Drug classification:
\[
\boxed{
\begin{aligned}
&\text{Analgesics}
&&\rightarrow \text{Pharmacological effect},
&\text{Antihistamines}
&&\rightarrow \text{Drug action},
&\text{Sulphonamides}
&&\rightarrow \text{Chemical structure}.
\end{aligned}
}
\]