| Summary: | Background: Optimal tuberculosis (TB) treatment remains the backbone of effective TB control programmes. However, TB drugs are often associated with adverse drug reactions (ADR) that affect treatment adherence and cure. Cutaneous adverse drug reactions (CADR) are more commonly associated with Human Immunodeficiency Virus (HIV)/TB co-infection, occurring in up to 7% of patients. If severe, CADR require treatment interruption and hospitalisation. There are no standardised guidelines for managing CADR to TB therapy. Current practice in South Africa involves drug rechallenge, a process, which aims to identify the offending drug and modify the treatment regimen. This practice can carry significant risks that need to be weighed against the benefits. Despite significant resources required to manage CADR, there is no available data regarding their economic impact. Alternate strategies to manage TB therapyassociated CADRs and their cost have never been evaluated. The purpose of this study is to evaluate the economic impact of TB therapy-associated CADRs in South Africa and compare the cost of drug rechallenge with alternative strategies. Methods: Data was obtained from 97 patients, admitted to the Groote Schuur Hospital dermatology ward with TB therapy-associated CADR. Clinical data pertaining to hospitalisation, diagnostic/monitoring tests and drug prescriptions was extracted from patient medical records. Healthcare and patient-related costs were obtained from financial department records, interviews and hospital admission records. Alternative drug regimens for CADR management were derived from literature and expert clinical advice. Costs were estimated using an ingredient's approach in 2016 US dollars. A cost-comparative analysis was performed comparing the cost of the current practice with alternative options. Univariate sensitivity analysis was used to investigate the uncertainties around cost components. Results: The cost of managing a TB therapy-associated CADR was $6,525 per patient. Within this population the average cost of managing a CADR in a patient with DS-TB was $5,831 (95% CI: 8438; 10727). The main contributor of CADR costs was hospitalisation amounting to $3,638/patient (62% of total cost). Alternative CADR management strategies using outpatient-initiated second-line regimens containing rifabutin, bedaquiline and delamanid cost 44-55% less than drug rechallenge depending on the drug regimen used ($2,651/patient to $3,276/patient). Sensitivity analyses indicated that drug rechallenge was most sensitive to hospitalisation costs, whereas second-line treatment strategies were sensitive to TB drug costs. The average total loss experienced by patients as a result of the CADR was $530 (25% of their annual income), as compared to an estimated loss in the alternate regimens of $154 (10% of their annual income). Societal costs with alternate regimens were also lower at 46-66% that of current cost of $6,134. Conclusion: CADR to TB treatment represent a significant economic burden to the healthcare system and affected patient. The alternate strategy of outpatient-initiated second-line therapy provides an economically feasible option by implementing an ambulatory practice of care despite using more expensive drugs. Shorter hospitalisation reduces patient and healthcare costs. This data should inform policy makers on optimal resource use within the healthcare system. Once the effectiveness and risk of drugresistance of these strategies has been determined, further research should estimate their cost-effectiveness.
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