Pharmacology for Dentistry

186 Section 4/ Drugs Acting on Cardiovascular & Urinary System

Effect on coronary blood of flow: Myo-
cardial oxygen extraction is nearly maxi-
mum at rest, so, there is little reserve to meet
increased demands. So, increased myocar-
dial demand for O 2 can only be met by in-
creased coronary blood flow which depends
on diastolic pressure and duration of dias-
tole because coronary blood flow is negli-
gible during systole.

Pharmacokinetics

They are administered through buccal,
sublingual and parenteral routes. Skin oint-
ments are also available. GTN is rapidly in-
activated by hepatic first pass metabolism.
So, oral tablets which are swallowed are in-
effective.

Excretion is primarily as glucuronide
derivatives of the denitrated metabolite via
kidney. IV infusion has rapid onset of ac-
tion but effects are quickly reversed on stop-
ping the infusion. So, it is used only in treat-
ment of severe, recurrent angina at rest.

Adverse Effects

1. Throbbing headache: It is due to arte-
   riolar dilatation of meningeal arteries.
   It usually decreases over a few days if
   treatment is continued and can be con-
   trolled by decreasing the dose.


2. Weakness and dizziness: It may arise due
   to postural hypotension especially if pa-
   tient is standing in a single position for a
   while. This is because, venodilatation re-
   sults in ‘venous pooling’ i.e. accumulation
   of blood in peripheral vessels leads to
   postural hypotension.


3. Flushing: It is due to arteriolar dilata-
   tion in face and neck region.


4. Sweating: Arteriolar dilatation in arter-
   ies beneath the skin tends to warm up
   and sweating is the body’s mechanism
   to dispel heat.


5. Tachycardia and palpitation: In small
   doses of GTN, arteriolar dilatation re-
   sults in decreased arterial pressure.
   This leads to reflex sympathetic dis-

Table 4.3.1: Classification of antianginal agents.

I. Nitrates

Glyceryl trinitrate (Nitroglycerine; ANGISED) 2.5-15 mg BD-TDS, 0.5 mg SL, 2.5-6.5 mg SR

Amyl nitrate (VAPOROLE) 0.3 ml capsule inhalation

Isosorbide dinitrate (SORBITRATE) 5-10 mg TDS-QID SL, 40-80 mg SR BD

Isosorbide 5-mononitrate (MONOTRATE) 10-20 mg/day, 40 mg SR

Erythrityl tetranitrate (CARDILATE) (30-60 mg/day oral, 5-10 mg SL)

Pentaerythritol tetranitrate (PERITRATE) 30 mg/day

II. Beta blockers

Propranolol, atenolol etc. (For details see chapter on ‘Antihypertensive drugs’).

III.Calcium channel blockers

Verapamil, nifedipine etc. (For details see chapter on ‘Antihypertensive drugs’).

IV.Potassium channel openers

Nicorandil, diazoxide etc. (For details see chapter on ‘Antihypertensive drugs’).

V. Miscellaneous

Dipyridamole (PERSANTIN) 25-100 mg TDS

Nicotinyl xanthinate (COMPLAMINA) 300-600 mg TDS