Nalmefene Hydrochloride - Mechanism of Action, Indications, Dosage, and Adverse Drug Reactions

Overview

Nalmefene hydrochloride injection is an opioid receptor antagonist used in treating an acute opioid overdose, therefore reversing its effects such as respiratory depression (mental disorder), sedation (a state of calmness caused by drugs), and hypotension (low blood pressure). Recently, Nalmefene hydrochloride auto-injector was approved by the FDA (Food and Drug Administration) for emergency use in adult and pediatric patients aged 12 years and older for 1.5 mg (milligrams) administered subcutaneously (under the skin) or intramuscularly (into the muscle). The FDA approved a new formulation of Nalmefene hydrochloride injection in an auto-injector form on August 7, 2024.

Drug Group

Nalmefene hydrochloride is an opioid antagonist for the management of opioid overdose and for decreasing alcohol consumption in adults with dependence. It competes with opioids on receptors; hence, reversing the effect of opioid overdose as well as minimizing an alcohol dependent’s desire for alcohol.

Indications

• Nalmefene hydrochloride injection is another antagonizing drug that is used in reversing the effects of opioid drugs, particularly those of natural and synthetic opioids, with reliance on managing suspected as well as known opioid overdosages.

• Nalmefene hydrochloride injection can be used in cases associated with opioids as an emergency measure.

• It is also important not to replace the Nalmefene hydrochloride injection with emergency medical help if needed.

Contraindications

Nalmefene hydrochloride injection is not recommended for patients with known hypersensitivity (exaggerated immune response) to Nalmefene or its components.

Dosage Forms and Available Strengths

Nalmefene hydrochloride injection is available as a Nalmefene base in a single-dose prefilled autoinjector syringe with a strength of 1.5 mg (milligrams) per 0.5 mL (milliliters).

Warnings and Precautions

When using Nalmefene hydrochloride injection, it is essential to be aware of the following warnings and precautions:

• Risk of Recurrent Respiratory Depression: The duration of action of opioids is longer than the duration of action of Nalmefene, and therefore, respiratory depression may again be encountered. Monitoring the patient constantly and giving him multiple doses may be necessary.

• Severe Opioid Withdrawal: Self-administration of Nalmefene causes withdrawal symptoms in opioid-dependent persons, such as body aches, fever, sweating, nasal discharge, and gastrointestinal (GI) discomfort.

• Cardiovascular Effects: Sudden withdrawal from opioids can cause cardiovascular (involving heart and blood vessels) emergencies due to changes in the patient’s cardiovascular state.

• Limited Efficacy with Partial Agonists: Based on comparison with other drugs of the same class, Nalmefene may not always completely reverse the effects of opioids like Buprenorphine and Pentazocine and may need repeated doses.

• Risk of Opioid Overdose from Attempts to Overcome the Blockade: Trying to alleviate opioid withdrawal signs and symptoms using increased or repeated doses of exogenous opioids may result in opioid overdose (a severe condition through which a person takes excessive opioids and suffers from respiratory depression) and death.

For Patients

How Does Nalmefene Work?

Nalmefene’s mechanism of action is to inhibit central opioid receptors, primarily the mu and delta receptors, that elicit pleasure and reward. This reduces cravings and urges to drink by reducing the rewarding effects of alcohol. Nalmefene also balances neurotransmitters, such as dopamine, which play a significant role in the brain's reward pathways, further reducing the desire to consume alcohol.

What Are the Benefits of Nalmefene?

Nalmefene offers several benefits, including:

• Reduces Alcohol Consumption: Nalmefene is used to reduce strongly the amount of alcohol consumed because it reduces the craving and urge to drink.

• Flexible Dosing: It is different from the others in the sense that Nalmefene is taken only when needed and can be taken when the patient feels that the patient is likely to be confronted with high-risk situations to drink.

• Improves Health Outcomes: Nalmefene helps moderate alcohol consumption, hence increasing overall health standards in the body, such as liver, cardiovascular, and even mental (brain) health.

• Non-Addictive: Moreover, Nalmefene does not cause dependency; hence, it is safer for long-term use as compared to other drugs.

• Supports Behavioral Therapy: This approach may be applied together with other medical interventions, such as behavior therapies and counseling, thereby improving the usefulness of treatment in general.

How Is Nalmefene Administered?

Nalmefene is an injectable preparation for intramuscular (IM) and subcutaneous use. If required, it can be injected through clothing onto the outer thigh. It needs subsequent administrations, and every administration should use a different autoinjector. Suppose the patient does not respond or the response is followed by respiratory depression. In that case, further doses of Nalmefene may be administered every two to five minutes until help is sought from emergency medical services.

The use of Nalmefene is accompanied by the risks that it should be injected rapidly, the patient should urgently contact a doctor after being given the first dose, and the patient should remain monitored until assistance is sought. The presence of particles and color change should be checked before the device is administered. It should be used in the manner depicted by the label on the exterior and interior of the carton.

What Are the Side Effects of Nalmefene?

There are side effects associated with Nalmefene injection, including the following.

Tell the doctor if any of these symptoms of Nalmefene are very serious or persist:

• Nausea.

• Vomiting.

• Fever.

• Chills.

• Headache.

• Dizziness.

• Tiredness.

• Ringing in ear.

• A feeling of rapid heartbeat.

Some of the Nalmefene side effects can be life-threatening. If patients experience any of these symptoms of Nalmefene, call the doctor immediately or get emergency medical treatment:

• The common symptoms of opioid withdrawal are body aches, diarrhea, fast pounding or irregular heartbeat, fever, runny nose, sneezing, sweating, yawning, nausea or vomiting, nervousness or restlessness and irritability, shivering or tremor, stomach cramps, sudden weakness, and, very importantly, the hairs standing on the skin.

• Seizures (abnormal electrical activity in the brain).

The patient should always contact the doctor if the patient is developing any strange symptoms while on Nalmefene.

What Are the Things to Inform the Doctor Before Taking Nalmefene?

Before the administration of Nalmefene injection,

• Inform the doctor and the pharmacist if patients have any allergies to Nalmefene injection, other similar drugs, other medications, or any ingredients found in Nalmefene injection or Nalmefene autoinjector (a medical device for injection of a premeasured dose of Nalmefene).

• Inform the doctor and the pharmacist about all the prescription and nonprescription medicines that patients use or plan to use.

• If patients have had surgery or operations, seizures, heart disease, liver disease, or kidney disease, inform the doctor.

Dietary Considerations

No diet restrictions are required when taking Nalmefene.

Overdose

The incidence of Nalmefene overdose is quite low. Symptoms include severe nausea, vomiting, dizziness, headache, and signs and symptoms of opioid withdrawal in patients who are physically dependent on opioids. If an overdose is believed to have occurred, the patient should go to the nearest hospital as soon as possible. Physicians offer psychosocial support and manage symptoms, and emergency clients must be hospitalized.

Storage and Handling

Nalmefene liquid should be stored in a cool, dry place at room temperature between 20 and 25 degrees Celsius (68 and 77 degrees Fahrenheit); however, a temperature between 15 and 30 degrees Celsius (59 and 86 degrees Fahrenheit) is occasionally acceptable. It should be clear, with a color varying from no color at all to a light yellow, and it does not freeze or refrigerate. Please keep Nalmefene dry and clean, away from direct sunlight.

Do not take or use the Nalmefene within children’s access, and inspect the solution in the auto-injector before injecting. Do not use Nalmefene if the solution is discolored or contains any precipitate. It should be replaced with a new Nalmefene. Any Nalmefene can simply be utilized once and cannot be utilized again for another subsequent use.

Disposal

Nalmefene should be stored in a carton and disposed of properly in a sharps container. The FDA has specifically recommended against flushing any unused or expired Nalmefene down the toilet and has suggested a better way of disposal through a medicine take-back program.

For Doctors

Pharmacodynamics

Nalmefene directly opposes the effects of opioids, like the depression of the respiratory center, sedation, and hypotension. Compared to Naloxone, it has a longer half-life, and in five minutes, it wins 80 percent of opioid receptors in the brain. There is, therefore, no evidence of drug tolerance, physical dependence, or abuse related to Nalmefene. It does not cause respiratory depression, psychotic effects, or miosis. However, it is known to cause severe withdrawal symptoms in those with opioid dependence. These symptoms should be treated with symptomatic and supportive measures since the use of large amounts of opioids in cases of patients receiving opioid antagonists may lead to adverse respiratory and circulatory reactions.

Mechanism of Action

The objective of the present study is to summarize the state of knowledge regarding the role of the opioid system, which is a group of three G protein-coupled receptors (mu, delta, and kappa) involved in the modulation of mood, pain, reward, addictive behaviors, and substance use disorders.

These receptors get involved with several brain signals, affecting the mesolimbic pathway, which plays the central role in positive reinforcement of rewards naturally arising from foods, drugs, etc. Alcohol also releases endogenous opioids that interact with mu and delta receptors, stimulating dopamine release in the nucleus accumbens, thereby provoking rewarding and reinforcing outcomes. An antagonist at the mu and delta-opioid receptors and a partial agonist at the kappa-opioid receptors, Nalmefene blocks ligands from binding to the opioid receptor. It may decrease alcohol consumption and correct the dysregulation of the MOR (Mu opioid receptor)/endorphins and KOR (Kappa opioid receptor)/dynorphin system induced by alcohol.

Pharmacokinetics

• Absorption: Nalmefene pharmacokinetics show that the drug is rapidly absorbed when taken orally, with an absolute oral bioavailability of 41 percent. Its Cmax (maximum plasma concentration) is 16.5 ng/mL (nanograms per milliliter), and its Tmax (time to peak drug concentration) is 1.5 hours. The exposure area under the curve is 131 ng x h/mL (nanograms per hour per milliliter). Intravenous Nalmefene shows dose-proportional pharmacokinetics, while intramuscular Nalmefene shows a Tmax of 2.3±1.1 hours and subcutaneous nalmefene Tmax of 1.5±1.2 hours. The achievement of therapeutic plasma concentration is probable in case of an emergency after one mg dose of five to 15 minutes. Intramuscular and subcutaneous absorption is not equal; there is variation in the rate at which absorption takes place.

• Distribution: Following a one mg parenteral dose, the drug was rapidly distributed in the body with a central volume of distribution values of 3.9± 1.1 L/kg and a steady state of 8.6± 1.7 L/kg. It simply penetrated the blood-brain barrier, and the protein binding varied between 30 and 45 percent. With regard to the issue, the in vitro distribution ratio of Nalmefene was 67 percent in red blood cells and 39 percent in plasma, with a whole blood to plasma ratio of 1.3.

• Metabolism: Nalmefene is a substance that undergoes hepatic biotransformation, chiefly through the formation of glucuronide conjugates. The major metabolite is Nalmefene 3-O-glucuronide, which has no activity almost the same as the parent compound after 3-O-glucuronidation. It can be transformed through dealkylation to nornalmefene and other inactive metabolites nornalmefene 3-O-glucuronide and nornalmefene 3-sulfate. Another metabolite is Nalmefene 3-O-sulfate, which arises from the sulfation of Nalmefene and possesses less than 10 percent of the activity of the parent compound. Some subjects propose that Nalmefene is subject to enterohepatic recycling.

• Excretion: Nalmefene and its metabolites excretion was predominantly renal, with 54 percent total radioactivity recovered in the urine and 17 percent in the feces. The terminal half-life is about 12.5 hours following oral administration; however, plasma concentration reduces by following biexponential dispersion. The oral clearance of Nalmefene is about 169 L/h (liters per hour), and the systemic clearance is 0.8 ± 0.2 L/hr/kg (liters per hour per kilogram), together with the renal clearance of 0.08 ± 0.04 L/hr/kg after intravenous administration of one milligram of Nalmefene.

Toxicity

The toxicity of Nalmefene was demonstrated from the following LD50 values: oral in mice: 230 and less than 200 mg/kg (milligrams per kilogram) in male and female mice, less than 300 and 150 mg/kg in male and female rats, and less than 225 and 225 mg/kg in male and female rabbits, respectively. For mice, rats, and rabbits, intravenous LD50 is 150 to 485 mg/kg, and subcutaneous is 157 to 1150 mg/kg. Concerning adverse effects, an overdose of Nalmefene may be hazardous to health, much so when administered at a dose 15 times the maximum recommended.

At doses more significant than the injection dose, Nalmefene elicits indications that characterize endogenous opioid antagonism, such as nausea, chilling, muscle pains, feelings of discomfort, abdominal discomfort, and joint pains. No dosing-dependent side effects have been reported, although the patient should be monitored during acute overdose and managed symptomatically.

Drug Interactions

Combinations of this medicine with the following medications are contraindicated. The clinician may choose not to use this medicine or adjust other drugs patients use.

• Alfentanil.

• Anileridine.

• Benzhydrocodone.

• Buprenorphine.

• Butorphanol.

• Codeine.

• Dezocine.

• Diacetylmorphine.

• Difenoxin.

• Dihydrocodeine.

• Diphenoxylate.

• Ethylmorphine.

• Fentanyl.

• Hydrocodone.

• Hydromorphone.

• Ketobemidone.

• Levorphanol.

• Meperidine.

• Meptazinol.

• Methadone.

• Morphine.

• Morphine sulfate liposome.

• Nalbuphine.

• Nicomorphine.

• Opium.

• Opium alkaloids.

• Oxycodone.

• Oxymorphone.

• Papaveretum.

• Paregoric.

• Pentazocine.

• Piritramide.

• Remifentanil.

• Sufentanil.

• Tapentadol.

• Tilidine.

• Tramadol.

Clinical Studies

The Clinical Outcomes from Injectable Nalmefene in the Emergency Department (COINED) study was a 14-month, observational cohort study in patients receiving Nalmefene HCI injection for the management of opioid overdose in the emergency department. The purpose of the work was to assess the rate of successful opioid antagonism when Nalmefene or Naloxone was administered and to assess the clinical outcomes of patients who received an opioid antagonist. The potential outcomes of the study might, therefore, give insights into the practical utility of Nalmefene in emergency-sensitive clinical practice to inform improved care delivery to patients with opioid overdose.

Use in Specific Populations

• Pregnancy: Like Methadone and Buprenorphine, Nalmefene can be used in pregnant women during an opioid overdose; the benefits outweigh the potential danger to the fetus.

• Breastfeeding: The effects of Nalmefene on the breastfed child and lactation are unknown. Nonetheless, Nalmefene and its metabolites are detected in rat milk, which means it should be present in human milk whenever there is a drug in animal milk.

• Pediatric Use: Nalmefene is currently approved for use in children older than 12 as an antidote for opioid overdose. However, there were no young people in the study.

• Geriatric Use: Patients may develop different acute and chronic diseases, which can be critical for the patient’s health, including kidney or hepatic diseases or heart diseases for elderly patients.

• Renal Impairment: The drug's effect will be compounded in patients with kidney disorders because the drug's clearance will be lower. Larger doses should be given gradually to prevent side effects such as hypertension and dizziness.

• Hepatic Impairment: Patients with liver problems may have poor elimination of Nalmefene. Nonetheless, there is usually no need for dosage modification in either case.