Pirenzepine. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic efficacy in peptic ulcer disease and other allied diseases.

Pirenzepine is a 'selective' antimuscarinic agent which, unlike classic anticholinergic agents, inhibits gastric acid secretion at lower doses than are required to affect gastrointestinal motility, salivary, central nervous system, cardiovascular, ocular and urinary functions. On a weight basis, pirenzepine has one-tenth to one-eighth the potency of atropine in inhibiting stimulated gastric acid secretion in humans. Extensive controlled trials utilising endoscopy in outpatients with duodenal ulcers indicate that patient response to pirenzepine is dose related. Doses of 100 to 150 mg/day are superior to placebo in promoting duodenal ulcer healing and in diminishing day and night pain and supplementary antacid consumption. At such doses, the efficacy of pirenzepine appears to be superior to that of gefarnate 300 mg/day and generally not significantly different from that of cimetidine 1 g/day in treating duodenal ulcers. A beneficial effect of pirenzepine in the prevention of duodenal ulcer recurrence was apparent in preliminary studies in small numbers of patients, but its efficacy in this regard needs further confirmation and the optimum dosage determined. Less extensive data on the treatment of benign gastric ulcers suggest that pirenzepine 100 to 150 mg/day is superior to placebo and gefarnate 300 mg/day and does not differ significantly from cimetidine 1 g/day promoting gastric ulcer healing. Pirenzepine is well tolerated by most patients, with a low incidence of typical antimuscarinic effects on the gastrointestinal tract, genitourinary system or heart being reported in clinical studies. However, dry mouth and blurred vision are the more common side effects with clinically effective doses. Thus, pirenzepine appears to have relatively selective antimuscarinic activity, although controlled studies comparing pirenzepine and conventional antimuscarinics in patients with peptic ulcer disease have not been reported.

Acyclovir. A review of its pharmacodynamic properties and therapeutic efficacy.

Acyclovir (aciclovir) is a nucleoside analogue antiviral drug related to cytarabine, idoxuridine, trifluridine and vidarabine. In common with these earlier antivirals, acyclovir is active against some members of the herpesvirus group of DNA viruses. The efficacy of topical acyclovir has been convincingly demonstrated in ocular herpetic keratitis, and in initial and primary initial genital herpes infection, but little or no clinical benefit was seen when non-primary initial genital infections were assessed separately. Acyclovir ointment demonstrated little benefit in recurrent genital herpes but topical acyclovir cream decreased the course of the infection by 1 to 2 days. Orally and intravenously administered acyclovir were beneficial in initial genital herpes infections, and oral therapy shortened the duration of recurrent infections by 1 to 2 days but did not ameliorate pain. In non-immunocompromised patients with recurrent herpes simplex labialis, generally little clinical benefit was seen with the use of topical acyclovir ointment even when therapy was initiated during the prodromal phase, while topical acyclovir cream effected small but significant improvements in the clinical but not the symptomological course of the disease. However, in immunocompromised patients, both intravenous and topical acyclovir shortened the clinical course of herpes simplex virus infections occurring mainly on the lips, oral mucosa and face, and prophylaxis with either oral or intravenous acyclovir suppressed the appearance of recurrent lesions from latent virus for the period of drug administration, but acyclovir did not eradicate latent herpesviruses. In non-immunocompromised patients, intravenous acyclovir was shown to decrease the acute pain of zoster, especially in the elderly, but postherpetic neuralgia was not ameliorated. When immunocompromised patients were studied, intravenous acyclovir inhibited the progression of zoster infections and shortened the healing time and duration of viral shedding in patients with cutaneous disseminated zoster. However, acute and post-herpetic pain were not significantly affected. Well designed controlled studies are underway to establish the efficacy of acyclovir in herpes simplex encephalitis and cytomegalovirus infections in immunocompromised patients, infections due to Epstein-Barr virus, and neonatal herpesvirus infections. Despite some aspects of the drug's use which require further clarification, acyclovir will make a major impact on the treatment of herpesviral infections. Barring unexpected findings with wider clinical use, it will become the agent of choice in several conditions.

Moxalactam (latamoxef). A review of its antibacterial activity, pharmacokinetic properties and therapeutic use.

Moxalactam (latamoxef) is a new synthetic oxa-beta-lactam antibiotic administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria, is particularly active against Enterobacteriaceae and is resistant to hydrolysis by beta-lactamases. Moxalactam has moderate activity against Pseudomonas aeruginosa, but on the basis of present evidence can not be recommended as sole antibiotic treatment of known or suspected pseudomonal infections. Like the related compounds, the cephalosporins, moxalactam is effective in the treatment of complicated urinary tract infections and lower respiratory tract infections caused by Gram-negative bacilli. As moxalactam is also active against Bacteroides fragilis it has considerable potential in the treatment of intra-abdominal infections in patients with normal immunological mechanisms, as well as in immunocompromised patients, when used alone or in combination with other antibiotics. Likewise, its ready penetration into the diseased central nervous system, its high level of activity against Gram-negative bacilli, and the lack of necessity to monitor drug plasma concentrations, indicate its potential value in the treatment of neonatal Gram-negative bacillary meningitis. Further clinical experience is needed before it can be determined whether moxalactam alone can be used in the treatment of conditions for which the aminoglycosides are drugs of choice, but if established as equally effective, moxalactam has the advantage of being devoid of nephrotoxicity. Bleeding is a potentially serious problem, however, particularly in the elderly, malnourished and in the presence of renal impairment.

Cefotaxime. A review of its antibacterial activity, pharmacological properties and therapeutic use.

SYNOPSIS: Cefotaxime is a new 'third generation' semisynthetic cephalosporin administered intravenously or intramuscularly. It has a broad spectrum of activity against Gram-positive and Gram-negative aerobic and anaerobic bacteria, and is generally more active against Gram-negative bacteria than the 'first' and 'second generation' cephalosporins. Although cefotaxime has some activity against Pseudomonas aeruginosa, on the basis of present evidence it cannot be recommended as sole antibiotic therapy for pseudomonal infections. However, cefotaxime has been effective in treating infections due to other 'difficult' organisms, such as multidrug-resistant Enterobacteriaceae. Like other cephalosporins, cefotaxime is effective in treating patients with complicated urinary tract and lower respiratory tract infections, particularly pneumonia caused by Gram-negative bacilli. High response rates have also been achieved in patients with Gram-negative bacteraemia. Although favourable clinical results have been obtained in patients with infections caused by mixed aerobic/anaerobic organisms (such as peritonitis or soft tissue infections), the relatively low in vitro activity of cefotaxime against Bacteroides fragilis may restrict its usage in situations where this organism is the suspected or proven pathogen. In preliminary studies, males and females treated with a single intramuscular dose of cefotaxime for uncomplicated gonorrhoea caused by penicillinase-producing strains of Neisseria gonorrhoeae responded very favourably. Encouraging results have also been reported in open studies in children including neonates, treated with cefotaxime for meningitis and various other serious infections. In some situations, cefotaxime has been given in combination with another antibiotic such as an aminoglycoside, but the merits of such a combination have not been clearly established. Whether cefotaxime alone is appropriate therapy for conditions previously treated with aminoglycosides (other than pseudomonal infections) also needs additional clarification, but if established as equally effective in such conditions cefotaxime offers potentially important clinical and practical advantages in its apparent lack of serious adverse effects and freedom from the need to undertake drug plasma concentration monitoring.

Domperidone. A review of its pharmacological activity, pharmacokinetics and therapeutic efficacy in the symptomatic treatment of chronic dyspepsia and as an antiemetic.

Domperidone is a dopamine antagonist that does not readily enter the central nervous system. Given parenterally or orally it increases gastric emptying of liquids and increases lower oesophageal sphincter pressure in healthy subjects. The antiemetic and pharmacodynamic profile of domperidone is similar to that of metoclopramide, although domperidone has a lower propensity to cause extrapyramidal side effects. Domperidone effectively alleviates symptoms of chronic postprandial dyspepsia and nausea and vomiting due to a wide variety of underlying causes and in some studies has been superior to metoclopramide. Vomiting associated with the administration of moderately emetic cytotoxic drugs is controlled in the majority of patients. Alleviation of the dose-limiting peripheral side effects (nausea and vomiting) of the anti-Parkinsonian drugs bromocriptine and levodopa, enables a higher optimum dose, with consequent improvement in Parkinsonian symptoms. Domperidone does not aggravate the extrapyramidal side effects of neuroleptic drugs. Control of cytotoxic-induced, and postprandial nausea and vomiting in children has been achieved with domperidone without evidence of extrapyramidal side effects. Indeed, side effects have seldom occurred with therapeutic doses of domperidone.

Ranitidine: a review of its pharmacology and therapeutic use in peptic ulcer disease and other allied diseases.

Ranitidine is a new histamine H2-receptor antagonist which, unlike cimetidine, does not contain an imidazole group. On a weight basis, ranitidine is 4 to 10 times more potent than cimetidine in inhibiting stimulated gastric acid secretion in humans. Therapeutic trials comparing ranitidine and cimetidine have demonstrated that ranitidine 150 mg twice daily is an effective alternative to cimetidine 1000 mg daily in 4 divided doses in increasing the rate of healing of duodenal and gastric ulcers over a period of 4 to 6 weeks. Ranitidine, given as a single 150 mg dose at night, decreases the incidence of ulcer recurrence. Preliminary studies in the Zollinger-Ellison syndrome and in patients intolerant of, or unresponsive to cimetidine, indicate that ranitidine controls the gastric hyperacidity and heals most ulcers, including those which failed to respond to months of treatment with cimetidine 1 to 1.6 g daily. Ranitidine, unlike cimetidine, has no antiandrogenic effects and does not alter hepatic metabolism of drugs. Ranitidine is well tolerated. Preliminary reports of the resolution of cimetidine-induced adverse effects following substitution of ranitidine, suggest that ranitidine may be of value in patients intolerant of cimetidine. However, wider clinical experience with ranitidine is needed to determine the clinical relevance of these reports.

Zimelidine: a review of its pharmacological properties and therapeutic efficacy in depressive illness.

Zimelidine is a new antidepressant, which is structurally unrelated to the tricyclic and tetracyclic antidepressants. The pharmacological profile of zimelidine is different to that of other antidepressants in that it appears to owe the major part of its activity to the inhibition of serotonin uptake within the central nervous system. It appears that the demethylated metabolite, norzimelidine, may be responsible for most of the pharmacological activity. Studies to date suggest that zimelidine has overall efficacy comparable with that of amitriptyline, desipramine, maprotiline and doxepin in depressive illness, but at dosages which have achieved a similar overall clinical improvement zimelidine does not cause sedation, and anticholinergic side effects are mild and occur infrequently. Preliminary evidence suggests that zimelidine is effective against concomitant anxiety in depressed patients, and that it may also be useful in treating phobic anxiety. Zimelidine appears less likely to cause serious cardiotoxicity, in therapeutic dosages or an overdosage, than the tricyclic antidepressants, but it has not been studied in patients with cardiovascular disease. Sleep disturbance has occurred significantly more frequently during zimelidine therapy than during therapy with other sedative antidepressants, but whether this simply reflects the absence of sedation with zimelidine, or an effect on sleep as such, is presently unclear. Zimelidine appears to be effective and well tolerated in elderly patients. Thus, some aspects of the drug's profile (e.g. apparent low incidence of anticholinergic effects or drowsiness) may offer potential advantages in some patients; however, clinical experience with zimelidine to date has been limited, and further well designed studies are required to define the role of the drug more clearly in treating depressive illness compared with other antidepressants, and particularly to define whether some types of depression may respond more readily to zimelidine than to other antidepressants.

Tinidazole in anaerobic infections: a review of its antibacterial activity, pharmacological properties and therapeutic efficacy.

Tinidazole, like the structurally-related drug metronidazole, was initially introduced for treating protozoal infections. However, both these nitroimidazole compounds are also active in vitro against most clinically important obligate anaerobes. Most of the clinical experience with tinidazole to date has involved prophylactic use to prevent postoperative anaerobic infection. Prospective placebo-controlled studies demonstrated that a single dose of tinidazole administered orally prior to elective colorectal surgery significantly reduced postoperative infection. Similarly, when given intravenously prior to appendectomy, tinidazole reduced the incidence of postoperative infection in some subgroups of patients. Although results of non-blinded studies with prophylactic tinidazole were encouraging when used in women undergoing gynaecological surgery (mainly hysterectomy), results from double-blind placebo-controlled studies in this situation have been somewhat equivocal. Thus, although the overall weight of evidence suggests that the drug is effective in this area of use, further study is needed to clarify its role in preventing anaerobic infection following gynaecological surgery compared with other antibiotics which can also be used for this purpose. Relatively few studies have been conducted with tinidazole in the treatment of established anaerobic infections, and this is an area needing further investigation. The drug is well tolerated when administered orally or intravenously.

Trimethoprim: a review of its antibacterial activity, pharmacokinetics and therapeutic use in urinary tract infections.

Trimethoprim, which has been widely available for several years in combination with sulphamethoxazole as co-trimoxazole, is now available for use alone in the treatment of acute uncomplicated urinary tract infections. Trimethoprim, which is active against a wide range of Gram-positive and Gram-negative aerobic bacteria, is readily absorbed by the oral route and is widely distributed in body fluids and tissues. In therapeutic trials, trimethoprim 200 to 400mg daily has been shown to be comparable in efficacy with co-trimoxazole, ampicillin 2g, cephalexin 2g, oxolinic acid 1.5g and nitrofurantoin 200mg daily in the treatment of acute urinary tract infection. Similarly, in long term prophylaxis of recurrent urinary tract infection, trimethoprim 100mg daily given as a single dose at night was comparable with nitrofurantoin 50 to 100mg, methenamine 1g, oxolinic acid 375mg or co-trimoxazole (80mg trimethoprim/400mg sulphamethoxazole) each given as a single daily dose. Emergence of acquired resistance has been infrequent during years of therapeutic use of co-trimoxazole. Nevertheless, results of serial laboratory surveys suggest that resistance to trimethoprim among enterobacteria is increasing. However, at present, there is no conclusive evidence that there will be a more rapid increase following the introduction of trimethoprim for use alone in the treatment of urinary tract infections. At the dosages used, trimethoprim has generally been well tolerated and in studies comparing it with co-trimoxazole overall, skin rashes and gastrointestinal upset have occurred less frequently with trimethoprim than with co-trimoxazole.

Trifluridine: a review of its antiviral activity and therapeutic use in the topical treatment of viral eye infections.

Trifluridine (trifluorothymidine) is an antiviral agent for topical use in the eye, and is structurally related to idoxuridine. In vitro studies have shown that it effectively inhibits the replication of herpes simplex virus type 1, which causes primary keratoconjunctivitis and recurrent epithelial keratitis in man. In masked comparative studies, predominantly in patients with dendritic ulcers, trifluridine 1% solution was effective in over 90% of patients; in such studies it was comparable with vidarabine in treating dendritic ulcers, and was at least as effective as, and in some studies more effective than, idoxuridine. The drug was also effective in treating a small number of patients with geographic ulcers (sometimes associated with the usage of topical corticosteroids), and this could be an important advantage if confirmed in further well-designed studies. However, experience at present is too limited to reliably determine the usual response rate in this difficult therapeutic area. In open studies the drug proved to be particularly useful in treating ulcers previously unresponsive to idoxuridine or vidarabine, and in treating patients intolerant of idoxuridine, with a high success rate and minimal side effects being reported. The role of trifluridine in treating deep stromal disease, uveitis, or adenovirus kerato-conjunctivitis has not been established. The drug is well tolerated and cross-hypersensitivity and cross-toxicity between trifluridine, idoxuridine and vidarabine are rare. Thus, trifluridine is an effective alternative to the drugs available for treating herpetic keratitis, and seems especially useful in 'difficult' cases.

Zomepirac: a review of its pharmacological properties and analgesic efficacy.

Zomepirac is an analgesic which is closely related chemically to the nonsteroidal anti-inflammatory agent, tolmetin. In short term studies mainly involving patients with acute pain of moderately severity, zomepirac was at least as effective as usual therapeutic doses of aspirin, codeine alone or with aspirin, phenacetin and caffeine, dextropropoxyphene with paracetamol, or orally administered pentazocine. Additionally, zomepirac may provide analgesia comparable to that with standard doses of intramuscular morphine in patients with acute pain of moderate intensity, but in severe pain states strong analgesics may be more appropriate. Zomepirac has also been studied in patients with chronic orthopaedic pain or osteoarthritic pain for up to several months, without the need for increased doses. It appears to be at least as effective as usual doses of aspirin when used in this way, with a lower incidence of some side effects such as gastrointestinal disturbances and hearing disorders. Preliminary studies suggest that zomepirac may also be effective in patients with chronic cancer pain who have not been previously maintained on strong analgesics, but further experience is needed to clarify its usefulness in this difficult treatment area.