Sultamicillin

BRAND NAMES

The most well-known international brand name for sultamicillin is Unasyn, which is also the brand name for the injectable ampicillin/sulbactam combination. 

Brand names in India

In India, sultamicillin is marketed under numerous brand names, including: 

Bactomin

Marzon

Recontrex

Santum

Sultaclin

Sultafit

Sultamylin

Sultazed

Sultacef 

MECHANISM OF ACTION

Sultamicillin is a prodrug that, once absorbed, is converted into ampicillin and sulbactam. Ampicillin, a β-lactam antibiotic, works by inhibiting bacterial cell wall synthesis through binding to penicillin-binding proteins, which prevents the cross-linking of peptidoglycan chains, ultimately causing bacterial cell lysis. Sulbactam, a β-lactamase inhibitor, protects ampicillin from enzymatic degradation by β-lactamase–producing bacteria, thereby extending its spectrum of activity. Together, this combination exhibits a synergistic effect, making sultamicillin effective against both susceptible and β-lactamase–producing bacterial strains in infections such as respiratory, urinary tract, and skin infections.

PHARMACOKINETICS

Absorption

Sultamicillin is a prodrug developed to enhance the oral absorption of the combination antibiotic ampicillin and sulbactam. Once administered orally, it is absorbed from the gastrointestinal tract and rapidly converted into its two active constituents.

Distribution

The volume of distribution of sultamicillin is closely related to its active components, ampicillin and sulbactam, after hydrolysis.

Volume of distribution: approximately 0.2–0.3 L/kg

This indicates that sultamicillin is mainly distributed in extracellular fluids rather than extensively into tissues or fat.

It achieves therapeutic concentrations in blood, urine, and various body fluids, making it effective for infections of the respiratory tract, urinary tract, and skin/soft tissue.

Metabolism

Sultamicillin is a prodrug that, after oral administration, is hydrolyzed in the intestinal wall to release the active antibiotics ampicillin and sulbactam in a 1:1 molar ratio. Once released, both components are absorbed into the bloodstream and are predominantly excreted by the kidneys.

Excretion

Sultamicillin is primarily excreted via the kidneys after being hydrolyzed into ampicillin and sulbactam. Both components are mostly eliminated unchanged through glomerular filtration and tubular secretion, making dose adjustment necessary in patients with renal impairment.

PHARMACODYNAMICS

Sultamicillin, a prodrug of ampicillin and sulbactam, exhibits time-dependent bactericidal activity. Ampicillin inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins, while sulbactam protects ampicillin from β-lactamase degradation, extending its spectrum. The combination acts synergistically, with efficacy depending on the time the drug concentration remains above the bacterial minimum inhibitory concentration (MIC).

ADMINISTRATION

Sultamicillin is an oral antibiotic that serves as a mutual prodrug of ampicillin and sulbactam. It is available in oral tablet or suspension form and is used to treat a variety of bacterial infections. For more severe infections, ampicillin/sulbactam is administered intravenously, as sultamicillin itself is not available in IV form.

DOSAGE AND STRENGTH

Available Forms:

Oral tablets: commonly 375 mg, 500 mg, or 750 mg (equivalent to ampicillin:sulbactam in a 1:1 molar ratio)

Oral suspension: typically 125 mg/5 mL, 250 mg/5 mL

Recommended Adult Dosage:

Mild to moderate infections: 375–500 mg orally every 8–12 hours

Severe infections: up to 750 mg orally every 8 hours

DRUG INTERACTIONS

Sultamicillin may interact with several drugs, including oral anticoagulants, where it can increase the risk of bleeding, and methotrexate, by reducing its renal clearance and raising toxicity risk. Concurrent use with allopurinol may increase the likelihood of rash, while bacteriostatic antibiotics like tetracyclines can antagonize its bactericidal effect. There is also a theoretical risk of reduced efficacy of oral contraceptives. Careful monitoring is recommended when sultamicillin is combined with these medications.

FOOD INTERACTIONS

Sultamicillin can be taken with or without food, as food does not significantly affect its absorption or effectiveness. Taking it with meals may help reduce gastrointestinal side effects such as nausea or diarrhea, while alcohol should be avoided as it can worsen these effects.

CONTRAINDICATIONS

Sultamicillin is contraindicated in patients with a known allergy to penicillins or other β-lactam antibiotics, as well as those with a history of severe allergic reactions such as anaphylaxis or angioedema. It should be used cautiously or avoided in individuals with severe renal impairment or a history of antibiotic-associated colitis.

SIDE EFFECTS

• Diarrhea, nausea, vomiting

• Abdominal pain, stomach cramps

• Skin rash or itching

• Sore mouth

• Fatigue or malaise

• Headache, dizziness, blurred vision 

• Severe allergic reactions

• Serious skin reactions

• Liver problems

• Severe diarrhea

• Blood disorders

OVERDOSE

• Gastrointestinal issues

• Neurological effects

• Allergic reactions

• Liver problems

TOXICITY

Sultamicillin toxicity is uncommon but can occur, especially with overdose or prolonged use. It may cause gastrointestinal symptoms like nausea, vomiting, and diarrhea, as well as hypersensitivity reactions such as rash or, rarely, anaphylaxis. Hematologic effects like leukopenia or thrombocytopenia, liver enzyme elevations, and neurological symptoms such as seizures can occur, particularly in patients with renal impairment. Management involves discontinuing the drug and providing supportive care.