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Method of action:
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Medically reviewed by Oliinyk Elizabeth Ivanovna, PharmD. Last updated on 31.03.2022
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Natrix SR hemihydrate tablets are indicated for the oral treatment of essential hypertension.
Natrix SR hemihydrate tablets may be used as sole therapy or combined with other antihypertensive agents.
Posology
Adults
The dosage is one tablet, containing 2.5 mg Natrix SR hemihydrate, daily to be taken in the morning.
Patients with renal failure
In severe renal failure (creatinine clearance below 30 ml/min), treatment is contraindicated. Thiazide and related diuretics are fully effective only when renal function is normal or only minimally impaired.
Older people
In the older people, the plasma creatinine must be adjusted in relation to age, weight and gender. Older people can be treated with Natrix SR when renal function is normal or only minimally impaired.
Patients with hepatic impairment
In severe hepatic impairment, treatment is contraindicated.
Paediatric population
Natrix SR is not recommended for use in children and adolescents due to a lack of data on safety and efficacy.
The action of Natrix SR is progressive and the reduction in blood pressure may continue and not reach a maximum until several months after the start of therapy. A larger dose than 2.5 mg Natrix SR daily is not recommended as there is no appreciable additional antihypertensive effect but a diuretic effect may become apparent.
If a single daily tablet of Natrix SR does not achieve a sufficient reduction in blood pressure, another antihypertensive agent may be added; those which have been used in combination with Natrix SR include beta-blockers, ACE inhibitors, methyldopa, clonidine and other adrenergic blocking agents. The co-administration of Natrix SR with diuretics may cause hypokalaemia and, therefore, is not recommended.
There is no evidence of rebound hypertension on withdrawal of Natrix SR.
Method of administration
Natrix SR tablets are for oral administration only.
Severe renal failure
Hepatic encephalopathy, severe impairment of liver function, severe hepatic failure
Hypokalaemia
Recent cerebrovascular accident.
In case of hepatic impairment, thiazide-related diuretics may cause hepatic encephalopathy, particularly in case of electrolyte imbalance. Administration of the diuretic must be stopped immediately if this occurs.
Photosensitivity
Cases of photosensitivity reactions have been reported with thiazides and thiazide-related diuretics. If photosensitivity reaction occurs during treatment, it is recommended to stop the treatment. If a re-administration of the diuretic is deemed necessary, it is recommended to protect exposed areas to the sun or to artificial UVA.
Patients likely to be exposed to direct sunlight or ultraviolet light should be advised that photosensitivity leading to exaggerated sunburn may occur and treatment should be discontinued at the first sign of skin erythema.
Angioneurotic oedema
Angioneurotic oedema of the face, extremities, lips, tongue, glottis and/or larynx has been reported infrequently in patients receiving treatment with Natrix SR. In such cases, treatment with Natrix SR should be stopped immediately and the patient should be monitored until the oedema has disappeared.
Water and electrolyte balance
Plasma sodium
Plasma sodium must be measured before treatment is initiated and subsequently at regular intervals. Any kind of treatment with diuretics may cause hyponatraemia, sometimes with very serious consequences. A drop in plasma sodium may be asymptomatic in the beginning. Therefore, regular monitoring is essential and should be carried out even more frequently in elderly patients and in cirrhotic patients. Hyponatraemia with hypovolaemia may be responsible for dehydration and orthostatic hypotension. Concomitant loss of chloride ions may lead to secondary compensatory metabolic alkalosis: the incidence and degree of this effect are slight.
Plasma potassium
Potassium depletion with hypokalaemia constitutes the greatest risk in the treatment with thiazides and related diuretics. The risk of onset of hypokalaemia (< 3.4 mmol/l) must be prevented in certain high risk populations, i.e. the elderly, malnourished and/or polymedicated , cirrhotic patients with oedema and ascites, coronary artery disease, cardiac failure patients, patients with hyperaldosteronism, patients predisposed to or suffering from gout.
In cardiac patients, hypokalaemia increases the cardiac toxicity of digitalis preparations (e.g. digoxin) and the risks of arrhythmias.
Individuals with a long QT interval are also at risk, whether the origin is congenital or iatrogenic. Hypokalaemia, as well as bradycardia, is then a predisposing factor to the onset of severe arrhythmias, in particular, potentially fatal torsades de pointes.
More frequent monitoring of plasma potassium is required in all the situations indicated above. The first measurement of plasma potassium should be obtained during the first week following the start of treatment and subsequently at regular intervals, especially in the mentioned risk patients.
If hypokalaemia (< 3.4 mmol potassium) is detected, it must be corrected and it should be prevented in risk patients.
Plasma calcium
Thiazides and related diuretics may decrease urinary calcium excretion and cause a slight and transitory increase in plasma calcium. Frank hypercalcaemia may be due to previously unrecognised hyperparathyroidism.
Treatment with Natrix SR hemihydrate should be stopped if hypercalcaemia occurs in patients with hyperparathyroidism.
Treatment should be withdrawn before the investigation of parathyroid function.
Blood glucose
Monitoring of blood glucose is important in diabetic patients, especially in the presence of hypokalaemia.
Uric acid
Serum urate should be monitored in patients with gout. Tendency to gout attacks may be increased in hyperuricaemic patients.
Renal function and diuretics
Caution should be exercised when administering Natrix SR hemihydrate to patients with severe renal impairment. However, the drug has been safely given to patients with impaired renal function.
However, if renal insufficiency worsens, treatment should be stopped.
Thiazides and related diuretics are fully effective at normal or only minimally impaired renal function (plasma creatinine below levels of the order of 25 mg/l, i.e. < 220 µmol/l in an adult). In elderly patients, the plasma creatinine values must be adjusted according to age, body weight and sex.
Secondary hypovolaemia, as a result of loss of water and sodium induced by the diuretic at the start of treatment results in reduced glomerular filtration which, may increase plasma concentrations of blood urea and creatinine. This temporary impairment of renal function is harmless to patients with normal renal function but may exacerbate pre-existing renal insufficiency.
Athletes
The attention of athletes is drawn to the fact that this medicinal product contains a drug substance, which may give a positive result in doping tests.
Lactose
Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose- galactose malabsorption should not take this medicine.
Natrix SR hemihydrate does not affect vigilance but different reactions in relation with the decrease in blood pressure may occur in individual cases, especially at the start of the treatment or when another antihypertensive agent is added. As a result, the ability to drive vehicles or to operate machinery may be impaired.
Summary of safety profile
The most commonly reported adverse reactions are hypersensitivity reactions, mainly dermatological, in subjects with a predisposition to allergic and asthmatic reactions and maculopapular rashes.
During clinical trials, hypokalaemia (plasma potassium <3.4 mmol/l) was seen in 25 % of patients and < 3.2 mmol/l in 10 % of patients after 4 to 6 weeks treatment. After 12 weeks treatment, the mean fall in plasma potassium was 0.41 mmol/l.
The majority of adverse reactions concerning clinical or laboratory parameters are dose-dependent.
Tabulated summary of adverse reactions
The following undesirable effects have been observed with Natrix SR during treatment ranked under the following frequencies:
Very common (>1/10), common (>1/100 to <1/10), uncommon (>1/1,000 to <1/100), rare (>1/10,000 to <1/1,000), very rare (<1/10,000) and not known (cannot be estimated from the available data).
| System Organ Class | Adverse Event | Frequency |
| Blood and lymphatic system disorders | Thrombocytopenia, leucopenia, agranulocytosis, aplastic anaemia, haemolytic anaemia | Very rare |
| Metabolism and nutrition disorders | Hypercalcaemia | Very rare |
| Potassium depletion with hypokalaemia, particularly serious in certain high risk populations , hyponatraemia , loss of weight | Not known | |
| Nervous system disorders | Fatigue, headache, paraesthesia, vertigo | Rare |
| Dizziness, syncope | Not known | |
| Eye disorders | Myopia, blurred vision, visual impairment | Not known |
| Cardiac disorders | Arrhythmia | Very rare |
| Torsades de pointes (potentially fatal) | Not known | |
| Vascular disorders | Orthostatic hypotension | Uncommon |
| Hypotension | Very rare | |
| Gastrointestinal disorders | Vomiting | Uncommon |
| Nausea, constipation, dryness of the mouth | Rare | |
| Pancreatitis | Very rare | |
| Hepatobiliary disorders | Abnormal hepatic function | Very rare |
| Possibility of onset of hepatic encephalopathy in patients with impaired liver function , hepatitis | Not known | |
| Skin and subcutaneous tissue disorders | Hypersensitivity reactions, mainly dermatological, may be observed in patients predisposed to allergic and asthmatic manifestations: Maculopapular rash | Common |
| Purpura | Uncommon | |
| Erythema multiforme | Rare | |
| Angioneurotic oedema, urticaria, toxic epidermal necrolysis, Steven Johnson syndrome | Very rare | |
| Photosensitivity , possible exacerbation of acute disseminated lupus erythematosus | Not known | |
| Musculoskeletal and connective tissue disorders | Muscular cramps | Rare |
| Renal and urinary disorders | Renal failure | Very rare |
| Renal insufficiency | Not known | |
| Reproductive system and breast disorders | Impotence | Not known |
| Investigations | Electrocardiogram QT prolonged , elevated liver enzyme levels, increased blood uric acid , hyperglycaemia | Not known |
Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via:
Yellow Card Scheme
Website: www.mhra.gov.uk/yellowcard
Symptoms
Natrix SR has been found free of toxicity at up to 40 mg, i.e. 16 times the therapeutic dose. Signs of acute poisoning take the form above all of water/ electrolyte disturbances; (hyponatraemia, hypokalaemia). Clinically, possibility of nausea, vomiting, hypotension, cramps, vertigo, drowsiness, confusion, polyuria or oliguria possibly to the point of anuria (by hypovolaemia).
Management
Initial measures involve the rapid elimination of the ingested substance(s) by gastric wash-out and/or administration of activated charcoal, followed by restoration of water/electrolyte balance to normal in a specialised centre.
Pharmacotherapeutic group: Sulfonamides, plain, ATC code: C03BA11
Natrix SR is a non-thiazide sulfonamide with an indole ring, belonging to the diuretic family which has certain structural similarities to furosemide as well as the thiazides and has actions and uses similar to those of chlorothiazide.
Diuresis is initiated within about 1 to 2 hours and has been reported to last for up to 36 hours. Its inhibitory action on carbonic anhydrase is only weak. At the dose of 2.5 mg per day Natrix SR exerts a prolonged antihypertensive activity in hypertensive human subjects.
Dose-effect studies have demonstrated that, at the dose of 2.5 mg per day, the antihypertensive effect is maximal and the diuretic effect is sub-clinical.
Mechanism of action
At this antihypertensive dose of 2.5 mg per day, Natrix SR reduces vascular hyperreactivity to noradrenaline in hypertensive patients and decreases total peripheral resistance and arteriolar resistance.
The implication of an extrarenal mechanism of action in the antihypertensive effect is demonstrated by maintenance of its antihypertensive efficacy in functionally anephric hypertensive patients.
The vascular mechanism of action of Natrix SR involves:
- a reduction in the contractility of vascular smooth muscle due to a modification of transmembrane ion exchanges, essentially calcium;
- vasodilatation due to stimulation of the synthesis of prostaglandin PGE2 and the vasodilator and platelet antiaggregant prostacyclin PGI2;
- potentiation of the vasodilator action of bradykinin.
It has also been demonstrated that in the short-, medium- and long-term, in hypertensive patients, Natrix SR:
- reduces left ventricular hypertrophy;
- does not appear to alter lipid metabolism: triglycerides, LDL-cholesterol and HDL-cholesterol;
- does not appear to alter glucose metabolism, even in diabetic hypertensive patients.
Normalisation of blood pressure and a significant reduction in microalbuminuria have been observed after prolonged administration of Natrix SR in diabetic hypertensive subjects.
Lastly, the co-prescription of Natrix SR with other antihypertensives (beta-blockers, calcium channel blockers, angiotensin converting enzyme inhibitors) results in an improved control of hypertension with an increased percentage of responders compared to that observed with single-agent therapy.
Absorption
Natrix SR is rapidly and completely absorbed from the gastrointestinal tract and peak plasma concentrations are seen 1-2 hours after oral dosing.
Distribution
Natrix SR is concentrated in the erythrocytes and is 79% bound to plasma protein and to erythrocytes. It is taken up by the vascular wall in smooth vascular muscle according to its high lipid solubility.
Biotransformation and elimination
70% of a single oral dose is eliminated by the kidneys and 23% by the gastrointestinal tract. Natrix SR is metabolised to a marked degree with 7% of the unchanged product found in the urine during the 48 hours following administration. Elimination half-life (β phase) of Natrix SR is approximately 15 - 18 hours.
Natrix SR has been tested negative concerning mutagenic and carcinogenic properties.
The highest doses administered orally to different animal species (40 to 8000 times the therapeutic dose) have shown an exacerbation of the diuretic properties of Natrix SR. The major symptoms of poisoning during acute toxicity studies with Natrix SR administered intravenously or intraperitoneally were related to the pharmacological action of Natrix SR, i.e. bradypnoea and peripheral vasodilation.
Reproductive toxicity studies have not shown embryotoxicity and teratogenicity.
Fertility was not impaired either in male or in female rats.
None stated.
Not applicable
