Administration of which classes of medications can decrease secretions of the upper respiratory tract?

Antihistamine

Explanation:

E. g. chlopheniramine

The correct answer is - Cholinergic antagonists.

Explanation:

The cholinergic antagonist is a class of medication that is general terms of agents that bind with choline receptors such as nicotinic and muscarinic that inhibit the effect of acetylcholine and another agonist.

It is a class of drugs that mimics, inhibit, or enhance the action of the neurotransmitter ACh which is the very first transmitter of nerve impulse within PNS that includes the region of ANS that regulates contraction of smooth muscle, such as upper respiratory tract.

Thus, the correct answer is - Cholinergic antagonist.