The Zinc Paradox in Tuberculosis: A Systematic Review of Anti-Tuberculosis Drug–Induced Zinc Depletion and Its Implications for Optic Neuropathy and Visual Loss

Background: Tuberculosis remains a leading cause of infectious disease mortality, with over 10 million new cases annually. The standard first-line regimen—isoniazid, rifampicin, pyrazinamide, and ethambutol—has dramatically improved survival, yet drug-induced micronutrient depletion, particularly zinc, is an underappreciated complication that may contribute to treatment-related morbidity. Ethambutol-induced optic neuropathy (EON) affects 1–5% of treated patients, and accumulating evidence implicates zinc chelation as its central mechanism. We hypothesize that anti-TB therapy creates a “multi-hit” zinc depletion state through convergent drug- and disease-mediated pathways.Methods: We conducted a systematic search of PubMed, Scopus, Web of Science, and Cochrane databases from 1944 (discovery of streptomycin) through March 2026. Search terms combined anti-TB drug names with zinc, copper, micronutrient, optic neuropathy, and visual loss. We included randomized controlled trials, cohort studies, case-control studies, case series, in vitro investigations, and animal models. PRISMA 2020 guidelines were followed. Risk of bias was assessed using the Newcastle–Ottawa Scale for observational studies and the Cochrane RoB 2.0 tool for trials.Results: From 2,847 initial records, 186 studies met inclusion criteria. Serum zinc was significantly lower in TB patients versus controls (pooled mean difference: −12.1 μmol/L; 95% CI: −14.5 to −9.7; I² = 68%). Ethambutol directly chelates zinc and copper in retinal ganglion cells via its metabolite EDBA, causing lysosomal membrane permeabilization and mitochondrial dysfunction. Isoniazid depletes pyridoxine, impairing zinc-dependent enzymatic cascades. Rifampicin induces CYP3A4 via PXR activation, accelerating retinol catabolism and functionally coupling zinc deficiency to vitamin A insufficiency through impaired retinol-binding protein synthesis. The zinc–vitamin A axis demonstrates a strong positive correlation (r = 0.86, p < 0.01) in TB cohorts. Zinc supplementation (50 mg elemental zinc/day) improved sputum conversion rates and reduced hepatotoxicity markers in three randomized trials.Conclusions: Anti-TB drugs collectively create a “multi-hit” zinc depletion syndrome that extends beyond simple ethambutol chelation. We propose a clinical algorithm for baseline zinc assessment, risk stratification, and prophylactic supplementation during TB therapy. Persistent visual loss despite ethambutol discontinuation should prompt evaluation of concurrent zinc depletion from isoniazid, rifampicin, and the underlying TB disease itself.