Antihistamine adverse effects

SkUl Keeper Antihistamine Adverse Effects (see Chapters 8 and 10)... 

Intranasal anticholinergic agents (e.g., ipratropium) reduce the severity and duration of rhinorrhea but have no effect on other nasal symptoms.11,12,21 Ipratropium reduces cholinergic hyperreactivity and cholinergically mediated histamine- and antigen-induced secretion. Intranasal ipratropium acts locally, with only minimal systemic absorption. Clinical trials demonstrated that ipratropium bromide 0.3% reduced rhinorrhea in adults and children with PAR.11,12 Intranasal ipratropium is an option for patients in whom rhinorrhea is refractory to topical intranasal corticosteroids and/or antihistamines.8,12 Intranasal ipratropium is available only by prescription, and the dose is two sprays nasally two to three times daily.15 Adverse effects are minimal, but dry nasal membranes have been reported.11,12... 

Is the patient taking antihistamines and/or intranasal steroids Is the patient experiencing adverse effects (e.g., sedation from antihistamines or nasal itching, burning, or bleeding from intranasal corticosteroids) ... 

Although anticholinergic (drying) effects contribute to efficacy, adverse effects such as dry mouth, difficulty in voiding urine, constipation, and potential cardiovascular effects may occur (see Table 79-1). Antihistamines should be used with caution in patients predisposed to urinary retention and in those with increased intraocular pressure, hyperthyroidism, and cardiovascular disease. 

These antihistamines infreguently cause typical phenothiazine adverse effects. See the Antipsychotic Agents monograph for a complete discussion. 

Uses Partial onset Szs Action Unknown Dose Adults >16y. 500 mg PO bid, may T 3000 mg/d max Peds. 4—15 y 10-20 mg/kg/d in 2 doses, 60 mg/kg/d max ( l in renal insuff) Caution [C, /—] Fiddly, w/ renal impair, psych disorders Contra Component aU gy Disp Tabs, sol SE Dizziness, somnolence, HA, hostility, aggression, myelosuppression, impaired coordination Interactions T Effects W/ antihistamines, TCAs, benzodiaz ines, narcotics, phenytoin, EtOH EMS Concurrent benzodiaz ine, antihistamine and narcotic use can cause ovCTsedation D/C abruptly may cause Szs concurrent EtOH use can T adverse effects OD May cause drowsiness s5rmptomatic and supportive... 

Its most important adverse effects are nephrotoxicity and ototoxicity. The risks for nephrotoxicity can be limited by adequate hydration. Marked nausea and vomiting are frequent. Only mild-to-moderate myelosuppression is seen. Pseudo-allergic reactions may occur which respond to intravenous epinephrine and corticosteroids or antihistamines. 

The most frequently occurring adverse effects are bone marrow suppression alopecia and hypersensitivity reactions. Patients must be protected with corticosteroids and HI antihistamines. For mucositis also H2 antagonists are sometimes recommended. Neurotoxicity and cardiotoxicity are mostly mild but can pose serious problems. 

As first choice treatment a well-established antihistamine such as meclozine is recommended. Promethazine is another antihistamine which reduces nausea, but sedation is a not always desired adverse effect. Metoclopramide increases intestinal motility and could be used short term also early in pregnancy. A neuroleptic such as prochlorperazine reduces nausea but should only be used for shortterm treatment due to the risk of extrapyramidal adverse reactions. Serotonin receptor antagonists can be used in post-operahve nausea and during treatment with cytostatics. 

Other medications, which will not be discussed in the following chapters, have psychotropic actions that are considered to be side effects or adverse effects. Thus, some antihistamines (Le. products used to counteract allergic reactions) induce fatigue and drowsiness, and the same applies to some myorelaxants. Older antihypertensives (Le. agents reducing blood pressure) such as alpha-methyldopa (Aldomet ) or clonidine (Catapres 1) can cause fatigue and depression. 

Bupropion, the only marketed aminoketone antidepressant, also has a side-effect profile different from the other classes of antidepressants. It is essentially devoid of anticholinergic, antihistaminic, and orthostatic hypotensive effects. Its principal adverse effects are consistent with its indirect agonism of dopamine and NE via uptake inhibition and include the following ... 

Substituted benzamides include metodopramide (discussed previously) and trimethobenzamide. Their primary mechanism of antiemetic action is believed to be dopamine-receptor blockade. Trimethobenzamide also has weak antihistaminic activity. For prevention and treatment of nausea and vomiting, metodopramide may be given in the relatively high dosage of 10-20 mg orally or intravenously every 6 hours. The usual dose of trimethobenzamide is 250 mg orally, 200 mg rectally, or 200 mg by intramuscular injection. The principal adverse effects of these central dopamine antagonists are extrapyramidal restlessness, dystonias, and parkinsonian symptoms. 

The use of antihistamines can be traced back to the beginning of 1940s. The applications of the first-generation antihistamines were limited since they cause significant adverse effects such as sedation, memory impairment and psychomotor dysfunction. The second-generation antihistamines have significantly fewer central nervous system (CNS) adverse effects because they penetrate the blood-brain barrier much less extensively. 

Dicyclomine (Bentyl) [Anrimuscarinic, GI Anrispasmodic/ Anticholinergic] Uses Functional IBS Action Smooth-muscle relaxant Dose Adults. 20 mg PO qid T to 160 mg/d max or 20 mg EM q6h, 80 mg/d - qid then T to 160 mg/d, max 2 wk Feds. Infants >6 mo 5mg/dose tid-qid Children 10 mg/dose tid-qid Caution [B, -] Contra Infants <6 mo, NAG, MyG, severe UC, BOO Disp Caps, tabs, syrup, inj SE Anticholinergic SEs may limit dose Interactions T Anticholinergic effects W/ anticholinergics, antihistamines, amantadine, MAOIs, TCAs, phenothiazides T effects OF atenolol, digoxin X effects H7 antacids X effects OF haloperidol, ketoconazole, levodopa, phenothiazines EMS Avoid procainamide usage, may T adverse effects may T effects of digoxin, monitor... 

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