The Clinical Guide to Supportive and Palliative Care for HIV/AIDS

A Clinical Guide to Supportive and Palliative Care for HIV/AIDS • Chapter 27: Pharmacologic Interactions of Clinical SignificanceTable 27-6a: Medications Known to Prolong QTC IntervalAntiarrhythmics26 picasAntibiotics and Antiviral AgentsPsychotropicsQuinidine, procainamide, disopyramide, amiodarone,sotalol, bretylium, dofetilide, bepridilErythromycin, quinine, chloroquine, moxifloxacin,sparfloxacin, gatifloxacin, and amantadineTricyclic antidepressants, citalopram, chloral hydrate,lithium, pimozide, thioridazine, droperidol,ziprasidoneTable 27-6b: Clinical Monitoring for Drugs That May Prolong QTCTips for Counseling Patients• Immediately report tachycardia, lightheadedness, palpitations, vomiting or diarrhea.• Avoid use of street drugs, substances of abuse, or excessive use of alcohol. Notify psychiatristbefore taking any prescription or over-the-counter drugs.• Baseline and periodic screening should be done for serum potassium (K+), serum magnesium(Mg+), and electrocardiogram (ECG).Interactions between HAART Drugs andOther Drugs Used by Patients with Advancing HIV DiseaseClinicians should become familiar with these interactions of clinical significance betweenantiretroviral drugs and ancillary drugs needed to manage the many complications of advancingHIV disease. Providers should avoid drug combinations likely to result in potentially seriousinteractions. Table 27-5 provides a detailed list of the drug interaction studies in the presence ofritonavir, the most potent CYP-modifying protease inhibitor, while Tables 27-6a and 27-6b offerclinical monitoring highlights and counseling tips for patients using drugs that may prolong theQTC interval.Drug Interactions Involving Amprenavir (Agenerase) and Vitamin EOne capsule of amprenavir (Agenerase) contains 109 international units (IUs) of vitamin E.The daily dose of eight capsules of amprenavir, taken twice daily which adds up to 1,200 IUs, hasbeen established as the minimum toxic dose (MTD); this is the smallest dose that has beenfound to be harmful when taken over a period of time. The manufacturer, Glaxo-Wellcome, notesin the package insert that people taking amprenavir should not take any extra vitamin E. Highdoses of vitamin E can create problems because vitamin E is a blood thinner and so can causeproblems with other blood thinners such as warfarin (Coumadin), vitamin K or clotting factors.One woman on long-term warfarin experienced intracranial bleeding less than a week afterstarting amprenavir. People taking low-dose aspirin daily to prevent heart attacks as well aspeople on herbal blood thinners like ginger, garlic, feverfew, ginseng and ginkgo biloba shouldalso be careful with the extra vitamin E in amprenavir. Symptoms of vitamin E toxicity (which isordinarily rare) include spontaneous nosebleeds, cuts that will not stop bleeding and bruisesacquired easily. 9XXVIIU.S. Department of Health and Human Services • Health Resources and Services Administration • HIV/AIDS Bureau 561