Background: Quality pharmaceutical services are an integral part of primary healthcare and a key determinant of patient outcomes. The study focuses on pharmaceutical service delivery among private healthcare facilities serving informal settlements within Nairobi County, Kenya and aims at understanding the drug procurement practices, task-shifting and ethical issues associated with drug brand preference, competition and disposal of expired drugs. Methods: Forty-five private facilities comprising of hospitals, nursing homes, health centres, medical centres, clinics and pharmacies were recruited through purposive sampling. Structured electronic questionnaires were administered to 45 respondents working within the study facilities over an 8-week period. Results: About 50% of personnel carrying out drug procurement belonged to non-pharmaceutical cadres namely; doctors, clinical officers, nurses and pharmacy assistants. Drug brand preferences among healthcare facilities and patients were mainly pegged on perceived quality and price. Unethical business competition practices were recorded, including poor professional demeanour and waiver of consultation fees veiled to undercut colleagues. Government subsidized drugs were sold at 100% profit in fifty percent of the facilities stocking them. In 44% of the facilities, the disposal of expired drugs was not in conformity to existing government regulatory guidelines. Conclusions: There is extensive task-shifting and delegation of pharmaceutical services to non-pharmaceutical cadres and poor observance of ethical guidelines in private facilities. Strict enforcement of regulations is required for optimal practices.