In Vitro Dissolution, In Vivo Bioavailability, and IVIVC Assessment of Chloroquine Phosphate Tablets Marketed in Afghanistan

Background Malaria remains a major public health challenge in Afghanistan, where Plasmodium vivax is the dominant species. Chloroquine (CQ) phosphate is the first-line treatment. Concerns over substandard and falsified anti-malarial necessitate rigorous dissolution and bioavailability monitoring. This study evaluated the in vitro quality and in vivo bioavailability of five CQ phosphate tablet brands in Afghanistan and established a Level C in vitro–in vivo correlation (IVIVC). Methods The study was conducted from June, 2025 – August, 2025 on five brands of CQ phosphate (250 mg) tablets. In vitro quality was assessed for weight variation and dissolution using a verified High-Performance Liquid Chromatography with Ultraviolet detection (HPLC-UV) (n = 6 tablets/brand), following United States Pharmacopeia (USP) guidelines. HPLC method was verified for repeatability, linearity, and accuracy as per ICH Q2(R2) guidelines. In vivo bioavailability was assessed by measuring whole blood CQ concentrations at 24 hours post dose in 20 P. vivax patients using HPLC-UV. A Level C IVIVC was established by correlating mean dissolution percentage with mean blood concentration. Results All brands met USP dissolution criteria (≥ 75% release in 45 min), but inter-brand variability was significant. CQ-004 showed the highest and most consistent dissolution (97.62% ± 1.32%) and bioavailability (362 ± 57 ng/mL), followed by CQ-003 (96.41% ± 2.74%; 359 ± 56 ng/mL) and CQ-002 (96.17% ± 2.55%; 318 ± 53 ng/mL). CQ-005 had the lowest dissolution (89.2% ± 2.99%) and moderate bioavailability (336 ± 58 ng/mL), while CQ-001showed lowest bioavailability (291 ± 66 ng/mL) despite acceptable dissolution (94.26% ± 2.83%). A positive Level C IVIVC was observed, confirming that higher in vitro dissolution predicts greater systemic exposure. Conclusion All tested brands met minimum standards, but CQ-004 and CQ-003 demonstrated superior dissolution and bioavailability. The established Level C IVIVC confirms that in vitro dissolution can predict in vivo exposure, reinforcing the value of routine dissolution testing in post-market surveillance.