Pharmacokinetic drug interactions

Potential drug-drug interaction and its determinants among patients with cancer receiving chemotherapy in oncology centres of Northwest Ethiopia: an institutional-based cross-sectional study

OBJECTIVE

The study was conducted to assess potential drug-drug interactions (PDDIs) and its determinants among patients with cancer receiving chemotherapy.

DESIGN AND SETTING

An institutional-based cross-sectional study was used. This study was conducted from 1 June 2021 to 15 December 2021, in Northwest Ethiopia oncology centres.

PARTICIPANTS

All eligible patients with cancer received a combination of chemotherapy.

OUTCOMES

The prevalence and severity of PDDIs were evaluated using three drug interaction databases. Characteristics of participants were presented, arranged and summarised using descriptive statistics. The predictors and outcome variables were examined using logistic regression. The cut-off point was a p value of 0.05.

RESULTS

Of 422 patients included in the study, 304 patients were exposed to at least one PDDI with a prevalence of 72.1% (95 % CI: 68% to 76%) using three drug interaction databases. There were varied reports of the severity of PDDI among databases, but the test agreement using the kappa index was 0.57 (95% CI: 0.52 to 0.62, p=0.0001) which is interpreted as a moderate agreement among three databases. Patients aged ≥50 years old had the risk to be exposed to PDDI by odds of 3.1 times (adjusted OR (AOR)=3.1, 95% CI (1.8 to 5.3); p=0.001) as compared with patients <50 years old. Similarly, patients with polypharmacy and comorbidity were more likely to be exposed to PDDI than their counterparts (AOR=2.4, 95% CI (1.4 to 4.1); p=0.002 and AOR=1.9, 95% CI (1.1 to 3.4); p=0.02, respectively).

CONCLUSION

The main finding of this study is the high prevalence of PDDI, signifying the need for strict patient monitoring for PDDIs among patients with cancer receiving chemotherapy. We suggest the use of at least three drug databases for quality screening. Patients with an age ≥50 years old, polypharmacy and comorbidity were significantly associated with PDDIs. The establishment of oncology clinical pharmacists and computerised reminder mechanisms for PDDIs through drug utilisation review is suggested.

Examination of the Impact of CYP3A4/5 on Drug-Drug Interaction between Schizandrol A/Schizandrol B and Tacrolimus (FK-506): A Physiologically Based Pharmacokinetic Modeling Approach

Schizandrol A (SZA) and schizandrol B (SZB) are two active ingredients of Wuzhi capsule (WZC), a Chinese proprietary medicine commonly prescribed to alleviate tacrolimus (FK-506)-induced hepatoxicity in China. Due to their inhibitory effects on cytochrome P450 (CYP) 3A enzymes, SZA/SZB may display drug–drug interaction (DDI) with tacrolimus. To identify the extent of this DDI, the enzymes’ inhibitory profiles, including a 50% inhibitory concentration (IC₅₀) shift, reversible inhibition (RI) and time-dependent inhibition (TDI) were examined with pooled human-liver microsomes (HLMs) and CYP3A5-genotyped HLMs. Subsequently, the acquired parameters were integrated into a physiologically based pharmacokinetic (PBPK) model to quantify the interactions between the SZA/SZB and the tacrolimus. The metabolic studies indicated that the SZB displayed both RI and TDI on CYP3A4 and CYP3A5, while the SZA only exhibited TDI on CYP3A4 to a limited extent. Moreover, our PBPK model predicted that multiple doses of SZB would increase tacrolimus exposure by 26% and 57% in CYP3A5 expressers and non-expressers, respectively. Clearly, PBPK modeling has emerged as a powerful approach to examine herb-involved DDI, and special attention should be paid to the combined use of WZC and tacrolimus in clinical practice.

Pharmaceuticals targeting signaling pathways of endometriosis as potential new medical treatment: A review

Endometriosis (EM) is defined as endometrial tissues found outside the uterus. Growth and development of endometriotic cells in ectopic sites can be promoted via multiple pathways, including MAPK/MEK/ERK, PI3K/Akt/mTOR, NF-κB, Rho/ROCK, reactive oxidative stress, tumor necrosis factor, transforming growth factor-β, Wnt/β-catenin, vascular endothelial growth factor, estrogen, and cytokines. The underlying pathophysiological mechanisms include proliferation, apoptosis, autophagy, migration, invasion, fibrosis, angiogenesis, oxidative stress, inflammation, and immune escape. Current medical treatments for EM are mainly hormonal and symptomatic, and thus the development of new, effective, and safe pharmaceuticals targeting specific molecular and signaling pathways is needed. Here, we systematically reviewed the literature focused on pharmaceuticals that specifically target the molecular and signaling pathways involved in the pathophysiology of EM. Potential drug targets, their upstream and downstream molecules with key aberrant signaling, and the regulatory mechanisms promoting the growth and development of endometriotic cells and tissues were discussed. Hormonal pharmaceuticals, including melatonin, exerts proapoptotic via regulating matrix metallopeptidase activity while nonhormonal pharmaceutical sorafenib exerts antiproliferative effect via MAPK/ERK pathway and antiangiogenesis activity via VEGF/VEGFR pathway. N-acetyl cysteine, curcumin, and ginsenoside exert antioxidant and anti-inflammatory effects via radical scavenging activity. Natural products have high efficacy with minimal side effects; for example, resveratrol and epigallocatechin gallate have multiple targets and provide synergistic efficacy to resolve the complexity of the pathophysiology of EM, showing promising efficacy in treating EM. Although new medical treatments are currently being developed, more detailed pharmacological studies and large sample size clinical trials are needed to confirm the efficacy and safety of these treatments in the near future.

Pharmacokinetic drug–drug interactions: an insight into recent US FDA-approved drugs for prostate cancer

Pharmacokinetic drug–drug interaction is a significant safety and efficiency concern as it results in considerable concentration changes. Drug–drug interactions are a substantial concern in anticancer drugs that possess a narrow therapeutic index. These interactions remain as the principal regulatory obstacle that can lead to termination in the preclinical stage, restrictions in the prescription, dosage adjustments or withdrawal of the drugs from the market. Drug metabolizing enzymes or transporters mediate the majority of clinically relevant drug interactions. Cancer diagnosed aged patients use multiple medications and are more prone to significant drug–drug interactions. This review provides detailed information on clinically relevant drug–drug interactions resulting from drug metabolism by enzymes and transporters with a particular emphasis on recent FDA approved antiprostate cancer drugs.

Drug-drug interactions in cancer chemotherapy: an observational study in a tertiary health care centre

BACKGROUND

The objective of this study was to evaluate the occurrence of drug-drug interactions (DDIs) in patients on cancer chemotherapy, with the identification of risk factors for these DDIs.

METHODS

This was a cross-sectional, descriptive study carried out at the Department of Onco-Radiation at Guru Gobind Singh Medical College, Faridkot, Punjab. The DDIs were recorded with the help of a drug interaction/interplay information software.

RESULTS

In total, 354 interactions were identified from 283 patient records. The mean age of the patients in the study was 49.05±14.35 years. According to the mechanism of interaction, 306 (86.44%) drug interactions were classified as pharmacokinetic and 48 (13.56%) as pharmacodynamic in nature.

CONCLUSIONS

Sensitization of the treating oncologist and the establishment of alerts, such as electronic alerts or a novel fully digital computerized technology that gives a warning when a health expert enters a patient's prescription orders into the electronic medical documentation, can be helpful in controlling DDIs.

Urinary D-glucaric acid excretion and plasma antipyrine kinetics during enzyme induction

1 Changes in urinary D-glucaric acid excretion following a 14 day course of antipyrine to produce enzyme induction have been compared in normal volunteers with changes in plasma half lives and steady state levels of antipyrine. 2 Urinary D-glucaric acid excretion for the group rose significantly with induction, while there was a significant fall in the mean plasma antipyrine half life and steady state levels. The extent of the increase in urinary D-glucaric acid excretion was inversely related to the pre-induction level, and this also applied to the change in antipyrine half lives. 3 Although in individuals, urinary D-glucaric acid excretion and plasma levels of antipyrine changed in parallel, there was no numerical correlation in the group as a whole between these two tests either before or after enzyme induction. 4 These findings are consistent with other recently reported evidence that plasma drug kinetics and other microsomal enzyme functions are not necessarily affected to the same degree by agents with enzyme inducing properties.

Toxicological consequences of multiple chemical interactions: a primer

The capacity to understand and successfully predict the toxicological consequences of multiple chemical interactions is a critical challenge facing the scientific community. This article is designed to provide a broad framework introducing the concept of interaction, use of consistent and meaningful terminology and a descriptive assessment of toxicological foundations within which chemical interactions may be evaluated. The article offers guidance on the need to place a high priority on assessing the mechanistic basis of 'superinteractions', that is, unique interactions far exceeding even those of a multiplicative nature. The final section of the article provides a detailed perspective on how the extensive and successful experience of the pharmaceutical industry in assessing and interpreting any interaction for patients can be useful to the issues and concerns of chemical interactions for the field of environmental toxicology and risk assessment.

Drug-antacid interactions: assessment of clinical importance

Antacids and adsorbents are commonly used preparations that are generally considered to be pharmacologically inert and free from adverse effects. They may, however, interact with a diverse range of primary drugs and the sequelae can be disadvantageous to the efficacy of the primary medication. Many such reports in the literature are based on animal experiments, or on single-dose studies in healthy subjects. Some reports are anecdotal and are unconfirmed; others are based solely on in vitro evidence. Potentially important interactions have been suggested for a relatively small group of drugs: tetracyclines, phenytoin, digoxin, chloroquine, cimetidine, quinidine, nonsteroidal antiinflammatory drugs, and beta-blocking agents. The evidence for these has been critically evaluated, as well as for antacid-anticoagulant and antacid-nitrofurantoin interactions that have been wrongly emphasized in the literature. The majority of literature reports on interactions with antacids have been overemphasized; only ferrous sulfate-, isoniazid-, and tetracycline-antacid interactions fall into a category I importance (scale I-III of descending importance). This category is for those interactions with good evidence of actual or potential importance in patients or in relevant studies on normal subjects.

Drug-drug and drug-disease interactions with nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs may cause a number of drug interactions. They can displace other drugs from serum proteins, and some can affect the metabolism or decrease the renal elimination of other drugs. In addition, they can attenuate the pharmacologic effect of other drugs, such as diuretic and antihypertensive agents, without affecting their disposition. Lastly, many disease states and aging can affect the handling of nonsteroidal anti-inflammatory drugs, mandating dose adjustment of some of these agents in certain clinical conditions. Some drugs may require more of these adjustments than others.

Potentiation of methotrexate-induced gastrointestinal toxicity by non-steroidal anti-inflammatory drugs (NSAIDs) and vincristine

Inhibition of intestinal nutrient absorption by the folate antagonist methotrexate (MTX) and the effects of several organic acid drugs and vincristine on MTX-induced gastrointestinal toxicity were investigated. Male Swiss-Webster mice received MTX, 25 mg/kg, i.p. once daily for 4 successive days. Using the everted sac technique, the rates of D-glucose and L-tyrosine transport were decreased by MTX to 10.9 and 6.3 mumol/g/h from control values of 35.0 and 10.0 mumol/g/h, respectively. Probenecid, sodium salicylate, phenylbutazone, or vincristine administered simultaneously with MTX, further decreased the rates of D-glucose transport to 3.6, 2.0, 0.8, and 2.6 mumol/g/h, respectively, and the rates of L-tyrosine transport to 1.2, 1.9, 0.6 and 0.9 mumol/g/h, respectively. When intestinal sacs from untreated animals were exposed to MTX (10(-3) M) on the serosal side only, the drug had no significant effect on the rate of transport of D-glucose or L-tyrosine. The rate of lactate production in everted intestinal sacs from MTX treated animals decreased to 11.8 from a control value of 30.3 mumol/g/h. Co-administration of phenylbutazone with MTX further decreased the rate of lactate production to 8.2 mumol/g/h. Body weight loss caused by MTX treatment (15.0%) was potentiated by the concurrent administration of probenecid (19.4%), salicylate (22.4%), phenylbutazone (23.0%) or vincristine (22.8%). These results demonstrate that vincristine and several commonly used organic acid drugs can potentiate the inhibitory effect of MTX on intestinal nutrient absorption. Thus, MTX dosage adjustment may be required in patients receiving such drugs.

A link between liver microsomal enzyme activity and thyroid hormone metabolism in man

1 The effect of different combinations of liver microsomal enzyme inducing drugs on thyroidal hormone steady state concentrations was investigated. Three groups of healthy volunteers were given daily either antipyrine 1200 mg together with phenobarbitone 100 mg, antipyrine 1200 mg combined with rifampicin 600 mg or rifampicin 600 mg alone for a period of 14 days. 2 Before and after each treatment the total body clearance of antipyrine, gamma-glutamyl transferase (gamma-GT), 6 beta-OH-cortisol as in vivo parameters of liver microsomal enzyme activity were measured. In addition, thyroxine (T4), free thyroxine (FT4), T3 resin uptake, tri-iodothyronine (T3) reverse T3 (rT3) and TSH were estimated. 3 After rifampicin administration there was a 60% increase in antipyrine clearance while following combinations of antipyrine-phenobarbitone or antipyrine-rifampicin an 80% and 128% increase respectively occurred. 4 A marked decrease of T4, FT4 and rT3 was seen in all groups while T3 remained stable in all groups investigated. This effect may be partly due to an increase in extrathyroidal metabolism of T4 as found previously by a kinetic turnover study using 125I-T4. It also depends on the extent of the liver microsomal enzyme inducing capacity rather than on the nature of the drugs used. The striking disparity of liver enzyme induction of T4 and rT3 disposal on the one hand and T3 metabolism on the other is a unique phenomenon whose pathogenesis is not clear at the present time.

Enzyme-inducing drug combinations and their effects on liver microsomal enzyme activity in man

The effect of 2 different drug combinations on liver microsomal activity was investigated in healthy volunteers by administering antipyrine 1200 mg and phenobarbitone 100 mg, or the same dose of antipyrine with rifampicin 600 mg daily for 14 days. The effect of rifampicin 1200 mg given for only 8 days was also studied. Before and after each drug regimen, estimates were made of the total body clearance of antipyrine, gamma-glutamyl-transferase (gamma-GT) and urinary excretion of 6-beta-hydroxycortisol as in vivo parameters of liver microsomal enzyme activity. Following combined antipyrine and phenobarbitone administration, the antipyrine clearance was increased by 80%, after antipyrine with rifampicin by 128%, and after rifampicin alone by 104%. 6-beta-hydroxycortisol, corrected for 17-hydroxycorticosteroids, increased from 2.6% to 8% following antipyrine plus phenobarbitone, from 4.4% to 27.9% following antipyrine plus rifampicin, and from 5.4% to 29.7% after rifampicin given alone. Based on previous studies, antipyrine given with phenobarbitone produced slightly more induction than phenobarbitone given alone. Following antipyrine 1200 mg with rifampicin 600 mg for 14 days a significantly greater increase in antipyrine clearance and 6-beta-hydroxycortisol excretion was observed than when either drug was given alone.

Potentiation of myelosuppression from cancer chemotherapy and thiazide diuretics

Fourteen patients with metastatic breast cancer and concomitant essential hypertension received treatment with combination chemotherapy (cyclophosphamide, methotrexate, and 5-fluorouracil) and thiazide diuretics. Significant augmentation of granulocytopenia during thiazide-chemotherapy combination, as compared with chemotherapy without thiazides, was observed in all patients. The most consistent changes in the neutrophil count were observed during the period of maximal myelosuppression from the antitumor drugs. An interaction between the thiazide diuretic and one or more of the cytotoxic agents is a possible explanation for the findings. The implications of this phenomenon are discussed.

The effect of antipyrine, phenobarbitol and rifampicin on thyroid hormone metabolism in man

The effect of three different live microsomal enzyme inducing drugs on thyroid hormone metabolism was investigated. Seven volunteers were randomly allocated in a crossover design to either antipyrine (1200 mg), phenobarbital (100 mg) or rifampicin (1200 mg) daily for 14 days. Before and after each treatment the following parameters of enzyme induction were measured: antipyrine clearance, gamma-glutamyltranspeptidase, d-glucaric acid and 6-beta-hydroxycortisol urinary excretion. In addition, thyroxine-binding globulin (TBG), T3-resin uptake (RT3U), thyroxine (T4), free thyroxine (FT4), triiodothyronine (T3), reverse T3 (rT3), and thyroid stimulating hormone were estimated. Following antipyrine and phenobarbital antipyrine clearance increased by about 45%, while with rifampicin an increase of 125% was observed. The indices of thyroid function did not change following phenobarbital and antipyrine, but after rifampicin T4, FT4 and rT3 decreased by about 14%, and T3 increased by 25%. In addition, the impact of rifampicin on the clearance of injected 125I-T4 was investigated in six additional volunteers by blocking thyroid iodine uptake. The 125I-T4 halflife decreased from 155 to 106 h and its clearance increased from 25 to 50 ml/h, while a fall in T4, FT4 and rT3 by about 40% and no rise but a decrease in T3 by 25% occurred. Therefore an increased clearance of T4 and rT3 but not of T3 seems likely following rifampicin, which might be due to enhanced hepatic metabolism and biliary excretion.

In vitro studies on drug--antibiotic interactions I: analgesics, antipyretics, antimalarials, and tranquilizers

The antimicrobial effects of some analgesics, antipyretics, antimalarials, and tranquilizers were determined. The phenothiazines were the most active group. The effect of the chosen drugs when combined with a selected number of antibiotics was studied on Staphylococcus aureus and Escherichia coli to determine the type of interaction. Most analgesics, antipyretics, and antimalarials showed either no effect or a synergistic action. However, some exhibited antagonistic effects. All tested tranquilizers were synergistic. Preliminary studies, using electronic absorption spectrometry, indicated that the antagonistic action may be attributed to a physical interaction.

Micromeasurement of plasma salicylate in arthritic children

A micromethod has been developed for determination of plasma salicylate. Frequent determinations of plasma salicylate levels in children with juvenile rheumatoid arthritis may be expected to provide greater therapeutic efficacy with reduced incidence of aspirin toxicity and consequently less need for use of secondary, more toxic, agents.

Enzyme induction and renal function in man

1. In a previous study in rats, an increased PAH clearance was found following chronic phenobarbitone administration. These results formed the basis for the present study in which fifteen healthy male volunteers were investigated and the parameters of liver microsomal enzyme activity and renal function were measured. 2. As parameters of liver microsomal enzyme activity, the antipyrine elimination in the plasma, the gamma-glutamyl-transpeptidase and the D-glucaric excretion in the urine were measured. Endogenous creatinine clearance, 51Cr-EDTA and 125I-Hippuran clearance were determined as measurements of renal function. 3. No correlation was found between any of the parameters of microsomal enzyme activity and renal function. 4. Of the fifteen volunteers, seven having a mean antipyrine half-life of 13.3 h were given antipyrine (500 mg) daily for 3 weeks. Afterwards all measurements of liver microsomal enzyme activity and renal function were repeated. The antipyrine half-life decreased to 8.5 h, while the antipyrine clearance was increased by about 56%. gamma-glutamyl-transpeptidase and D-glucaric acid were also significantly increased, while renal function remained unchanged. 5. Therefore, an increased PAH-clearance, as found in the rat, is not obtained in man following induction of liver microsomal enzyme activity.

Protein binding and kinetics of drugs in liver diseases

Although the liver is the major site for drug biotransformation, the effect of hepatic dysfunction on drug disposition has not been consistent or predictable. Most early studies of drug kinetics in liver disease measured only half-life. Only in the past few years has it been realised that liver diseases can affect drug absorption, hepatic metabolism, tissue distribution, and protein binding, which complicate interpretation of any change, or lack of change in drug half-life. Furthermore, it is now apparent that the efficiency with which a drug is metabolised by the liver, the extent of binding to blood constituents, and the aetiology and stage of the hepatic disorder are each important in determining whether significant alterations in drug disposition will occur. A pharmacokinetic perfusion model which takes into account many of the above factors has been proposed, and appears to be useful for predicting changes in the disposition of rapidly metabolised compounds. Nevertheless, the state of knowledge about those factors which limit the rate of metabolism of individual drugs or classes of drugs in inadequate, and no general model or guidelines which are useful clinically have been developed. Patients with hepatic disorders may show increases or decreases in sensitivity independent of alterations in drug disposition. The clinician caring for such patients must be cautious about the use of any drugs, and rely heavily on careful patient observation to determine efficacy or toxicity.

Kinetic interaction of nomifensine with a 1, 5-benzodiazepine (clobazam)

1. Among the numerous possibilities of drug interactions, pharmacokinetic interactions may cause mutual changes in absorption, distribution, metabolism and elimination of either drug. In the present study this approach was used to investigate pertinent effects of nomifensine and clobazam. 2. Ten normal subjects participated in an intra-individual comparison of nomifensin 75 mg alone and in combination with clobazam 15 and 30 mg. The study design was carried out according to a Latin square in double-blind conditions. One-week wash-out periods were used between the trial days. Serum levels of nomifensine were measured by radioimmunoassay (RIA) and of original clobazam by gas chromatography (GC). Classical criteria for bioavailability (peak serum levels, time of peak, area under the serum level time curve) and the half-life of elimination from the serum were used for retrieval of pharmacokinetic information. 3. Results showed no relevant differences in the criteria mentioned above, after administration of each drug alone or in combination. Therefore, extrapolations were made to multiple dose kinetics based on assumptions derived from practical therapy. They showed comprehensive agreement with therapeutic results in depressed patients. 4. The use of the classical criteria for bioavailability, in addition to the calculation of the half-time of elimination from serum, provides sufficient information for the decision whether pharmacokinetic drug interaction is present or absent. There was no such interaction after single doses of nomifensine or clobazam.

Drug interactions and clinical pharmacokinetics

Some drugs influence the gastro-intestinal absorption, distribution , metabolism or renal excretion of other drugs, i.e., processes involved in pharmacokinetic interactions. The clinical consequences of pharmacokinetic drug-drug interactions will be either an increase or a decrease in known therapeutic or toxic effects of the interacting drug. In order to evaluate the importance of drug interaction affecting gastro-intestinal absorption, it is necessary to distinguish between interactions which alter the rate of absorption of another drug and those which alter the amount of drug absorbed. Many drugs displace other drugs from their protein binding sites in vitro. This may cause an increase in the pharmacological effect of the displaced drug. However, much discrepancy exists between in vitro findings. In some cases, the enhanced effect only seems to be a temporary phenomenon. The degree of protein binding and the size of apparent volume of distribution (Vd) must also be taken into consideration. Perhaps the importance of interaction involving protein binding has been overemphasized. Barbiturates, glutethimide, rifampicin and phenytoin increase the rate of drug metabolism in man. The most important interactions reported are between oral anti-coagulants and barbiturates. After withdrawal of these hepatic microsomal enzyme inducing drugs, it takes 2 to 3 weeks before the rate of drug metabolism reaches the pretreatment level. In this period, risk of haemorrhage exists. Induction seems to be dose-dependent, but not all persons are inducible. Many drugs compete for the drug metabolising enzyme system in the liver and consequently some drugs inhibit the biotransformation of other drugs. The time course of these interactions depends on the pharmacokinetic properties of the drug involved, and these interactions also seem to be dose-dependent. The most important of such interactions, clinically involved the oral sulphonylurea hypoglycaemic drugs and the antiepilepic drug phenytoin. Drugs are eliminated by urinary excretion through three mechanisms: glomerular filtration, tubular reabsorption, and active tubular secretion. The most important interactions seem to be those involving competition for tubular secretion.

Effect of diphenylhydantoin on the biotransformation and biliary excretion of imipramine in rats

1. Rats with biliary fistula excrete 18% of an intraperitoneal dose of [14C]imipramine (80 mg/kg) in bile within 2-5 h. Diphenylhydantoin (46 mg/kg) simultaneously administered intravenously decreases the biliary excretion of imipramine plus metabolites to 7% dose. With or without diphenylhydantoin, the highest biliary concentration of imipramine plus metabolites occurs 30-60 min after dosage. 2. With or without administration of diphenylhydantoin, 83% of the bile radioactivity is present as the conjugated 2-hydroxylated metabolites of imipramine. With imipramine alone, more conjugated 2-hydroxydesmethyl-imipramine than conjugated 2-hydroxyimipramine is excreted in the bile. Diphenylhydantoin reverses this order. 3. Administration of diphenylhydantoin does not significantly alter the concentration of imipramine plus metabolites in plasma, liver, lung and brain measured at five consecutive 30 min periods after dosage.

Idiosyncratic reactions to the antiepileptic drugs

Idiosyncratic drug reactions can be defined as those adverse drug effects caused by genetically determined enzymatic abnormalities. For the clinician, however, this definition is too limited, and other rare and unusual adverse reactions to the antiepileptic drugs are discussed, including drug interactions, drug allergies, and organ toxicities, as well as true idiosyncrasies. Responsibility for initial recognition and later diagnosis of these reactions falls heavily upon the clinician. In addition to discussing the more common or serious rare reactions, the epidemiology and general mechanisms underlying the reactions are discussed. Treatment involves drug withdrawal, plus general supportive and specific therapy determined by the type and severity of the individual reaction. If primum non nocere should guide the treatment in general, then secundum non plus nocere should guide the treatment of adverse drug reactions.

Spectroscopic techniques in the study of protein binding. A fluorescence technique for the evaluation of the albumin binding and displacement of warfarin and warfarin-alcohol

1. The binding of racemic mixtures of warfarin and warfarin-alcohol to human serum albumin (HSA) is accompanied by an increase in the fluorescence quantum yield of these compounds. This property has been used to measure the characteristics of the binding of warfarin and warfarin-alcohol to HSA at 22 degrees C and 37 degrees C. Within the limits of the technique, no significant differences between the number of binding sites and strength of binding at the tight site at either temperature were observed. 2. The fluorescence of warfarin and warfarin-alcohol was used to label their binding site on HSA and to study the effects of other drugs on their binding. The results indicate that these two molecules are bound to the same site on HSA. 3. The validity of using changes in the fluorescence of warfarin as a measure of its displacement from HSA was investigated. Good correlations were observed between drug-induced decreases in the fluorescence of bound warfarin and displacement as measured by equilibrium dialysis. The displacement of warfarfin, as detected by fluorescence, correlates well with the increase in free warfarin resulting from addition of therapeutic drug concentrations to undiluted human serum. 4. The most potent displacing agents, by all the methods used, were iophenoxic acid, phenylbutazone and oxyphenylbutazone. The first of these is no longer used clinically, but the latter two are and have been reported to cause hypoprothrominaemia by displacing warfarin from HSA. The present study indicates that changes in the fluorescence of warfarin bound to HSA can be used to measure displacement of bound warfarin and to screen drugs that may cause clinically significant interactions by this mechanism.

Trade names or approved names. Part III. Special cases. Combination products

Drugs that do not have a critical dosage and are commonly used together, can justifiably be combined in a single product. Such combinations are more convenient to doctor and patient and have reduced risk of treatment error and drug interaction.

Combination products include more than one active drug, each of which has its own chemical and physical properties, so that they are complex formulations. Copies of combination products are, therefore, even less likely to have comparable performance than copies of single drugs.

Generic copies are encouraged by pharmacopoeial monographs and the current inclusion of complex formulations and combinations in the BP may allow a new era of clinical non-equivalence from products considered to be generically equivalent.

Interactions between sympathomimetic amines and antidepressant agents in man

Intravenous infusions of phenylephrine, noradrenaline, adrenaline, and isoprenaline were given to healthy human volunteers after five to seven days on phenelzine, tranylcypromine, or imipramine, and cardiovascular responses were compared with those observed under control conditions. With monoamine oxidase inhibitors there was a 2-2(1/2) fold potentiation of the pressor effect of phenylephrine, but no clinically significant potentiation of cardiovascular effects of noradrenaline, adrenaline, or isoprenaline. With imipramine there was potentiation of the pressor effects of phenylephrine (2-3 fold), noradrenaline (4-8 fold), and adrenaline (2-4 fold); there were dysrhythmias during adrenaline infusions, but no noticeable or consistent changes in response to isoprenaline.Noradrenaline and adrenaline in amounts contained in local anaesthetics used in dentistry are not likely to be significantly potentiated in otherwise healthy patients receiving monoamine oxidase inhibitors. Hazardous potentiation of their cardiovascular effects might occur in patients receiving tricyclic antidepressants.Our observations do not indicate that the hazards associated with isoprenaline inhalation by bronchial asthmatics would be increased by coincident therapy with a monoamine oxidase inhibitor or tricyclic antidepressant.