternate site for Heart Conditions, please click

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To see medications currently available from our alternate site for Thyroid, please click

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Heart conditions

Congestive heart failure (CHF) is when the heart muscle becomes weakened so that it does not pump efficiently and is a common condition in dogs. It can be due by a variety of causes. Dilated cardiomyopathy (DCM) is the most common cause of CHF in dogs, particularly large breeds and some dogs have an inherited predisposition for DCM. It is characterised by dilated or enlarged chambers of the heart, and reduced contraction of the heart muscle, resulting in congestive heart failure. Warning signs of DCM include heart murmur and arrhythmias (abnormal heart beat). CHF can also be caused by degeneration of heart valves, called endocardiosis causing them to become leaky, resulting in mitral valve disease. 

Symptoms of CHF include lethargy, exercise intolerance, shortness of breath, difficulty breathing, cough, swelling of the abdomen due to collection of fluid around the lungs and abdomen, peripheral oedema, which is fluid collection in the tissues and weight loss; but very rarely does it result in chronic artery disease or a heart attack. If CHF progresses it can be fatal particularly in older dogs or breeds with a genetic predisposition. 

Treatment for heart conditions

Heart failure in dogs can be treated by using medications that help improve the efficiency of the heart and increase blood flow; also with diuretics that help remove fluid in the tissues. 

  • Pimobendan is a drug specifically used for treating heart failure in dogs and is classified as an inodilator that works by two mechanisms of action. It acts directly on the cells of the heart muscle making them more sensitive to calcium, which is needed for muscle cells to contract and this increases the strength of muscular contraction. Pimobendan also inhibits an enzyme found in vascular smooth muscle cells, called phosphodiesterase lll that causes blood vessels to contract and narrow. This action causes peripheral and coronary blood vessels to widen, which reduces the workload on the heart and allows it to pump more efficiently. Pimobendan helps treat dogs with heart failure due to DCM or mitral valve disease and can be used in conjunction with other heart drugs.

  • Propentofylline is a xanthine derivative drug that is used to treat dogs with circulation and breathing problems, particularly in older dogs, to improve lethargy, willingness to and tolerance for exercise and loss of general wellbeing due to impaired circulation or heart problems like arrhythmia. Propentofylline is as a vasodilator that acts directly on vascular smooth muscle cells and inhibits the phosphodiesterase enzyme that causes blood vessels to contract and narrow. This action widens blood vessels and increases blood flow particularly to the heart, skeletal muscle and brain; also reduces the workload on the heart. Propentofylline is also a bronchodilator and has the same action of the airways of the lung causing the bronchioles to dilate and widen, which increases air flow into the lungs. Propentofylline also helps improve the efficiency of the heart by improving the strength of muscular contraction and by increasing heart rate; it also has anti-arrhythmic actions to help return to a normal heart beat.

  • Frusemide is a diuretic medication for cats, dogs, horses and cattle, to reduce oedema, which is a symptom of congestive heart failure. Frusemide acts directly on the kidneys to help remove fluid that has built up in the tissues. It works by inhibiting the reabsorption of salts back into the blood, so that more salts are excreted into the urine so that more water is removed from the blood and this draws more water out of the tissues.

Thyroid Information

The thyroid gland, which sits just below the Adam’s apple in the neck, is an endocrine gland that produces hormones secreted directly into the blood. The thyroid gland produces two hormones; calcitonin, which regulates calcium metabolism and thyroid hormone, which controls many important body functions, including how the body uses energy, regulates temperature, metabolises nutrients, and controls growth and development. Thyroid hormone synthesis is dependent on iodine and a deficiency of iodine can result in a deficiency of thyroid hormone and a swelling of the thyroid gland known as goitre, in which the thyroid tissue grows to compensate for lack of thyroid hormone. 

Thyroid hormone

Thyroid hormone exists in two forms. Thyroxine or levothyroxine, also known as T4 and liothyronine or L-triiodothyronine also known as T3. Up to 90% of thyroid hormone secreted by the thyroid gland is T4, which is inactive but is converted to the active form of thyroid hormone T3 when it reaches its target tissue. This conversion takes place in the liver, kidney and other tissues of the body and T3 then interacts with a specific receptor inside the nucleus of cells, to influence the transcription of specific pieces of DNA (genes) to produce proteins needed to manage and control a variety of processes, including carbohydrate, fat, protein and vitamin metabolism. 

The production of thyroid hormone is regulated by a hormone produced by the pituitary gland in hypothalamus, which is an area at the base of the brain and is called thyroid stimulating hormone (TSH). When levels of thyroid hormone in the blood are low, this stimulates increased production of TSH and thereby increases production of more thyroid hormone. Conversely, when thyroid hormone levels increase, TSH production is decreased. This is known as a negative feedback loop, which helps maintain normal levels of thyroid hormone in the blood. 

Hypothyroidism and thyroid hormone

Underactive thyroid, known as hypothyroidism is caused by a lack of thyroid hormone. The most common cause for this is the development of autoantibodies against the thyroid hormone producing cells of the thyroid, a condition known as Hashimoto’s disease. Another common cause is a deficiency in iodine. Other causes include, viral infection, cancer radiotherapy and it can occur temporarily in women after giving birth (postpartum thyroiditis). 

Symptoms of hypothyroidism include: tiredness, muscle weakness, cramps, feeling cold, a slow heart rate, dry and flaky skin, hair loss, a deep husky voice, weight gain, constipation, depression, joint or muscle pain, menstrual disturbances. 

Treatments for hypothyroidism

Treatment of hypothyroidism involves hormone replacement for the lack of thyroid hormone. Several sources of thyroid hormone supplement are available, including synthetic thyroxine and thyroid gland extracts.

  • Levothyroxine,a synthetic form of naturally occuring T4 that is more stable but less active than T3 and is carried in the blood to the target tissues where it is converted to T3.

  • Liothyronine, a synthetic form of naturally occurring T3 that is less stable than T4 but is up to four times more active and acts rapidly.

  • Extract produced from pig thyroid glands containing both T3 and T4

These hormone supplements need to be taken continually and often for long periods to replace thyroid hormone deficiency that may be lifelong.
 

Synthroid to Armour conversion table 

Hyperthyroidism

Overactive thyroid, also known as hyperthyroidism, is caused by high levels of thyroid hormone or thyrotoxicosis. The most common form of hyperthyroidism is Grave’s Disease or goitre, which is thought to be an autoimmune disease where autoantibodies called thyroid stimulating immunoglobulins bind to the receptor for Thyroid Stimulating Hormone (TSH). This causes over production of thyroid hormone due to loss of regulation of thyroid hormone production. Hyperthyroidism can also be caused by inflammation, a tumour or a virus infection. 

Symptoms of hyperthyroidism are due to increased production of thyroid hormone, which causes increased rate of metabolism. They include nervousness, restlessness, irritability difficulty concentrating, tiredness, rapid heartbeat, heat intolerance, increased perspiration, difficulty sleeping, hand tremors, weight loss, increased appetite, frequent bowel movements, and muscular weakness.

Treatments for hyperthyroidism

Treatment for hyperthyroidism involves blocking the production of thyroid hormone to restore normal hormone levels. 
Carbimazole is an anti-thyroid drug that inhibits the action of thyroid peroxidase, an enzyme that is involved in the coupling and iodination of thyroglobulin, which is important for the synthesis of thyroid hormone and when its action is blocked, synthesis of thyroid hormone is also blocked. 

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