Nifedipine Glyceryl trinitrate

Paraesthesiae in hands or feet give warning of peripheral ischaemia. Overdose can cause peripheral gangrene. Due to its complex actions on receptors, vasoconstriction is best antagonised by a nonselective vasodilator such as glyceryl trinitrate, nifedipine or sodium nitroprusside (rather than by an a-adreno-ceptor blocker). Patients with vascular disease, coronary and peripheral, are particularly at risk. 

Glyceryl trinitrate overdose should be treated with the patient s head lowered. Other measures include respiration maintenance, use of plasma expanders, and electrolyte balance. Withdrawal of heparin treatment or dose reduction should be performed with the overdose of heparin. Protamine sulfate may be used to reduce severe bleeding. Heparin should be used with caution with glyceryl trinitrate, aprotinine, alcohol, tobacco, and ACE inhibitors. Nifedipine should be used with care when coadministering with immunosuppressants, magnesium salts, tobacco, digoxin, antineoplastics, calcium channel blockers, antihistamines, antifungals, antiepileptics, antiarrhythmics, and alcohol. 

Raynaud s phenomenon may be helped by nifedipine, reserpine (an a-adrenoceptor blocker, in low doses) and also by topical glyceryl trinitrate indeed any vasodilator is worth trying in resistant cases enalapril (ACE inhibitor) seems to lack efficacy. In severe cases, especially patients with ulceration, intermittent infusions over several hours of the endogenous vasodilator, prostacyclin (epoprostenol), achieves long-lasting improvements in symptoms. 

For immediate pre-exertional prophylaxis glyceryl trinitrate sublingually or nifedipine (bite the capsule and hold the liquid in the mouth or swallow it). 

Key BJ, Wilkes MP, Keen M. Reduced responsiveness to glyceryl trinitrate following antihypertensive treatment with nifedipine in man. BrJ Clin Pharmacol ( 993) 36, 499P. 

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