Bioavailability of intranasal scopolamine in normal subjects.

The bioavailability of scopolamine in three dosage forms was compared in 12 healthy nonsmoking male volunteers. Subjects received 0.4-mg doses of scopolamine bromide in intravenous (i.v.), intranasal (i.n.), or oral (p.o.) dosage forms on three occasions, with at least 2 weeks separating the doses. Scopolamine concentrations in plasma were determined with a combined reverse-phase liquid chromatographic-radioreceptor binding assay. Saliva volume and flow rate and percent suppression of control flow rate were determined from each sample. Absorption after i.n. and po scopolamine administration was rapid; plasma concentrations [1680 (i.n.) and 164 pg/mL (p.o.)] peaked within 1 h of dosing [0.37 (i.n.) and 0.78 h (p.o.)], respectively. i.n. and i.v. scopolamine suppressed salivary flow rate to similar extents (95% and 99.7%), respectively. Times to reach maximum effect were 1.05 and 0.27 h after i.n. and i.v. dosage, respectively. Absolute intranasal bioavailability, calculated from the area under the drug concentration vs time curve, was found to be significantly greater than that of p.o. scopolamine (83% vs 3.7%, p < 0.05). The i.n. route may provide a noninvasive, reliable, fast, and effective route for administering scopolamine.

Factors affecting drug bioavailability in space.

Microgravity-induced changes in the bioavailability of drugs may influence the efficacy or toxicity of drugs. The bioavailability of orally administered drugs may be altered by changes in dissolution rate, intestinal microflora, intraluminal enzymes, epithelial enzymes, rate of passage across the gastrointestinal epithelium, gastric emptying rate, intestinal transit time, hepatic first pass metabolism, and gastrointestinal and hepatic blood flow. Limited data from antiorthostatic bed rest and inflight studies provide preliminary evidence that the bioavailability of orally administered drugs in space may be decreased or subject to more interindividual variation than expected from ground-based studies.

Theophylline pharmacokinetics: effect of continuous versus intermittent cimetidine i.v. infusion.

The comparative effects of continuous versus intermittent cimetidine infusion on theophylline pharmacokinetics were evaluated in 12 nonsmoking healthy male volunteers. Each subject received aminophylline 0.9 mg/kg/hr over 6 hours alone (control) and in random order at 1 week intervals, in combination with intermittent cimetidine (300 mg IV over 15 minutes every 6 hours) and continuous cimetidine (50 mg/hr IV) infusions. Both cimetidine regimens were administered for a total of 50 hours. Serial plasma samples were obtained and assayed for theophylline by HPLC. No significant differences existed in mean theophylline clearance and mean volume of distribution among control, intermittent or continuous cimetidine regimens; the power was greater than 80% to detect a 30% change in clearance. Only a minor difference in theophylline half-life between control and continuous cimetidine infusion (7.59 +/- 2.52 vs. 9.05 +/- 3.17 hr; P less than .05) was observed. These findings do not support a clinically significant interaction between IV aminophylline and cimetidine administered IV either as a low dose continuous infusion or as an intermittent infusion.

Nimodipine in the treatment of subarachnoid hemorrhage.

Nimodipine, a calcium-channel antagonist with a relatively selective vasodilatory effect on cerebral blood vessels, has recently been approved for improvement of neurologic deficits due to spasm following subarachnoid hemorrhage. Nimodipine has low oral bioavailability (2.7-27.9 percent), a short half-life (2 h), is highly protein bound (98-99 percent), and is hepatically metabolized. Clinical studies have evaluated topical, intravenous, and oral administration of nimodipine for the treatment of cerebral artery spasm associated with subarachnoid hemorrhage. These studies document some benefit of the drug in reducing the occurrence of severe neurologic deficit, although this effect is not universal. Few adverse effects have been noted. Further studies are necessary to evaluate the pharmacologic and pharmacokinetic characteristics, the appropriate dose and route of administration, adverse effects, drug interactions, and the therapeutic efficacy of nimodipine before routine use can be recommended.

Nonsedating histamine H1-receptor antagonists.

The chemistry, pharmacology, pharmacokinetics, clinical efficacy, adverse effects, and dosages of the nonsedating histamine H1-receptor antagonists terfenadine, astemizole, loratadine, and acrivastine are reviewed. Terfenadine and astemizole are chemically unrelated to histamine H1-receptor antagonists such as diphenhydramine and chlorpheniramine. Loratadine is structurally related to the antihistamine azatadine, and acrivastine is a side-chain-reduced metabolite of the antihistamine triprolidine. Like other histamine H1-receptor antagonists, they competitively block histamine receptor sites rather than inhibiting histamine release. All four drugs have relatively long half-lives and are rapidly absorbed after oral administration. Terfenadine, astemizole, and loratadine are metabolized extensively in the liver; terfenadine and astemizole are both 97% protein bound. Terfenadine 60 mg twice daily has been shown to be as effective as conventional antihistamines for the treatment of seasonal allergic rhinitis. In clinical trials, astemizole 10 mg daily was comparable to or better than chlorpheniramine for treatment of chronic rhinitis. Both terfenadine and astemizole were effective for treatment of chronic urticaria. For treatment of seasonal allergic rhinitis, loratadine combined with pseudoephedrine may be preferable to triprolidine-pseudoephedrine and acrivastine-pseudoephedrine combinations that require more frequent dosing. Acrivastine must be administered more frequently than the other nonsedating antihistamines. None of these four agents impairs psychomotor activity. Infrequently reported adverse effects include dry mouth, skin reactions, and weight gain. The absence of substantial sedative effects and the less-frequent dosing schedules make these agents good alternatives to the classic antihistamines for treatment of seasonal and chronic rhinitis and chronic urticaria.

Use of ipratropium bromide in obstructive lung disease.

The chemistry, pharmacology, pharmacokinetics, clinical efficacy, adverse effects, and dosage of ipratropium bromide are reviewed. Ipratropium bromide, a synthetic quaternary isopropyl derivative of atropine, interrupts vagally mediated bronchoconstriction by inhibiting the cyclic guanosine 3',5'-monophosphate system at parasympathetic nerve endings. Ipratropium bromide is poorly absorbed after oral and inhaled administration but diffuses rapidly into tissue after i.v. or i.m. administration. The elimination half-life is 3.2-3.8 hours. After inhalation, the drug is eliminated in the urine and feces. The bronchodilatory effect of ipratropium bromide in stable chronic obstructive pulmonary disease appears to be comparable, and may be superior, to that of the beta-sympathomimetic agents. In acute exacerbations, ipratropium bromide is useful but may not be the preferred agent because of a delayed onset of action (within 15 minutes; mean dose-dependent duration of effect, three to five hours). Combination therapy with other bronchodilating drugs has proved useful. Ipratropium bromide may be a useful adjunctive agent in the treatment of asthma. Since the onset of action is delayed, ipratropium bromide should not be used as single-drug therapy in an acute asthmatic exacerbation. Reported adverse effects, including cough, nausea, palpitations, dry mouth, nervousness, gastrointestinal distress, and dizziness, have been mild. The usual dosage is two inhalations (36 micrograms) four times daily, and the maximum number of doses per day should not exceed 12. Although ipratropium bromide is currently indicated only for maintenance therapy in stable chronic bronchitis and emphysema, it may be useful as adjunctive therapy in asthma and in the management of acute exacerbations of chronic bronchitis and asthma. Additional experience in a variety of chronic obstructive pulmonary disorders will help to clarify the role of ipratropium bromide in the treatment of obstructive pulmonary disease.

Thrombocytopenia and vomiting due to difluoromethylornithine.

A 32-year-old Haitian male with acquired immunodeficiency syndrome presented with complications of Isospora belli enteritis. Therapy with the investigational drug difluoromethylornithine was initiated. Severe thrombocytopenia, nausea, and vomiting developed during intravenous drug therapy and recurred upon rechallenge with low-dose oral difluoromethylornithine. Therapy was discontinued because of these severe adverse effects.

Pharmacist facilitation of a home IV therapy treatment program.

A pharmacist's knowledge and experience had strong impact on the success of a home intravenous (IV) infusion treatment program, as stated in the following case study. After reviewing the patient's medical history, clinical course, and drug therapy plan, the pharmacist made recommendations that simplified the home IV self-care program, without compromising the results. The article describes how the pharmacist's liaison between patient and physician resulted in successful treatment and avoided significant costs to the hospital and the State Medical Assistance Program (Pennsylvania Department of Public Welfare). As Diagnosis Related Groups (DRGs) become fully implemented, the pharmacist's services will become an even more important component of discharge planning.

Grand rounds. Immune globulin in the treatment of autoimmune thrombocytopenic purpura.

Two patients with autoimmune thrombocytopenic purpura (ATP) who received high-dose intravenous immune globulin before undergoing splenectomy are described, and the pathogenesis, clinical presentation, diagnosis, and treatment of chronic ATP are reviewed. One patient was a 62-year-old white man who was admitted to the hospital with a history of thrombocytopenia and probable steroid-induced diabetes mellitus. The second patient was a 24-year-old black woman who was admitted for recurrent bleeding episodes and splenectomy. In both patients, immune globulin 1.5 g/kg administered over four to six days resulted in marked elevations of platelet counts. ATP is a platelet disorder of unknown etiology. Platelets with surface-bound antiplatelet antibody are destroyed by the reticuloendothelial system. As the platelet count falls below 30,000-50,000/cu mm, the patient may manifest signs of bleeding such as petechiae, purpura, ecchymosis, menorrhagia, epistaxis, and bleeding from other mucosal surfaces. Corticosteroids are the initial treatment of choice. Splenectomy is considered for children with the life-threatening hemorrhage and for patients who do not respond to corticosteroids. Patients who are refractory to steroid therapy and splenectomy may respond to immunosuppressant agents. Approximately, 80% of patients treated with immune globulin have responded with an increase in platelet count, although this increase is sometimes transient. Immune globulin therapy is recommended for emergency treatment of ATP, as preoperative medication before splenectomy, and for young children in order to postpone splenectomy. Despite a good response to treatment, immune globulin therapy should not be considered a cure for ATP.