ARBITEL H-80

Indications

• Hypertension
• Edema associated with congestive heart failure
• Edema due to liver cirrhosis
• Nephrotic syndrome
• Chronic renal failure

Dosage

Children: Refer to the BNF for Children for specific dosing recommendations.

Adults: Refer to the BNF for specific dosing recommendations.

Mechanism of action

Hydrochlorothiazide inhibits the sodium-chloride symporter in the distal convoluted tubule of the nephron, leading to increased excretion of sodium and chloride. This diuretic effect results in a decrease in blood volume, which subsequently lowers blood pressure. Additionally, thiazide diuretics may have a direct vasodilatory effect on blood vessels.

Pharmacodynamics

The pharmacodynamic effects of hydrochlorothiazide include decreased peripheral vascular resistance and diuresis, leading to reduced preload and afterload on the heart. The onset of diuresis typically occurs within 1-2 hours of administration, with peak effects seen around 4-6 hours. The duration of action can last up to 24 hours, making it suitable for once-daily dosing in many patients.

Pharmacokinetics

Hydrochlorothiazide is well absorbed from the gastrointestinal tract, with peak plasma concentrations occurring approximately 1-2 hours post-administration. It has a bioavailability of 60-80%. The drug is primarily eliminated unchanged in the urine, with a half-life of about 6-15 hours. Renal function significantly affects its clearance, and dosage adjustment may be necessary in patients with renal impairment.

Contra-indications

• Hypersensitivity to hydrochlorothiazide or any component of the formulation
• Anuria
• Severe renal impairment
• Electrolyte imbalance, particularly hypokalemia
• Pregnancy, particularly in the first trimester without medical supervision

Adverse effects

• Electrolyte disturbances, including hypokalemia, hyponatremia, and hypercalcemia
• Dehydration and hypotension
• Dizziness and light-headedness
• Gastrointestinal disturbances, such as nausea and diarrhea
• Allergic reactions including rash, pruritus, and in rare cases, Stevens-Johnson syndrome
• Increased uric acid levels leading to gout
• Pancreatitis
• Photosensitivity reactions

Interactions

• May enhance the effects of other antihypertensive agents
• Non-steroidal anti-inflammatory drugs (NSAIDs) may reduce the diuretic effect
• Corticosteroids may increase the risk of electrolyte imbalance
• Digoxin levels may be increased due to hypokalemia
• Lithium levels may be affected, requiring monitoring
• Antidiabetic agents may have reduced efficacy

Precautions

• Monitor renal function before and during treatment
• Assess electrolyte levels regularly, particularly potassium
• Caution in patients with a history of gout or diabetes
• Use with caution in elderly patients and those with hepatic impairment
• Consider potential interactions with other medications

Pregnancy

Hydrochlorothiazide should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. It is not recommended during the first trimester.

Breast-feeding

Hydrochlorothiazide is excreted in breast milk. Caution is recommended when administering to nursing mothers.

Storage

Store in a cool, dry place away from light. Keep out of reach of children.

Formulations

• Oral tablets
• Oral solution

Indications

• Hypertension
• Heart failure
• Chronic kidney disease
• Diabetic nephropathy

Dosage

Children: For paediatric patients, refer to the BNF for Children for appropriate dosing guidelines.

Adults: The usual starting dose is 40 mg once daily, which may be adjusted based on blood pressure response. The maximum recommended dose is 80 mg per day.

Mechanism of action

Telmisartan interferes with the binding of angiotensin II to the angiotensin II AT1 receptor by selectively binding to these receptors in vascular smooth muscle and the adrenal gland. This blockage leads to reduced systemic vascular resistance and lower blood pressure. Telmisartan is not an ACE inhibitor and does not affect other hormone receptors or ion channels. It may also enhance carbohydrate and lipid metabolism via its PPARγ activity.

Pharmacodynamics

Telmisartan exhibits high affinity for the AT1 receptor subtype, making it an effective angiotensin II antagonist. It plays a significant role in lowering blood pressure by preventing vasoconstriction and aldosterone release. The potential PPARγ agonistic properties suggest additional metabolic advantages, including improved glucose and lipid metabolism.

Pharmacokinetics

Telmisartan is administered orally and has a high bioavailability. It is extensively bound to plasma proteins and undergoes hepatic metabolism, primarily via glucuronidation. The drug has a long half-life, allowing for once-daily dosing. Excretion occurs mainly through the feces, with minimal renal elimination.

Contra-indications

• Hypersensitivity to telmisartan or any of the excipients
• Severe hepatic impairment
• Severe renal impairment or patients on dialysis

Adverse effects

• Dizziness
• Fatigue
• Hypotension
• Hyperkalemia
• Renal impairment
• Angioedema

Interactions

• Other antihypertensives
• Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Lithium
• Potassium-sparing diuretics
• Renin-angiotensin-aldosterone system (RAAS) inhibitors

Precautions

• Monitor renal function, particularly in patients with renal artery stenosis
• Caution in patients with a history of angioedema
• Use with caution in patients with diabetes
• Monitor potassium levels in patients at risk for hyperkalemia

Pregnancy

Telmisartan is not recommended during pregnancy, particularly in the second and third trimesters, due to potential harm to the fetus.

Breast-feeding

The effects of telmisartan on breastfed infants are unknown; caution should be exercised.

Storage

Store at room temperature, away from moisture and heat.

Formulations

• Tablets: 20 mg, 40 mg
• Combination tablets with hydrochlorothiazide: 20 mg/12.5 mg, 40 mg/12.5 mg

Mechanism of action

Telmisartan interferes with the binding of angiotensin II to the angiotensin II AT₁-receptor by binding reversibly and selectively to the receptors in vascular smooth muscle and the adrenal gland. As angiotensin II is a vasoconstrictor, which also stimulates the synthesis and release of aldosterone, blockage of its effects results in decreases in systemic vascular resistance. Telmisartan does not inhibit the angiotensin converting enzyme, other hormone receptors, or ion channels. Studies also suggest that telmisartan is a partial agonist of PPAR&gamma;, which is an established target for antidiabetic drugs. This suggests that telmisartan can improve carbohydrate and lipid metabolism, as well as control insulin resistance without causing the side effects that are associated with full PPAR&gamma; activators. Migration of CD4-positive lymphocytes into the vessel wall represents an important step in early atherogenesis. Telmisartan is an angiotensin type 1 receptor (AT1R) blocker with peroxisome proliferator-activated receptor (PPAR)-gamma-activating properties. The present study examined the effect of telmisartan on CD4-positive cell migration and the role of PPARgamma in this context. CD4-positive lymphocytes express both the AT1R and PPARgamma. Stimulation of CD4-positive lymphocytes with stromal cell-derived factor (SDF)-1 leads to a 4.1+/-3.1-fold increase in cell migration. Pretreatment of cells with telmisartan reduces this effect in a concentration-dependent manner to a maximal 1.6+/-0.7-fold induction at 10 mumol/L of telmisartan (P<0.01 compared with SDF-1-treated cells; n=22). Three different PPARgamma activators, rosiglitazone, pioglitazone, and GW1929, had similar effects, whereas eprosartan, a non-PPARgamma-activating AT1R blocker, did not affect chemokine-induced lymphocyte migration. Telmisartan's effect on CD4-positive lymphocyte migration was mediated through an early inhibition of chemokine-induced phosphatidylinositol 3-kinase activity. Downstream, telmisartan inhibited F-actin formation, as well as intercellular adhesion molecule-3 translocation. Transfection of CD4-positive lymphocytes with PPARgamma small interfering RNA abolished telmisartan's effect on migration, whereas blockade of the AT1R had no such effect. Telmisartan inhibits chemokine-induced CD4-positive cell migration independent of the AT1R via PPARgamma. These data provide a novel mechanism to explain how telmisartan modulates lymphocyte activation by its PPARgamma-activating properties. Angiotensin II is formed from angiotensin I in a reaction catalyzed by angiotensin-converting enzyme (ACE, kininase II). Angiotensin II is the principal pressor agent of the renin-angiotensin system, with effects that include vasoconstriction, stimulation of synthesis and release of aldosterone, cardiac stimulation, and renal reabsorption of sodium. Telmisartan blocks the vasoconstrictor and aldosterone-secreting effects of angiotensin II by selectively blocking the binding of angiotensin II to the AT1 receptor in many tissues, such as vascular smooth muscle and the adrenal gland. Its action is therefore independent of the pathways for angiotensin II synthesis. There is also an AT2 receptor found in many tissues, but AT2 is not known to be associated with cardiovascular homeostasis. Telmisartan has much greater affinity (>3,000 fold) for the AT1 receptor than for the AT2 receptor. Blockade of the renin-angiotensin system with ACE inhibitors, which inhibit the biosynthesis of angiotensin II from angiotensin I, is widely used in the treatment of hypertension. ACE inhibitors also inhibit the degradation of bradykinin, a reaction also catalyzed by ACE. Because telmisartan does not inhibit ACE (kininase II), it does not affect the response to bradykinin. Whether this difference has clinical relevance is not yet known. Telmisartan does not bind to or block other hormone receptors or ion channels known to be important in cardiovascular regulation. Block

Pharmacodynamics

Telmisartan is an orally active nonpeptide angiotensin II antagonist that acts on the AT₁ receptor subtype. It has the highest affinity for the AT₁ receptor among commercially available ARBs and has minimal affinity for the AT₂ receptor. New studies suggest that telmisartan may also have PPAR&gamma; agonistic properties that could potentially confer beneficial metabolic effects, as PPAR&gamma; is a nuclear receptor that regulates specific gene transcription, and whose target genes are involved in the regulation of glucose and lipid metabolism, as well as anti-inflammatory responses. This observation is currently being explored in clinical trials. Angiotensin II is formed from angiotensin I in a reaction catalyzed by angiotensin-converting enzyme (ACE, kininase II). Angiotensin II is the principal pressor agent of the renin-angiotensin system, with effects that include vasoconstriction, stimulation of synthesis and release of aldosterone, cardiac stimulation, and renal reabsorption of sodium. Telmisartan works by blocking the vasoconstrictor and aldosterone secretory effects of angiotensin II.