Histex-dm

For the treatment of non-productive cough, the typical adult dosage ranges are as follows:

• Immediate-release (syrup/capsules): 10 mg to 20 mg every 4 hours, or 30 mg every 6 to 8 hours.
• Extended-release (suspension): 60 mg twice daily (every 12 hours).
• Maximum Dose: Do not exceed 120 mg in a 24-hour period unless directed by a physician.

Pediatric dosing must be calculated carefully based on age and weight. According to the American Academy of Pediatrics (AAP), OTC cough medications should be used with caution in children.

• Children 6 to 12 years: 5 mg to 10 mg every 4 hours, or 15 mg every 6 to 8 hours (Max 60 mg/day).
• Children 4 to 6 years: 2.5 mg to 5 mg every 4 hours, or 7.5 mg every 6 to 8 hours (Max 30 mg/day).
• Children under 4 years: Use is generally not recommended unless specifically directed by a pediatrician.

Renal Impairment

No specific dose adjustments are provided in the standard labeling; however, patients with severe renal disease should use caution as metabolites are cleared through the kidneys.

Hepatic Impairment

Since Dextromethorphan is extensively metabolized by the liver, individuals with hepatic impairment may require lower doses or longer dosing intervals to prevent drug accumulation.

Elderly Patients

Older adults should start at the lower end of the dosing range due to a higher likelihood of decreased hepatic or renal function and potential sensitivity to central nervous system (CNS) effects.

Dextromethorphan can be taken with or without food. If using the liquid form, always use the provided measuring device (cup or syringe) to ensure an accurate dose; household spoons are not reliable. Extended-release formulations should be shaken well before use and swallowed without crushing or chewing the granules. Store at room temperature away from moisture and heat.

If you miss a dose, take it as soon as you remember. If it is nearly time for your next scheduled dose, skip the missed dose and resume your regular schedule. Do not double the dose to catch up.

Signs of overdose include extreme drowsiness, blurred vision, confusion, hallucinations, and respiratory depression (slowed breathing). In the event of a suspected overdose, contact a poison control center or seek emergency medical attention immediately.

> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance.

At standard therapeutic doses, Dextromethorphan is generally well-tolerated. However, some patients may experience:

• Dizziness: A feeling of lightheadedness or unsteadiness.
• Drowsiness: Mild sedation or a feeling of being tired.
• Gastrointestinal Upset: Mild nausea, stomach pain, or constipation.

• Nervousness or Restlessness: A feeling of jitteriness, especially in children.
• Fatigue: General lack of energy.
• Dry Mouth: A decrease in saliva production.

• Skin Rash: Itching or hives (urticaria).
• Serotonin Syndrome Symptoms: Mild tachycardia (fast heart rate) or sweating when taken with other serotonergic drugs.

> Warning: Stop taking Dextromethorphan and call your doctor immediately if you experience any of these.

• Hallucinations: Seeing or hearing things that are not there (often associated with high doses).
• Severe Confusion: Disorientation or inability to speak clearly.
• Seizures: Involuntary muscle contractions and loss of consciousness.
• Severe Respiratory Depression: Difficulty breathing or very shallow breaths.
• Anaphylaxis: Severe allergic reaction characterized by swelling of the face, tongue, or throat, and difficulty swallowing.

Dextromethorphan is intended for short-term use (usually less than 7 days). Prolonged use or misuse can lead to psychological dependence and a phenomenon known as "dexing" or "robotripping," which involves dissociative states similar to ketamine or PCP. Long-term high-dose use may result in cognitive impairment and persistent neurological disturbances.

No FDA black box warnings currently exist for Dextromethorphan when used at recommended therapeutic doses. However, the FDA has issued safety communications regarding its potential for abuse among teenagers and the risks of serious breathing problems in young children.

Report any unusual symptoms to your healthcare provider.

Dextromethorphan should only be used for dry, non-productive coughs. If a cough persists for more than 7 days, returns, or is accompanied by fever, rash, or persistent headache, a healthcare provider should be consulted as these may be signs of a more serious condition.

No FDA black box warnings for Dextromethorphan.

• Allergic Reactions: Patients with a known hypersensitivity to dextromethorphan or any components of the formulation (such as dyes or preservatives) should avoid use.
• Chronic Lung Disease: Caution is advised in patients with asthma, emphysema, or chronic obstructive pulmonary disease (COPD), as suppressing the cough reflex may lead to the accumulation of mucus in the airways.
• CYP2D6 Metabolism: Approximately 5-10% of the population are "poor metabolizers" of CYP2D6. In these individuals, dextromethorphan levels can rise significantly, increasing the risk of toxicity and side effects.
• Abuse Potential: Dextromethorphan has a high potential for misuse. At high doses, it acts as a dissociative hallucinogen.

No routine lab monitoring is required for short-term OTC use. However, if used long-term or for off-label indications, healthcare providers may monitor liver function and neurological status.

Dextromethorphan may cause drowsiness or dizziness. Patients should determine how they react to the medication before driving, operating heavy machinery, or performing tasks that require mental alertness.

Alcohol can increase the sedative effects of Dextromethorphan. Combining the two can lead to excessive drowsiness, impaired motor coordination, and increased risk of respiratory depression.

For standard cough suppression, the drug can be stopped abruptly without tapering. However, if the drug has been misused at high doses for a long period, withdrawal symptoms like anxiety and tremors may occur.

> Important: Discuss all your medical conditions with your healthcare provider before starting Dextromethorphan.

• Monoamine Oxidase Inhibitors (MAOIs): Dextromethorphan must NOT be used within 14 days of taking an MAOI (e.g., phenelzine, selegiline). This combination can cause a fatal "serotonin syndrome," characterized by high blood pressure, hyperthermia (dangerously high body temperature), and coma.

• Selective Serotonin Reuptake Inhibitors (SSRIs): Drugs like fluoxetine or paroxetine can inhibit the metabolism of dextromethorphan (via CYP2D6 inhibition) and increase serotonin levels, raising the risk of serotonin syndrome.
• Quinidine: This medication significantly increases the blood concentration of dextromethorphan by blocking its primary metabolic pathway.

• CNS Depressants: Benzodiazepines, opioids, and certain sleep medications can enhance the sedative effects of dextromethorphan.
• Memantine: As both drugs have NMDA antagonist properties, combining them may increase the risk of neurological side effects.

• Grapefruit Juice: Grapefruit juice can inhibit certain metabolic enzymes, potentially increasing the levels of dextromethorphan in the blood, though the effect is less pronounced than with CYP2D6 inhibitors.
• Alcohol: As noted, alcohol synergistically increases CNS depression.

• St. John's Wort: This supplement increases serotonin levels and may contribute to serotonin syndrome when combined with dextromethorphan.
• Valerian/Kava: These may increase the drowsiness associated with dextromethorphan use.

Dextromethorphan may cause false-positive results in some urine drug screens for phencyclidine (PCP) or opioids. Always inform laboratory staff if you have taken dextromethorphan before a drug test.

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking.

• MAOI Use: Taking Dextromethorphan while on an MAOI or within 14 days of stopping one is strictly contraindicated due to the risk of serotonin syndrome.
• Known Hypersensitivity: Any previous severe allergic reaction to dextromethorphan or its inactive ingredients.

• Chronic Bronchitis or Emphysema: Patients with excessive mucus production should generally not suppress their cough, as coughing is necessary to clear the lungs.
• Productive Cough: Using a cough suppressant for a cough that produces a lot of phlegm can lead to fluid buildup in the lungs and potentially pneumonia.
• Liver Disease: Due to extensive hepatic metabolism, patients with significant liver impairment require careful clinical evaluation.

There is no established cross-sensitivity between dextromethorphan and other common drug classes like penicillins or NSAIDs; however, patients sensitive to other morphinan derivatives should exercise caution.

> Important: Your healthcare provider will evaluate your complete medical history before prescribing Dextromethorphan.

Dextromethorphan is generally classified as Pregnancy Category C. While animal studies have not shown clear evidence of teratogenicity at therapeutic doses, there are no adequate, well-controlled studies in pregnant humans. It should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus, particularly in the first trimester.

It is not known whether dextromethorphan or its metabolites are excreted in human milk. Because many drugs are excreted in breast milk, caution should be exercised. Most experts consider occasional therapeutic doses to be compatible with breastfeeding, but long-term use should be avoided.

Dextromethorphan is FDA-approved for children 4 years and older. However, the FDA and manufacturers have warned against its use in infants and toddlers under age 4 due to the risk of life-threatening respiratory depression and lack of proven efficacy in that age group.

Clinical studies have not identified significant differences in responses between the elderly and younger patients. However, due to the higher prevalence of polypharmacy (taking multiple medications) in the elderly, the risk of drug-drug interactions is significantly higher.

No specific GFR-based adjustments are provided. However, since the kidneys excrete the metabolites, patients with a GFR < 30 mL/min should be monitored for increased side effects.

In patients with Child-Pugh Class B or C hepatic impairment, the half-life of dextromethorphan may be significantly prolonged. Dose reductions of 50% or longer intervals between doses are often recommended by clinical pharmacologists.

> Important: Special populations require individualized medical assessment.

Dextromethorphan acts primarily as an agonist at Sigma-1 receptors in the cough center of the medulla. It also functions as an uncompetitive antagonist at the N-methyl-D-aspartate (NMDA) receptor complex. Unlike opioid antitussives, it does not bind significantly to mu-opioid receptors, which explains its lack of analgesic effects at therapeutic doses. It also has minor activity as a serotonin and norepinephrine reuptake inhibitor.

The antitussive effect of a single dose usually lasts for 3 to 6 hours for immediate-release forms and up to 12 hours for extended-release forms. It increases the threshold for the cough reflex without significantly inhibiting ciliary activity in the respiratory tract.

| Parameter | Value |

|---|---|

| Bioavailability | Highly variable (extensive first-pass) |

| Protein Binding | ~7% |

| Half-life | 3 - 4 hours (Extensive Metabolizers) |

| Tmax | 2 - 3 hours |

| Metabolism | Hepatic (CYP2D6, CYP3A4) |

| Excretion | Renal (>90%) |

• Molecular Formula: C18H25NO (as Hydrobromide: C18H26BrNO)
• Molecular Weight: 271.4 g/mol (Base)
• Solubility: Sparingly soluble in water; freely soluble in ethanol.
• Structure: A d-isomer of the codeine analog of levorphanol.

Dextromethorphan is a morphinan-class antitussive. It is often grouped with other cough suppressants like benzonatate or codeine, though its mechanism is distinct from both.