**Core Concept**
Coloured urine is a common side effect of certain medications due to their metabolites or direct interaction with urine components. This phenomenon is primarily due to the presence of compounds that undergo oxidation or conjugation, leading to visible discoloration of urine, especially in the presence of light or pH changes.

**Why the Correct Answer is Right**
Quinine, used in malaria treatment, is known to cause **greenish or yellowish discoloration** of urine in some cases due to its metabolism and excretion. However, it does not typically cause a **persistent or pronounced colour change** like other drugs. In contrast, **rifampin** causes orange-red urine due to its strong redox properties, **nitrofurantoin** leads to yellow or orange urine due to its nitro group oxidation, and **pyridium** (phenazopyridine) causes yellow-orange urine by forming a yellow complex with urine constituents. Quinine is less likely to produce a noticeable colour change under normal conditions compared to these drugs.

**Why Each Wrong Option is Incorrect**
Option B: Rifampin causes **distinct orange-red urine** due to its strong chromophore, making it a classic example of coloured urine.
Option C: Nitrofurantoin produces **yellow to orange urine** due to oxidation of its nitro group in the urinary tract.
Option D: Pyridium (phenazopyridine) is a well-known urinary analgesic that causes **yellow-orange urine** due to its metabolite binding to urine components.

**Clinical Pearl / High-Yield Fact**
Remember: **Rifampin → orange-red urine**, **Pyridium → yellow-orange urine**, **Nitrofurantoin → yellow/orange urine**, and **Quinine → rarely causes discoloration**; thus, quinine is the exception among these. This makes it the correct choice for a question asking about **which does NOT cause coloured urine**.

✓ Correct Answer: A. Quinine