Klorzoxazon Orifarm

What Is Klorzoxazon Orifarm and What Is It Used For?

Klorzoxazon Orifarm contains the active substance chlorzoxazone, a centrally acting muscle relaxant. It is used for the short-term treatment of painful skeletal muscle spasms, such as those associated with acute lower back pain (lumbago), muscle strains, and other acute musculoskeletal conditions.

Chlorzoxazone belongs to the benzoxazolone class of drugs and has been used in clinical practice since the 1950s. It acts primarily at the level of the spinal cord and subcortical areas of the brain, where it inhibits multisynaptic reflex arcs that are involved in producing and maintaining skeletal muscle spasm. Unlike neuromuscular blocking agents used during surgery, chlorzoxazone does not directly affect skeletal muscle fibres or the neuromuscular junction. Instead, it reduces abnormally elevated muscle tone by dampening the central nervous system signals that perpetuate the spasm cycle.

The primary indication for Klorzoxazon Orifarm is the short-term relief of acute, painful musculoskeletal conditions, most commonly acute low back pain (lumbago). Acute low back pain is one of the most prevalent medical complaints globally, affecting up to 80% of adults at some point in their lives according to the World Health Organization. When back pain is accompanied by significant muscle spasm – characterised by involuntary, sustained contraction of the paraspinal muscles – a short course of a centrally acting muscle relaxant may be prescribed alongside other treatments such as analgesics and physical therapy.

International clinical guidelines, including those from the American College of Rheumatology (ACR) and the European Alliance of Associations for Rheumatology (EULAR), generally recommend muscle relaxants as a second-line or adjunctive option for acute low back pain with prominent muscle spasm, particularly when first-line analgesics (such as paracetamol or non-steroidal anti-inflammatory drugs) provide insufficient relief. The evidence supports their use for short periods only, typically up to two to three weeks.

It is important to understand that chlorzoxazone is a symptomatic treatment – it helps relieve muscle spasm and associated pain but does not address the underlying cause of the musculoskeletal condition. Therefore, it is typically used as part of a comprehensive treatment plan that may include rest, physical therapy, analgesics, and gradual return to normal activities.

What Should You Know Before Taking Klorzoxazon Orifarm?

Before starting Klorzoxazon Orifarm, tell your doctor about all your medical conditions, especially liver disease and porphyria. This medication is contraindicated in patients with impaired liver function. Elderly patients and those taking other sedating medications require particular caution.

Contraindications

You should not take Klorzoxazon Orifarm if any of the following apply to you:

• Allergy to chlorzoxazone or any of the other ingredients in the tablet (listed in the composition section below) – symptoms of an allergic reaction may include rash, itching, swelling, or difficulty breathing
• Impaired liver function – chlorzoxazone is extensively metabolised by the liver, and its use in patients with liver disease significantly increases the risk of hepatotoxicity. Patients with pre-existing liver damage, hepatitis, or elevated liver enzymes must not use this medication
• Porphyria – a group of inherited metabolic disorders affecting the production of haem. Chlorzoxazone may trigger acute porphyric attacks in susceptible individuals and is therefore strictly contraindicated in patients with any form of porphyria

Warnings and Precautions

Talk to your doctor or pharmacist before taking Klorzoxazon Orifarm:

• Risk of serious liver damage: There have been reports of serious hepatotoxicity associated with chlorzoxazone use, including cases that have led to liver transplantation or have been life-threatening. Although this is rare, it is a serious concern. Contact your doctor immediately if you develop any signs of liver problems, including unexplained nausea, vomiting, loss of appetite, upper abdominal pain, dark urine, or jaundice (yellowing of the skin or whites of the eyes)
• Elderly patients (over 65 years): Older adults are more susceptible to the sedating effects of chlorzoxazone, including drowsiness, dizziness, and fatigue. These effects can increase the risk of falls, which may lead to fractures or other serious injuries. Your doctor should prescribe the lowest effective dose for the shortest possible duration
• Risk of misuse: Misuse and inappropriate use have been observed with muscle relaxant medications. While the specific abuse potential of chlorzoxazone is not well established, caution is warranted, particularly in patients with a history of substance use disorders

Use in Children and Adolescents

Klorzoxazon Orifarm should not be given to children weighing less than 40 kg, which generally corresponds to children under 12 years of age. There is insufficient safety and efficacy data to support the use of chlorzoxazone in younger or lighter children. For children and adolescents weighing 40 kg or more (typically 12 years and older), the recommended dose is 1 tablet (250 mg) three to four times daily, as directed by a doctor. Paediatric use should always be under close medical supervision.

Pregnancy and Breastfeeding

The effects of chlorzoxazone on pregnancy have not been adequately studied. There are no well-controlled clinical trials in pregnant women, and it is not known whether chlorzoxazone can cause foetal harm or affect reproductive capacity. If you are pregnant, think you may be pregnant, or are planning to have a baby, consult your doctor before taking Klorzoxazon Orifarm. Your doctor will weigh the potential benefits against the possible risks before recommending treatment.

It is not known whether chlorzoxazone passes into breast milk. Because many drugs are excreted in human milk and because of the potential for adverse effects in nursing infants, you should talk to your doctor before using Klorzoxazon Orifarm while breastfeeding. Your doctor may recommend an alternative treatment or advise you to stop breastfeeding during treatment.

Driving and Operating Machinery

Klorzoxazon Orifarm can cause drowsiness, dizziness, and fatigue, which may significantly impair your alertness and ability to react. If you experience any of these side effects, you must not drive a car or other vehicle, and you must not use tools or operate machinery. You are personally responsible for assessing whether you are fit to drive or perform tasks that require alertness. Be particularly careful at the start of treatment or after dose adjustments. Discuss with your doctor or pharmacist if you are unsure.

How Does Klorzoxazon Orifarm Interact with Other Drugs?

Chlorzoxazone can interact with several medications, most notably disulfiram (which is contraindicated), isoniazid (which increases risk of side effects), and other CNS depressants. Alcohol must be avoided during treatment. Always inform your doctor of all medications you are taking.

Drug interactions can alter the way chlorzoxazone or other medications work, potentially increasing the risk of side effects or reducing therapeutic effectiveness. It is essential that you tell your doctor or pharmacist about all medicines you are currently taking, have recently taken, or plan to take, including prescription drugs, over-the-counter medicines, and herbal products.

Major Interactions

Disulfiram (used as an alcohol deterrent therapy) must not be used together with chlorzoxazone. Disulfiram inhibits the CYP2E1 enzyme, which is the primary metabolic pathway for chlorzoxazone. This interaction leads to significantly elevated blood levels of chlorzoxazone, greatly increasing the risk of adverse effects including excessive sedation and potentially liver toxicity.

Isoniazid (an antituberculosis drug) also inhibits CYP2E1 and can substantially increase chlorzoxazone blood levels when the two drugs are taken together. This combination raises the risk of side effects and may also lead to reduced therapeutic efficacy of either drug. If you are taking isoniazid, your doctor will need to carefully assess whether chlorzoxazone is appropriate for you, and close monitoring will be required if the combination is deemed necessary.

Minor Interactions

Other medications that cause drowsiness – such as sedating antihistamines, certain antidepressants (especially tricyclics and mirtazapine), antipsychotic medications, and gabapentinoids (gabapentin, pregabalin) – may have additive sedating effects when taken alongside chlorzoxazone. While these are not absolute contraindications, your doctor should be aware of all sedating medications you are taking so that the cumulative risk of excessive drowsiness can be properly assessed.

What Is the Correct Dosage of Klorzoxazon Orifarm?

The standard adult dose is 250 mg (1 tablet) three to four times daily. In severe muscle spasm, the initial dose may be increased to 500–750 mg (2–3 tablets) three to four times daily, to a maximum of 2,250 mg (9 tablets) per day. Always follow your doctor’s instructions.

Always take Klorzoxazon Orifarm exactly as your doctor or pharmacist has told you. Do not change the dose or stop treatment without consulting your doctor first. The tablets can be taken with or without food. The score line on the tablet is only to help you break the tablet if you have difficulty swallowing it whole – it does not indicate a half-dose.

Adults

The recommended dose for adults is 1 tablet (250 mg) three to four times daily. For patients experiencing severe muscle spasm, the doctor may prescribe a higher initial dose of 2 or possibly 3 tablets (500–750 mg) three to four times daily, with a maximum daily dose of 9 tablets (2,250 mg). This higher initial dose should be reduced as symptoms improve. Treatment should be limited to the shortest duration necessary to achieve symptom relief, typically no more than two to three weeks.

Children and Adolescents

Children and adolescents weighing 40 kg or more (12 years and older) may be prescribed 1 tablet (250 mg) three to four times daily, as directed by a doctor. Klorzoxazon Orifarm should not be given to children weighing less than 40 kg (generally under 12 years of age) due to insufficient safety and efficacy data.

Elderly Patients

If you are over 65 years of age, your doctor should prescribe the lowest effective dose for the shortest possible treatment period. Elderly patients are more susceptible to side effects such as drowsiness, dizziness, and fatigue, which increase the risk of falls and related injuries. Careful monitoring is recommended throughout the treatment period.

Missed Dose

If you forget to take a dose, skip the missed dose and take the next dose at the usual time. Do not take a double dose to make up for the one you missed. Taking a double dose increases the risk of side effects, particularly drowsiness and dizziness.

Overdose

If you take more Klorzoxazon Orifarm than you should, or if a child accidentally ingests the medication, contact your doctor, go to the nearest hospital emergency department, or call your local poison control centre immediately. Symptoms of overdose may include nausea, vomiting, diarrhoea, drowsiness, dizziness, lightheadedness, headache, malaise, and sluggishness. In severe cases, overdose can lead to loss of consciousness, respiratory depression, and decreased blood pressure. Early medical intervention is critical.

What Are the Side Effects of Klorzoxazon Orifarm?

Like all medicines, chlorzoxazone can cause side effects, although not everyone gets them. The most common side effects are drowsiness, dizziness, and fatigue. Rare but serious effects include liver damage and severe allergic reactions. Stop taking the medicine and seek medical help immediately if you experience signs of angioedema or liver problems.

The following side effects have been reported with chlorzoxazone. If you experience any side effects not listed below, or if any side effect becomes severe, contact your doctor or pharmacist.

The most clinically significant adverse effect associated with chlorzoxazone is hepatotoxicity. Although rare, cases of serious liver injury, including liver failure requiring transplantation, have been documented in post-marketing surveillance. The mechanism of chlorzoxazone-induced hepatotoxicity is not fully understood but is believed to involve idiosyncratic metabolic pathways. Risk factors may include pre-existing liver disease, concomitant use of other hepatotoxic agents, and genetic variations in CYP2E1 enzyme activity.

Patients should be educated about the warning signs of liver damage – specifically unexplained nausea, vomiting, loss of appetite, right upper quadrant abdominal pain, dark urine, pale stools, and jaundice – and instructed to discontinue the medication and seek prompt medical evaluation if any of these symptoms develop.

The sedating side effects (drowsiness, dizziness, fatigue) are generally dose-dependent and tend to be most pronounced during the first few days of treatment. For most patients, these effects are mild and transient. However, they can be potentiated by concurrent use of alcohol or other CNS depressants, and elderly patients are particularly susceptible.

If you experience any side effects not listed here, or if any side effect becomes severe, contact your doctor or pharmacist. Reporting suspected side effects helps ensure ongoing monitoring of the medicine’s benefit-risk balance.

How Should You Store Klorzoxazon Orifarm?

Store Klorzoxazon Orifarm below 30°C, out of the sight and reach of children. Do not use after the expiry date printed on the label. Return unused medication to your pharmacy for safe disposal.

Keep this medicine out of the sight and reach of children at all times. Store at a temperature not exceeding 30°C. Keep the container tightly closed to protect the tablets from moisture. Do not use this medicine after the expiry date which is stated on the label after “EXP”. The expiry date refers to the last day of that month.

Do not throw away any medicines via the toilet or household waste. Ask your pharmacist how to dispose of medicines you no longer use. These measures help to protect the environment from pharmaceutical contamination and prevent accidental ingestion by children, pets, or other individuals.

If you notice any change in the appearance of the tablets, such as discolouration, crumbling, or an unusual odour, do not take them and consult your pharmacist. Damaged or deteriorated tablets may have reduced efficacy or altered safety profiles.

What Does Klorzoxazon Orifarm Contain?

Each tablet contains 250 mg of chlorzoxazone as the active ingredient. The tablets are white to yellowish-white, round, convex, scored on one side, and 10 mm in diameter. They are available in plastic containers of 25, 50, 56, 100, or 105 tablets.

Active Ingredient

The active substance is chlorzoxazone. Each tablet contains 250 mg of chlorzoxazone. Chlorzoxazone is a synthetic benzoxazolone derivative (chemical name: 5-chloro-2(3H)-benzoxazolone) with muscle relaxant properties. It acts centrally to reduce skeletal muscle spasm by inhibiting multisynaptic reflex arcs in the spinal cord and brainstem.

Inactive Ingredients (Excipients)

The other ingredients are:

• Calcium hydrogen phosphate dihydrate – used as a diluent and filler
• Gelatin – used as a binder to hold the tablet together
• Microcrystalline cellulose – used as a filler and aids tablet disintegration
• Stearic acid – used as a lubricant during tablet manufacture
• Talc – used as a glidant to improve powder flow
• Potato starch – used as a disintegrant to help the tablet break apart after ingestion

Tablet Appearance and Packaging

Appearance: White to yellowish-white, round, convex tablet with a score line on one side, approximately 10 mm in diameter. The score line is only to facilitate breaking the tablet for easier swallowing – it does not divide the tablet into equal doses.

Pack sizes: Available in plastic containers of 25, 50, 56, 100, or 105 tablets. Not all pack sizes may be marketed in your country.

Marketing Authorisation Holder

Orifarm Generics A/S, Energivej 15, 5260 Odense S, Denmark. Klorzoxazon Orifarm is a generic medication manufactured under strict pharmaceutical quality standards.

How Does Chlorzoxazone Work in the Body?

Chlorzoxazone acts primarily at the spinal cord and subcortical brain regions, where it inhibits multisynaptic reflex arcs involved in muscle spasm. It reduces abnormally elevated muscle tone without directly paralysing skeletal muscle. The drug is rapidly absorbed, extensively metabolised by the liver (CYP2E1), and has a short half-life of approximately 1–2 hours.

Muscle spasm is a protective but often counterproductive response to musculoskeletal injury. When tissues such as muscles, ligaments, or intervertebral discs are damaged, sensory nerve signals travel to the spinal cord and trigger reflex motor responses that cause the surrounding muscles to contract. While this initially serves to immobilise and protect the injured area, sustained spasm can become a self-perpetuating cycle of pain and contraction: the spasm itself causes pain, which triggers further reflex contraction, creating a pain-spasm-pain cycle.

Chlorzoxazone interrupts this cycle by acting at the central nervous system level. Specifically, it inhibits multisynaptic reflex arcs at the spinal cord and in subcortical brain areas (including the brainstem reticular formation). By dampening these central reflex pathways, chlorzoxazone reduces the excitatory neural signals that maintain skeletal muscle spasm, leading to decreased muscle tone and relief of associated pain. Importantly, it does not directly affect the neuromuscular junction or the contractile apparatus of skeletal muscle itself.

The precise molecular mechanism by which chlorzoxazone produces its central muscle relaxant effect is not completely elucidated. It is thought to involve modulation of inhibitory interneurons in the spinal cord and possibly enhancement of descending inhibitory pathways from supraspinal centres. Some evidence suggests that chlorzoxazone may facilitate GABAergic and glycinergic neurotransmission in the spinal cord, although this remains an area of active research.

Pharmacokinetic Profile

After oral administration, chlorzoxazone is rapidly and well absorbed from the gastrointestinal tract. Peak plasma concentrations are typically reached within 1 to 2 hours after dosing. The drug is widely distributed throughout the body and readily crosses the blood-brain barrier, which is essential for its central mechanism of action.

Chlorzoxazone undergoes extensive first-pass hepatic metabolism, primarily by the cytochrome P450 enzyme CYP2E1. It is converted to its principal metabolite, 6-hydroxychlorzoxazone, which is pharmacologically inactive. This metabolite is then conjugated with glucuronic acid and excreted predominantly in the urine. The elimination half-life of chlorzoxazone is relatively short, approximately 1 to 2 hours, which necessitates multiple daily dosing (typically three to four times per day) to maintain therapeutic plasma levels.

Because CYP2E1 is the primary enzyme responsible for chlorzoxazone metabolism, drugs that inhibit this enzyme (such as disulfiram and isoniazid) can significantly increase chlorzoxazone blood levels and prolong its effects, as detailed in the drug interactions section above. Genetic polymorphisms in CYP2E1 may also affect individual responses to chlorzoxazone, contributing to interpatient variability in both efficacy and adverse effects.

Frequently Asked Questions About Klorzoxazon Orifarm