Relexid200 mg

Relexid 200 mg is a penicillin-class antibiotic indicated for the treatment of uncomplicated urinary tract infections (acute cystitis) in adult women, caused by susceptible isolates of Escherichia coli, Proteus mirabilis, and Staphylococcus saprophyticus. It is reserved for uncomplicated infections in patients with no structural urinary tract abnormalities.

Contains Relexid 200 mg hydrochloride as the active ingredient, available as oral tablets, commonly in 185 mg and 400 mg strengths.

Relexid 200 mg is an oral prodrug of mecillinam, a synthetic penicillin derivative with a long-established history of use in Europe and Canada, more recently approved in the United States for uncomplicated urinary tract infections given rising resistance to older first-line agents. It has a distinctive mechanism among penicillins, targeting a different bacterial cell wall protein than most other beta-lactams, which contributes to its notably low resistance rates despite decades of use. Its "pivalate" prodrug component, which allows the drug to be absorbed effectively, carries a specific, well-recognized risk of depleting the body's carnitine stores, particularly with repeated or prolonged courses, and it is specifically contraindicated in patients with porphyria, given a documented association with triggering acute porphyria attacks.

Therapeutic Class: Antibiotic (Amidinopenicillin)

Relexid 200 mg is a prodrug, hydrolyzed by esterases in the body into its active form, mecillinam; oral bioavailability is approximately 60-70%. It has a short half-life of about 1 hour and is eliminated mainly by the kidneys. Each dose of Relexid 200 mg releases a pivalate moiety as a by-product of its conversion to the active drug, and pivalate binds to and depletes the body's carnitine, an amino-acid-derivative essential for fatty acid metabolism - a mechanism unique to pivalate-ester prodrugs (shared with certain other pivalate-releasing medicines) and the basis for the carnitine-related warnings associated with this drug.

• Take orally, with or without food, at evenly spaced intervals through the day
• Complete the full prescribed course, even if symptoms improve before the course is finished
• Do not use for extended or repeated courses without specific medical guidance, given the carnitine depletion risk with prolonged use

The following interactions are particularly important:

• Valproic acid, valproate, or other pivalate-generating drugs: avoid combining, since these also deplete carnitine, and using them together with Relexid 200 mg significantly increases the risk of clinically significant carnitine deficiency.
• Probenecid: inhibits renal tubular excretion of mecillinam, increasing its blood concentration.
• Oral hormonal contraceptives: penicillin-class antibiotics may reduce their effectiveness; an additional contraceptive method is generally advised during treatment.

Common side effects

• Nausea
• Diarrhoea
• Vaginal yeast infection

Serious side effects (require prompt medical attention)

• Carnitine depletion (hypocarnitinemia): clinically significant, symptomatic depletion has been observed with long-term treatment, though short-term courses have not been linked to clinical effects; symptoms can include anxiety, confusion, muscle pain, unusual tiredness, nausea, palpitations, or, in severe cases, seizures - report these promptly, particularly if you have risk factors such as significant renal impairment or reduced muscle mass.
• Acute porphyria attacks: Relexid 200 mg has been specifically associated with precipitating this serious reaction in susceptible patients, which is why it is contraindicated in known porphyria.
• Serious hypersensitivity reactions, including anaphylaxis: more likely in patients with a history of penicillin, cephalosporin, or carbapenem hypersensitivity; discontinue and seek emergency treatment if this occurs.
• Severe or persistent diarrhoea, which may occur even 2 months or more after stopping the medicine, and may indicate Clostridioides difficile-associated colitis; do not self-treat diarrhoea with an antidiarrheal medicine without checking with your doctor first.
• Oesophageal ulceration (rare), particularly relevant in patients with swallowing or passage disorders.
• Liver dysfunction (uncommon).

Pregnancy

Relexid 200 mg is generally considered safe for use during pregnancy when clinically indicated; however, it can interfere with certain newborn screening tests if used shortly before delivery, so inform the delivering care team if you have taken this medicine close to your due date.

Breastfeeding

Limited data are available on Relexid 200 mg use during breastfeeding; discuss use with your doctor.

• Carnitine depletion: not recommended for prolonged or repeated antibacterial courses, given the risk of clinically significant carnitine deficiency with extended use; consider alternative antibacterial therapy in patients with risk factors for reduced serum carnitine, such as significant renal impairment or decreased muscle mass.
• Porphyria: strictly avoided in patients with this condition, given the risk of triggering an acute, potentially severe attack.
• Penicillin allergy: take a careful allergy history before starting, given the risk of serious cross-reactive hypersensitivity reactions.
• Avoid concurrent use with valproic acid or other pivalate-generating drugs, given increased carnitine depletion risk.
• Take the full prescribed course, even though the three-times-daily schedule can be inconvenient, to ensure the infection is fully treated.

Limited data exist on Relexid 200 mg overdose; excessive dosing may be expected to cause exaggerated gastrointestinal effects and an increased risk of carnitine-related symptoms. Suspected significant overdose should be evaluated by a healthcare professional; treatment is generally supportive.

Store at room temperature, protected from moisture, as directed on the product label.

• Renal impairment: Relexid 200 mg is eliminated by the kidneys; dosage adjustment may be necessary in patients with reduced kidney function, and this population is also at increased risk for carnitine depletion.
• Hepatic impairment: No dosage adjustment is generally needed.
• Elderly: Clinical trials have not shown differences in safety or effectiveness compared to younger adults.
• Infants under 3 months: Contraindicated.

Treatment for uncomplicated urinary tract infection is typically a short course of 3 to 7 days (commonly 3 days for the FDA-approved indication), three times daily. Relexid 200 mg is not recommended when prolonged antibacterial treatment is needed, given the carnitine depletion risk with extended use.

Drug Class: Amidinopenicillin (pivaloyloxymethyl ester prodrug of mecillinam)

Mecillinam, the active form of Relexid 200 mg, works by binding selectively to penicillin-binding protein 2 (PBP2), a target distinct from the PBP1 and PBP3 proteins that most other penicillins primarily target. This distinctive binding site is thought to contribute to mecillinam's activity against many bacteria that have developed resistance to other penicillins, disrupting bacterial cell wall synthesis and causing the bacteria to die.

Relexid 200 mg has an established history of use in children over 6 years in some countries, with weight-based dosing (20-40 mg/kg/day divided into 3 doses, up to 1,200 mg/day); it is contraindicated in infants under 3 months of age. Its FDA-approved indication is specifically for adult women 18 years and older.