Norpropoxyphene
Norpropoxyphene[edit | edit source]
Norpropoxyphene is a major metabolite of the opioid analgesic propoxyphene. It is formed in the liver through the process of N-demethylation of propoxyphene. Norpropoxyphene itself is pharmacologically active and contributes to the overall effects and side effects of propoxyphene use.
Pharmacology[edit | edit source]
Norpropoxyphene acts primarily as a central nervous system depressant. It has a longer half-life than its parent compound, propoxyphene, which can lead to accumulation in the body, especially with repeated dosing. This accumulation can increase the risk of adverse drug reactions, particularly in the elderly or those with impaired liver function.
Mechanism of Action[edit | edit source]
Norpropoxyphene, like propoxyphene, exerts its effects by binding to opioid receptors in the brain and spinal cord. However, it has a lower affinity for these receptors compared to propoxyphene. The primary action of norpropoxyphene is believed to be related to its ability to inhibit the reuptake of norepinephrine and serotonin, contributing to its analgesic and sedative properties.
Clinical Significance[edit | edit source]
The presence of norpropoxyphene in the body is significant due to its potential to cause cardiotoxicity. It can lead to cardiac arrhythmias and conduction abnormalities, particularly in cases of overdose. The risk of such adverse effects has led to the withdrawal of propoxyphene from the market in several countries.
Metabolism and Excretion[edit | edit source]
Norpropoxyphene is primarily metabolized in the liver and excreted in the urine. The metabolic pathway involves cytochrome P450 enzymes, which convert propoxyphene to norpropoxyphene. The excretion of norpropoxyphene is slower than that of propoxyphene, contributing to its longer duration of action and potential for accumulation.
Toxicity[edit | edit source]
The toxicity of norpropoxyphene is a major concern in the context of propoxyphene use. Symptoms of toxicity may include respiratory depression, hypotension, and seizures. In severe cases, it can lead to coma and death. The risk of toxicity is heightened in individuals with renal impairment or those taking other central nervous system depressants.
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