P1: PSB Printer: Yet To Come
9780521704632c18 CUFX213A/Peck 9780521618168 December 28, 2007 13:51
18 Antiemetics and related drugs
Gut–itisaless effective anti-sialagogue than hyoscine. The tone of the lower
oesophageal sphincter is decreased and there is a small decrease in gastric acid
secretion.
Miscellaneous – sweating is inhibited and this may provoke a pyrexia in paedi-
atric patients. When administered topically it may increase intra-occular pressure,
which may be critical for patients with glaucoma.Kinetics
Intestinal absorption is rapid but unpredictable. It is 50% plasma protein bound
and extensively metabolized by liver esterases. It is excreted in the urine, only a tiny
fraction unchanged.Glycopyrrolate
Gylcopyrrolate is indicated for anti-sialagogue premedication, the treatment of
bradycardias and to protect against the unwanted effects of anticholinesterases.
Itscharged quaternary structure gives it a different set of characteristics compared
to the tertiary amines. Intestinal absorption is negligible and the oral bioavailability
is consequently less than 5%. It does not cross the blood–brain barrier and so it is
devoid of central effects. It is minimally metabolized and 80% is excreted in the urine
unchanged.Antihistamines
Cyclizine
Cyclizine is a piperazine derivative. The parenteral preparation is prepared with
lactic acid at pH 3.2. Consequently intramuscular and intravenous injection may be
particularly painful.Uses
Cyclizine is used as an antiemetic in motion sickness, radiotherapy, PONV and emesis
induced by opioids. It is also used to control the symptoms of Meni ́ ere’s disease.`Mechanism of action
Cyclizine is a histamine (H 1 )antagonist, but also has anticholinergic properties that
may contribute significantly to its antiemetic actions.Effects
Gut–itincreases lower oesophageal sphincter tone.
Anticholinergic – these are mild although it may cause an increase in heart rate
following intravenous injection.
Extrapyramidal effects and sedation do not complicate its use.