MERSALYL-THEOPHYLLINE

Clinical safety rating: safe

Many drugs can increase (eg ciprofloxacin) or decrease (eg phenytoin) levels due to CYP1A2 metabolism Has a narrow therapeutic index and can cause seizures and arrhythmias in overdose.

How it works

Mersalyl inhibits sodium-potassium-chloride cotransporter (NKCC2) in the thick ascending limb of the loop of Henle, reducing reabsorption of Na+, K+, and Cl-. Theophylline is a phosphodiesterase inhibitor that increases intracellular cAMP, enhancing cardiac contractility and causing mild diuresis. The combination provides synergistic diuretic effect.

What the body does with it

Metabolism	Mersalyl: not significantly metabolized; excreted renally. Theophylline: primarily hepatic via CYP1A2, CYP2E1, and CYP3A4; minor renal excretion.
Excretion	Renal: >90% as unchanged mersalyl and theophylline metabolites; biliary/fecal: <5%.
Half-life	Mersalyl: 2-4 hours; theophylline: 3-8 hours (prolonged in hepatic impairment).
Protein binding	Mersalyl: 40-50% to albumin; theophylline: 40-60% to albumin.
Volume of Distribution	Mersalyl: 0.2-0.3 L/kg; theophylline: 0.3-0.5 L/kg.
Bioavailability	IM: 100%; oral: not applicable (administered parenterally).
Onset of Action	IM: 30-60 minutes; IV: 5-15 minutes.
Duration of Action	IM/IV: 6-12 hours; effects may persist longer in renal impairment.

Classification & Brands

Dosing & administration

Mersalyl (with theophylline) is administered intramuscularly or intravenously at a dose of 0.5 to 2 mL of a 10% solution (50-200 mg of mersalyl) once daily or every other day. The specific product Mersalyl-Theophylline typically contains mersalyl 100 mg and theophylline 50 mg per mL. Maximum single dose is 2 mL.

Dosage form	INJECTABLE
Renal impairment	Contraindicated in severe renal impairment (GFR < 30 mL/min). For GFR 30-60 mL/min, reduce dose by 50% and monitor electrolytes and fluid status. No data for GFR > 60 mL/min.
Liver impairment	No specific dose adjustments for hepatic impairment. Use with caution in severe liver disease due to risk of electrolyte disturbances.
Pediatric use	Not recommended for pediatric use due to limited safety data and risk of mercury toxicity. Alternative diuretics preferred.
Geriatric use	Start at lower end of dosing range (0.5 mL) due to increased risk of electrolyte imbalance and renal impairment. Monitor renal function and fluid status closely.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Many drugs can increase (eg ciprofloxacin) or decrease (eg phenytoin) levels due to CYP1A2 metabolism Has a narrow therapeutic index and can cause seizures and arrhythmias in overdose.

FDA category	Animal
Breastfeeding	Contraindicated in breastfeeding. Mercury is excreted into breast milk (M/P ratio not established). Risk of neonatal mercury accumulation and renal toxicity. Use alternative diuretics.
Teratogenic Risk	Mersalyl-theophylline is contraindicated in pregnancy. First trimester: Potential teratogenicity due to mercury content; risk of fetal renal tubular damage and growth restriction. Second and third trimesters: Increased risk of oligohydramnios, fetal nephrotoxicity, and premature closure of ductus arteriosus. Use only for life-threatening maternal conditions.

Warnings & precautions

■ FDA Black Box Warning

May cause severe hypokalemia, hypotension, and dehydration. Requires close monitoring of electrolytes and renal function.

Side Effect Profile

Common Effects	COPD
Serious Effects

Absolute Contraindications

Anuria, severe renal failure, pre-existing hypokalemia, hypersensitivity to mercurial compounds or theophylline, patients receiving other nephrotoxic or ototoxic drugs.

Clinical Precautions

Precautions

Risk of electrolyte imbalances (hypokalemia, hyponatremia, hypochloremia), dehydration, hypotension, ototoxicity, renal impairment, hypersensitivity reactions. Use caution in patients with hepatic impairment, prostatic hypertrophy, or gout.

Clinical Tips & Counseling

Drug interactions

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MERSALYL-THEOPHYLLINE

Clinical safety rating: safe

Many drugs can increase (eg ciprofloxacin) or decrease (eg phenytoin) levels due to CYP1A2 metabolism Has a narrow therapeutic index and can cause seizures and arrhythmias in overdose.

How it works

What the body does with it

Metabolism	Mersalyl: not significantly metabolized; excreted renally. Theophylline: primarily hepatic via CYP1A2, CYP2E1, and CYP3A4; minor renal excretion.
Excretion	Renal: >90% as unchanged mersalyl and theophylline metabolites; biliary/fecal: <5%.
Half-life	Mersalyl: 2-4 hours; theophylline: 3-8 hours (prolonged in hepatic impairment).
Protein binding	Mersalyl: 40-50% to albumin; theophylline: 40-60% to albumin.
Volume of Distribution	Mersalyl: 0.2-0.3 L/kg; theophylline: 0.3-0.5 L/kg.
Bioavailability	IM: 100%; oral: not applicable (administered parenterally).
Onset of Action	IM: 30-60 minutes; IV: 5-15 minutes.
Duration of Action	IM/IV: 6-12 hours; effects may persist longer in renal impairment.

Classification & Brands

Dosing & administration

Dosage form	INJECTABLE
Renal impairment	Contraindicated in severe renal impairment (GFR < 30 mL/min). For GFR 30-60 mL/min, reduce dose by 50% and monitor electrolytes and fluid status. No data for GFR > 60 mL/min.
Liver impairment	No specific dose adjustments for hepatic impairment. Use with caution in severe liver disease due to risk of electrolyte disturbances.
Pediatric use	Not recommended for pediatric use due to limited safety data and risk of mercury toxicity. Alternative diuretics preferred.
Geriatric use	Start at lower end of dosing range (0.5 mL) due to increased risk of electrolyte imbalance and renal impairment. Monitor renal function and fluid status closely.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Many drugs can increase (eg ciprofloxacin) or decrease (eg phenytoin) levels due to CYP1A2 metabolism Has a narrow therapeutic index and can cause seizures and arrhythmias in overdose.

FDA category	Animal
Breastfeeding	Contraindicated in breastfeeding. Mercury is excreted into breast milk (M/P ratio not established). Risk of neonatal mercury accumulation and renal toxicity. Use alternative diuretics.
Teratogenic Risk	Mersalyl-theophylline is contraindicated in pregnancy. First trimester: Potential teratogenicity due to mercury content; risk of fetal renal tubular damage and growth restriction. Second and third trimesters: Increased risk of oligohydramnios, fetal nephrotoxicity, and premature closure of ductus arteriosus. Use only for life-threatening maternal conditions.

Warnings & precautions

■ FDA Black Box Warning

May cause severe hypokalemia, hypotension, and dehydration. Requires close monitoring of electrolytes and renal function.

Side Effect Profile

Common Effects	COPD
Serious Effects

Absolute Contraindications

Anuria, severe renal failure, pre-existing hypokalemia, hypersensitivity to mercurial compounds or theophylline, patients receiving other nephrotoxic or ototoxic drugs.