A Textbook of Clinical Pharmacology and Therapeutics

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Case history A 20-year-old female medical student attended her GP requesting a course of Septrin® (co-trimoxazole) for cystitis. She tells her GP that her last menstrual bleed was about six weeks earlier. She did not think she was at risk of pregnancy as her periods had been irregular since stopping the oral contraceptive one year previously due to fears about thrombosis, and her boyfriend used a condom. Physical examination, which did not include a vaginal examination, was normal. Urinalysis was 1� positive for blood and a trace of protein. Question Why should the GP not prescribe co-trimoxazole for this patient? Answer Until proven otherwise, it should be assumed that this woman is pregnant. Co-trimoxazole (a combination of sulfamethoxazole and trimethoprim) has been superseded by trimethoprim alone as a useful drug in lower urinary tract infection (UTI). The sulfamethoxazole does not add significant antibacterial advantage in lower UTI, but does have sulphonamide-associated side effects, including the rare but life-threatening Stevens–Johnson syndrome. Both sulfamethoxazole and trimethoprim inhibit folate synthesis and are theoretical teratogens. If pregnancy is confirmed (urinary frequency is an early symptom of pregnancy in some women, due to a progesterone effect) and if the patient has a lower UTI confirmed by pyuria and bacteria on microscopy whilst awaiting culture and sensitivity results, amoxicillin is the treatment of choice. Alternatives include an oral cephalosporin or nitrofurantoin. Note that lower urinary tract infection in pregnancy can rapidly progress to acute pyelonephritis. FURTHER READING Anon. Antiepileptics, pregnancy and the child. Drugs and Therapeutics Bulletin 2005; 43 no 2. Koren G. Medication, safety in pregnancy and breastfeeding: the evidencebased A–Z clinicians pocket guide. Maidenhead: McGraw-Hill, 2006. Rubin PC. Prescribing in pregnancy, 3rd edn. London: Blackwell, BMJ Books, 2000. McElhatton PR. General principles of drug use in pregnancy. Pharmaceutical Journal 2003; 270: 305–7. FURTHER INFORMATION FOR HEALTH PROFESSIONALS National Teratology Information Service Regional Drug and Therapeutics Centre Wolfson Unit Clarement Place Newcastle upon Tyne NE1 4LP Tel. 0191 232 1525 PRESCRIBING IN PREGRANCY 51
● Introduction 52 ● Pharmacokinetics 52 ● Pharmacodynamics 53 INTRODUCTION CHAPTER 10 DRUGS IN INFANTS AND CHILDREN Children cannot be regarded as miniature adults in terms of drug response, due to differences in body constitution, drug absorption and elimination, and sensitivity to adverse reactions. Informed consent is problematic and commercial interest has been limited by the small size of the market, so clinical trials in children have lagged behind those in adults. Regulatory agencies in the USA and Europe now recognize this problem and are attempting to address it, for example, by introducing exclusivity legislation designed to attract commercial interest. Traditionally, paediatricians have used drugs ‘off-label’ (i.e. for unlicensed indications), often gaining experience in age groups close to those for which a product is licensed and then extending this to younger children. That this empirical approach has worked (at least to some extent) is testament to the biological fact that while not just ‘miniature adults’ children do share the same drug targets (e.g. receptors, enzymes), cellular transduction mechanisms and physiological processes with their parents. Drug responses are thus usually qualitatively similar in children and adults, although there are important exceptions, including some central nervous system (CNS) responses and immunological responses to ciclosporin. Furthermore, some adverse effects occur only during certain stages of development, for example, retrolental fibroplasia induced by excess oxygen in the premature neonate and staining of teeth by tetracycline which occurs only in developing enamel. The processes of drug elimination are, however, immature at birth so quantitative differences (e.g. in dose) are important. Establishing optimal doses for drugs prescribed for children is thus an extremely important clinical challenge. Current regimes have been arrived at empirically, but guidelines are evolving for paediatric dosing in clinical trials and in future greater use may be made of pharmacokinetic/pharmacodynamic modelling in children, so hopefully this Cinderella ● Breast-feeding 53 ● Practical aspects of prescribing 54 ● Research 54 of therapeutics will soon be making her (belated) entry to the ball. PHARMACOKINETICS ABSORPTION Gastro-intestinal absorption is slower in infancy, but absorption from intramuscular injection is faster. The rate of gastric emptying is very variable during the neonatal period and may be delayed by disease, such as respiratory distress syndrome and congenital heart disease. To ensure that adequate blood concentrations reach the systemic circulation in the sick neonate, it is common practice to use intravenous preparations. In older and less severely ill children, oral liquid preparations are commonly used, resulting in less accurate dosing and a more rapid rate of absorption. This is important for drugs with adverse effects that occur predictably at high plasma concentration, and which show lack of efficacy if trough concentration is low (e.g. carbamazepine and theophylline). Infant skin is thin and percutaneous absorption can cause systemic toxicity if topical preparations (e.g. of potent corticosteroids) are applied too extensively. DISTRIBUTION Body fat content is relatively low in children, whereas water content is greater, leading to a lower volume of distribution of fat-soluble drugs (e.g. diazepam) in infants. Plasma protein binding of drugs is reduced in neonates due to a lower plasma albumin concentration and altered binding properties. The risk of kernicterus caused by displacement of bilirubin from albumin by sulphonamides (see Chapter 12) is well recognized. The blood–brain barrier is more permeable in neonates and young children, leading to an increased risk of CNS adverse effects.
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A Textbook of Clinical Pharmacology
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A Textbook of Clinical Pharmacology
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This fifth edition is dedicated to
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FOREWORD viii PREFACE ix ACKNOWLEDG
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PREFACE Clinical pharmacology is th
Page 12 and 13: PART I GENERAL PRINCIPLES
Page 14 and 15: ● Use of drugs 3 ● Adverse effe
Page 16 and 17: and acquired factors, notably disea
Page 18 and 19: 100 Effect (%) 0 0 5 10 1 10 100 (a
Page 20 and 21: Dose ratio -1 100 50 The relationsh
Page 22 and 23: ● Introduction 11 ● Constant-ra
Page 24 and 25: In reality, processes of eliminatio
Page 26 and 27: lood (from which samples are taken
Page 28 and 29: ● Introduction 17 ● Bioavailabi
Page 30 and 31: ROUTES OF ADMINISTRATION ORAL ROUTE
Page 32 and 33: Transdermal absorption is sufficien
Page 34 and 35: FURTHER READING Fix JA. Strategies
Page 36 and 37: and thromboxanes are CYP450 enzymes
Page 38 and 39: and lorazepam. Some patients inheri
Page 40 and 41: Orally administered drug Parenteral
Page 42 and 43: ● Introduction 31 ● Glomerular
Page 44 and 45: ACTIVE TUBULAR REABSORPTION This is
Page 46 and 47: DISTRIBUTION Drug distribution is a
Page 48 and 49: Detailed recommendations on dosage
Page 50 and 51: DIGOXIN Myxoedematous patients are
Page 52 and 53: ● Introduction 41 ● Role of dru
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Page 56 and 57: ● Introduction 45 ● Harmful eff
Page 58 and 59: vagina in girls in their late teens
Page 60 and 61: an anti-analgesic effect when combi
Page 64 and 65: METABOLISM At birth, the hepatic mi
Page 66 and 67: lifelong effects as a result of tox
Page 68 and 69: DISTRIBUTION Ageing is associated w
Page 70 and 71: DIGOXIN Digoxin toxicity is common
Page 72 and 73: FURTHER READING Dhesi JK, Allain TJ
Page 74 and 75: Factors involved in the aetiology o
Page 76 and 77: analgesic. Following its release, t
Page 78 and 79: antibiotics, such as penicillin or
Page 80 and 81: predisposes to non-immune haemolysi
Page 82 and 83: ● Introduction 71 ● Useful inte
Page 84 and 85: Response Therapeutic range Toxic ra
Page 86 and 87: Table 13.1: Interactions outside th
Page 88 and 89: Table 13.5: Competitive interaction
Page 90 and 91: ● Introduction: ‘personalized m
Page 92 and 93: Table 14.2: Variations in drug resp
Page 94 and 95: lipoprotein (LDL) is impaired. LDL
Page 96 and 97: Key points • Genetic differences
Page 98 and 99: • Discovery • • Screening Pre
Page 100 and 101: Too many statistical comparisons pe
Page 102 and 103: ETHICS COMMITTEES Protocols for all
Page 104 and 105: Table 16.1: Recombinant proteins/en
Page 106 and 107: duration and benefit. Adenoviral ve
Page 108 and 109: ● Introduction 97 ● Garlic 97
Page 110 and 111: A case report has suggested a possi
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including hypericin and pseudohyper
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PART II THE NERVOUS SYSTEM
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● Introduction 105 ● Sleep diff
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and daytime sleeping should be disc
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Key points • Insomnia and anxiety
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Box 19.1: Dopamine theory of schizo
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The Boston Collaborative Survey ind
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Oral medication, especially in liqu
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e.g. interpersonal difficulties or
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Partial response to first-line trea
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Key points Drug treatment of depres
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Case history A 45-year-old man with
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Levodopa PRINCIPLES OF TREATMENT IN
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• pulmonary, retroperitoneal and
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CHOREA The γ-aminobutyric acid con
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Cholinergic crisis Treatment of mya
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● Introduction 133 ● Mechanisms
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absolute arbiter. The availability
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Table 22.2: Metabolic interactions
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FURTHER ANTI-EPILEPTICS Other drugs
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Case history A 24-year-old woman wh
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Assessment of migraine severity and
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● General anaesthetics 145 ● In
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is the theoretical concern of a ‘
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• Respiratory system - apnoea fol
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Competitive antagonists (vecuronium
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have also proved useful in combinat
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● Introduction 155 ● Pathophysi
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ASPIRIN (ACETYLSALICYLATE) Use Anti
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Key points Drugs for mild pain •
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increases, correlating with the hig
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• If possible, use oral medicatio
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PART III THE MUSCULOSKELETAL SYSTEM
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● Introduction: inflammation 167
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Chapter 33). All NSAIDs cause wheez
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• Stomatitis suggests the possibi
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Pharmacokinetics Allopurinol is wel
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PART IV THE CARDIOVASCULAR SYSTEM
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esponsible for the strong predilect
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Ezetimibe Fat Muscle Dietary fat In
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educed). The risk of muscle damage
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Each of these classes of drug reduc
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AT 1 receptor) produce good 24-hour
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Table 28.2: Examples of calcium-cha
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Key points Drugs used in essential
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Case history A 72-year-old woman se
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Assess risk factors Investigations:
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Persistent ST segment elevation Thr
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Mechanism of action GTN works by re
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Because of the risks of haemorrhage
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Intrinsic pathway XIIa XIa the acti
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that the pharmacodynamic response i
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used with apparent benefit in acute
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The drugs that are most effective i
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therapeutic plasma concentration ca
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● Common dysrhythmias 217 ● Gen
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BASIC LIFE SUPPORT CARDIOPULMONARY
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arrest. The electrocardiogram is li
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should be given to insertion of an
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Drug interactions Amiodarone potent
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effect when treating sinus bradycar
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Case history A 24-year-old medical
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PART V THE RESPIRATORY SYSTEM
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CHAPTER 33 THERAPY OF ASTHMA, CHRON
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STEP 5: CONTINUOUS OR FREQUENT USE
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Adenylyl cyclase Table 33.1: Compar
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Drug interactions Although synergis
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use in asthma has declined consider
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α 1-antitrypsin deficiency, neutro
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PART VI THE ALIMENTARY SYSTEM
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● Peptic ulceration 247 ● Oesop
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PEPTIC ULCERATION 249 • With rega
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Ranitidine has a similar profile of
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Vestibular stimulation ? via cerebe
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cortical centres affecting vomiting
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• in hepatocellular failure to re
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Ciprofloxacin is occasionally used
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withdrawal), small doses of benzodi
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Table 34.7: Dose-independent hepato
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● Introduction 265 ● General ph
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dinucleotide (NAD) and nicotinamide
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Table 35.1: Common trace element de
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PART VII FLUIDS AND ELECTROLYTES
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● Introduction 273 ● Volume ove
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Key points Diuretics Diuretics are
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is sometimes caused by drugs, notab
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or with potassium-sparing diuretics
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Greger R, Lang F, Sebekova, Heidlan
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PART VIII THE ENDOCRINE SYSTEM
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in prefilled injection devices (‘
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Metformin should be withdrawn and i
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FURTHER READING American Diabetes A
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deficiency. Potassium iodide (3 mg
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fertility. It is contraindicated du
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● Introduction 297 ● Vitamin D
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effective in life-threatening hyper
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Further reading Block GA, Martin KJ
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Table 40.1: Actions of cortisol and
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injection may be useful, but if don
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CHAPTER 41 REPRODUCTIVE ENDOCRINOLO
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elease by the pituitary via negativ
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Treatment with depot progestogen in
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infusion using an infusion pump to
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significant proportion of men who r
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with symptoms caused by the release
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FURTHER READING Birnbaumer M. Vasop
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PART IX SELECTIVE TOXICITY
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● Principles of antibacterial che
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2. transfer of resistance between o
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Pharmacokinetics Absorption of thes
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Mechanism of action Macrolides bind
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asic quinolone structure dramatical
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Case history A 70-year-old man with
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PRINCIPLES OF MANAGEMENT OF MYCOBAC
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Pharmacokinetics Absorption from th
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MYCOBACTERIUM LEPRAE INFECTION Lepr
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POLYENES AMPHOTERICIN B Uses Amphot
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therapy is adequate though more fre
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NUCLEOSIDE ANALOGUES ACICLOVIR Uses
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Table 45.3: Summary of available ac
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Uses Interferon-α when combined wi
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● Introduction 351 ● Immunopath
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Table 46.1: Examples of combination
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NON-NUCLEOSIDE ANALOGUE REVERSE TRA
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FUSION INHIBITORS Uses Currently, e
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salvage therapy include azithromyci
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● Malaria 361 ● Trypanosomal in
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Pharmacokinetics Chloroquine is rap
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Table 47.2: Drug therapy of non-mal
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Table 48.1: Classification of commo
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Polymorph count/mm 3 (a) (b) 10 000
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doses are used to prepare patients
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Adverse effects Methotrexate Inhibi
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Table 48.7: Summary of clinical pha
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Table 48.9: Summary of the clinical
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Plasma membrane Signal transduction
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Table 48.10: Monoclonal antibodies
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INTERFERON-ALFA 2B Interferon-alfa
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PART X HAEMATOLOGY
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● Haematinics - iron, vitamin B 1
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one marrow to produce red cells. Th
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EPO Erythroid precursors Erythrocyt
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Therapeutic principles The extent o
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PART XI IMMUNOPHARMACOLOGY
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● Introduction 399 ● Immunity a
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Key points Antigen recognition Expr
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Table 50.1: Novel anti-proliferativ
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Key points Treatment of anaphylacti
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DRUGS THAT ENHANCE IMMUNE SYSTEM FU
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PART XII THE SKIN
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● Introduction 411 ● Acne 411
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DERMATITIS (ECZEMA) PRINCIPLES OF T
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SPECIALISTS ONLY SPECIALISTS ONLY E
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TREATMENT OF OTHER SKIN INFECTIONS
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effect of too high a dose of UVB in
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PART XIII THE EYE
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● Introduction: ocular anatomy, p
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to cause pupillary dilatation, name
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Table 52.3: Antibacterial agents us
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Table 52.6: Common drug-induced pro
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PART XIV CLINICAL TOXICOLOGY
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Table 53.2: Central nervous system
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which provide anonymized data to th
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Peak plasma levels after smoking ci
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Key points Acute effects of alcohol
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FURTHER READING Goldman D, Oroszi G
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Table 54.2: Common indications for
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Table 54.5: Antidotes and other spe
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Commission on Human Medicines (CHM)
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Note: Page numbers in italics refer
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atrial fibrillation 217, 221 digoxi
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Cushing’s syndrome 302 cyclic ade
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5-fluorouracil 375-6 fluoxetine, mo
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children 54 diazepam 108 iron prepa
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non-steroidal anti-inflammatory dru
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puberty (male), delay 314 puerperiu
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tolerance 9, 433 benzodiazepines 10
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A Textbook of Clinical Pharmacology and Therapeutics

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