McKenna's Pharmacology for Nursing, 2e

C H A P T E R 2 6 Opioids, opioid antagonists and antimigraine agents 411

TABLE 26.2

DRUGS IN FOCUS Antimigraine agents

Drug name

Dosage/route

Usual indications

Ergot derivatives

2 tabs PO up to 6 tabs/day, or one supp PR up to three supps/day

Prevention and abortion of migraine attacks in adults

ergotamine (Cafergot)

Triptans eletriptan (Relpax)

Initially, 40 mg PO repeat after 2 hours if needed Maximum 160 mg/day 1–2.5 mg PO with fluid; may repeat in 4 hours if needed 5–10 mg PO; may repeat in 2 hours; do not exceed 30 mg/day 50–100 mg PO at first sign of headache, may repeat in 2 hours; by nasal spray in one nostril, may repeat in 2 hours; do not exceed 40 mg/day 2.5 mg PO; may repeat in 2 hours; do not exceed 10 mg/day

Treatment of acute migraines in adults

naratriptan (Naramig)

Treatment of acute migraines in adults

rizatriptan (Maxalt)

Treatment of acute migraines in adults; orally disintegrating tablet may be useful if there is difficulty swallowing Treatment of acute migraines, cluster headaches in adults

sumatriptan (Imigran, Sumagran, Sumatab)

zolmitriptan (Zomig)

Treatment of acute migraines in adults

artery bed (see Figure 26.2). These drugs are indicated for the prevention or abortion of migraine or vascular headaches. Ergotamine, the prototype drug in this class, was the mainstay of migraine headache treatment before the development of triptans. (See Table 26.2 for usual indications for each drug.) Pharmacokinetics The ergot derivatives are rapidly absorbed from many routes, with an onset of action ranging from 15 to 30 minutes. They are metabolised in the liver and pri- marily excreted in the bile. Ergotamine is administered orally or rectally for rapid absorption. Contraindications and cautions Ergot derivatives are contraindicated in the following circumstances: presence of allergy to ergot preparations to avoid hypersensitivity reactions ; CAD, hypertension or peripheral vascular disease, which could be exacer- bated by the CV effects of these drugs ; impaired liver function, which could alter the metabolism and excre- tion of these drugs ; and pregnancy or breastfeeding because of the potential for adverse effects on the fetus and neonate. Ergotism (vomiting, diarrhoea, seizures) has been reported in affected infants. Caution should be used in two instances: with pruritus, which could become worse with drug- induced vascular constriction, and with malnutri- tion because ergot derivatives stimulate the CTZ and can cause severe GI reactions, possibly worsening malnutrition.

Adverse effects The adverse effects of ergot derivatives can be related to the drug-induced vascular constriction. CNS effects include numbness, tingling of extremities and muscle pain; CV effects such as pulselessness, weakness, chest pain, arrhythmias, localised oedema and itching and MI may also occur. In addition, the direct stimulation of the CTZ can cause GI upset, nausea, vomiting and diarrhoea. Ergotism, a syndrome associated with the use Prototype summary: Ergotamine Indications: Prevention or abortion of vascular headaches. Actions: Constricts cranial blood vessels, decreases pulsation of cranial arteries and decreases hyperperfusion of the basilar artery vascular bed; mechanism of action is not understood. Pharmacokinetics: Route Onset Peak Oral Rapid 0.5–3 hours PR Varies Unknown T 1/2 : 2.7 hours, then 21 hours; metabolised in the liver, excreted in the faeces. Adverse effects: Numbness, tingling in the fingers and toes, muscle pain in the extremities, pulselessness or weakness in the legs, praecordial distress, tachycardia, bradycardia, ergotism (nausea, vomiting, diarrhoea, severe thirst, hypoperfusion, chest pain, confusion).