Compounds available are: benzocaine, cinchocaine and lidocaine.

How do they act?
Local anaesthetics reversibly block excitation of pain receptors and sensory nerve fibres in and around the area of application. Local anaesthetics used in haemorrhoidal preparations are weak basic amines with the same basic chemical structure of an aromatic lipophilic group joined to a hydrophilic amino group by a linking ester or amide moiety. They reach their site of action by penetrating the lipophilic nerve structure in their lipid-soluble uncharged form, but exert their anaesthetic action in the ionised form. At the cellular level, the ionised form of the anaesthetic blocks conduction of nerve impulses across cell membranes by decreasing their permeability to cations, mainly sodium ions.

• Benzocaine is an ester-type local anaesthetic. It is the sole constituent of one product, a cream.
• Cinchocaine is a potent and long-acting amide-type compound. It is reported to have less sensitising potential than benzocaine, and is the sole constituent of one product, an ointment.
• Lidocaine is an amide-type compound with a relatively long duration of action and is the local anaesthetic most widely used in haemorrhoidal preparations, in creams, ointments and suppositories.

Usage, cautions and restrictions
Local anaesthetics are included in haemorrhoidal preparations to relieve pain, burning and itching. Use should be restricted to the perianal region and lower anal canal; they should not be used in the rectum as there is little sensory tissue there and they can be rapidly absorbed through the rectal mucosa to cause potentially toxic systemic effects. They are also absorbed rapidly through damaged skin, and skin sensitisation and systemic allergic reactions are possible with prolonged use. Use should be limited to no more than three applications daily for benzocaine and cinchocaine and four daily for lidocaine, for up to a maximum of seven days.