This study aims to evaluate the pharmacokinetic of gepotidacin in fed healthy lactating women.

Inclusion Criteria:

• Participants must be healthy lactating women, 18 to 50 years of age, inclusive, at Screening.
• Actively breastfeeding or expressing breast milk.
• At least 28 days postpartum with a full milk supply established, and with no persistent complications from delivery (there is no maximal length of time postpartum required).
• Willingness to temporarily discontinue feeding breast milk to infants from dosing through to 72 hours after dosing (approximately 3 days), with the ability to pump and provide reserve milk for bottle feeding prior to the study OR has decided to permanently discontinue breastfeeding but has not started weaning, provided the infant accepts bottle feeding and a sufficient milk supply is maintained by pumping 3 to 4 times daily, considering changes in milk composition during weaning process.
• Is willing to fully express breast milk from both breasts during the duration of the milk collection portion of the study. Participants must be able to express milk from each breast at each pumping session using a breast pump.
• Has a body mass index (BMI) of less than or equal to (<=) 36 kilograms per meter square (kg/m^2) and weighs at least 45 kilograms (kg) with all clinical assessments considered as clinically non-significant per investigator.
• Non-smoker (including vaping) or prior smokers (having smoked less than 10 cigarettes per day) who have stopped smoking for at least 1 month prior to screening.
• Understands the study procedures and is capable of providing written informed consent.
• A negative highly sensitive pregnancy test ([urine or serum] as required by local regulations) will be required at Baseline before the dose of study intervention.

Exclusion Criteria:

• Participant is unwilling or unable to comply with the study restrictions or lifestyle guidelines presented in the protocol during the study period and through the post study visit.
• History or evidence of any clinically significant hematological, endocrine, pulmonary, gastrointestinal, cardiovascular, psychiatric (including post-natal depression), neurologic, infectious, neoplastic, active cancer or allergic disease (including drug allergies, but excluding untreated asymptomatic, seasonal allergies at time of dosing) or clinical findings that, in the opinion of the study investigator, might confound the results of the study or poses an additional risk to the participant or infant by participation in the study.
• Has had major surgery in the past 3 months (except delivery through a C section and/or tubal ligation).
• History of significant multiple and/or severe allergies (including latex allergy, but with exception of seasonal rhinitis [hay fever]) or has had an anaphylactic reaction or significant intolerability to prescription or non-prescription drugs or food.
• Hypersensitivity to gepotidacin.
• Current or recent (less than [<] 14 days) mastitis, or history of breast surgery (augmentation or reduction).
• Use of any QT prolonging medications within 7 days prior to first dose, use of strong or moderate Cytochrome P450 3A4 (CYP3A4) inhibitors within 7 days prior to first dose, or use of strong or moderate CYP3A4 inducers (including vitamins, herbal and dietary supplements such as St. John's wort) within 14 days prior to first dose.
• Currently a user of illicit drugs or has a history of drug (including alcohol) abuse within approximately 1 year.
• Donated or lost 1 unit of blood (approximately 500 milliliters [mL]) or participated in another investigational study within 30 days or 5 half-lives of the investigational product prior to the screening. The 30 days window will be derived from the date of the last study procedure (i.e., poststudy, AE follow-up, etc.) in the previous study to the screening visit of the current study.
• The participant has participated in a clinical trial and has received an investigational product within 30 days or 5 half-lives, whichever is longer.
• Participants with excessive caffeine intake (defined as greater than [>] 6 servings [1 serving is approximately equivalent to 120 milligram [mg] of caffeine] of coffee, tea, cola or other caffeinated beverages per day) within 14 days prior to first dose.
• The participant has known severe renal impairment (creatinine clearance <30 milliliters per minute [mL/min] or clinically significant elevated serum creatinine as determined by the investigator).
• The participant presents with (self-reported) vaginal discharge suspected for infection at Baseline.
• The participant has congenital long QT syndrome or known prolongation of the corrected QT (QTc) interval.
• The participant has a family history of QT prolongation or sudden death.
• The participant has a recent history of vasovagal syncope or episodes of symptomatic bradycardia or brady arrhythmia within the last 12 months.
• Having two or more of the following risk factors: 1. Body weight between 45 kg and 60 kg, 2. Moderate renal impairment (creatinine clearance 30 to 59 mL/min), 3. Moderate hepatic impairment (Child Pugh Class B)
• QTc >450 milliseconds (msec) or QTc >480 msec for participants with bundle branch block.
• Severe hepatic impairment (Child Pugh Class C)
• Alanine aminotransferase >1.5*upper limit of normal (ULN).
• Total bilirubin >1.5*ULN; Participants with Gilbert's syndrome can be included with total bilirubin >1.5*ULN if direct bilirubin is <=1.5*ULN.
• Current or chronic history of liver disease or known hepatic or biliary abnormalities (except for Gilbert's syndrome or asymptomatic gallstones).

Healthy lactating women will be enrolled in this study.

Study Sponsor will assess requests from qualified researchers for anonymized individual patient-level data and related study documents. Data sharing is subject to certain criteria, conditions, and exceptions. For further information, refer to https://www.gsk-studyregister.com/gsk-patient-level-data-sharing-july2025.pdf

Anonymized IPD will be made available within 6 months of publication of primary, key secondary and safety results for studies in product with approved indication(s) or terminated asset(s) across all indications.

Anonymized IPD is shared with researchers whose proposals are approved by an Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months but an extension may be granted, when justified, for up to 6 months.

This is an open label study