NITROCONTIN 2.6

Indications

• Pediatric dosing adjustments
• Intravenous therapy
• Intramuscular injections
• Topical applications
• Oral medications for easier swallowing

Dosage

Children: Refer to the BNF for Children for appropriate dosing adjustments based on age and weight.

Adults: Refer to specific drug guidelines for appropriate dilution and dosage based on the active ingredient.

Mechanism of action

The mechanism of action of a diluted drug depends on the specific active ingredient within the solution. Generally, when a drug is diluted, its pharmacological effects are proportional to its concentration. The active molecules interact with specific receptors or enzymes in the body, leading to a desired therapeutic effect. For example, an analgesic diluted for oral administration will still bind to pain receptors, albeit at a lower intensity compared to its concentrated form.

Pharmacodynamics

Pharmacodynamics refers to the relationship between drug concentration and its effect on the body. In diluted solutions, the pharmacodynamic properties of the active ingredient remain intact, though the therapeutic effect may be reduced due to the lower concentration. The efficacy of the drug is influenced by factors such as receptor affinity, intrinsic activity, and the presence of other substances in the formulation.

Pharmacokinetics

Pharmacokinetics involves the absorption, distribution, metabolism, and excretion (ADME) of drugs. For diluted drugs, absorption can be affected by the dilution medium, which may enhance or delay the onset of action. Distribution is generally influenced by the volume of distribution of the active ingredient. Metabolism occurs primarily in the liver, where the drug is biotransformed, and excretion is typically via the kidneys. The pharmacokinetic profile may differ based on the dilution level and formulation.

Pregnancy

Consult a healthcare provider, as the effects of diluted preparations can vary depending on the active ingredient.

Breast-feeding

Consult a healthcare provider, as the safety of diluted preparations during breastfeeding can depend on the active ingredient.

Storage

Store in a cool, dry place away from direct sunlight. Ensure that the specific active ingredient's storage requirements are followed.

Indications

• Angina pectoris
• Acute coronary syndrome
• Heart failure

Dosage

Children: Refer to the BNF for Children for specific

Adults: For acute angina, the usual sublingual dose is 0.3 to 0.6 mg, taken as needed, with a maximum of 3 doses within 15 minutes. For chronic management, dosage forms such as patches or sustained-release tablets are used, with the specific regimen depending on clinical situation and patient response.

Mechanism of action

Nitroglycerin is converted by mitochondrial aldehyde dehydrogenase in smooth muscle cells to nitric oxide (NO), a potent vasodilator. NO activates guanylate cyclase, leading to the conversion of guanosine triphosphate (GTP) to cyclic guanosine 3',5'-monophosphate (cGMP). This process results in relaxation of vascular smooth muscle, increased blood flow, and reduced myocardial oxygen requirements by decreasing both preload and myocardial tension.

Pharmacodynamics

Nitroglycerin induces relaxation of vascular smooth muscles, leading to arteriolar and venous dilatation. This increases blood flow to the myocardium while reducing cardiac preload and afterload, thereby alleviating anginal symptoms. It also mitigates coronary artery spasm and decreases systemic vascular resistance as well as blood pressure. Tolerance to nitroglycerin can develop with prolonged use, reducing its efficacy due to desensitization of vascular smooth muscle to vasorelaxation.

Pharmacokinetics

Nitroglycerin is rapidly absorbed and metabolized, primarily through first-pass metabolism when taken orally. Its onset of action is quick, particularly with sublingual administration, typically within minutes. The half-life of nitroglycerin is short, necessitating multiple doses for sustained effect. It is primarily eliminated via hepatic metabolism, with renal excretion of metabolites.

Contra-indications

• Severe anemia
• Cardiomyopathy
• Severe hypotension
• Concomitant use of phosphodiesterase-5 inhibitors
• Increased intracranial pressure

Adverse effects

• Headache
• Dizziness
• Flushing
• Hypotension
• Tachycardia
• Nausea
• Vomiting

Interactions

• Phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil) - increased risk of severe hypotension
• Antihypertensive agents - additive hypotensive effects
• Alcohol - may enhance vasodilatory effects

Precautions

• Use with caution in patients with renal or hepatic impairment
• Monitor blood pressure regularly
• Assess for signs of tolerance with prolonged use
• Avoid abrupt discontinuation to prevent rebound angina

Pregnancy

Nitroglycerin is classified as category C. It should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Nitroglycerin is excreted in breast milk. Caution should be exercised when administered to a nursing mother.

Storage

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

Formulations

• Sublingual tablets
• Transdermal patches
• Intravenous infusion
• Oral extended-release capsules
• Ointment

Mechanism of action

Nitroglycerin is converted by mitochondrial aldehyde dehydrogenase in smooth muscle cells to nitric oxide (NO), a potent vasodilator. NO activates the enzyme guanylate cyclase, which converts guanosine triphosphate (GTP) to cyclic guanosine 3',5'-monophosphate (cGMP) in vascular smooth muscle and other tissues. cGMP is an endogenous vasodilator of vascular smooth muscle: it causes protein kinase-dependent phosphorylation and activates downstream cascades that promote relaxation and increased blood flow in veins, arteries and cardiac tissue. An _in vitro_ study using mouse aorta suggests that nitric oxide, an active metabolite of nitroglycerin, targets the natriuretic peptide receptors. The drugs used to treat angina alleviate symptoms by increasing blood flow to the ischemic myocardium and/or by reducing myocardial oxygen requirements. ... /Nitrates/ reduce myocardial oxygen requirements through their effects on the systemic circulation. Their major systemic action is a reduction in venous tone, which leads to pooling of blood in peripheral veins, decreased venous return, and reduced ventricular volume and myocardial tension (preload). /Org nitrates/ Although it predominately affects vascular smooth muscle /nitroglycerin/, the bronchioles, gastrointestinal tract (including biliary system), ureters, and uterus are affected. Free radicals of nitric oxide may activate guanylate cyclase, resulting in increased synthesis of cyclic GMP. Nitric oxide may combine with sulfhydryl groups in the endothelium and produce S-nitrosothiols, which stimulate guanylate cyclase production. N-acetyl-cycteine may enhance this process by providing a source of sulfhydryl groups. Cyclic GMP appears to reduce stored calcium and interfere with calcium-activated smooth muscle contractions. Organic nitrates... lead to the formation of the reactive free radical nitric oxide, which can activate guanylyl cyclase and increase the synthesis of cyclic GMP in smooth muscle and other tissues... A cyclic GMP-dependent protein kinase catalyzes the phosphorylation of various proteins in smooth muscle. Eventually, the light chain of myosin is dephosphorylated. Phosphorylation of the myosin chain regulates the maintenance of the contractile state in smooth muscle. Nitrates also may alter the prostaglandin system by inhibiting thromboxane synthetase and permitting preferential formation of prostacyclin over thromboxane A2. Both of these two short-acting vasoactive substances are formed from prostaglandin precursors. Prostacyclin is a potent vasodilator which causes smooth muscle relaxation through phosphorylation of the myosin light chain kinase. This reduces its ability to to be activated by calciun and calmodulin.

Pharmacodynamics

Nitroglycerin causes the relaxation of vascular smooth muscles, causing arteriolar and venous dilatation. It increases blood flow to the myocardium and reduces cardiac preload and afterload, decreasing myocardial wall stress and ameliorating anginal symptoms. Nitroglycerin also reduces coronary artery spasm, decreasing systemic vascular resistance as well as systolic and diastolic blood pressure. Like other organic nitrates, repeated and prolonged administration of nitroglycerin can lead to the development of tolerance or desensitization of vascular smooth muscle to further nitroglycerin-induced vasorelaxation. This loss of efficacy may be associated with the inhibition of mitochondrial aldehyde dehydrogenase, which is an important enzyme involved in the bioactivation of nitroglycerin. Nitroglycerin tolerance may be accompanied by pro-oxidant effects, endothelial dysfunction, and increased sensitivity to vasoconstrictors.