The diminishing effectiveness of antimicrobials raises serious concerns for human health. While policy makers grapple to reduce the overuse of antimicrobial medicines to stem the rise of antimicrobial resistance, insufficient attention has been paid to how this applies to low-resource contexts. We provide an in-depth portrayal of antimicrobial prescribing at primary health care level in rural Chikwawa District, Malawi. Ethnographic fieldwork took place over 18 months (2018-2020). We surveyed 22 health facilities in the district, observed 1348 health worker-patient consultations, and carried out 49 in-depth interviews with staff and patients. Care was centred around provision of an antimicrobial. Amid chronic lack of essential medicines and other resources, clinic interactions were tightly scripted, providing patients little time to question or negotiate their treatment. We develop the concept of 'antibiotic vulnerabilities' to reveal multiple ways in which provision of antimicrobials in rural Malawi impacts care in conditions of extreme scarcity. Antibiotics are central and essential to primary care. As targets for optimal antimicrobial prescribing take a more central role in global policy, close attention is required of the ramifications for the delivery of care to ensure that efforts to stem resistance do not undermine the goal of improved health for all.