Pharmaceutical excipients. Adverse effects associated with inactive ingredients in drug products (Part I).

Excipient reactions have resulted from the use of clearly toxic substances (e.g. diethyleneglycol), the use of certain excipients in a susceptible group (e.g. very low birthweight neonates, patients with large surface area burns, patients with a history of asthma or contact dermatitis), the alteration of an excipient mixture resulting in altered bioavailability (e.g. phenytoin), and the deliberate or inadvertent extradural administration of preserved medications intended for intravenous use. Inadvertent excipient overdose has also occurred when unusually large doses of a drug containing a preservative were used [chlorbutol in morphine, ethanol in glyceryl trinitrate (nitroglycerin)]. Most excipient problems are preventable with knowledge of the currently available formulation. Government drug regulatory agencies have largely prevented introduction of a new toxic excipient; however, the new use of previously approved (but not adequately studied) excipients continues to result in unfortunate tragedies (e.g. the E-ferol incident). Populations at risk should be monitored carefully. Very low birthweight infants (less than 100g) have a well-demonstrated intolerance to many excipients, particularly during the first 2 weeks of life. Research should be directed toward development of non-preserved medications and safer diluents for this population. Drugs and excipients which have previously been demonstrated to be safer in other populations (e.g. doxapram) should be meticulously studied in this age group before widespread use is recommended. Asthmatic patients comprise another population that are frequently sensitive to excipient toxicity. In some cases, as in sulphiting agents, which are ubiquitous in foods as well as in medications, total avoidance may not be possible and prophylactic therapy may be beneficial. Inactive ingredients are clearly not consistently inert in their biological activity and therefore should not be listed as such. A more useful and concise term is excipient. It is highly recommended that all pharmaceutical manufacturers list all their excipients and make this available to practitioners and drug information centres. Alternatively or additionally, the package insert should list these excipients in accordance with good manufacturing procedures. This disclosure will help to determine the relative frequency and magnitude of problems (bioequivalence, toxicity, etc.) that excipients may have in the population, as well as enabling susceptible patients to avoid inadvertent exposure.

Documenting the activity and effectiveness of a regional drug information center.

The methods of data collection, storage, and retrieval used by the Rocky Mountain Drug Consultation Center (RMDCC) are described. To substantiate that drug information services provided by RMDCC are clinically useful and have a beneficial effect on therapy, data on medication-related problems and case outcomes, as well as demographic data, are stored in an IBM PC-XT using a system that allows searching and linkage of any number of recorded categories. Data were compiled on 28,081 inquiries from health-care professionals and consumers during 1985 and 1986. Analysis revealed that (1) medication-related problems are common (involving 34% of consumer inquiries), especially among the elderly; (2) a positive effect on therapy was made in the majority (76%) of problem cases; and (3) consumers were given drug information by their physician or pharmacist in fewer than half of the cases in which medications were prescribed and dispensed. A computer-based system to assist in analyzing information can be an important asset in documenting the activity and effectiveness of a regional drug information center.

Long-term follow-up of a patient with quadruple valve replacement.

A 60-year-old woman who had suffered from rheumatic fever as a child required replacement of the aortic, mitral, and pulmonary valves. Subsequently, because of severe regurgitation, the tricuspid valve was also replaced. This case proves that, with satisfactory intraoperative cardiac protection, quadruple valve replacement can produce a good long-term functional result.

Exercise and beta-blocking agents.

Beta-adrenoceptor-blocking agents produce noticeable effects on exercise performance. In patients with coronary heart disease, exercise capacity may in some cases increase during beta-blockade. Training effects (increased functional capacity, increased maximal oxygen uptake) may be somewhat attenuated in relatively healthy individuals taking beta-blockers, although with vigorous exercise programs, physiologic adaptations to exercise probably do occur.

Phenytoin toxicity and blood levels after a large oral dose.

The pharmacokinetics and side effects of a single oral 900-mg dose of phenytoin sodium were studied in six healthy men. Nine 100-mg phenytoin sodium capsules were administered with water to six fasting healthy men. Phenytoin plasma levels were measured by gas chromatography for up to 48 hours after dosing. Patients were observed and tested for gastrointestinal, cardiovascular, and neurologic side effects. Peak total (bound and free) plasma phenytoin levels were within the therapeutic range (10--20 microgram/ml) for two subjects and close (not less than 8.39 microgram/ml) for the remaining four. Peak free drug levels were 1.01--1.60 microgram/ml. Time to reach total and free peak plasma levels was long and variable (6--14 hours and 2--10 hours, respectively). Phenytoin protein binding (11.9--13.6%) was relatively stable among patients and at various plasma levels. A few mild transient side effects were noted; most occurred within two to four hours after dosing. Sinus bradycardia and a shortened PR interval were noted in two patients but did not correlate with peak plasma phenytoin levels. It appears that an oral loading dose of phenytoin sodium may be useful in ambulatory patients but further study of its side effects is recommended.

Displacement of phenytoin from plasma binding sites by salicylate.

Six healthy male subjects received phenytoin sodium as 9 100-mg capsules alone or with aspirin in a randomized, crossover fashion. Aspirin, 975 mg every 6 hr, was started 22 hr before a phenytoin dose and continued for an additional 48 hr during blood sampling. Mean 4-hr plasma salicylate levels ranged from 104 to 157 micrograms/ml during the sampling period. Individual mean values for the free fraction of salicylate varied from 0.107 to 0.167. The fraction of free phenytoin in plasma rose from 0.128 +/- 0.004 to 0.163 +/- 0.009 when aspirin was given (p less than 0.001). Subjects had lower total phenytoin 48-hr area under the curve (AUC) values when on aspirin (323 +/- 36 without and 261 +/- 49 micrograms . hr . ml-1 with aspirin; p less than 0.001) but free phenytoin AUC values were unchanged (41.4 +/- 4.5 and 42.4 +/- 9.0 micrograms . hr . ml-1; p less than 0.5). Thus, more rapid clearance of total phenytoin probably compensated for salicylate displacement of phenytoin from plasma protein binding sites. Total phenytoin levels for therapeutic monitoring must be interpreted cautiously when patients also receive salicylate.

Adenosine 3':5'-monophosphate content and actions in the division cycle of synchronized HeLa cells.

The involvement of adenosine 3':5'-monophosphate (cAMP) in the regulation of the cell cycle was studied by determining intracellular fluctuations in cAMP levels in synchronized HeLa cells and by testing the effects of experimentally altered levels on cell cycle traverse. Cyclic AMP levels were lowest during mitosis and were highest during late G-1 or early S phase. These findings were supported by results obtained when cells were accumulated at these points with Colcemid or high levels of thymidine. Additional fluctuations in cAMP levels were observed during S phase. Two specific effects of cAMP on cell cycle traverse were found. Elevation of cAMP levels in S phase or G-2 caused arrest of cells in G-2 for as long as 10 h and lengthened M. However, once cells reached metaphase, elevation of cAMP accelerated the completion of mitosis. Stimulation of mitosis was also observed after addition of CaCl2. The specificity of the effects of cAMP was verified by demonstrating that: (a) intracellular cAMP was increased after exposure to methylisobutylxanthine (MIX) before any observed effects on cycle traverse; (b) submaximal concentrations of MIX potentiated the effects of isoproterenol; and (c) effects of MIX and isoproterenol were mimicked by 8-Br-cAMP. MIX at high concentrations inhibited G-1 traverse, but this effect did not appear to be mediated by cAMP. Isoproterenol slightly stimulated G-1 traverse and partially prevented the MIX-induced delay. Moreover, low concentrations of 8-Br-cAMP (0.10-100 muM) stimulated G-1 traverse, whereas high concentrations (1 mM) inhibited. Both of these effects were also observed with the control, Br-5'-AMP, at 10-fold lower concentrations.

Apparent multiple forms of cyclic AMP phosphodiesterase from rat erythrocytes.

Bio-Gel A-5m chromatography has been used to separate apparent multiple forms of cyclic nucleotide phosphodiesterase from rat erythrocytes. Cyclic AMP phosphodiesterase was resolved by gel filtration into three peaks of activity with apparent molecular weights of about 300,000, 225,000 and 100,000, while cyclic GMP phosphodiesterase activity in gel column fractions was too low to permit meaningful estimates of its molecular weight. All three of the separated peaks of cyclic AMP phosphodiesterase activity displayed anomalous kinetic behaviour suggestive of negative cooperativity. The possibility that multiple phosphodiesterase activities could arise from in vitro alterations of a single enzyme was investigated. Similar changes in gel filtration profiles resulted when erythrocyte extracts were treated with trypsin or ammonium sulfate or were incubated at 37 degrees C. After these treatments, a large proportion of the enzyme activity occurred in low (ca. 100,000) molecular weight regions. The low molecular weight phosphodiesterase activities from untreated, incubated, and trypsin-treated extracts possessed similar properties. All were inhibited by methylxanthines, had pH optima of approximately 8.0, and similar kinetic properties and requirements for divalent cations. These observations raise the possibility that preparative procedures or limited proteolysis occurring during preparation and handling of extracts can contribute to the apparent multiplicity of enzyme forms seen after gel filtration of phosphodiesterase from rat erythrocytes and perhaps other cell types.

Cellular levels of feedback regulator of adenylate cyclase and the effect of epinephrine and insulin.

We have obtained direct evidence that shows the cellular formation and subsequent release of a potent inhibitor (feedback regulator) of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] by adipocytes, upon stimulation with epinephrine. The appearance of such a feedback regulator in adipocytes preceded its release into the medium. During a 30 min incubation, intracellular regulator levels rose rapidly and reached 39-61 units/g of adipocyte at 10 min. Release of inhibitor into the medium increased slowly and was 11-16 units/g of adipocyte at 10 min. Upon continued incubation, the cells at 30 min contained 30-41 units/g of ingibitor, slightly less than the content at 30 min; meanwhile, the medium content rose more than 3-fold. The inhibitor from both locations appeared to have the same characteristics, judging from the purification procedures and the biological activities on hormone-stimulated adenylate cyclase. Adenylate cyclase was inhibited by the feedback regulator in vitro when either epinephrine, corticotropin (ACTH), or glucagon was used as activator. The site of action of this inhibitor is therefore most likely beyond the specific hormone receptors. A new in vitro action of insulin has been found. Insulin, 50-500 microunits/ml, inhibited the formation and release of this factor from isolated rat or hamster adipocytes by 29-81% after these cells were stimulated by hormones that raise intracellular adenosine 3':5'-cyclic monophosphate. This factor enhaced the effect of insulin in lowering the adenosine 3':5'-cyclic monophosphate levels in fresh rat adipocytes. A reduced formation of such a factor may modify the metabolic events in adipocytes, and some as yet unexplained effects of insulin could therefore be linked to the metabolic effects of this factor.

Concepts for the rational selection of assays to be used in monitoring therapeutic drugs.

As the domain of monitoring therapeutic drugs rapidly expands from experimental investigations to everyday patient care, all clinical laboratory scientists, but especially clinical chemists, must learn to deal with their involvement in this expansion. First, the theoretical concepts underlying clinical pharmacology must be appreciated so that the laboratory's participation in it can succeed. Individual differences cause unpredictable variations of response to the customarily standardized drug dosage. Properly used, assays of drugs in blood can eliminate such variabilities. Second, the practical selection of which drug assays a laboratory intends to provide must be based on a rational evaluation of assay usefulness, integrating both clinical and laboratory considerations. Such a decision model is suggested; it is generally applicable in allocating priorities among an ever-increasing number of proposed tests under the constraint of finite resources.

Action of feedback regulator on adenylate cyclase.

A factor [the feedback regulator (FR)] formed by adipocytes after the stimulation of a cAMP raising hormone has been found to be a potent inhibitor of membrane-bound adenylate cyclase [EC 4.6.1.1.; ATP pyrophosphate-lyase (cyclizing)]. In a standard assay system using rat adipocyte plasma membrane as the source of adenylate cyclase, the FR inhibited adenylate cyclase by lowering the Vmax without affecting the apparent Km for ATP (0.3-0.6 mM). The apparent Ka for epinephrine (5-6 muM) was also not affected by FR. The inhibitory action of FR was partially countered by Mg2+ ions. An increase in phosphorylation of plasma membrane was observed when FR was present in the incubation system. The concentration required for a 50% inhibition was four times higher when adenosine 5-(beta,gamma-imino) triphosphate [AMP-P(NH)P] replaced ATP as the substrate for adenylate cyclase, implying that adenylate cyclase was inactivated by phosphorylation caused by FR. Increase in FR inhibition obtained by adding low concentrations of adenosine 5-(alpha,beta-methylene) triphosphate or ATP to AMP-(NH)P as the substrate supports this view. The inhibitory action was reversible. These results are consistent with the previously reported phenomena that (1) the undue to the formation of FR, and (2) the recovery of responsiveness of the stimulated cells by washing the cells with regular buffer medium is a result of the removal of FR. The hormone-initiated biphasic curve of cAMP levels in adipocytes is believed to be due to the negative feedback action of FR on adenylate cyclase. The mechanism of action of FR on inhibition of adenylate cyclase appears to be related to the phosphorylation of certain membrane components.

Hydrolysis of guanosine and adenosine 3',5'-monophosphates by rat blood.

Cyclic nucleotide phosphodiesterase activity was measured in whole blood, plasma, and suspensions of platelets and erythrocytes from rats. In fresh whole blood, apparent phosphodiesterase activity was low, but it rose strikingly during the hour after blood withdrawal. The apparent phosphodiesterase activity in platelet-free plasma showed no such increase, but that in platelet-enriched plasma increased in parallel with that in whole blood. The apparent phosphodiesterase activity of blood or of platelet-enriched plasma also was increased markedly by sonication. The increase in rat blood phosphodiesterase activity with aging thus appeared to be due to damage of platelets. Most of the phosphodiesterase activity in rat erythrocytes and platelets was located in the soluble fraction of sonicated preparations, but the total enzyme activities from the two sources exhibited marked differences in substrate specificity. With erythrocyte preparations, the rate of hydrolysis of muM concentrations of cyclic AMP was approx. 50 times that of cyclic GMP, while with platelet preparations, cyclic GMP was hydrolyzed about 20 times faster than cyclic AMP at muM levels. The activity of phosphodiesterase in platelets was much greater than that in erythrocytes at all concentrations of both substrates.