Plasma diphenylhydantoin levels in Australian adults

Sex Variation and Drug Therapy

A literature review of gender differences with drug therapy is presented.

Physiological differences between the sexes in basal metabolic rate and in levels of certain of the circulating hormones and enzymes affect or influence the metabolism of various drugs. Differences in muscle mass, disposition of adipose tissue and vascular resistance can lead to variations in response between the sexes to IM injections, while plasma levels of orally administered drugs can be influenced by sex differences such as gastric motility and secretion, metabolic rate, pregnancy, and differences in drug distributive compartments. These differences in gender response to a given therapy can vary according to the patient's age. Adverse reactions to drugs are also affected by the patient's gender, and certain drugs have been shown to induce adverse reactions predominantly in one sex.

The review illustrates the confusion surrounding this subject and stresses the importance of sex differences in the consideration and monitoring of drug therapy. Information on sex and age of patients, and possible sex differences in response to drug therapy is requested of all future therapeutic studies.

It was further suggested that the dual genetic coverage may be the mechanism by which the sex difference in susceptibility to infection can be explained. Support for this theory can best be found in a brief discussion of sex-linked diseases. The transmission from parents to offspring of defects, which may manifest themselves as disease, may be genetic in origin (Table 2).41

Due to the transmission of these diseases by the sex chromosomes, the male, having only one X-chromosome, is afflicted more often by these diseases. This leads one to conclude that given like conditions, females are better adapted to cope with many human diseases because they are genetically and chemically better evolved.

Phenytoin and postoperative epilepsy. A double-blind study

A double-blind trial of phenytoin therapy following craniotomy was performed to test the hypothesis that phenytoin is effective in reducing postoperative epilepsy. A significant reduction in the frequency of epilepsy was observed in the group receiving the active drug up to the 10th postoperative week. Half of the seizures occurred in the first 2 weeks and two-thirds within 1 month of cranial surgery. High rates of epilepsy were observed after surgery in patients with meningioma, metastasis, aneurysm, and head injury. Routine prophylaxis with phenytoin (in a dosage of 5 to 6 mg/kg/day) would seem to be indicated, particularly in high-risk patients and, where possible, this treatment should be started 1 week preoperatively. Seizure control is best when therapeutic levels of phenytoin are maintained.

The effect of activated dimethicone and a proprietary antacid preparation containing this agent on the absorption of phenytoin

1 The bioavailabilty of phenytoin sodium (Epanutin both alone and in combination with activated dimethicone and Asilone (a proprietary antacid preparation containing activated dimethicone) was examined in six healthy male volunteers. 2 The bioavailability of phenytoin when given concomitantly with Asilone was decreased in five of six volunteer subjects (by greater than 30% in three subjects) although this decrease was not shown to be statistically significant. 3 Dimethicone, which has been shown to decrease phenytoin absorption in vitro did not affect phenytoin bioavailability in vivo. 4 It is recommended that when treating patients stabilised on phenytoin one should exercise caution with concomitant phenytoin and antacid therapy to guard against possible changed drug absorption.

Postoperative epilepsy: a double-blind trial of phenytoin after craniotomy

In a double-blind trial of phenytoin for the prevention of postoperative epilepsy in craniotomy patients, epilepsy was observed in 7.9% (8/101) of patients treated with phenytoin and in 16.7% (17/102) of those receiving placebo. Therapeutic drug levels were associated with a significant reduction in the frequency of epilepsy. Three-quarters of the fits occurred within a month of cranial surgery. High rates of epilepsy have been observed after cranial surgery in patients with meningioma, aneurysm, and head injury with or without intracranial clots, and routine prophylaxis with phenytoin would seem to be indicated in such patients.

Compliance with anticonvulsant therapy in a hospital clinic and in the community

1 Seizure control, saliva anticonvulsant concentration, prescribing habits and compliance with anticonvulsant medication have been compared in 86 epileptic subjects attending either a specialist hospital clinic or general practice surgeries. 2 Of all subjects experiencing recurrent seizures 70% had saliva concentrations of phenytoin below the range equivalent to the 'therapeutic range' of plasma concentration. Mean saliva phenytoin concentrations did not differ significantly between the two treatment settings and were low largely because of the low mean dosage prescribed. 3 Eleven subjects in all had no detectable phenytoin in their and could clearly be identified as noncompliant. Freedom from seizures appeared to predispose to poor compliance in these subjects as well as among those admitting repeated omission of doses.