Concept:
Loading dose is an initial higher dose of a drug given to rapidly achieve the desired therapeutic concentration.
Step 1: Some drugs take a long time to reach steady-state concentration if only maintenance dose is given.
Step 2: In urgent situations, waiting for steady state may delay therapeutic effect.
Step 3: A loading dose rapidly raises plasma drug concentration to the therapeutic range.
Step 4: After that, maintenance doses are given to maintain the drug level.
Step 5: Hence, loading dose is given to achieve therapeutic level quickly.
\[
\boxed{\text{Achieve therapeutic level quickly}}
\]