Evaluation of a glutamine-containing oral rehydration solution for the treatment of calf diarrhoea using an Escherichia coli model

A high-calorie oral rehydration solution (ORS) with glutamine (n=11) was more effective in correcting plasma, extracellular fluid and blood volume than solutions without (one WHO-type solution, n=6, and two high-glucose but glutamine-free solutions, n=7, n=12). It was the only solution to improve plasma volume significantly within 48 h and sustain the improvement throughout treatment; similarly, it was the only solution to correct packed-cell volume within 48 h and sustain the benefit to the end of treatment. At the end of treatment, the glutamine-treated calves were the only ones to avoid a significant weight loss compared with their pre-diarrhoeic values. The crucial difference between this solution and those used with glutamine previously is that it gave significant nutritional support whereas WHO type solutions did not. It also had more favourable effects on hyponatraemia and metabolic acidosis than a standard ORS. Use of a high-calorie ORS for 4 days (rather than 2 days of 50:50 admixture with milk replacer) brought additional beneficial effects on blood glucose and body weight.

Liarozole

Liarozole prevents the catabolism of retinoic acid via inhibition of 4-hydroxylase and exhibits retinoid-sparing and retinoid-mimetic effects in vivo. Liarozole is also a potent inhibitor of estrogen (via inhibition of aromatase) and testicular androgen synthesis (inhibition of 17, 20-lyase). Although testosterone levels decrease in vivo after single dose administration of liarozole, testosterone levels normalise as a result of pituitary feedback after multiple doses. Liarozole reduced the tumour size of androgen-dependent and -independent prostatic carcinomas in animal models. Liarozole also demonstrated chemopreventive activity in vivo. In phase I and II trials in patients with relapsed prostate cancer, liarozole achieved a complete response (assessed using prostate specific antigen levels) in 4% and a partial response in 26% of patients. Cutaneous adverse events, similar to those associated with excess levels of retinoic acid, were the most frequently reported events associated with liarozole.

Evaluation of a nutritive oral rehydration solution for the treatment of calf diarrhoea

The essential constituents of a conventional oral rehydration solution (ORS) are sodium, glucose and a bicarbonate precursor. The glucose promotes sodium uptake but because these solutions are isotonic, it is insufficient to sustain calorie requirements. This paper examines the performance of a novel ORS with over three times the conventional glucose concentration, by comparing it with two leading commercial ORSs in calves with induced Escherichia coli diarrhoea. This solution showed greater ability than the current market-leading ORS to repair extracellular fluid and plasma volume and to correct both hyponatraemia and metabolic acidosis, especially in more severely affected calves. In acidotic calves it was more effective in correcting hyperkalaemia, probably by supplying glucose to promote cellular potassium uptake as well as by correcting the acidosis. It therefore appears possible to depart from the traditional isotonic formulations for calf ORSs and gain significant nutritional support while retaining effective rehydration and correction of acid-base and electrolyte disturbances. This seems especially important in young animals where energy deprivation imposes a particular penalty; the use of hypertonic ORSs should not, however, be extended to other species without further research.

A cellular pertussis vaccine (Infanrix-DTPa; SB-3). A review of its immunogenicity, protective efficacy and tolerability in the prevention of Bordetella pertussis infection

SB-3 (Infanrix-DTPa) is one of a new generation of vaccines for immunisation against pertussis (whooping cough), diphtheria and tetanus. It is a 3-component (pertussis toxin, filamentous haemagglutinin and pertactin) chemically inactivated acellular pertussis pertussis-diphtheria-tetanus toxoid (DTaP) vaccine, and it differs from conventional whole-cell pertussis-diphtheria-tetanus toxoid (DTwP) vaccines in that it comprises inactivated purified Bordetella pertussis antigens rather than whole cells of the bacillus. SB-3, like a number of other DTaP vaccines, elicits a similar or more often, a significantly greater immune response than various DTwP vaccines in healthy infants and young children. initial data from comparative studies indicate that SB-3 also remains immunogenic when given in combination with hepatitis B vaccine or concurrently administered with Haemophilus influenzae type b (HbOC) conjugate vaccine. A combination of SB-3 and H. influenzae type b tetanus (PRP-T) conjugate vaccine results in lower anti-PRP antibody response than when both vaccines are administered concurrently. Data from two large, multicentre, German and Italian studies in infants indicate that the protective efficacy of SB-3 against pertussis was significantly better than one DTwP (DTwP-CON) but similar to another one (DTwP-BW) under investigation. Compared with another DTaP vaccine (BIO-3), SB-3 was just as protective. Overall, the data from these 2 studies indicate that primary vaccination with SB-3 provides effective protection against pertussis, even under the stringent conditions of a household contact with typical pertussis. As the other DTaP vaccines, SB-3 is better tolerated than DTwP vaccines, with a significantly lower incidence of common adverse events such as local reactions (swelling, pain and a erythema), irritability, fever, persistent crying and local tenderness. Clinical experience with SB-3 thus far indicates that, like other DTaP vaccines, it is associated with significantly fewer common (non-serious) adverse events than DTwP vaccines. Less clear is whether it has any advantage over DTwP vaccines with respect to protective efficacy or over other DTaP vaccines with respect to tolerability and protective efficacy. Nevertheless, the available data support the use of SB-3 for infant immunisation, as well as providing a suitable basis for the development of new combination vaccines.

Fosinopril: a reappraisal of its pharmacology and therapeutic efficacy in essential hypertension

Fosinopril is a phosphinic acid derivative which undergoes rapid hydrolysis after oral administration to the active diacid ACE inhibitor fosinoprilat. Cardiotropic effects have been associated with the drug, and the compensatory dual elimination route of fosinopril via renal and hepatic systems offers an opportunity for ACE inhibitor treatment of hypertension in patients with renal or hepatic impairment. Comparative trials of monotherapy with fosinopril 10 to 40 mg/day have demonstrated antihypertensive efficacy equivalent to that of sustained release nifedipine 40 mg/day, hydrochlorothiazide 25 to 50 mg/day, enalapril 5 to 10 mg/day amlodipine 5 to 10 mg/day and sustained release verapamil 240 to 480 mg/day, and superior to that of isradipine 5 mg/day. The efficacy of combination therapy with fosinopril 10 to 20 mg/day and hydrochlorothiazide 12.5 mg/day was significantly superior to that of hydrochlorothiazide alone, tended to be superior to that of fosinopril 20 mg/day alone and was similar to that of sustained release nifedipine 40 mg/day alone. The combination of fosinopril/chlorthalidone 20 to 40/25 mg/day was as effective as propranolol/chlorthalidone 80 to 160/25 mg/day. The incidence of adverse effects associated with fosinopril is low, and cough may possibly occur less often with this drug than with other ACE inhibitors. Fosinopril thus offers an effective and well tolerated option for the treatment of hypertension in adult and elderly patients, including those with renal or hepatic impairment.

Losartan potassium: a review of its pharmacology, clinical efficacy and tolerability in the management of hypertension

Losartan potassium is an orally active, nonpeptide angiotensin II (AII) receptor antagonist. It is the first of a new class of drugs to be introduced for clinical use in hypertension. This novel agent binds competitively and selectively to the AII subtype 1 (AT(1)) receptor, thereby blocking AII-induced physiological effects. An active metabolite, E3174, contributes substantially to its antihypertensive effect, which persists throughout 24 hours after once-daily administration. In patients with mild to moderate hypertension, losartan potassium 50 to 100mg once daily as monotherapy lowers blood pressure to a similar degree to enalapril, atenolol and felodipine extended release (ER). Losartan potassium combined with hydrochlorothiazide reduces blood pressure further than either drug given separately. About one-third of patients with severe hypertension have responded to the combination product. Losartan potassium appears to be effective in elderly patients. Losartan potassium is very well tolerated. In clinical trials, dizziness was the only drug-related event reported more frequently with losartan potassium monotherapy than with placebo. First-dose hypotension is uncommon. An aspect of the drug's tolerability profile which may prove to be particularly advantageous is that it is associated with a similar incidence of cough to placebo in patients with a history of ACE inhibitor-related cough. Additionally, clinically relevant adverse metabolic effects or laboratory abnormalities have not been documented during losartan potassium therapy and renal function is preserved in patients with or without renal insufficiency. The adverse effect profile of the losartan potassium-hydrochlorothiazide combination resembles those for losartan potassium monotherapy and placebo. Long term tolerability data are limited (<2 years) but support the very good tolerability profile in shorter studies. Elements of the drug's profile yet to be assessed or reported fully in the literature include long term efficacy; potential to favourably influence cardiovascular and renovascular systems (and ultimately mortality) in patients with hypertension and, lastly, cost effectiveness and influence on quality of life. In summary, losartan potassium is the first AT(1)+ receptor antagonist to become available for the management of hypertension and, as such, it is an important new antihypertensive agent. Pending long term data as outlined above, it is likely to find initial use in patients with mild to severe hypertension who are unresponsive to, or intolerant of their current therapy. However, with its novel mechanism of action, good efficacy and favourable tolerability profile, losartan potassium is well placed to claim a prominent position in the management of patients with essential hypertension in the future.

Fluvastatin: a review of its pharmacology and use in the management of hypercholesterolaemia

Fluvastatin, a member of the group of drugs known as HMG-CoA reductase inhibitors, is used in the treatment of patients with hypercholesterolaemia. In clinical trials in patients with primary hypercholesterolaemia, fluvastatin 20 or 40 mg/day achieved marked reductions from baseline in serum levels of low density lipoprotein (LDL)-cholesterol (19 to 31%) and total cholesterol (15 to 21%), along with modest declines in serum triglyceride levels (1 to 12%) and small increases in high density lipoprotein (HDL)-cholesterol levels (2 to 10%). These beneficial effects on the serum lipid profile were similar to those demonstrated with other HMG-CoA reductase inhibitors, although direct comparative trials are limited. Concomitant administration of fluvastatin plus another lipid-lowering agent, such as a bile acid sequestrant, a fibrate or nicotinic acid, usually reduced serum levels of total cholesterol and LDL-cholesterol by at least a further 5 to 10% from baseline compared with fluvastatin monotherapy. Fluvastatin has a similar tolerability profile to that of other HMG-CoA reductase inhibitors. Gastrointestinal disturbances, which are usually mild and transient, were the most frequently reported adverse events with fluvastatin in clinical trials. Persistent elevation of serum transaminase levels occurred in approximately 1% of fluvastatin recipients, which is similar to the rate for other HMG-CoA reductase inhibitors. Unlike other HMG-CoA reductase inhibitors, which have been infrequently associated with myopathy and rarely with rhabdomyolysis, these events have not been associated with fluvastatin to date, although fluvastatin has not been used as extensively as agents such as lovastatin. HMG-CoA reductase inhibitors other than fluvastatin, when given in combination with drugs such as fibrates, nicotinic acid, cyclosporin or erythromycin, can increase the risk of these potentially serious adverse events. Thus far, myopathy or rhabdomyolysis have not been reported among patients receiving fluvastatin concomitantly with any of these drugs. Therefore, fluvastatin can be given with caution in combination with fibrates, nicotinic acid, cyclosporin or erythromycin. In conclusion, fluvastatin has similar efficacy and tolerability profiles to other HMG-CoA reductase inhibitors, which are among the most effective agents available for treating patients with hypercholesterolaemia. Pharmacoeconomic studies performed to date suggest an advantage for fluvastatin over other HMG-CoA reductase inhibitors, predominantly because of its relatively low acquisition costs (at least in those countries in which the evaluations were conducted). Thus, fluvastatin is effective and well tolerated in patients with hypercholesterolaemia and appears to have an economic advantage over other HMG-CoA reductase inhibitors, primarily as a result of its relatively low acquisition costs.

Fallibility of faecal consistency as a criterion of success in the evaluation of oral fluid therapy for calf diarrhoea

It is often said that the success of oral rehydration in humans depends on the adequacy of the improvement in the composition and volume of extracellular fluid, not reduction of faecal output. Indeed, the latter may increase initially. Such increases do not prevent the treatment from being effective but they may, falsely, undermine its acceptability to patients or those caring for them. This paper provides data to show that standard oral rehydration solutions used to treat experimentally induced calf diarrhoea procure identical improvements in plasma volume during the first 48 h, whether faeces improve or not, and those calves whose faecal consistency improved actually showed greater deterioration of extracellular fluid volume. While it is important for this to be appreciated by clinicians and explained to owners, it is absolutely imperative that those responsible for the approval of new therapeutic products for registration understand and accept that faecal consistency offers no reliable insight into the effectiveness of oral rehydration therapy for calf diarrhoea. It was, however, interesting that there was some relationship with correction of acidosis--perhaps because some of the contributing factors arise from colonic dysfunction.

Tiaprofenic acid. A reappraisal of its pharmacological properties and use in the management of rheumatic diseases

Tiaprofenic acid is a nonsteroidal anti-inflammatory drug (NSAID) used in the treatment of patients with rheumatic diseases and other clinical conditions of pain and inflammation. Like other propionic acid derivatives, tiaprofenic acid is effective and generally well tolerated. Comparative studies in patients with rheumatoid arthritis or osteoarthritis receiving tiaprofenic acid 600 mg/day demonstrated improvements in pain intensity, duration of morning stiffness, articular index and other clinical variables which were similar to those achieved with alternative NSAIDs. Tolerability was also comparable between tiaprofenic acid and other NSAIDs in most trials; the most frequently reported adverse events involved the gastrointestinal tract. Some studies showed a trend towards fewer patient withdrawals because of adverse events with tiaprofenic acid than with NSAIDs such as indomethacin. Current evidence suggests that nonbacterial cystitis is more likely to be associated with tiaprofenic acid than with other NSAIDs. This reaction should, however, be considered in the perspective of its infrequent occurrence and its typical reversibility, and against the wider background of the established usage of tiaprofenic acid and its overall tolerability profile which is similar to that of other NSAIDs. Unlike indomethacin, tiaprofenic acid was not associated with increased cartilage degradation in a recently completed large clinical trial known as LINK, which evaluated the effects of long term administration in patients with osteoarthritis of the knee. Thus, tiaprofenic acid is an established option among the range of NSAIDs used in the treatment of patients with rheumatic diseases, with efficacy and tolerability profiles that are relatively well characterised. The availability of a sustained release dosage form of tiaprofenic acid, which has a similar efficacy and tolerability profile to the standard formulation, provides a convenient once daily dosage regimen.

Amlodipine. A reappraisal of its pharmacological properties and therapeutic use in cardiovascular disease

Amlodipine belongs to the dihydropyridine class of calcium channel blockers. Both short and long term studies indicate that amlodipine effectively lowers mild to moderately elevated blood pressure and relieves symptoms of angina pectoris. In comparative studies, its antihypertensive efficacy is similar to that of other established agents such as beta-blockers, diuretics, ACE inhibitors and other calcium channel blockers (including the dihydropyridines); limited comparative data are, however, available in patients with angina pectoris. Amlodipine may offer potential in patients with congestive heart failure. Vasodilator adverse events such as oedema, headaches, and flushing are commonly observed with amlodipine. The drug does not appear to cause postural hypotension, reflex tachycardia or cardiac conduction disturbances. Comparative studies suggest that amlodipine is at least as well tolerated as other standard agents. Thus, amlodipine provides an attractive therapeutic option for the treatment of hypertension, and offers potential for patients with angina pectoris. Its beneficial effects in patients with congestive heart failure require confirmation in future studies.

Alteplase. A reappraisal of its pharmacology and therapeutic use in vascular disorders other than acute myocardial infarction

Alteplase is the product of recombinant DNA technology and is chemically identical to endogenous tissue-type plasminogen activator: Plasminogen is converted to plasmin by alteplase, and fibrinolysis of blood thrombi is subsequently stimulated. Alteplase is now firmly established as a treatment of choice in the management of acute myocardial infarction. The efficacy of intravenous alteplase in the treatment of pulmonary thromboembolism has also been established and appears to be similar to that of streptokinase and urokinase in this indication and in arterial thrombotic occlusion. However, its use in this latter indication and in other vascular disorders has not been as extensively documented. Although trials demonstrating the efficacy of intravenous alteplase in patients with deep vein thrombosis and intra-arterial alteplase in patients with arterial thrombotic occlusion exist, reliable data on the efficacy of the fibrinolytic in ischaemic stroke and intracranial haemorrhage are scarce. Little clinical benefit is apparent in patients with unstable angina, although careful use may be warranted in those with definite pretreatment coronary thrombi. Of concern, there is a suggestion that general use of alteplase in patients with unstable angina may be associated with increased incidence of myocardial infarction. The incidence of major haemorrhage associated with alteplase therapy increases with increasing dose and appears to be similar to that seen with other fibrinolytic agents. Thus, further well-designed studies of the use of alteplase in ischaemic stroke and cerebral haemorrhage are required. However, a small subset of patients with unstable angina and definite pretreatment coronary thrombi may benefit from alteplase therapy. Further, preliminary data suggest efficacy in the therapy of deep vein thrombosis and arterial thrombotic occlusion, and alteplase has a proven place in the fibrinolytic treatment of pulmonary thromboembolism.

Epoetin alfa. A review of its clinical efficacy in the management of anaemia associated with renal failure and chronic disease and its use in surgical patients

Epoetin alfa is a recombinant form of erythropoietin, a glycoprotein hormone which stimulates red blood cell production by stimulating the activity of erythroid progenitor cells. This review discusses the use of the drug in the management of anaemia in diseases often associated with advancing age [renal failure, cancer, rheumatoid arthritis (RA) and other chronic diseases, and the myelodysplastic syndromes (MDS)] and in surgical patients. Intravenous and subcutaneous therapy with epoetin alfa raises haematocrit and haemoglobin levels, and reduces transfusion requirements, in anaemic patients with end-stage renal failure undergoing haemodialysis or peritoneal dialysis. The drug is also effective in the correction of anaemia in patients with chronic renal failure not yet requiring dialysis and does not appear to affect renal haemodynamics adversely or to precipitate the onset of end-stage renal failure. Response rates of 32 to 82% with epoetin alfa therapy have been reported in patients with anaemia associated with cancer or cytotoxic chemotherapy. Limited data in patients with anaemia associated with RA show correction of anaemia after epoetin alfa treatment. Response rates to the drug of 0 to 56% have been noted in patients with MDS. Epoetin alfa also reduces anaemia, increases the capacity for autologous blood donation and reduces the need for allogeneic blood transfusion in patients scheduled to undergo surgery. Hypertension occurs in 30 to 35% of patients with end-stage renal failure who receive epoetin alfa, but this can be managed successfully with correction of fluid status and antihypertensive medication where necessary, and is minimised by avoiding rapid increases in haematocrit. Although vascular access thrombosis has not been conclusively linked to therapy with the drug, increased heparinisation may be required when it is administered to patients on haemodialysis. Epoetin alfa does not appear to exert any direct cerebrovascular adverse effects. Thus, epoetin alfa is a well established and effective therapy for the management of anaemia associated with renal failure. It also improves haematocrit and quality of life in patients with anaemia associated with cancer or chemotherapy. Epoetin alfa increases the capacity for blood donation and reduces the decrease in haematocrit seen in patients donating autologous blood prior to surgery. It also reduces, but may not eliminate, the need for allogeneic blood transfusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Famciclovir. A review of its pharmacological properties and therapeutic efficacy in herpesvirus infections

Famciclovir, a synthetic acyclic guanine derivative, is a prodrug which, after oral administration, is rapidly metabolised to the highly bioavailable antiviral compound penciclovir. Penciclovir is active in vitro against the herpesviruses herpes simplex virus (HSV)-1, HSV-2 and varicella zoster virus (VZV). Famciclovir is an effective treatment of immunocompetent patients with acute herpes zoster (shingles) caused by VZV. Comparative studies have demonstrated that famciclovir has therapeutic efficacy similar to that of oral aciclovir (acyclovir) in attenuating the acute signs and symptoms of infection (including pain during the acute phase of infection). In a placebo-controlled study, famciclovir significantly reduced the duration of postherpetic neuralgia; this effect was more pronounced (almost a 3-fold reduction) in patients aged > or = 50 years. In immunocompetent patients with recurrent genital herpes infection, suppressive treatment with oral famciclovir effectively prolonged the time to recurrence of symptomatic episodes of infection compared with placebo. In addition, famciclovir significantly reduced the duration of viral shedding, accelerated healing of genital herpes lesions and reduced the duration of symptoms. Famciclovir is reported to be the first antiviral agent to significantly reduce symptoms associated with multiple genital herpes lesions. Famciclovir is a well-tolerated drug with a tolerability profile similar to that of placebo and aciclovir. Thus, famciclovir is now established as an effective treatment of immunocompetent patients with herpes zoster or genital herpes infection, particularly as famciclovir is administered in a convenient dosage regimen that may improve compliance compared with aciclovir.

Alteplase. A reappraisal of its pharmacological properties and therapeutic use in acute myocardial infarction

Alteplase (recombinant tissue-type plasminogen activator) stimulates the fibrinolysis of blood clots by converting plasminogen to plasmin. The efficacy of intravenous alteplase in the early treatment of patients with acute myocardial infarction has been unequivocally proven, and recent results from the GUSTO trial indicate a significant advantage in 30-day survival for alteplase in an accelerated dosage regimen (< or = 100mg infused over 90 minutes rather than 3 hours) over streptokinase. The advantage of the accelerated alteplase dosage regimen seems to be maintained for at least 1 year. The role of heparin as adjunctive therapy to thrombolysis remains to be fully defined but heparin administration appears to be more important in conjunction with alteplase than with streptokinase. Ideally, patients should receive alteplase as soon as possible after the onset of symptoms of acute myocardial infarction and, while therapy is most beneficial when administered early, survival is improved when the drug is administered up to 12 hours after symptom onset. The accelerated regimen of alteplase used in the GUSTO trial demonstrated a survival advantage in patients < or = 75 as well as those > 75 years of age which was at least as great as that seen with streptokinase. Similarly, alteplase reduces mortality in patients with both anterior and inferior infarctions; however, those with anterior wall infarctions show an improved outcome over those with inferior infarcts. On the basis of pharmacoeconomic analysis of GUSTO data, the accelerated alteplase regimen cost an estimated additional $US32,678 per year of life saved compared with a conventional streptokinase regimen. Cumulative 1-year costs were greater in patients who received the accelerated alteplase regimen but survival was significantly greater than in patients who received streptokinase. No difference in quality of life was evident in patients who received either treatment. The incidence of major haemorrhage associated with alteplase therapy appears to be similar to that seen with other fibrinolytic agents, increasing with increasing dose; however, the risk of stroke, particularly haemorrhagic stroke, is higher with alteplase than with streptokinase. Thus, alteplase has become firmly established as a first-line option in the management of acute myocardial infarction. On the basis of accumulated evidence, the greatest risk reduction with alteplase therapy may be in certain high risk groups, such as those with anterior infarcts, selected elderly patients and those who present late after symptom onset.

Meropenem. A review of its antibacterial activity, pharmacokinetic properties and clinical efficacy

The parenteral carbapenem meropenem is relatively stable to inactivation by human renal dehydropeptidase (DHP-1) and does not require concomitant administration of a DHP-1 inhibitor such as cilastatin. It has a broad spectrum of antibacterial activity in vitro, the majority of Gram-negative, Gram-positive and anaerobic pathogens being highly susceptible to the drug. Meropenem has shown clinical and bacteriological efficacy in the treatment of a wide range of serious infections in adults and children which is at least comparable with that of currently available treatment options. Its clinical and bacteriological efficacy is similar to that of imipenem/cilastatin, clindamycin plus tobramycin and cefotaxime plus metronidazole in the treatment of intraabdominal infections; cefotaxime or ceftriaxone in the treatment of meningitis; imipenem/cilastatin, and ceftazidime with or without an aminoglycoside, in lower respiratory tract infections; and imipenem/cilastatin or ceftazidime in the treatment of urinary tract infections. Satisfactory clinical and bacteriological response rates have also been achieved in patients with skin and skin structure infections, obstetric and gynaecological infections or septicaemia, and in immunocompromised patients with febrile episodes. Preliminary findings also indicate efficacy in the treatment of respiratory tract infections in patients with cystic fibrosis. The tolerability profile of meropenem is generally similar to that of comparator agents, although it is associated with a lower incidence of adverse gastrointestinal effects (nausea and vomiting) than imipenem/cilastatin. Importantly, the incidence of seizures in patients with meningitis is not increased following administration of meropenem. Thus, meropenem is an effective broad spectrum antibacterial drug for the treatment of a wide range of infections including polymicrobial infections in both adults and children, with comparable efficacy to imipenem/cilastatin and various other treatment regimens. Meropenem is likely to be of greatest value as empiric monotherapy in the treatment of serious infections for those caused by multiply-resistant pathogens. Further clinical experience is necessary, however, to ultimately define its place in therapy.

Tretinoin. A review of its pharmacological properties and clinical efficacy in the topical treatment of photodamaged skin

Tretinoin (all-trans-retinoic acid) is a retinol (vitamin A) derivative which has been evaluated as a topical treatment for the symptoms of photodamaged skin. In several well-controlled clinical trials, the proportion of patients showing improvement was significantly higher with 0.01 or 0.05% tretinoin cream than with placebo for criteria such as global assessment, fine and coarse wrinkling, pigmentation and roughness. Improvements in the overall severity of photodamage were also significantly greater with tretinoin than with placebo. The extent of clinical improvement with tretinoin has generally been moderate, but cytological and histological studies have shown that extensive changes in the epidermis and dermis occur during treatment. However, the permanency and clinical significance of these changes has yet to be fully evaluated. Topical tretinoin has also demonstrated potential for the treatment and eradication of premalignant skin growths such as actinic keratoses, and may be useful as combination therapy with fluorouracil in this indication. Dermatitis (the retinoid skin reaction) is the most common adverse event experienced by patients receiving topical tretinoin; this condition may persist for up to 3 months, but is usually mild or moderate in nature. Thus, topical tretinoin has been shown to be an effective form of treatment for the characteristic signs of photodamaged skin. Its ability to produce significant, albeit moderate, clinical improvements in symptoms such as fine wrinkling, roughness and pigmentation, together with its relatively mild or moderate adverse event profile, suggests that it is likely to be of considerable value in this indication. The treatment and eradication of potentially malignant growths such as actinic keratoses may also prove to be an important application for topical tretinoin.

Trimetrexate. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic potential in the treatment of Pneumocystis carinii pneumonia

Trimetrexate is a folinic acid analogue structurally related to methotrexate, whose primary mechanism of action is believed to be inhibition of dihydrofolate reductase. This reduces the production of DNA and RNA precursors and leads to cell death. Trimetrexate is lipophilic and can passively diffuse across cell membranes including those of Pneumocystis carinii and its mammalian host. To minimise toxicity, trimetrexate must be coadministered with calcium folinate (leucovorin calcium), a reduced folate coenzyme, which is transported into, and protects, mammalian host cells but not P. carinii cells. In noncomparative trials trimetrexate was effective in the treatment of P. carinii pneumonia (PCP) in patients with AIDS who were intolerant of or refractory to cotrimoxazole (trimethoprim/sulfamethoxazole) and pentamidine treatment. In these patients, 2- to 4-week survival rates of 48 to 69% were reported. In a comparative trial in the initial therapy of PCP, trimetrexate was less effective than cotrimoxazole in moderate to severe disease as evidenced by a significantly higher failure rate. Trimetrexate was better tolerated than cotrimoxazole when used in this setting, however. Significantly fewer patients receiving trimetrexate plus calcium folinate discontinued treatment because of adverse events than did patients receiving cotrimoxazole. The most common adverse effect associated with trimetrexate is myelosuppression (neutropenia and thrombocytopenia); this is mitigated by coadministration of calcium folinate and is generally reversible upon dosage reduction or discontinuation. Other adverse effects include increases in serum aminotransferase levels, anaemia, fever, rash/pruritus, and increased alkaline phosphatase or serum creatinine levels. Further research into the use of trimetrexate, including its efficacy as prophylaxis, in combination with other agents and as an oral formulation, is needed to clearly define its role in the treatment of PCP and to identify patients most likely to benefit. Currently, trimetrexate should be considered as an alternative treatment option in immunocompromised patients with moderate to severe PCP who have not responded to or are intolerant of first-line therapy.

Doxazosin. An update of its clinical pharmacology and therapeutic applications in hypertension and benign prostatic hyperplasia

Doxazosin is a long-acting alpha 1-adrenoceptor antagonist structurally related to prazosin and terazosin. Its antihypertensive effect is produced by a reduction in the smooth muscle tone of peripheral vascular beds resulting in a decrease in total peripheral resistance without significant effect on cardiac output or heart rate. In benign prostatic hyperplasia, doxazosin's effect of relieving bladder outflow obstruction is produced through a reduction in prostatic tone mediated via alpha 1-adrenoceptor blockade. In most comparative trials doxazosin has proven to be equally effective as the comparator drug in the treatment of mild to moderate hypertension. It has been used in a variety of patient populations including the elderly, Blacks, smokers, and patients with concomitant disease states such as renal dysfunction, hypercholesterolaemia, non-insulin dependent diabetes mellitus (NIDDM) and respiratory disease. Doxazosin has also been used successfully in combination with beta-adrenoceptor antagonists, diuretics, calcium channel antagonists, and angiotensin-converting enzyme inhibitors in patients with hypertension that is uncontrolled with monotherapy. Doxazosin has a beneficial effect on some of the risk factors associated with coronary heart disease including elevated serum lipid levels, impaired glucose metabolism, insulin resistance and left ventricular hypertrophy. Modest decreases in total cholesterol, low density lipoprotein cholesterol and triglycerides are seen with doxazosin therapy while small increases in high density lipoprotein cholesterol and the high density lipoprotein cholesterol/total cholesterol ratio are consistently reported. Some studies have reported an improvement in glucose tolerance although this effect has been more consistently seen in nondiabetic patients than in patients with NIDDM. Additionally, doxazosin produces a similar reduction in left ventricular hypertrophy to other antihypertensive agents. Modelling-based calculations suggest that doxazosin significantly reduces the risk of developing coronary heart disease in patients with mild to moderate hypertension, although this remains to be confirmed in long term prospective studies. Doxazosin appears to be a promising agent in the treatment of urinary symptoms associated with benign prostatic hyperplasia. Similar to other alpha 1-adrenoceptor antagonists, doxazosin treatment produces increases in peak and mean urinary flow rates and improves other objective and symptomatic measures.(ABSTRACT TRUNCATED AT 400 WORDS)

Foscarnet. A reappraisal of its antiviral activity, pharmacokinetic properties and therapeutic use in immunocompromised patients with viral infections

The DNA polymerase of human herpes viruses, including cytomegalovirus (CMV), and the reverse transcriptase of human immunodeficiency virus (HIV) are selectively inhibited in vitro by the pyrophosphate analogue foscarnet. Inhibition is reversible on withdrawal of foscarnet and additive or synergistic effects have been demonstrated in vitro with other antiviral drugs, including ganciclovir and zidovudine. Foscarnet appears to have negligible effects on host enzymes and cells. Complete or partial clinical resolution of ocular symptoms is obtained in more than 89% of patients with acquired immunodeficiency syndrome (AIDS) and CMV retinitis during foscarnet induction therapy, but relapse occurs soon after ceasing treatment. Maintenance treatment given daily can extend the period of remission considerably. Foscarnet and ganciclovir monotherapy had similar efficacy in the treatment of CMV retinitis in patients with AIDS in several studies, and have been used concomitantly in immunocompromised patients with recalcitrant CMV infections. In 1 trial, patients receiving foscarnet survived for significantly longer than those receiving ganciclovir. Foscarnet has been used successfully in the treatment of limited numbers of immunocompromised patients with CMV-associated gastrointestinal (improvement in over 67% of patients) and other infections. Aciclovir-resistant herpes simplex infections in immunocompromised patients have also been treated successfully with foscarnet. Almost 90% of a foscarnet dose is excreted in the urine. Reversible nephrotoxicity is common during foscarnet therapy, but may be reduced by dosage adjustment and adequate hydration. Anaemia, nausea and vomiting, disturbances in electrolyte levels and genital ulceration have also been associated with administration of the drug. The different tolerability profiles of foscarnet and zidovudine facilitate the use of these agents in combination in patients with AIDS and CMV infection; whereas ganciclovir, like zidovudine, is associated with dose-limiting haematological toxicity. The apparent survival benefits seen in these patients when receiving foscarnet and zidovudine (possibly linked to synergy between zidovudine and foscarnet and/or the inherent anti-HIV activity of foscarnet), appear to offer potentially important advantages for foscarnet over ganciclovir in the treatment of selected patients with AIDS and CMV infections.

Tacrine. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in Alzheimer's disease

Tacrine is a centrally acting cholinesterase inhibitor with additional pharmacological activity on monoamine levels and ion channels. It has been postulated that some or all of these additional properties may also be relevant to the mode of action of the drug. There are wide interindividual variations in pharmacological and clinical response to tacrine, possibly related to interindividual variation in bioavailability. Tacrine appears to improve cognitive function and behavioural deficits in a proportion of patients with Alzheimer's disease, at dosages of 80 to 160 mg/day. In the best designed trials, 30 to 51% of evaluable patients showed an improvement of at least 4 points on the cognitive subscale of the Alzheimer's Disease Assessment Scale, versus 16 to 25% of placebo recipients. A similar proportion of tacrine recipients were judged to have improved when global assessment scales were used. There was a significant dose-response relationship up to 160 mg/day. However, large numbers of patients were withdrawn during the trials, many because of tacrine-associated increases in transaminase levels. Elevated liver enzyme levels occurred in about 50% of tacrine recipients (reaching clinical significance in about 25%). Cholinergic symptoms also occurred more often in tacrine recipients than in those receiving placebo. A gradual increase in tacrine dosage, at 6-week intervals, is recommended when initiating therapy, and weekly serum transaminase monitoring is required for 6 weeks after each dosage increase. Despite the limitations implied by the low proportion of responders and high incidence of hepatic adverse effects associated with therapy, tacrine appears to make a measurable difference in both cognitive and behavioural function in a proportion of patients with Alzheimer's disease--a welcome advance in an area previously devoid of acceptable treatment options.

Aciclovir. A reappraisal of its antiviral activity, pharmacokinetic properties and therapeutic efficacy

Aciclovir (acyclovir) is a nucleoside analogue with antiviral activity in vitro against the herpes simplex viruses (HSV), varicella zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV) and human herpesvirus 6 (HHV-6). Topical, oral or intravenous aciclovir is well established in the treatment of ophthalmic, mucocutaneous and other HSV infections, with intravenous aciclovir the accepted treatment of choice in herpes simplex encephalitis. The efficacy of aciclovir is increased with early (preferably during the prodromal period) initiation of treatment but, despite significant clinical benefit, viral latency is not eradicated, and pretreatment frequencies of recurrence usually continue after episodic acute treatment is completed. Intravenous administration has also shown benefit in the treatment of severe complications of HSV infection in pregnancy, and neonatal HSV infections. Recurrence of HSV has been completely prevented or significantly reduced during suppressive therapy with oral aciclovir in immunocompetent patients. Use of oral aciclovir is effective but controversial in the treatment of otherwise healthy individuals with varicella (chickenpox), and in some countries it has been recommended for use only in cases which may be potentially severe. The development of rash and pain associated with herpes zoster (shingles) is attenuated with oral or intravenous aciclovir therapy, ocular involvement is prevented, and post-herpetic neuralgia appears to be decreased. Similarly, in a few patients with zoster ophthalmicus, oral aciclovir has reduced the frequency and severity of long term ocular complications and post-herpetic neuralgia, and herpes zoster oticus is improved with intravenous aciclovir. Oral aciclovir has prevented recurrence of HSV genital or orofacial infections during suppressive therapy in > 70% of immunocompetent patients in most clinical trials. Suppression of latent HSV, VZV and CMV infections has been achieved in many immunocompromised patients receiving the oral or intravenous formulations. Aciclovir also appears to offer partial protection from invasive CMV disease in CMV-seropositive bone marrow transplant recipients. The few comparative trials published have shown aciclovir to be at least as effective as other investigated antivirals in the treatment of HSV infections in immunocompetent patients, and more effective than inosine pranobex in the prophylaxis of genital herpes. Similarly, in isolated clinical trials, oral aciclovir appears as effective as topical idoxuridine and oral brivudine in some parameters in immunocompetent patients with VZV infections, and the intravenous formulation appears at least as effective as oral brivudine and intravenous vidarabine in treating these infections in immunocompromised patients.(ABSTRACT TRUNCATED AT 400 WORDS)

The comparative effectiveness of three commercial oral solutions in correcting fluid, electrolyte and acid-base disturbances caused by calf diarrhoea

Three commercial oral rehydration solutions (Effydral ('E'), Lectade ('L') and Lectade Plus ('LP')) were evaluated in young calves with diarrhoea following the administration of E. coli. Twenty calves with non-fatal diarrhoea were included in each group and examined for electrolytes, acidosis (pH, PCO2 and TCO2), PCV and selected biochemical parameters. Faecal consistency and clinical state were also assessed. Eight calves were examined for plasma and ECF volume. Calves were treated with the appropriate ORS only for 2 days and with ORS plus milk substitute for a further 2 days. No other treatments were given. Solutions E, L and LP were chosen specifically to test the hypothesis that their ability to repair extracellular volume would depend on their sodium content (E > L > LP) and their ability to correct metabolic acidosis would reflect their content of bicarbonate precursor (E > LP > L). Both hypotheses were confirmed as was the fact that the higher sodium content of E helps it to repair ECF volume without predisposing to hypernatraemia. The importance of correcting hyponatraemia as well as ECF volume is emphasized. Direct measurement of such changes proved much more sensitive than traditional clinical parameters such as weight loss, skin elasticity, etc. Although this study was not designed to examine mortality, it is noted that nine treated calves died, none in the E-treated group.

Plasma and extracellular volume in calves: comparison between isotopic and 'cold' techniques

While isotopic techniques have largely superseded traditional markers for the determination of the volume of fluid compartments in vivo, they are not always convenient, especially with diarrhoeic animals. A direct comparison was therefore made in week-old calves between Evans blue and radio-iodinated serum albumin as measures of plasma volume and thiocyanate or 24sodium as measures of extracellular fluid space. The correlation coefficients were excellent (1.00, 0.96; P < 0.001) and the calves had plasma and extracellular fluid volumes of 72 +/- 2 and 438 +/- 2 ml kg-1, respectively. The latter value is, though high, typical of young animals and comparable with other data in calves.

The effects of salbutamol on blood pressure and heart rate in Large White and Pietrain-cross breeds of pig

The effects of the beta 2-agonist salbutamol, on pig heart rate and blood pressure were evaluated at the expected commercially used concentration of 3 ppm in final feed, and at three times this level. Salbutamol was administered to pigs previously fed on control diet ('naive'), and in a second study to pigs fed 3 ppm salbutamol for 19 days ('acclimatized'). Heart rate and blood pressure were measured in conscious 30 kg pigs before (pre-ingestive), during (ingestive) and after ingestion (absorptive) of feed containing 3 or 9 ppm salbutamol. To assess any interaction with 'stress genotype' pigs, measurements were performed in Large White and Pietrain-cross breeds. The mean preingestive heart rates for the Large White and Pietrain-cross pigs were 127 and 109 beats/min, respectively. The corresponding figures for mean arterial blood pressure were 121 and 122 mmHg. The act of ingesting control feed caused heart rate to rise by 36-39% and blood pressure to increase by 17-27%. During the absorptive phase for 'naive' pigs fed 3 ppm salbutamol in the diet, blood pressure fell 5-11% and heart rate increased 20-24%, reflecting a classical baroreceptor mediated response. At 9 ppm the fall in blood pressure of 5-11% was similar to that at 3 ppm, while the rise in heart rate was larger at 31-38%. The magnitude of the changes at both 3 and 9 ppm was less than that evoked by the act of ingestion, with the exception of the heart rate response in Large Whites at 9 ppm, which was similar. The responses of the two breeds were comparable, indicating that salbutamol is unlikely to exacerbate the cardiovascular responses seen in potentially stress-susceptible pigs. The acute changes elicited by 3 ppm salbutamol during the absorptive phase in 'naive' pigs were abolished or substantially less in acclimatized pigs, implying a tachyphylaxis to the agonist's actions. This was confirmed by 9 ppm of salbutamol increasing heart rate of 'acclimatized' Large Whites to the same degree as 3 ppm in 'naive' counterparts. The desensitization in Pietrain-cross pigs was even more marked with no increase in heart rate produced by 9 ppm salbutamol following acclimatization. These data, combined with the rapid tachyphylaxis of response, indicate that salbutamol at the intended commercial inclusion of 3 ppm will not compromise the cardiovascular stability of the growing pig at rest.

Carboplatin. A preliminary review of its pharmacodynamic and pharmacokinetic properties and therapeutic efficacy in the treatment of cancer

Carboplatin is a 'second-generation' platinum compound advocated for use in the treatment of patients with ovarian cancer and it has also shown promise in small cell lung cancer, squamous cell carcinomas of the head and neck, and seminomas. Overall, it would appear to have a similar qualitative spectrum of activity to cisplatin. There have been few comparative trials with carboplatin, either alone or in combination with other chemotherapeutic agents, but the limited data suggest comparable efficacy with cisplatin in ovarian cancer. Importantly, the toxicity profile of carboplatin is markedly different from that of cisplatin, with nephrotoxicity, neurotoxicity and ototoxicity occurring only infrequently with carboplatin. As with cisplatin, nausea and vomiting occur in many patients after carboplatin administration, but symptoms are usually delayed for several hours and are mild to moderate in severity - dose-limiting nausea and vomiting are infrequent with carboplatin. The dose-limiting toxicity of carboplatin is myelosuppression, with severe thrombocytopenia and less often leucopenia, which may be more severe in older patients or in those with renal impairment or those who have had previous chemotherapy. Thus, preliminary data suggest that carboplatin is a therapeutically equivalent alternative to cisplatin, but with a differing toxicity profile that should offer advantages over cisplatin in many patients.

Colloidal bismuth subcitrate. A review of its pharmacodynamic and pharmacokinetic properties, and its therapeutic use in peptic ulcer disease

Colloidal bismuth subcitrate (CBS) possesses at least equal efficacy with histamine H2-receptor antagonist drugs in the treatment of peptic ulcer disease. However, CBS has the advantage of slower ulcer relapse rates than those seen after initial healing with the H2-antagonists. It has been postulated that this effect may be partly due to the antibacterial properties of CBS against Campylobacter pylori, a bacterium found in the gastric mucosa and gastric metaplasia within the duodenum of most patients with peptic ulcer and closely associated with gastritis. However, the role of C. pylori in the aetiology of peptic disease is far from clear. The mechanism by which CBS heals ulcers has not been fully elucidated, but several actions may be involved. CBS and mucus form a glycoprotein-bismuth complex in vitro. This provides a diffusion barrier to HCl and may, therefore, provide a protective coating in the ulcer crater which allows healing of the lesion to occur. Prostaglandin E2 production is also stimulated by CBS with subsequent secretion of alkali into the mucus layer. In addition, CBS has a direct inhibitory effect on C. pylori. Administration of CBS results in low levels of bismuth absorption. Most of the ingested bismuth is excreted as bismuth sulphide, causing blackening of the faeces, and the small amount absorbed is excreted in the urine. Bismuth intoxication (encephalopathy) has been reported with prolonged administration of bismuth salts, and there has been 1 report of similar intoxication in a patient receiving unusually high doses of CBS for a prolonged period. However, no such intoxication has been reported with CBS used at its recommended dosage in the acute treatment of peptic ulcer disease, and no other serious adverse effects have been associated with CBS. Tissue accumulation during prolonged therapy seems likely, and the safety of CBS during long term maintenance therapy has not been established. The lack of effect on gastric acid secretion is seen as an added advantage for CBS, since prolonged drug-induced hypochlorhydria has been postulated to have potentially detrimental effects. Thus, while the role of C. pylori in peptic ulceration requires further clarification, CBS would appear to have an important place in the treatment of peptic ulcer disease with the advantage of relatively slow relapse rates after initial healing and treatment discontinuation.