Which of the following does not penetrate intact skin?

D i.e. DexmeditomidineRef: KDT, 7th edition, page 384Explanation:Simple way to answer this is to ask, whether these are available as Transdermal patch. Scopolamine, Nitroglycerine and Clonidine are available as Transdermal patch because they can penetrate intact skin.Scopolamine is L-Hyoscine.Hyoscine:Most effective drug for motion sickness.Valuable in highly susceptible individuals and for vigorous motions.Drug should be given prophylactically (0.2 mg oral), because administration after symptoms have set in is less effective; action lasts 4-6 hours.A transdermal preparation applied behind the pinna 4 hours before journey has been shown to protect for 3 days.Side effects with low oral doses and transdermal medication are few, but dry mouth and sedation can occur: driving is risky.Another anticholinergic used for motion sickness is Dicyclomine.Nitroglycerine:Sublingual route is used when terminating angina or aborting an imminent one is the aim.Cutaneous application as ointment was found to produce haemodynamic effects for 4-6 hours.A transdermal patch in which the drug is incorporated into a polymer bonded to adhesive plaster has been developed which provides steady delivery for 24 hours.It starts working within 60 min and has a bioavailability of 70-90%.However, development of tolerance and dependence may jeopardise its value.It is advised that the patch be taken off for 8 hours daily.A transmucosal dosage form which has to be stuck to the gums under the upper lip has also been produced--acts in 5 min and releases the drug for 4-6 hours.Clonidine:Isa partial agonist with high affinity and high intrinsic activity at a2 receptors, especially a2A subtype in brainstem.Also activates imidazoline receptors.Activation of medullary imidazoline receptors also causes decreased sympathetic outflow and fall in BP.Transdermal delivery patch permits continuous administration of clonidine as an alternative to oral therapy. The drug is released at an approximately constant rate for a week; 3-4 days are required to reach steady- state concentrations in plasma. When the patch is removed, plasma concentrations remain stable for ~8 hours and then decline gradually over a period of several days.Dexmeditomidine:Acts by stimulation of central a2 adrenergic receptors.Known to cause sedation and analgesia.Used for sedating critically ill/ventilated patients in intensive care units.Also being used as an adjunct to anaesthesia.Analgesia and sedation are produced with little respiratory depression, amnesia or anaesthesia.Sympathetic response to stress and noxious stimulus is blunted.It is administered by I.V. infusion.